Staphylococcus aureus in the Community: Colonization Versus Infection

Background

Antibiotic-resistant Staphylococcus aureus infections have increased dramatically in the community, yet S. aureus nasal colonization has remained stable. The objectives of this study were to determine if S. aureus colonization is a useful proxy measure to study disease transmission and infection in community settings, and to identify potential community reservoirs.

Methodology/Principal Findings

Randomly selected households in Northern Manhattan, completed a structured social network questionnaire and provided nasal swabs that were typed by pulsed field gel electrophoresis to identify S. aureus colonizing strains. The main outcome measures were: 1) colonization with S. aureus; and 2) recent serious skin infection. Risk factor analyses were conducted at both the individual and the household levels; logistic regression models identified independent risks for household colonization and infection.

Results

321 surveyed households contained 914 members. The S. aureus prevalence was 25% and MRSA was 0.4%. More than 40% of households were colonized. Recent antibiotic use was the only significant correlate for household colonization (p = .002). Seventy-eight (24%) households reported serious skin infection. In contrast with colonization, five of the six risk factors that increased the risk of skin infection in the household at the univariate level remained independently significant in multivariable analysis: international travel, sports participation, surgery, antibiotic use and towel sharing. S. aureus colonization was not significantly associated with serious skin infection in any analysis. Among multiperson households with more than one person colonized, 50% carried the same strain.

Conclusions/Significance

The lack of association between S. aureus nasal colonization and serious skin infection underscores the need to explore alternative venues or body sites that may be crucial to transmission. Moreover, the magnitude of colonization and infection within the household suggests that households are an underappreciated and substantial community reservoir.     

Methicillin-Resistant Staphylococcus aureus USA300 Latin American Variant in Patients Undergoing Hemodialysis and HIV Infected in a Hospital in Bogotá, Colombia

We aimed to determine the prevalence of MRSA colonization and examine the molecular characteristics of colonizing isolates in patients receiving hemodialysis and HIV-infected in a Colombian hospital. Patients on hemodialysis and HIV-infected were prospectively followed between July 2011 and June 2012 in Bogota, Colombia. Nasal and axillary swabs were obtained and cultured. Colonizing S. aureus isolates were identified by standard and molecular techniques. Molecular typing was performed by using pulse-field gel electrophoresis and evaluating the presence of lukF-PV/lukS-PV by PCR. A total of 29% (n = 82) of HIV-infected and 45.5% (n = 15) of patients on hemodialysis exhibited S. aureus colonization. MSSA/MRSA colonization was observed in 28% and 3.6% of the HIV patients, respectively and in 42.4% and 13.3% of the hemodialysis patients, respectively. Staphylococcal cassette chromosome mec typing showed that four MRSA isolates harbored the type IV cassette, and one type I. In the hemodialysis group, two MRSA isolates were classified as belonging to the USA300-LV genetic lineage. Conversely, in the HIV infected group, no colonizing isolates belonging to the USA300-Latin American Variant (UDA300-LV) lineage were identified. Colonizing isolates recovered from the HIV-infected group belonged to the prevalent hospital-associated clones circulating in Latin America (Chilean [n = 1] and Pediatric [n = 2]). The prevalence of MRSA colonization in the study groups was 3.6% (HIV) and 13.3% (hemodialysis). Surveillance programs should be implemented in this group of patients in order to understand the dynamics of colonization and infection in high-risk patients.     

The environment as an unrecognized reservoir for community-associated methicillin resistant Staphylococcus aureus USA300: a case-control study

Background

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) infections are spreading, but the source of infections in non-epidemic settings remains poorly defined.

Methods

We carried out a community-based, case-control study investigating socio-demographic risk factors and infectious reservoirs associated with MRSA infections. Case patients presented with CA-MRSA infections to a New York hospital. Age-matched controls without infections were randomly selected from the hospital''s Dental Clinic patient population. During a home visit, case and control subjects completed a questionnaire, nasal swabs were collected from index respondents and household members and standardized environmental surfaces were swabbed. Genotyping was performed on S. aureus isolates.

