Further Studies on Staphylococci in Meats, : III. Occurrence and Characteristics of Coagulase-positive Strains from a Variety of Nonfrozen Market Cuts

From 34 retail grocery stores and meat markets, 209 samples of nonfrozen meats were obtained and analyzed for coagulase-positive Staphylococcus aureus, employing six selective media. Sixty-seven (38.7%) of 173 samples obtained from 27 stores yielded S. aureus. No coagulase-positive S. aureus was isolated from 36 samples obtained from 7 of the stores. The 67 meats yielded 272 isolates from 10 different kinds of meats. There were 162 physiological strains represented when classified by store and 36 strains classified without regard to store of origin. The larger stores yielded fewer meats with staphylococci than the smaller stores. The meats from which S. aureus was recovered in the order of frequency of percentage recovery are as follows: chicken, pork liver, fish, spiced ham, round beef steak, hamburger, beef liver, pork chops, veal steak, and lamb chops. The following seven meats did not yield staphylococci: bologna, shucked oysters, olive and pickle loaf, salami, wieners, and chopped ham. Eighty-eight per cent of the isolates produced pigment, 85% were gelatinase positive, only 1 strain failed to form a precipitate on egg yolk agar, 92% formed deoxyribonuclease, 87% produced bound coagulase, 91% produced the α-hemolysin, 70% the δ-, 22% the β-, and 6% were nil in this regard. The isolates are compared with hospital and other food strains, and their possible source in the meats is discussed.     

Prevalence of Campylobacter spp., Escherichia coli, and Salmonella Serovars in Retail Chicken, Turkey, Pork, and Beef from the Greater Washington, D.C., Area

A total of 825 samples of retail raw meats (chicken, turkey, pork, and beef) were examined for the presence of Escherichia coli and Salmonella serovars, and 719 of these samples were also tested for Campylobacter spp. The samples were randomly obtained from 59 stores of four supermarket chains during 107 sampling visits in the Greater Washington, D.C., area from June 1999 to July 2000. The majority (70.7%) of chicken samples (n = 184) were contaminated with Campylobacter, and a large percentage of the stores visited (91%) had Campylobacter-contaminated chickens. Approximately 14% of the 172 turkey samples yielded Campylobacter, whereas fewer pork (1.7%) and beef (0.5%) samples were positive for this pathogen. A total of 722 Campylobacter isolates were obtained from 159 meat samples; 53.6% of these isolates were Campylobacter jejuni, 41.3% were Campylobacter coli, and 5.1% were other species. Of the 212 chicken samples, 82 (38.7%) yielded E. coli, while 19.0% of the beef samples, 16.3% of the pork samples, and 11.9% of the turkey samples were positive for E. coli. However, only 25 (3.0%) of the retail meat samples tested were positive for Salmonella. Significant differences in the bacterial contamination rates were observed for the four supermarket chains. This study revealed that retail raw meats are often contaminated with food-borne pathogens; however, there are marked differences in the prevalence of such pathogens in different meats. Raw retail meats are potential vehicles for transmitting food-borne diseases, and our findings stress the need for increased implementation of hazard analysis of critical control point (HACCP) and consumer food safety education efforts.     

Staphylococcus aureus Bacteraemia in a Tropical Setting: Patient Outcome and Impact of Antibiotic Resistance

Background

Most information on invasive Staphylococcus aureus infections comes from temperate countries. There are considerable knowledge gaps in epidemiology, treatment, drug resistance and outcome of invasive S. aureus infection in the tropics.

Methods

A prospective, observational study of S. aureus bacteraemia was conducted in a 1000-bed regional hospital in northeast Thailand over 1 year. Detailed clinical data were collected and final outcomes determined at 12 weeks, and correlated with antimicrobial susceptibility profiles of infecting isolates.

