Clinical and molecular epidemiology of ciprofloxacin-susceptible MRSA encoding PVL in England and Wales

Clonal Complexes Distribution of Staphylococcus aureus Isolates from Clinical Samples from the Caribbean Islands

The aim of this study was to comprehensively characterise S. aureus from the Caribbean Islands of Trinidad and Tobago, and Jamaica. A total of 101 S. aureus/argenteus isolates were collected in 2020, mainly from patients with skin and soft tissue infections. They were characterised by DNA microarray allowing the detection of ca. 170 target genes and assignment to clonal complexes (CC)s and strains. In addition, the in vitro production of Panton-Valentine leukocidin (PVL) was examined by an experimental lateral flow assay. Two isolates were identified as S. argenteus, CC2596. The remaining S. aureus isolates were assigned to 21 CCs. The PVL rate among methicillin-susceptible S. aureus (MSSA) isolates was high (38/101), and 37 of the 38 genotypically positive isolates also yielded positive lateral flow results. The isolate that did not produce PVL was genome-sequenced, and it was shown to have a frameshift mutation in agrC. The high rate of PVL genes can be attributed to the presence of a known local CC8-MSSA clone in Trinidad and Tobago (n = 12) and to CC152-MSSA (n = 15). In contrast to earlier surveys, the USA300 clone was not found, although one MSSA isolate carried the ACME element, probably being a mecA-deficient derivative of this strain. Ten isolates, all from Trinidad and Tobago, were identified as MRSA. The pandemic ST239-MRSA-III strain was still common (n = 7), but five isolates showed a composite SCCmec element not observed elsewhere. Three isolates were sequenced. That showed a group of genes (among others, speG, crzC, and ccrA/B-4) to be linked to its SCC element, as previously found in some CC5- and CC8-MRSA, as well as in S. epidermidis. The other three MRSA belonged to CC22, CC72, and CC88, indicating epidemiological connections to Africa and the Middle East.

Current and emerging drug treatment strategies to tackle invasive community-associated methicillin-resistant Staphylococcus aureus (MRSA) infection: what are the challenges?

INTRODUCTION

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) infections represent a leading cause of purulent skin and soft tissue infections in some geographical regions. Traditionally, 'old antibiotics' such as trimethoprim-sulfamethoxazole, tetracyclines, clindamycin, chloramphenicol,vancomycin, and teicoplanin have been used to treat these infections, but these were often associated with low efficacy and excessive side effects and toxicity, especially nephrotoxicity. Along with the development of new compounds, the last decade has seen substantial improvements in the management of CA-MRSA infections.

AREAS COVERED

In this review, the authors discuss the current and emerging drug treatment strategies to tackle invasive CA-MRSA infections. Articles reported in this review were selected from through literature searches using the PubMed database.

EXPERT OPINION

The availability of new drugs showing a potent in vitro activity against CA-MRSA represents a unique opportunity to face the threat of resistance while potentially reducing toxicity. All these compounds represent promising options to enhance our antibiotic armamentarium. However, data regarding the use of these new drugs in real-life studies are limited and their best placement in therapy and in terms of optimization of medical resources and balance of cost-effectiveness requires further investigation.

Resistance and Molecular Characteristics of Methicillin-Resistant Staphylococcus aureus and Heterogeneous Vancomycin-Intermediate Staphylococcus aureus

Objective

To investigate the molecular epidemiology of Staphylococcus aureus (S. aureus) isolated from patients in the Yellow River Delta region and to construct antibiotic resistance profiles in different genetic backgrounds.

Methods

Antibiotics susceptibility testing, staphylococcal protein A (spa) typing and accessory gene regulator (agr) typing were performed for all the 204 strains. Isolates with the positive mecA gene and heterogeneous vancomycin-intermediate S. aureus (hVISA) were subjected to multilocus sequence typing (MLST) and Staphylococcal chromosomal cassettes mec (SCCmec) typing.

Results

Thirty-nine MRSA strains were identified by mecA gene. Twenty-two hVISA isolates including 9 MRSA and 13 methicillin-sensitive S. aureus (MSSA) strains were confirmed, the rest isolates (n = 182) were vancomycin-susceptible S. aureus (VSSA). 94.9% of MRSA and 63.6% of hVISA belonged to agrI. Fifty-seven distinct spa types including 5 novel types were mainly t309 (30.9%), t078 (11.8%) and t437 (11.8%). Fourteen sequence types (STs) containing 3 new STs were classified into 3 clone complexes (CCs) and 7 singletons among MRSA and hVISA isolates. Most MRSA isolates (87.2%) belonged to type Ⅳ SCCmec.

