Characteristics of the MRSA clone with reduced susceptibility to vancomycin

The MIC of vancomycin was determined for all S. aureus strains isolated during 1997 in one hospital. MIC values for most isolates were in the range of 0.5-2 mg/l. In 18 strains, MIC was = 6 mg/L. All these strains were MRSA. Recently described VISA strains possessed MIC values for vancomycin equal or higher than 8 mg/l and such strains were not detected in the investigated group. Although strains with MIC = 6 mg/l are not VISA, but they are candidate for reduced vancomycin susceptibility, e.g. during therapy in compromised patients. Analysis of DNA of these strains by pulsed-field gel electrophoresis (PFGE) revealed that 15 of them shared a significant similarity, allowing to place them in the same group. The comparison data of phage patterns as well as antibiotic resistance patterns strongly suggest that all these strains were derivatives of a single clone.     

MRSA lineage USA300 isolated from bloodstream infections exhibit altered virulence regulation

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Seasonality of MRSA infections

Using MRSA isolates submitted to our hospital microbiology laboratory January 2001–March 2010 and the number of our emergency department (ED) visits, quarterly community-associated (CA) and hospital-associated (HA) MRSA infections were modeled using Poisson regressions. For pediatric patients, approximately 1.85x (95% CI 1.45x–2.36x, adj. p<0.0001) as many CA-MRSA infections per ED visit occurred in the second two quarters as occurred in the first two quarters. For adult patients, 1.14x (95% CI 1.01x–1.29x, adj.p = 0.03) as many infections per ED visit occurred in the second two quarters as in the first two quarters. Approximately 2.94x (95% CI 1.39x–6.21x, adj.p = 0.015) as many HA-MRSA infections per hospital admission occurred in the second two quarters as occurred in the first two quarters for pediatric patients. No seasonal variation was observed among adult HA-MRSA infections per hospital admission. We demonstrated seasonality of MRSA infections and provide a summary table of similar observations in other studies.     

Methicillin-resistant Staphylococcus capitis with reduced vancomycin susceptibility causes late-onset sepsis in intensive care neonates

Background

Coagulase-negative staphylococci, mainly Staphylococcus epidermidis, are the most frequent cause of late-onset sepsis (LOS) in the neonatal intensive care unit (NICU) setting. However, recent reports indicate that methicillin-resistant, vancomycin-heteroresistant Staphylococcus capitis could emerge as a significant pathogen in the NICU. We investigated the prevalence, clonality and vancomycin susceptibility of S. capitis isolated from the blood of NICU infants and compared these data to adult patients.

Methodology/Principal Findings

We conducted a retrospective laboratory-based survey of positive blood cultures in NICU infants ≥3 days of age (n = 527) and in adult ICU patients ≥18 years of age (n = 1473) who were hospitalized from 2004 to 2009 in two hospital centers in Lyon, France. S. capitis was the most frequent pathogen in NICU infants, ahead of S. epidermidis (39.1% vs. 23.5% of positive blood cultures, respectively). Conversely, S. capitis was rarely found in adult ICU patients (1.0%) compared to S. epidermidis (15.3%). S. capitis bloodstream isolates were more frequently resistant to methicillin when collected from NICU infants than from adult patients (95.6% vs. 53.3%, respectively). Furthermore, we collected and characterized 53 S. capitis bloodstream isolates from NICU infants and adult patients from six distant cities. All methicillin-resistant S. capitis isolates from NICU infants were clonally related as determined by pulsed-field gel electrophoresis. These isolates harbored a type V-related staphylococcal chromosomal cassette mec element, and constantly showed either vancomycin resistance (37.5%) or heteroresistance (62.5%). Conversely, the isolates that were collected outside of the NICU were genetically diverse and displayed much lower rates of vancomycin resistance and heteroresistance (7.7% and 23.1%, respectively).