Principal Findings

Ninety-eight patients with S. aureus bacteraemia were recruited. The range of clinical manifestations was similar to that reported from temperate countries. The prevalence of endocarditis was 14%. The disease burden was highest at both extremes of age, whilst mortality increased with age. The all-cause mortality rate was 52%, with a mortality attributable to S. aureus of 44%. Methicillin-resistant S. aureus (MRSA) was responsible for 28% of infections, all of which were healthcare-associated. Mortality rates for MRSA and methicillin-susceptible S. aureus (MSSA) were 67% (18/27) and 46% (33/71), respectively (p = 0.11). MRSA isolates were multidrug resistant. Only vancomycin or fusidic acid would be suitable as empirical treatment options for suspected MRSA infection.

Conclusions

S. aureus is a significant pathogen in northeast Thailand, with comparable clinical manifestations and a similar endocarditis prevalence but higher mortality than industrialised countries. S. aureus bacteraemia is frequently associated with exposure to healthcare settings with MRSA causing a considerable burden of disease. Further studies are required to define setting-specific strategies to reduce mortality from S. aureus bacteraemia, prevent MRSA transmission, and to define the burden of S. aureus disease and emergence of drug resistance throughout the developing world.     

Multiplex Real-Time PCR for Detection of Staphylococcus aureus,mecA and Panton-Valentine Leukocidin (PVL) Genes from Selective Enrichments from Animals and Retail Meat

The aim of this study was to compare a real-time PCR assay, with a conventional culture/PCR method, to detect S. aureus, mecA and Panton-Valentine Leukocidin (PVL) genes in animals and retail meat, using a two-step selective enrichment protocol. A total of 234 samples were examined (77 animal nasal swabs, 112 retail raw meat, and 45 deli meat). The multiplex real-time PCR targeted the genes: nuc (identification of S. aureus), mecA (associated with methicillin resistance) and PVL (virulence factor), and the primary and secondary enrichment samples were assessed. The conventional culture/PCR method included the two-step selective enrichment, selective plating, biochemical testing, and multiplex PCR for confirmation. The conventional culture/PCR method recovered 95/234 positive S. aureus samples. Application of real-time PCR on samples following primary and secondary enrichment detected S. aureus in 111/234 and 120/234 samples respectively. For detection of S. aureus, the kappa statistic was 0.68–0.88 (from substantial to almost perfect agreement) and 0.29–0.77 (from fair to substantial agreement) for primary and secondary enrichments, using real-time PCR. For detection of mecA gene, the kappa statistic was 0–0.49 (from no agreement beyond that expected by chance to moderate agreement) for primary and secondary enrichment samples. Two pork samples were mecA gene positive by all methods. The real-time PCR assay detected the mecA gene in samples that were negative for S. aureus, but positive for Staphylococcus spp. The PVL gene was not detected in any sample by the conventional culture/PCR method or the real-time PCR assay. Among S. aureus isolated by conventional culture/PCR method, the sequence type ST398, and multi-drug resistant strains were found in animals and raw meat samples. The real-time PCR assay may be recommended as a rapid method for detection of S. aureus and the mecA gene, with further confirmation of methicillin-resistant S. aureus (MRSA) using the standard culture method.     

A Novel Gene,fudoh, in the SCCmec Region Suppresses the Colony Spreading Ability and Virulence of Staphylococcus aureus

Staphylococcus aureus colonies can spread on soft agar plates. We compared colony spreading of clinically isolated methicillin-sensitive S. aureus (MSSA) and methicillin-resistant S. aureus (MRSA). All MSSA strains showed colony spreading, but most MRSA strains (73%) carrying SCCmec type-II showed little colony spreading. Deletion of the entire SCCmec type-II region from these MRSA strains restored colony spreading. Introduction of a novel gene, fudoh, carried by SCCmec type-II into Newman strain suppressed colony spreading. MRSA strains with high spreading ability (27%) had no fudoh or a point-mutated fudoh that did not suppress colony spreading. The fudoh-transformed Newman strain had decreased exotoxin production and attenuated virulence in mice. Most community-acquired MRSA strains carried SCCmec type-IV, which does not include fudoh, and showed high colony spreading ability. These findings suggest that fudoh in the SCCmec type-II region suppresses colony spreading and exotoxin production, and is involved in S. aureus pathogenesis.     