Results

We enrolled 95 case and 95 control subjects. Cases more frequently reported diabetes mellitus and a higher number of skin infections among household members. Among case households, 53 (56%) were environmentally contaminated with S. aureus, compared to 36 (38%) control households (p = .02). MRSA was detected on fomites in 30 (32%) case households and 5 (5%; p<.001) control households. More case patients, 20 (21%) were nasally colonized with MRSA than were control indexes, 2 (2%; p<.001). In a subgroup analysis, the clinical isolate (predominantly USA300), was more commonly detected on environmental surfaces in case households with recurrent MRSA infections (16/36, 44%) than those without (14/58, 24%, p = .04).

Conclusions

The higher frequency of environmental contamination of case households with S. aureus in general and MRSA in particular implicates this as a potential reservoir for recolonization and increased risk of infection. Environmental colonization may contribute to the community spread of epidemic strains such as USA300.     

Methicillin-resistant Staphylococcus aureus nasal colonization among adult patients visiting emergency department in a medical center in Taiwan

Background

Within the past 10 years, methicillin-resistant Staphylococcus aureus (MRSA) has not only been a hospital pathogen but also a community pathogen. To understand the carriage rate of methicillin-resistant Staphylococcus aureus (MRSA) among the adult patients visiting emergency department (ED), we conducted this study.

Methodology/Principal Findings

From May 21 to August 12, 2009, a total of 502 adult patients visiting emergency department (ED) of a tertiary care hospital in northern Taiwan were recruited in this study and surveyed for nasal carriage of MRSA. A questionnaire regarding the risk factors for MRSA acquisition was also obtained.The overall prevalence of MRSA nasal carriage among the patients was 3.8%. The carriage rate was significantly higher in patients with risk factors for MRSA acquisition (5.94%) than those without risk factors (2.12%). Patients with urinary complaints, diabetes mellitus, chronic kidney disease and current percutaneous tube usage were significantly associated with MRSA colonization. By multiple logistic regression analysis, only current usage of catheters or tubes was the independent predictor for MRSA nasal colonization. Of the 19 MRSA, most isolates belonged to one of two linages, characterized as sequence type (ST) 239 (32%) and ST 59 (58%). The latter linage, accounting for 83% of 6 isolates from patients without risk factors, is a community-associated (CA) clone in Taiwan, while the former linage is among healthcare-associated clones.

Conclusion/Significance

A substantial proportion of patients visiting ED, particularly with current usage of percutaneous catheter or tubes, in northern Taiwan carried MRSA, mostly community strains, in nares.     

Nasal Staphylococcus aureus and Methicillin-Resistant S. aureus Carriage among Janitors Working in Hospitals in Northern Taiwan

Background

Staphylococcus aureus is an important cause of infection, and brings additional concern with methicillin resistance. In addition, nasal methicillin-resistant Staphylococcus aureus (MRSA) colonization rates among health care workers are higher than that for general population. To determine the prevalence rate and risk factors for the colonization of S. aureus, including MRSA, among janitors working in hospitals in northern Taiwan, we conducted this study.

Methods

Between June and August, 2014, a total of 186 janitors, 111 working in hospitals and 75 working in non-medical institutions, were recruited. Specimens were obtained from the nares of the subjects for the detection of S. aureus, with a questionnaire completed for each subject. All the S. aureus isolates, including MRSA and methicillin-susceptible S. aureus (MSSA), were further molecularly characterized.

Results

The nasal carriage rate of S. aureus was 15.3% for hospital janitors and 13.3% for non-medical janitors. The carriage rate of MRSA was 3.6% for hospital janitors and 1.3% for non-medical janitors. No statistically significant difference was found in the nasal carriage rate of S. aureus (p = 0.707) and MRSA (p = 0.65) between hospital janitors and non-medical janitors. Hospital janitors working in hospital more than 6 years and cleaning microbiologic laboratories were significantly associated with nasal S. aureus colonization. All 5 MRSA isolates carried either staphylococcal cassette chromosome type IV or V and three of them belonged to sequence type (ST) 59, the community clone prevailing in Taiwan. Of the 22 MSSA isolates, six pulsotypes were identified, with one major type for 14 isolates (shared by five STs) and another type for 4 isolates (all belonged to ST 188).