Conclusions/Significance

A clonal population of methicillin-resistant S. capitis strains has spread into several French NICUs. These isolates exhibit reduced susceptibility to vancomycin, which is the most widely used antimicrobial agent in the NICU setting.     

Rapid detection of Staphylococcus aureus strains having reduced susceptibility to vancomycin using a chemiluminescence-based drug-susceptibility test

Current drug-susceptibility tests used routinely in clinical laboratories sometimes fail to identify strains of Staphylococcus aureus with reduced susceptibility to vancomycin. To solve this problem, we have developed a more sensitive and rapid method that measures bacterial metabolic activity by a chemiluminescence-based technique. This method is able to discriminate such strains from vancomycin-susceptible S. aureus with a sensitivity and specificity of > 95%. This rapid and reliable method appears to be promising for detection of vancomycin-intermediate S. aureus strains in clinical laboratories, and may supersede classical susceptibility testing.     

主动监测培养对于控制院内MRSA感染的效果

目的探讨主动监测培养对于住院患者耐甲氧西林金黄色葡萄球菌（MRSA）感染控制情况的效果。方法统计沈阳军区总医院2011-2013年MRSA培养阳性率、感染率等相关数据,以6个月为单位,对实施主动监测培养前后各时间段情况进行比较。结果实施监测培养后MRSA培养阳性人数一度增加,由原平均每月不足10人,增至2012年下半年的平均约12人/月。后逐渐下降,2013年下半年降至约平均9人/月,与2012年上半年相比,差异有统计学意义（P〈0.05）。MRSA感染发病率在实施监测培养后呈下降趋势,由最初1.3‰-1.4‰降至2013年下半年的0.49‰,该数值与2013年上半年相比差异有统计学意义（P〈0.05）。抗MRSA抗生素使用量在引入监测培养后减少。2013年下半年用量降至约平均65支/月,与2013年上半年相比,差异有统计学意义（P〈0.05）。结论主动检测培养为院内原有MRSA感染检测的重要补充。若MRSA筛查培养阳性可早期采取相应干预手段,有效防止院内感染发生,促进了抗生素的合理应用。     

Trypanosoma cruzi benznidazole susceptibility in vitro does not predict the therapeutic outcome of human Chagas disease

Therapeutic failure of benznidazole (BZ) is widely documented in Chagas disease and has been primarily associated with variations in the drug susceptibility of Trypanosoma cruzi strains. In humans, therapeutic success has been assessed by the negativation of anti-T. cruzi antibodies, a process that may take up to 10 years. A protocol for early screening of the drug resistance of infective strains would be valuable for orienting physicians towards alternative therapies, with a combination of existing drugs or new anti-T. cruzi agents. We developed a procedure that couples the isolation of parasites by haemoculture with quantification of BZ susceptibility in the resultant epimastigote forms. BZ activity was standardized with reference strains, which showed IC?? to BZ between 7.6-32 μM. The assay was then applied to isolates from seven chronic patients prior to administration of BZ therapy. The IC?? of the strains varied from 15.6 ± 3-51.4 ± 1 μM. Comparison of BZ susceptibility of the pre-treatment isolates of patients considered cured by several criteria and of non-cured patients indicates that the assay does not predict therapeutic outcome. A two-fold increase in BZ resistance in the post-treatment isolates of two patients was verified. Based on the profile of nine microsatellite loci, sub-population selection in non-cured patients was ruled out.     

The antimicrobial susceptibility,biofilm formation and genotypic profiles of Staphylococcus haemolyticus from bloodstream infections

We analysed the antimicrobial susceptibility, biofilm formation and genotypic profiles of 27 isolates of Staphylococcus haemolyticus obtained from the blood of 19 patients admitted to a hospital in Rio de Janeiro, Brazil. Our analysis revealed a clinical significance of 36.8% and a multi-resistance rate of 92.6% among these isolates. All but one isolate carried the mecA gene. The staphylococcal cassette chromosome mec type I was the most prevalent mec element detected (67%). Nevertheless, the isolates showed clonal diversity based on pulsed-field gel electrophoresis analysis. The ability to form biofilms was detected in 66% of the isolates studied. Surprisingly, no icaAD genes were found among the biofilm-producing isolates.     