Detection and quantification of methicillin‐resistant Staphylococcus aureus (MRSA) clones in retail meat products

Aims: The objective of the study was to determine the prevalence of methicillin‐resistant Staphylococcus aureus (MRSA) contamination of retail meat and to determine the level of contamination. Methods and Results: Pork (pork chops and ground pork), ground beef and chicken (legs, wings and thighs) were purchased at retail outlets in four Canadian provinces and tested for the presence of methicillin‐resistant Staph. aureus using qualitative and quantitative methods. MRSA was isolated from 9·6% of pork, 5·6% of beef and 1·2% of chicken samples (P = 0·0002). Low levels of MRSA were typically present, with 37% below the detection threshold for quantification and <100 CFU g^?1 present in most quantifiable samples. All isolates were classified as Canadian epidemic MRSA‐2 (CMRSA‐2) by pulsed field gel electrophoresis (PFGE), with two different PFGE subtypes, and were spa type 24/t242. Conclusions: MRSA contamination of retail meat is not uncommon. While CMRSA‐2, a human epidemic clone, has been found in pigs in Canada, the lack of isolation of livestock‐associated ST398 was surprising. Significance and Impact of the Study: The relevance of MRSA contamination of meat is unclear but investigation is required because of the potential for exposure from food handling. Sources of contamination require investigation because these results suggest that human or animal sources could be involved.     

Antimicrobial Resistance in Salmonella enterica Serovar Heidelberg Isolates from Retail Meats, Including Poultry, from 2002 to 2006

Salmonella enterica serovar Heidelberg frequently causes food-borne illness in humans. There are few data on the prevalence, antimicrobial susceptibility, and genetic diversity of Salmonella serovar Heidelberg isolates in retail meats. We compared the prevalences of Salmonella serovar Heidelberg in a sampling of 20,295 meats, including chicken breast (n = 5,075), ground turkey (n = 5,044), ground beef (n = 5,100), and pork chops (n = 5,076), collected during 2002 to 2006. Isolates were analyzed for antimicrobial susceptibility and compared genetically using pulsed-field gel electrophoresis (PFGE) and PCR for the bla_CMY gene. A total of 298 Salmonella serovar Heidelberg isolates were recovered, representing 21.6% of all Salmonella serovars from retail meats. One hundred seventy-eight (59.7%) were from ground turkey, 110 (36.9%) were from chicken breast, and 10 (3.4%) were from pork chops; none was found in ground beef. One hundred ninety-eight isolates (66.4%) were resistant to at least one compound, and 49 (16.4%) were resistant to at least five compounds. Six isolates (2.0%), all from ground turkey, were resistant to at least nine antimicrobials. The highest resistance in poultry isolates was to tetracycline (39.9%), followed by streptomycin (37.8%), sulfamethoxazole (27.7%), gentamicin (25.7%), kanamycin (21.5%), ampicillin (19.8%), amoxicillin-clavulanic acid (10.4%), and ceftiofur (9.0%). All isolates were susceptible to ceftriaxone and ciprofloxacin. All ceftiofur-resistant strains carried bla_CMY. PFGE using XbaI and BlnI showed that certain clones were widely dispersed in different types of meats and meat brands from different store chains in all five sampling years. These data indicate that Salmonella serovar Heidelberg is a common serovar in retail poultry meats and includes widespread clones of multidrug-resistant strains.     

Molecular Typing of MRSA and of Clinical Staphylococcus aureus Isolates from Ia?i,Romania

Romania is one of the countries with the highest prevalence of methicillin-resistant Staphylococcus aureus (MRSA) in the world. To obtain data on affiliation of MRSA to strains and clonal complexes and on the population of methicillin susceptible S. aureus (MSSA), clinical isolates from bloodstream infections, skin and soft tissue infections as well as from screening swabs were collected at hospitals in Ia?i, a city in the North-Eastern part of Romania. Isolates were characterised by microarray hybridisation. Nearly half of all isolates (47%), and about one third (34%) of bloodstream isolates were MRSA. The prevalence of the Panton-Valentine leukocidin (PVL) was also high (31% among MRSA, 14% among MSSA). The most common MRSA strain was a PVL-negative CC1-MRSA-IV that might have emerged locally, as a related MSSA was also common. PVL-positive CC8-MRSA-IV (“USA300”) and PVL-negative ST239-like MRSA-III were also frequently found while other MRSA strains were only sporadically detected. Among MSSA, PVL-positive CC121 as well as PVL-negative CC1, CC22 and CC45 predominated. Although this study provides only a snapshot of S. aureus/MRSA epidemiology in Romania, it confirms the high burden of MRSA and PVL on Romanian healthcare settings.     