Conclusion

Exposure to the hospital environment may not increase the nasal carriage rate of S. aureus, including MRSA, among janitors in hospitals in Taiwan. However, for janitors in the hospital setting, working for more than six years in hospital and cleaning laboratories may be risks factors for carrying S. aureus.     

Environmental Contamination as a Risk Factor for Intra-Household Staphylococcus aureus Transmission

Background

The household is a recognized community reservoir for Staphylococcus aureus. This study investigated potential risk factors for intra-household S. aureus transmission, including the contribution of environmental contamination.

Methods

We investigated intra-household S. aureus transmission using a sample of multiple member households from a community-based case-control study examining risk factors for CA-MRSA infection conducted in Northern Manhattan. During a home visit, index subjects completed a questionnaire. All consenting household members were swabbed, as were standardized environmental household items. Swabs were cultured for S. aureus. Positive isolates underwent further molecular characterization. Intra-household transmission was defined as having identical strains among two or more household members. Multiple logistic regression was used to identify independent risk factors for transmission.

Results

We enrolled 291 households: 146 index cases, 145 index controls and 687 of their household contacts. The majority of indexes were Hispanic (85%), low income (74%), and female (67%), with a mean age of 31 (range 1–79). The average size of case and control households was 4 people. S. aureus colonized individuals in 62% of households and contaminated the environment in 54% of households. USA300 was the predominant clinical infection, colonizing and environmental strain. Eighty-one households had evidence of intra-household transmission: 55 (38%) case and 26 (18%) control households (P<.01). Environmental contamination with a colonizing or clinical infection strain (aOR: 5.4 [2.9–10.3] P<.01) and the presence of a child under 5 (aOR: 2.3 [1.2–4.5] P = .02) were independently associated with transmission. In separate multivariable models, environmental contamination was associated with transmission among case (aOR 3.3, p<.01) and control households (aOR 27.2, p<.01).

Conclusions

Environmental contamination with a colonizing or clinical infection strain was significantly and independently associated with transmission in a large community-based sample. Environmental contamination should be considered when treating S. aureus infections, particularly among households with multiple infected members.     

Basic Rules of Hygiene Protect Health Care and Lab Workers from Nasal Colonization by Staphylococcus aureus: An International Cross-Sectional Study

Acquisition of nasal Staphylococcus aureus (S. aureus) colonization by contaminated hands is likely an important determinant of its nasal carriage rate in health care and lab setting. The objective of our cross-sectional study was to assess the prevalence of nasal methicillin-sensitive (MSSA) or -resistant Staphylococcus aureus (MRSA) carriage among health care professionals (HCPs) attending an international symposium and to study the association between compliance with hygiene rules, individual-related parameters, and medical conditions with nasal S. aureus carriage in this population. After obtaining consent, two nasal swabs were collected. Nasal MSSA and MRSA carriage was measured by the: i) molecular approach targeting spa, mecA and mecA-orfX junction sequences, and ii) culture on selective S. aureus media combined with mecA molecular detection of isolated strains. Information on compliance with hygiene rules, demographic variables, sector of activity and long-term medication was collected by anonymous questionnaire. The participation rate was 32.3%. In total, 176 subjects from 34 countries were included in the analysis. S. aureus was isolated from the nasal swabs of 57 (32.4%) subjects, of whom 3 (5.3%) harbored MRSA strains. Overall, 123 subjects reported working in microbiology laboratories with direct manipulation of S. aureus, and 29 acknowledged regular contacts with patients. In this exposed population, hydro-alcoholic solutions appeared to have a significant protective effect against nasal S. aureus carriage (OR = 0.36; 95% CI: 0.15–0.85). Hospital work was associated with increased risk of nasal S. aureus carriage (OR = 2.38; 95% CI: 1.07–5.29). The results of this study showed that compliance with basic rules of hygiene, such as the use of hydro-alcoholic solutions, could reduce the risk of nasal S. aureus colonization. Hydro-alcoholic solution could interrupt auto-transmission of the pathogen, consequently decreasing the overall nasal carriage rate, specifically in transient carriers.     