Inactivation of mprF affects vancomycin susceptibility in Staphylococcus aureus

A chemically generated mutant of Staphylococcus aureus RN4220, GC6668, was isolated that had a fourfold increase in resistance to vancomycin. This phenotype reverted back to susceptibility by insertional mutagenesis with Tn917. In a selected set of revertants, Tn917 insertion was mapped to a unique chromosomal region upstream of mprF, a recently described gene that determines staphylococcal resistance to several host defense peptides. The genetic linkage between the vancomycin susceptibility and Tn917 insertion was then confirmed by transduction backcrosses into both GC6668 and GISA isolates, MER-S12 and HT2002 0127. Northern blot analysis, insertional inactivation and complementation experiments showed that mprF mediates vancomycin susceptibility in S. aureus. The inactivation of mprF by Tn917 insertion in HT2002 0127 caused a significant increase in the binding of vancomycin to the cell membranes. This observation serves as a likely mechanism of the increased vancomycin susceptibility associated with mprF inactivation.     

Alterations of cell wall structure and metabolism accompany reduced susceptibility to vancomycin in an isogenic series of clinical isolates of Staphylococcus aureus

A series of isogenic methicillin-resistant Staphylococcus aureus isolates recovered from a bacteremic patient were shown to acquire gradually increasing levels of resistance to vancomycin during chemotherapy with the drug (K. Sieradzki, T. Leski, L. Borio, J. Dick, and A. Tomasz, J. Clin. Microbiol. 41:1687-1693, 2003). We compared properties of the earliest (parental) vancomycin-susceptible isolate, JH1 (MIC, 1 microg/ml), to two late (progeny) isolates, JH9 and JH14 (vancomycin MIC, 8 microg/ml). The resistant isolates produced abnormally thick cell walls and poorly separated cells when grown in antibiotic-free medium. Chemical analysis of the resistant isolates showed decreased cross-linkage of the peptidoglycan and drastically reduced levels of PBP4 as determined by the fluorographic assay. Resistant isolates showed reduced rates of cell wall turnover and autolysis. In vitro hydrolysis of resistant cell walls by autolytic extracts prepared from either susceptible or resistant strains was also slow, and this abnormality could be traced to a quantitative (or qualitative) change in the wall teichoic acid component of resistant isolates. Some change in the structure and/or metabolism of teichoic acids appears to be an important component of the mechanism of decreased susceptibility to vancomycin in S. aureus.     

Impact of aging on viral infections

Older people are more susceptible to a variety of viral infections, including those that induce respiratory disease, resulting in higher morbidity and mortality than younger people. Aging impacts both innate and adaptive arms of the immune system to impair control of viral infections. This review will summarize key findings on how aging impacts immunity to viral infection.     

血流感中的病原菌分布及耐药性分析

目的了解血流感染中的病原菌种类、分布及耐药性,为临床合理选用抗菌药物提供依据。方法按照无菌操作方法采集疑为血流感染患者的血液标本进行血培养,采用美国BD公司PHOENIX-100全自动细菌鉴定药敏系统进行细菌鉴定及药敏试验,并对结果进行统计分析。结果共检出1080株病原菌,其中革兰阴性杆菌630株（占58．3％）,革兰阳性球菌428株（占39．6％）,真菌22株（占2．1％）。药敏结果显示：革兰阳性球菌对万古霉素、利奈唑胺敏感率最高,对青霉素、红霉素、头孢菌素等耐药率较高。革兰阴性杆菌对碳青霉烯类、哌拉西林／他唑巴坦、头孢哌酮／舒巴坦敏感率较高,对青霉素类、头孢菌素类和喹诺酮类耐药率较高。结论引起血流感染的病原菌分布复杂,耐药率较高,临床应提高血培养送检率,根据药敏结果合理选用抗菌药物,以减少多重耐药菌的发生和传播。     