Detection and Enumeration of Clostridium difficile Spores in Retail Beef and Pork

Recent studies have identified Clostridium difficile in food animals and retail meat, and concern has been raised about the potential for food to act as a source of C. difficile infection in humans. Previous studies of retail meat have relied on enrichment culture alone, thereby preventing any assessment of the level of contamination in meat. This study evaluated the prevalence of C. difficile contamination of retail ground beef and ground pork in Canada. Ground beef and ground pork were purchased from retail outlets in four Canadian provinces. Quantitative and enrichment culture was performed. Clostridium difficile was isolated from 28/230 (12%) samples overall: 14/115 (12%) ground beef samples and 14/115 (12%) ground pork samples (P = 1.0). For ground beef, 10/14 samples (71%) were positive by enrichment culture only. Of the 4 ground beef samples that were positive by direct culture, 20 spores/g were present in 2 while 120 and 240 spores/g were present in 1 each. For ground pork, 10/14 (71%) samples were positive by enrichment culture only. Of the 4 ground pork samples that were positive by direct culture, 20 spores/g were present in 3 while 60 spores/g were present in 1. Ribotype 078 predominated, consistent with some previous studies of C. difficile in food animals. Ribotype 027/North American pulsotype 1 was also identified in both retail beef and pork. This study has identified relatively common contamination of retail ground beef and pork with C. difficile spores; however, the levels of contamination were very low.Clostridium difficile is an important cause of enteric disease in humans. It is the most commonly diagnosed cause of hospital- and antimicrobial agent-associated diarrhea in people, and recent evidence suggests that it may be emerging as an important community-associated pathogen (2, 5). In addition to humans, C. difficile can be found in the intestinal tracts of a variety of animal species, including food animals, such as cattle and pigs (7, 10, 13). Clostridium difficile has also been found in retail meat (11, 12, 17), and concerns about the role of food in the epidemiology of community-associated C. difficile infection (CA-CDI) have been expressed (5, 8, 15).Initial studies have reported isolation of C. difficile from 4.6 to 45% of retail meat samples (11, 12, 17). However, all studies have used broth enrichment protocols, which could detect very low spore numbers and provide no information about the number of organisms present in a sample. No studies have evaluated numbers of C. difficile spores in food. While the infectious dose is not known, an understanding of the level of contamination may be an important factor in determining the relevance of contamination of food. Additionally, the use of different methods between studies hampers comparison of results. Recently a study was performed to evaluate different methods for qualitative and quantitative detection of C. difficile (21). This study determined that the detection threshold of enrichment culture could be at least as low as 10 spores/g of meat. It also determined that quantitative culture can accurately determine the level of contamination in experimentally inoculated meat samples, albeit with a higher detection threshold. The objective of this study was to determine the prevalence of C. difficile contamination of retail ground beef and ground pork using both qualitative and quantitative methods.     

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.     

Genome sequence of Staphylococcus aureus strain Newman and comparative analysis of staphylococcal genomes: polymorphism and evolution of two major pathogenicity islands