Differences in Epidemiological and Molecular Characteristics of Nasal Colonization with Staphylococcus aureus (MSSA-MRSA) in Children from a University Hospital and Day Care Centers

Background

Clinical significance of Staphylococcus aureus colonization has been demonstrated in hospital settings; however, studies in the community have shown contrasting results regarding the relevance of colonization in infection by community-associated MRSA (CA-MRSA). In Colombia there are few studies on S. aureus colonization. The aim of this study was to determine the molecular and epidemiological characteristics of nasal colonization by S. aureus (MSSA-MRSA) in children from a university hospital and day care centers (DCCs) of Medellin, Colombia.

Methods

An observational cross-sectional study was conducted in 400 children (200 in each setting), aged 0 months to 5 years, during 2011. Samples were collected from each nostril and epidemiological information was obtained from the parents. Genotypic analysis included spa typing, PFGE, MLST, SCCmec typing, detection of genes for virulence factors and agr groups.

Results

Frequency of S. aureus colonization was 39.8% (n = 159) (hospital 44.5% and DCCs 35.0%) and by MRSA, 5.3% (n = 21) (hospital 7.0% and DCCs 3.5%). Most S. aureus colonized children were older than two years (p = 0.005), the majority of them boys (59.1%), shared a bedroom with a large number of people (p = 0.028), with history of β-Lactamase inhibitors usage (p = 0.020). MSSA strains presented the greatest genotypic diversity with 15 clonal complexes (CC). MRSA isolates presented 6 CC, most of them (47.6%) belonged to CC8-SCCmec IVc and were genetically related to previously reported infectious MRSA strains.

Conclusion

Differences in epidemiological and molecular characteristics between populations may be useful for the understanding of S. aureus nasal colonization dynamics and for the design of strategies to prevent S. aureus infection and dissemination. The finding of colonizing MRSA with similar molecular characteristics of those causing infection demonstrates the dissemination capacity of S. aureus and the risk of infection among the child population.     

Changes in the nasal colonization with methicillin-resistant Staphylococcus aureus in children: 2004-2009

Background

Staphylococcus aureus is an important cause of infection, particularly in persons colonized with this organism. This study compared the annual prevalence and microbiological characteristics of methicillin-resistant S. aureus (MRSA) nasal colonization in Taiwanese children from 2004 through 2009. Risk factors for MRSA were determined for the overall study period.

Methods

Children from birth to ≤14 years of age presenting for health maintenance visits or attending 1 of 57 kindergartens were recruited. Nasal swabs were obtained, and a questionnaire was administered. The prevalence and microbiological characteristics of MRSA colonization were also calculated for two 3-year periods: 2004–2006 and 2007–2009.

Results

Cultures of the anterior nares were positive for S. aureus in 824 (25.8%) of the 3,200 children, and MRSA colonization was found in 371 (11.6%) children. The prevalence of S. aureus colonization decreased from 28.1% in 2004–2006 to 23.3% in 2007–2009 (p<0.01), whereas the prevalence of MRSA colonization increased from 8.1% to 15.1% during this period (p<0.0001). Multivariate analysis revealed that the independent risk factors for MRSA carriage were different for male and female children, and also among age groups. Most MRSA isolates belonged to sequence type 59 (ST59) (86.3%); however, a multiresistant MRSA clone with ST338 background emerged in 2007–2009. Ten (62.5%) of the 16 MRSA isolates expressed the genotypic profile ST338/staphylococcal cassette chromosome mec V_T/Panton-Valentine leukocidin-positive/staphylococcal enterotoxin B-positive, and differed only in their antimicrobial susceptibility patterns.

Conclusion

The prevalence of nasal colonization by MRSA increased among healthy Taiwanese children from 2004–2006 to 2007–2009, despite an overall decrease in the prevalence of nasal colonization by S. aureus. A multiresistant MRSA clone characterized as ST338 was identified from these children.     