鲍曼不动杆菌血流感染的危险因素及预后分析

目的研究院内获得性鲍曼不动杆菌血流感染的临床特点、治疗情况、分析导致鲍曼不动杆菌血流感染的危险因素,同时总结泛耐药鲍曼不动杆菌感染患者死亡危险因素,为临床防治泛耐药鲍曼不动杆菌血流感染提供指导。方法采用病例对照研究的方法,回顾性分析2012年4月至2015年6月丽水市中心医院住院的35例鲍曼不动杆菌血流感染患者临床资料,包括基础疾病,病原菌分布情况,临床特征,危险因素,治疗及预后转归情况,根据细菌耐药情况,分为泛耐药鲍曼不动杆菌17例与非耐药鲍曼不动杆菌18例。按入院28天预后转归情况,将35例鲍曼不动杆菌血流感染患者进一步分为好转组26例与死亡组9例。结果采取Fisher精确检验比较两组间差异,结果显示原发感染灶不明,不恰当使用广谱抗菌药物,住ICU大于2周,其他部位培养到鲍曼不动杆菌,同期ICU内泛耐药鲍曼不动杆菌流行等危险因素,存在显著性差异(P0.05);Logistic多因素回归分析鲍曼不动杆菌血流感染患者死亡危险因素,结果显示持续血小板减少3×109/L、APACHEII评分≥20分、脓毒症休克、多脏器功能衰竭是导致患者死亡的独立危险因素(P0.05)。结论原发感染灶不明和不恰当使用广谱抗菌药物是泛耐药鲍曼不动杆菌血流感染主要危险因素;持续血小板减少3×109/L、APACHEII评分≥20分、脓毒症休克、多脏器功能衰竭是鲍曼不动杆菌血流感染患者主要的死亡独立危险因素。     

Bacterial and fungal bloodstream infections in patients at the University Hospital of Cracow

In presented material evaluation of changes in sepsis and types of bloodstream infections of hospitalized patients in Wards of the University Hospital in Cracow were examined. Results of 9,138 blood cultures studied in years 1989-1999 were analysed. All of the blood samples were recovered from 4,656 infected adults at Clinics of the University Hospital in Cracow. Microbiological blood examinations were held in system of constant monitoring of isolated cultures applying BacT/Alert--colorimetric system (Organon Teknika). Cultured micro--organisms were identified using commercial biochemical tests (bio-Merieux). During period of research changes of profile of isolated microorganisms was observed. Percentage of blood infections of Enterococcus spp. etiology increased from 2.2% in 1989 to 9.8% in 1997-98 (p = 0.014). Dynamic growth of non-fermentative S. maltophilia bacilli to 5.5% (p = 0.036) and Serratia marcescens to 13.8% (p = 0.042) in 1999 was revealed. Designed according to our research review of fungal flora in years 1989-1999 revealed tendency of systematic growth of invasive candidemia frequency, from 1.1% to 10.4%. Diagnostic and therapeutic profile of Departments was in a strict connection with increase of the number and meaning of the politiological bacteremias (p = 0.036) in total number of systemic infections cases.     

Computer aided screening and evaluation of herbal therapeutics against MRSA infections