Strains of Staphylococcus aureus, an important human pathogen, display up to 20% variability in their genome sequence, and most sequence information is available for human clinical isolates that have not been subjected to genetic analysis of virulence attributes. S. aureus strain Newman, which was also isolated from a human infection, displays robust virulence properties in animal models of disease and has already been extensively analyzed for its molecular traits of staphylococcal pathogenesis. We report here the complete genome sequence of S. aureus Newman, which carries four integrated prophages, as well as two large pathogenicity islands. In agreement with the view that S. aureus Newman prophages contribute important properties to pathogenesis, fewer virulence factors are found outside of the prophages than for the highly virulent strain MW2. The absence of drug resistance genes reflects the general antibiotic-susceptible phenotype of S. aureus Newman. Phylogenetic analyses reveal clonal relationships between the staphylococcal strains Newman, COL, NCTC8325, and USA300 and a greater evolutionary distance to strains MRSA252, MW2, MSSA476, N315, Mu50, JH1, JH9, and RF122. However, polymorphism analysis of two large pathogenicity islands distributed among these strains shows that the two islands were acquired independently from the evolutionary pathway of the chromosomal backbones of staphylococcal genomes. Prophages and pathogenicity islands play central roles in S. aureus virulence and evolution.     

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.     

Identification of Gene Clusters Associated with Host Adaptation and Antibiotic Resistance in Chinese Staphylococcus aureus Isolates by Microarray-Based Comparative Genomics

A comparative genomic microarray comprising 2,457 genes from two whole genomes of S. aureus was employed for the comparative genome hybridization analysis of 50 strains of divergent clonal lineages, including methicillin-resistant S. aureus (MRSA), methicillin-susceptible S. aureus (MSSA), and swine strains in China. Large-scale validation was confirmed via polymerase chain reaction in 160 representative clinical strains. All of the 50 strains were clustered into seven different complexes by phylogenetic tree analysis. Thirteen gene clusters were specific to different S. aureus clones. Ten gene clusters, including seven known (vSa3, vSa4, vSaα, vSaβ, Tn5801, and phage ϕSa3) and three novel (C8, C9, and C10) gene clusters, were specific to human MRSA. Notably, two global regulators, sarH2 and sarH3, at cluster C9 were specific to human MRSA, and plasmid pUB110 at cluster C10 was specific to swine MRSA. Three clusters known to be part of SCCmec, vSa4 or Tn5801, and vSaα as well as one novel gene cluster C12 with homology with Tn554 of S. epidermidis were identified as MRSA-specific gene clusters. The replacement of ST239-spa t037 with ST239-spa t030 in Beijing may be a result of its acquisition of vSa4, phage ϕSa1, and ϕSa3. In summary, thirteen critical gene clusters were identified to be contributors to the evolution of host specificity and antibiotic resistance in Chinese S. aureus.     

Isolation of methicillin-resistant Staphylococcus aureus from caprine mastitis cases

There is no report on isolation of methicillin-resistant Staphylococcus aureus (MRSA) strains from mastitis infection in goats. This study reports two MRSA strains that were isolated from caprine mastitis. A total of 42 Staphylococcus aureus (S. aureus) strains collected from caprine mastitis cases between 2008 and 2009 were examined. Two (4.8%) out of 42 S. aureus strains were identified as MRSA by Kirby–Bauer disc diffusion and mecA polymerase chain reaction (PCR) methods. Based on the coa gene polymorphism, the goat strains were grouped into 6 types. By using rapid amplified polymorphic DNA (RAPD) assay, 10 different patterns were obtained from 42 S. aureus strains, and strains were located in 6 sub-groups. A total of 71% (n = 30) of the strains were clustered in one main group and placed 4 sub-groups by RAPD assay. The two MRSA strains produced identical patterns and distinguished from other S. aureus strains by RAPD method. This paper is the first report of MRSA isolation from caprine clinical mastitis cases.     

Prevalence of Livestock-Associated MRSA in Communities with High Pig-Densities in The Netherlands

Background

Recently, livestock-associated methicillin-resistant Staphylococcus aureus CC398 has been discovered in animals, livestock farmers and retail meat. This cross-sectional study aimed to determine the spread to persons not in direct contact with livestock in areas with a high density of pig farms.

Methodology/Principal Findings

With a random mailing in 3 selected municipalities in the Netherlands, adult persons were asked to fill in a questionnaire and to take a nose swab. In total, complete information was obtained on 583 persons. Of the 534 persons without livestock-contact, one was positive for MRSA (0.2%; 95% confidence interval, <0.01–1.2). Of the 49 persons who did indicate to be working at or living on a livestock farm, 13 were positive for MRSA (26.5%; 95% confidence interval, 16.1–40.4). All spa-types belonged to CC398.