Skin Barrier Function and Staphylococcus aureus Colonization in Vestibulum Nasi and Fauces in Healthy Infants and Infants with Eczema: A Population-Based Cohort Study

Atopic eczema (AE) is associated with Staphylococcus aureus (S. aureus) colonization and skin barrier dysfunction, often measured by increased transepidermal water loss (TEWL). In the present study, the primary aim was to see whether S. aureus colonization in the vestibulum nasi and/or fauces was associated with increased TEWL in infants with healthy skin and infants with eczema. Secondarily, we aimed to investigate whether TEWL measurements on non-lesional skin on the lateral upper arm is equivalent to volar forearm in infants. In 167 of 240 infants, recruited from the general population, TEWL measurements on the lateral upper arm and volar forearm, using a DermaLab USB, fulfilled our environmental requirements. The mean of three TEWL measurements from each site was used for analysis. The infants were diagnosed with no eczema (n = 110), possible AE (n = 28) or AE (n = 29). DNA samples were analysed for mutations in the filaggrin gene (FLG). Bacterial cultures were reported positive with the identification of at least one culture with S. aureus from vestibulum nasi and/or fauces. S. aureus colonization, found in 89 infants (53%), was not associated with increased TEWL (i.e. TEWL in the upper quartile), neither on the lateral upper arm or volar forearm (p = 0.08 and p = 0.98, respectively), nor with AE (p = 0.10) or FLG mutation (p = 0.17). TEWL was significantly higher on both measuring sites in infants with AE compared to infants with possible AE and no eczema. FLG mutation was significantly associated with increased TEWL, with a 47% difference in TEWL. We conclude that S. aureus in vestibulum nasi and/or fauces was not associated with TEWL, whereas TEWL measurements on the lateral upper arm and volar forearm appear equally appropriate in infants.     

Staphylococcus aureus Colonization of the Mouse Gastrointestinal Tract Is Modulated by Wall Teichoic Acid,Capsule, and Surface Proteins

Staphylococcus aureus colonizes the nose, throat, skin, and gastrointestinal (GI) tract of humans. GI carriage of S. aureus is difficult to eradicate and has been shown to facilitate the transmission of the bacterium among individuals. Although staphylococcal colonization of the GI tract is asymptomatic, it increases the likelihood of infection, particularly skin and soft tissue infections caused by USA300 isolates. We established a mouse model of persistent S. aureus GI colonization and characterized the impact of selected surface antigens on colonization. In competition experiments, an acapsular mutant colonized better than the parental strain Newman, whereas mutants defective in sortase A and clumping factor A showed impaired ability to colonize the GI tract. Mutants lacking protein A, clumping factor B, poly-N-acetyl glucosamine, or SdrCDE showed no defect in colonization. An S. aureus wall teichoic acid (WTA) mutant (ΔtagO) failed to colonize the mouse nose or GI tract, and the tagO and clfA mutants showed reduced adherence in vitro to intestinal epithelial cells. The tagO mutant was recovered in lower numbers than the wild type strain in the murine stomach and duodenum 1 h after inoculation. This reduced fitness correlated with the in vitro susceptibility of the tagO mutant to bile salts, proteases, and a gut-associated defensin. Newman ΔtagO showed enhanced susceptibility to autolysis, and an autolysin (atl) tagO double mutant abrogated this phenotype. However, the atl tagO mutant did not survive better in the mouse GI tract than the tagO mutant. Our results indicate that the failure of the tagO mutant to colonize the GI tract correlates with its poor adherence and susceptibility to bactericidal factors within the mouse gut, but not to enhanced activity of its major autolysin.     

Evaluation of Non-Invasive Biological Samples to Monitor Staphylococcus aureus Colonization in Great Apes and Lemurs

Introduction

Reintroduction of endangered animals as part of conservational programs bears the risk of importing human pathogens from the sanctuary to the natural habitat. One bacterial pathogen that serves as a model organism to analyze this transmission is Staphylococcus aureus as it can colonize and infect both humans and animals. The aim of this study was to evaluate the utility of various biological samples to monitor S. aureus colonization in great apes and lemurs.

Methods

Mucosal swabs from wild lemurs (n=25, Kirindy, Madagascar), feces, oral and genital swabs from captive chimpanzees (n=58, Ngamba and Entebbe, Uganda) and fruit wadges and feces from wild chimpanzees (n=21, Taï National Parc, Côte d’Ivoire) were screened for S. aureus. Antimicrobial resistance and selected virulence factors were tested for each isolate. Sequence based genotyping (spa typing, multilocus sequence typing) was applied to assess the population structure of S. aureus.