Methicillin resistant Staphylococcus aureus (MRSA), a pathogenic bacterium that causes life threatening outbreaks such as community-onset and nosocomial infections has emerged as 'superbug'. The organism developed resistance to all classes of antibiotics including the best known Vancomycin (VRSA). Hence, there is a need to develop new therapeutic agents. This study mainly evaluates the potential use of botanicals against MRSA infections. Computer aided design is an initial platform to screen novel inhibitors and the data finds applications in drug development. The drug-likeness and efficiency of various herbal compounds were screened by ADMET and docking studies. The virulent factor of most of the MRSA associated infections are Penicillin Binding Protein 2A (PBP2A) and Panton-Valentine Leukocidin (PVL). Hence, native structures of these proteins (PDB: 1VQQ and 1T5R) were used as the drug targets. The docking studies revealed that the active component of Aloe vera, β-sitosterol (3S, 8S, 9S, 10R, 13R, 14S, 17R) -17- [(2R, 5R)-5-ethyl-6-methylheptan-2-yl] -10, 13-dimethyl 2, 3, 4, 7, 8, 9, 11, 12, 14, 15, 16, 17- dodecahydro-1H-cyclopenta [a] phenanthren-3-ol) showed best binding energies of -7.40 kcal/mol and -6.34 kcal/mol for PBP2A and PVL toxin, respectively. Similarly, Meliantriol (1S-1-[ (2R, 3R, 5R)-5-hydroxy-3-[(3S, 5R, 9R, 10R, 13S, 14S, 17S)-3-hydroxy 4, 4, 10, 13, 14-pentamethyl-2, 3, 5, 6, 9, 11, 12, 15, 16, 17-decahydro-1H-cyclopenta[a] phenanthren-17-yl] oxolan-2-yl] -2- methylpropane-1, 2 diol), active compound in Azadirachta indica (Neem) showed the binding energies of -6.02 kcal/mol for PBP2A and -8.94 for PVL toxin. Similar studies were conducted with selected herbal compound based on pharmacokinetic properties. All in silico data tested in vitro concluded that herbal extracts of Aloe-vera, Neem, Guava (Psidium guajava), Pomegranate (Punica granatum) and tea (Camellia sinensis) can be used as therapeutics against MRSA infections.     

Bone grafts as vancomycin carriers in local therapy of resistant infections

The level of an antibiotic capable of inhibiting the etiological agent at the site of infection is an essential prerequisite for successful antibiotic therapy. In some cases, locally applied antibiotics may compensate for limitations of systemic administration and shorten systemic therapy. We aimed at verifying to what extent vancomycin (Van) bound to ground bone grafts is usable in the treatment of serious infections. The levels of released Van significantly exceeded the Van minimum inhibitory concentration, which can suppress Van-sensitive staphylococci and Van intermediate Staphylococcus aureus, for the whole period of a 16-day measurement. Our results indicate that bone grafts can be used as Van carriers in therapy of osteomyelitis caused by Van-sensitive Staphylococcus strains.     

Characteristics of nosocomial bloodstream infections at a Hungarian cardiac surgery centre

Nosocomial bloodstream infection (BSI) is a common finding in cardiac surgery intensive care units and is associated with excess mortality and hospital costs. Additional data are needed about incidence, characteristics, predictors, associated microorganisms of nosocomial BSI in cardiac surgical patients in order to refine measures to prevent nosocomial infections and to improve recovery outcomes in this patient population. The 3912 cardio-thoracic surgery patients from all age groups were admitted to the study at the Gottsegen Gy?rgy Hungarian Institute of Cardiology between January 1999 and December 2000. In each patient with BSI demographic, epidemiological and clinical variables were recorded along with potential risk factors. Incidence of associated pathogens and their possible sources were evaluated and outcome and mortality risk factors were assessed. There were a total of 134 episodes of BSI. The incidence was 34.25 per 1000 admissions. The leading microorganisms were staphylococci (37.7%). Bacteremic episodes developed secondary to an identifiable source in 27.6% of the cases, or were catheter-related (16.4%). In 56% of the cases the source was not identified. The crude mortality rate was 33.3%. Higher mortality rate was associated with intracardial grafts (p < 0.05), low left ventricular ejection fraction (p < 0.04), diabetes mellitus (p < 0.05), an age above 16 years (p < 0.02), severe sepsis (p < 0.001) and high APACHE II score (p < 0.001). As the identified main sources of BSI were intravascular lines, mortality from BSI could probably be reduced by paying more attention to the prevention, early recognition and prompt management of intravascular device associated infections.