Conclusions/Significance

Livestock-associated MRSA has a high prevalence in people with direct contact with animals. At this moment it has not spread from the farms into the community.     

Phage typing,PCR amplification for mecA gene,and antibiotic resistance patterns as epidemiologic markers in nosocomial outbreaks of methicillin resistant Staphylococcus aureus

Staphylococcus aureus is one of the major causes of community and hospital-acquired infections. Bacteriophage considered as a major risk factor acquires S. aureus new virulence genetic elements. A total number of 119 S. aureus isolated from different specimens obtained from (RKH) were distinguished by susceptibility to 19 antimicrobial agents, phage typing, and PCR amplification for mecA gene. All of MRSA isolates harbored mecA gene, except three unique isolates. The predominant phage group is belonging to the (mixed group). Phage group (II) considered as an epidemiological marker correlated to β-lactamase hyper producer isolates. MRSA isolates indicated high prevalence of phage group (II) with highly increase for phage types (Ø3A), which were correlated to the skin. Phage types (Ø80/Ø81) played an important roll in Community Acquired Methicillin Resistant S. aureus (CAMRSA). Three outpatients MRSA isolates had low multiresistance against Bacitracin (Ba) and Fusidic acid (FD), considered as CAMRSA isolates. It was detected that group I typed all FD-resistant MSSA isolates. Phage groups (M) and (II) were found almost to be integrated for Gentamycin (GN) resistance especially phage type (Ø95) which relatively increased up to 20% in MRSA. Tetracycline (TE) resistant isolates typed by groups (II) and (III) in MSSA. Only one isolate resistant to Sulphamethoxazole/Trimethoprim (SXT) was typed by (III/V) alone in MSSA. MRSA isolates resistant to Chloramphenicol (C) and Ba were typed by all groups except (V). It could be concluded that (PERSA) S. aureus isolates from the wound that originated and colonized, and started to build up multi-resistance against the topical treatment antibiotics. In this study, some unique sporadic isolates for both MRSA and MSSA could be used as biological, molecular and epidemiological markers such as prospective tools.     

The extreme drug resistance (XDR) Staphylococcus aureus strains among patients: A retrospective study

The objective of the present work was to observe and profile various antibiotic resistant strains of Staphylococcus aureus and highlight the need for continuous surveillance. Data regarding antibiotic-resistant S. aureus strains isolated and identified at the Medical Microbiology Department, King Khalid Hospital, Riyadh was obtained. Bacterial isolates were collected from several sites of infections in patients and an evaluation of susceptibility were carried out using a fully automated Vitek2 system. Relative frequency (%), odds ratios and Ward's minimum variance were calculated. The results showed that wounds were a source of more than 40% of the S. aureus (MRSA) strains that have ability to resist methicillin, and more than 45% of the methicillin-susceptible S. aureus (non-MRSA) strains. 40% of the isolates were MRSA (N = 251), and all MRSA strains were sensitive to vancomycin, daptomycin, teicoplanin, tigecycline, nitrofurantoin, and itraconazole while all non-MRSA (N = 338) strains were sensitive to vancomycin, cefoxitin, daptomycin, gentamicin, oxacillin, teicoplanin, tigecycline, and mupirocin. Strength of association between antibiotic-resistant S. aureus strains and source of samples (site of infection) was established. The study concluded that S. aureus strains had developed resistance towards 20 (for non-MRSA) and 22 (for MRSA) of the antibiotics tested. All MRSA strains were non-sensitive to amoxicillin/clavulanate, ampicillin cefoxitin, cefazolin, imipenem, oxacillin, and penicillin.     

Methicillin-Resistant Staphylococcus aureus (MRSA) Strain ST398 Is Present in Midwestern U.S. Swine and Swine Workers

Background

Recent research has demonstrated that many swine and swine farmers in the Netherlands and Canada are colonized with MRSA. However, no studies to date have investigated carriage of MRSA among swine and swine farmers in the United States (U.S.).