Results

Oro-pharyngeal carriage of S. aureus was high in lemurs (72%, n=18) and captive chimpanzees (69.2%, n=27 and 100%, n=6, respectively). Wild chimpanzees shed S. aureus through feces (43.8, n=7) and fruit wadges (54.5, n=12). Analysis of multiple sampling revealed that two samples are sufficient to detect those animals which shed S. aureus through feces or fruit wadges. Genotyping showed that captive animals are more frequently colonized with human-associated S. aureus lineages.

Conclusion

Oro-pharyngeal swabs are useful to screen for S. aureus colonization in apes and lemurs before reintroduction. Duplicates of stool and fruit wadges reliably detect S. aureus shedding in wild chimpanzees. We propose to apply these sampling strategies in future reintroduction programs to screen for S. aureus colonization. They may also be useful to monitor S. aureus in wild populations.     

Secondary Staphylococcus aureus intramammary colonization is reduced by non-aureus staphylococci exoproducts

Non-aureus staphylococci (NAS) and Staphylococcus aureus are pathogens that cause bovine mastitis, a costly disease for dairy farmers, however; many NAS are considered part of the normal udder microbiota. It has been suggested that through a mechanism that remains to be elucidated, NAS intramammary colonization can prevent subsequent infection with other bacterial pathogens. This study shows that in a murine mastitis model, secondary Staph. aureus intramammary colonization is reduced by exoproducts from Staph. chromogenes and Staph. simulans, both NAS, while Streptococcus spp. exoproducts have much less ability to affect the course of the infection caused by S. aureus.     

Crystal Structures Reveal the Multi-Ligand Binding Mechanism of Staphylococcus aureus ClfB

Staphylococcus aureus (S. aureus) pathogenesis is a complex process involving a diverse array of extracellular and cell wall components. ClfB, an MSCRAMM (Microbial Surface Components Recognizing Adhesive Matrix Molecules) family surface protein, described as a fibrinogen-binding clumping factor, is a key determinant of S. aureus nasal colonization, but the molecular basis for ClfB-ligand recognition remains unknown. In this study, we solved the crystal structures of apo-ClfB and its complexes with fibrinogen α (Fg α) and cytokeratin 10 (CK10) peptides. Structural comparison revealed a conserved glycine-serine-rich (GSR) ClfB binding motif (GSSGXGXXG) within the ligands, which was also found in other human proteins such as Engrailed protein, TCF20 and Dermokine proteins. Interaction between Dermokine and ClfB was confirmed by subsequent binding assays. The crystal structure of ClfB complexed with a 15-residue peptide derived from Dermokine revealed the same peptide binding mode of ClfB as identified in the crystal structures of ClfB-Fg α and ClfB-CK10. The results presented here highlight the multi-ligand binding property of ClfB, which is very distinct from other characterized MSCRAMMs to-date. The adherence of multiple peptides carrying the GSR motif into the same pocket in ClfB is reminiscent of MHC molecules. Our results provide a template for the identification of other molecules targeted by S. aureus during its colonization and infection. We propose that other MSCRAMMs like ClfA and SdrG also possess multi-ligand binding properties.     

Identification of Bacteriology and Risk Factor Analysis of Asymptomatic Bacterial Colonization in Pacemaker Replacement Patients

Background

Recent researches revealed that asymptomatic bacterial colonization on PMs might be ubiquitous and increase the risk of clinical PM infection. Early diagnosis of patients with asymptomatic bacterial colonization could provide opportunity for targeted preventive measures.

Objective

The present study explores the incidence of bacterial colonization of generator pockets in pacemaker replacement patients without signs of infection, and to analyze risk factors for asymptomatic bacterial colonization.

Methods

From June 2011 to December 2013, 118 patients underwent pacemaker replacement or upgrade. Identification of bacteria was carried out by bacterial culture and 16S rRNA sequencing. Clinical risk characteristics were analyzed.

Results

The total bacterial positive rate was 37.3% (44 cases), and the coagulase-negative Staphylococcus aureus detection rate was the highest. Twenty two (18.6%) patients had positive bacterial culture results, of which 50% had coagulase-negative staphylococcus. The bacterial DNA detection rate was 36.4 % (43 cases). Positive bacterial DNA results from pocket tissues and the surface of the devices were 22.0% and 29.7%, respectively. During follow-up (median, 27.0 months), three patients (6.8%, 3/44) became symptomatic with the same genus of microorganism, S. aureus (n=2) and S. epidermidis (n=1). Multivariable logistic regression analysis showed that history of bacterial infection, use of antibiotics, application of antiplatelet drugs, replacement frequency were independent risk factors for asymptomatic bacterial colonization.

Conclusion

There was a high incidence of asymptomatic bacterial colonization in pacemaker patients with independent risk factors. Bacterial culture combined genetic testing could improve the detection rate.     

Persistent Staphylococcus aureus colonization is not a strongly heritable trait in Amish families

About 20% of adults are persistently colonized with S. aureus in the anterior nares. Host genetic factors could contribute susceptibility to this phenotype. The objective of this study was to determine whether the phenotype of persistent S. aureus colonization aggregates in family members who live in different households. Healthy adults and their eligible same sex siblings who lived in different households were recruited from the Old Order Amish of Lancaster, Pennsylvania. All participants had two cultures of the anterior nares to determine if they were persistently colonized with S. aureus. Three hundred and ninety eight participants finished the study, of whom 166 were index cases and 232 were siblings of index cases. Eighteen per cent (71/398) of all participants and 17% (29/166) of index cases were persistently colonized with S. aureus. Twenty two per cent (8/36) of siblings of persistently colonized index cases were persistently colonized with S. aureus compared to 17% (34/196) of siblings of non-persistently colonized index cases, yielding a prevalence rate ratio of 1.28 (95% CI: 0.65–2.54, p = 0.64) and sibling relative risk of 1.25 (95% CI: 0.65–2.38, p = 0.51). The heritability of persistent colonization was 0.19±0.21 (p = 0.31). Persistent S. aureus colonization does not strongly aggregate in Amish family members in different households and heritability is low, suggesting that environmental factors or acquired host factors are more important than host genetic factors in determining persistent S. aureus colonization in this community.     

Beta-Hemolysin Promotes Skin Colonization by Staphylococcus aureus

Colonization by Staphylococcus aureus is a characteristic feature of several inflammatory skin diseases and is often followed by epidermal damage and invasive infection. In this study, we investigated the mechanism of skin colonization by a virulent community-acquired methicillin-resistant S. aureus (CA-MRSA) strain, MW2, using a murine ear colonization model. MW2 does not produce a hemolytic toxin, beta-hemolysin (Hlb), due to integration of a prophage, ϕSa3mw, inside the toxin gene (hlb). However, we found that strain MW2 bacteria that had successfully colonized murine ears included derivatives that produced Hlb. Genome sequencing of the Hlb-producing colonies revealed that precise excision of prophage ϕSa3mw occurred, leading to reconstruction of the intact hlb gene in their chromosomes. To address the question of whether Hlb is involved in skin colonization, we constructed MW2-derivative strains with and without the Hlb gene and then subjected them to colonization tests. The colonization efficiency of the Hlb-producing mutant on murine ears was more than 50-fold greater than that of the mutant without hlb. Furthermore, we also showed that Hlb toxin had elevated cytotoxicity for human primary keratinocytes. Our results indicate that S. aureus Hlb plays an important role in skin colonization by damaging keratinocytes, in addition to its well-known hemolytic activity for erythrocytes.     

Expression of Panton-Valentine Leukocidin mRNA among Staphylococcus aureus Isolates Associates with Specific Clinical Presentations

Panton-Valentine leukocidin (PVL; gene designation lukF/S-PV) is likely an important virulence factor for Staphylococcus aureus (S. aureus), as qualitative expression of the protein correlates with severity for specific clinical presentations, including skin and soft tissue infections (SSTIs). Development of genetic approaches for risk-assessment of patients with S. aureus infections may prove clinically useful, and whether lukF/S-PV gene expression correlates with specific clinical presentations for S. aureus has been largely unexplored. In the present study, we quantified lukS-PV mRNA among 96 S. aureus isolates to determine whether expression levels correlated with specific clinical presentations in adults and children. Expression level of lukS-PV mRNA among isolates from skin and soft tissue infections (SSTIs) was significantly greater than among isolates from blood stream infection (BSIs), and expression level of lukS-PV mRNA among BSI isolates from children was significantly greater than for BSI isolates among adults. Moreover, expression level of lukS-PV mRNA among community-acquired (CA) isolates was significantly greater than for hospital-acquired (HA) isolates. These data justify additional studies to determine the potential clinical utility for lukS-PV mRNA quantification as a predictive tool for severity of S. aureus infection.     