Methods

We sampled the nares of 299 swine and 20 workers from two different production systems in Iowa and Illinois, comprising approximately 87,000 live animals. MRSA isolates were typed by pulsed field gel electrophoresis (PFGE) using SmaI and EagI restriction enzymes, and by multi locus sequence typing (MLST). PCR was used to determine SCCmec type and presence of the pvl gene.

Results

In this pilot study, overall MRSA prevalence in swine was 49% (147/299) and 45% (9/20) in workers. The prevalence of MRSA carriage among production system A''s swine varied by age, ranging from 36% (11/30) in adult swine to 100% (60/60) of animals aged 9 and 12 weeks. The prevalence among production system A''s workers was 64% (9/14). MRSA was not isolated from production system B''s swine or workers. Isolates examined were not typeable by PFGE when SmaI was used, but digestion with EagI revealed that the isolates were clonal and were not related to common human types in Iowa (USA100, USA300, and USA400). MLST documented that the isolates were ST398.

Conclusions

These results show that colonization of swine by MRSA was very common on one swine production system in the midwestern U.S., suggesting that agricultural animals could become an important reservoir for this bacterium. MRSA strain ST398 was the only strain documented on this farm. Further studies are examining carriage rates on additional farms.     

Reduction of the Peptidoglycan Crosslinking Causes a Decrease in Stiffness of the Staphylococcus aureus Cell Envelope

We have used atomic-force microscopy (AFM) to probe the effect of peptidoglycan crosslinking reduction on the elasticity of the Staphylococcus aureus cell wall, which is of particular interest as a target for antimicrobial chemotherapy. Penicillin-binding protein 4 (PBP4) is a nonessential transpeptidase, required for the high levels of peptidoglycan crosslinking characteristic of S. aureus. Importantly, this protein is essential for β-lactam resistance in community-acquired, methicillin-resistant S. aureus (MRSA) strains but not in hospital-acquired MRSA strains. Using AFM in a new mode for recording force/distance curves, we observed that the absence of PBP4, and the concomitant reduction of the peptidoglycan crosslinking, resulted in a reduction in stiffness of the S. aureus cell wall. Importantly, the reduction in cell wall stiffness in the absence of PBP4 was observed both in community-acquired and hospital-acquired MRSA strains, indicating that high levels of peptidoglycan crosslinking modulate the overall structure and mechanical properties of the S. aureus cell envelope in both types of clinically relevant strains. Additionally, we were able to show that the applied method enables the separation of cell wall properties and turgor pressure.     

High genetic diversity among community-associated Staphylococcus aureus in Europe: results from a multicenter study

Background

Several studies have addressed the epidemiology of community-associated Staphylococcus aureus (CA-SA) in Europe; nonetheless, a comprehensive perspective remains unclear. In this study, we aimed to describe the population structure of CA-SA and to shed light on the origin of methicillin-resistant S. aureus (MRSA) in this continent.

Methods and Findings

A total of 568 colonization and infection isolates, comprising both MRSA and methicillin-susceptible S. aureus (MSSA), were recovered in 16 European countries, from community and community-onset infections. The genetic background of isolates was characterized by molecular typing techniques (spa typing, pulsed-field gel electrophoresis and multilocus sequence typing) and the presence of PVL and ACME was tested by PCR. MRSA were further characterized by SCCmec typing. We found that 59% of all isolates were associated with community-associated clones. Most MRSA were related with USA300 (ST8-IVa and variants) (40%), followed by the European clone (ST80-IVc and derivatives) (28%) and the Taiwan clone (ST59-IVa and related clonal types) (15%). A total of 83% of MRSA carried Panton-Valentine leukocidin (PVL) and 14% carried the arginine catabolic mobile element (ACME). Surprisingly, we found a high genetic diversity among MRSA clonal types (ST-SCCmec), Simpson’s index of diversity = 0.852 (0.788–0.916). Specifically, about half of the isolates carried novel associations between genetic background and SCCmec. Analysis by BURP showed that some CA-MSSA and CA-MRSA isolates were highly related, suggesting a probable local acquisition/loss of SCCmec.

Conclusions

Our results imply that CA-MRSA origin, epidemiology and population structure in Europe is very dissimilar from that of USA.