Eugenol: A Phyto-Compound Effective against Methicillin-Resistant and Methicillin-Sensitive Staphylococcus aureus Clinical Strain Biofilms

Background

Inhibition and eradication of Staphylococcus aureus biofilms with conventional antibiotic is difficult, and the treatment is further complicated by the rise of antibiotic resistance among staphylococci. Consequently, there is a need for novel antimicrobials that can treat biofilm-related infections and decrease antibiotics burden. Natural compounds such as eugenol with anti-microbial properties are attractive agents that could reduce the use of conventional antibiotics. In this study we evaluated the effect of eugenol on MRSA and MSSA biofilms in vitro and bacterial colonization in vivo.

Methods and Results

Effect of eugenol on in vitro biofilm and in vivo colonization were studied using microtiter plate assay and otitis media-rat model respectively. The architecture of in vitro biofilms and in vivo colonization of bacteria was viewed with SEM. Real-time RT-PCR was used to study gene expression. Check board method was used to study the synergistic effects of eugenol and carvacrol on established biofilms. Eugenol significantly inhibited biofilms growth of MRSA and MSSA in vitro in a concentration-dependent manner. Eugenol at MIC or 2×MIC effectively eradicated the pre-established biofilms of MRSA and MSSA clinical strains. In vivo, sub-MIC of eugenol significantly decreased 88% S. aureus colonization in rat middle ear. Eugenol was observed to damage the cell-membrane and cause a leakage of the cell contents. At sub-inhibitory concentration, it decreases the expression of biofilm-and enterotoxin-related genes. Eugenol showed a synergistic effect with carvacrol on the eradication of pre-established biofilms.

Conclusion/Major Finding

This study demonstrated that eugenol exhibits notable activity against MRSA and MSSA clinical strains biofilms. Eugenol inhibited biofilm formation, disrupted the cell-to-cell connections, detached the existing biofilms, and killed the bacteria in biofilms of both MRSA and MSSA with equal effectiveness. Therefore, eugenol may be used to control or eradicate S. aureus biofilm-related infections.     

Comparative Evaluation of MRSA Nasal Colonization Epidemiology in the Urban and Rural Secondary School Community of Kurdistan,Iraq

BackgroundTo study the nasal carriage rate of Staphylococcus aureus (S. aureus) (including methicillin-resistant strains) in secondary school community of the urban and rural districts of the Kurdistan region of Iraq, a cross-sectional population based survey was carried out in the city Duhok and rural areas of Amedya, Akre and Zakho.MethodsNasal swabs were obtained from nostrils of 509 students aged 14-23 years. Resistance to methicillin was assessed by Kirby-Bauer disk diffusion and agar dilution assay. Vancomycin sensitivity was also tested on Muller-Hinton agar.ResultsIt was found that the frequency of overall S. aureus nasal carriage (SANC) was 17.75% (90/509, CI₉₅, 14.58–21.42%). In urban areas, the carriage rate was 20.59% (49/239, CI₉₅, 15.64–26.29%), whereas it was 15.24% (41/270, CI₉₅, 11.17–20.10%) in rural districts. The frequency of methicillin-resistant S. aureus (MRSA) among the isolated strains was found to be 2.04% (1/49) and 21.95% (9/41) in urban and rural areas respectively. It was found that in urban residents, the odd ratio (OR) of acquiring SANC was 1.44 (CI₉₅, 0.91-2.27%) and risk ratio (RR) was at least 1.35 (CI₉₅, 0.92-1.96%) while OR decreased to 0.12 (CI₉₅, 0.01-0.96%) for MRSA carriage. Hence, the S. aureus carriage rate was higher in urban districts compared to rural areas while more MRSA were found in rural areas compared to urban districts. All studied strains were sensitive to vancomycin.ConclusionThis study provided baseline information for S. aureus nasal colonization in the region. Also, it showed that living in rural areas increased the odds of MRSA colonization. More attention should be paid to control MRSA colonization in rural communities.