Conclusion

The predominant genotype among MRSA population was ST59-t437-agrI-IVa (53.8%), followed by ST72-t2431-agrI-IVF (15.4%). ST72 and CC5 (ST5/965/7197) were the most common hVISA clones. Both CC59 (ST59/7437) and ST72 clones were resistant to erythromycin and clindamycin among MRSA population. Strains of MSSA with phenotypic hVISA (MS-hVISA) exhibited a striking genetic diversity accompanied by the diversification of drug resistance patterns.

Outpatient decolonization after recurrent skin infection with Panton-Valentine leukocidin (PVL)-producing S. aureus-The importance of treatment repetition

BACKGROUND

Recurrent skin abscesses are often associated with Panton-Valentine leukocidin-producing strains of S. aureus (PVL-SA). Decolonization measures are required along with treatment of active infections to prevent re-infection and spreading. Even though most PVL-SA patients are treated as outpatients, there are few studies that assess the effectiveness of outpatient topical decolonization in PVL-SA patients.

METHODS

We assessed the results of topical decolonization of PVL-SA in a retrospective review of patient files and personal interviews. Successful decolonization was defined as the absence of any skin abscesses for at least 6 months after completion of the final decolonization treatment. Clinical and demographic data was assessed. An intention-to-treat protocol was used.

RESULTS

Our cohort consisted of 115 symptomatic patients, 66% from PVL-positive MSSA and 19% from PVL-positive MRSA. The remaining 16% consisted of symptomatic patients with close contact to PVL-SA positive index patients but without detection of PVL-SA. The majority of patients were female (66%). The median age was 29.87% of the patients lived in multiple person households. Our results showed a 48% reduction in symptomatic PVL-SA cases after the first decolonization treatment. The results also showed that the decrease continued with each repeated decolonization treatment and reached 89% following the 5th treatment. A built multivariable Cox proportional-hazards model showed that the absence of PVL-SA detection (OR 2.0) and living in single person households (OR 2.4) were associated with an independently increased chance of successful decolonization.

CONCLUSION

In our cohort, topical decolonization was a successful preventive measure for reducing the risk of PVL-SA skin abscesses in the outpatient setting. Special attention should be given to patients living in multiple person households because these settings could confer a risk that decolonization will not be successful.

Empyema thoracis secondary to community-acquired Panton-Valentine leukocidin (PVL) methicillin-resistant Staphylococcus aureus (MRSA) infection

We report a case of a previously fit middle-aged man presenting to the outpatient setting with unilateral pleural effusion, with minimal symptoms. On subsequent investigations, he was diagnosed with empyema thoracis secondary to Panton-Valentine leukocidin (PVL)-toxin positive community-acquired methicillin-resistant Staphylococcus aureus (MRSA). The patient was treated with prolonged antibiotics and pleural drainage, and he remained haemodynamically stable throughout hospital admission. PVL is a cytolytic exotoxin produced by some strains of S. aureus Such strains often cause recurrent skin and soft tissue infections, usually in previously fit and healthy individuals. Less commonly, invasive infections occur; these carry a high mortality rate if associated with necrotising pneumonia or septic shock. PVL genes are present in approximately 2% of clinical isolates of S. aureus in the UK. PVL-producing MRSA infections are on the rise and present significant clinical and public health challenges.

Methicillin-Resistant Staphylococcus aureus: Molecular Characterization, Evolution, and Epidemiology

Staphylococcus aureus, a major human pathogen, has a collection of virulence factors and the ability to acquire resistance to most antibiotics. This ability is further augmented by constant emergence of new clones, making S. aureus a "superbug." Clinical use of methicillin has led to the appearance of methicillin-resistant S. aureus (MRSA). The past few decades have witnessed the existence of new MRSA clones. Unlike traditional MRSA residing in hospitals, the new clones can invade community settings and infect people without predisposing risk factors. This evolution continues with the buildup of the MRSA reservoir in companion and food animals. This review focuses on imparting a better understanding of MRSA evolution and its molecular characterization and epidemiology. We first describe the origin of MRSA, with emphasis on the diverse nature of staphylococcal cassette chromosome mec (SCCmec). mecA and its new homologues (mecB, mecC, and mecD), SCCmec types (13 SCCmec types have been discovered to date), and their classification criteria are discussed. The review then describes various typing methods applied to study the molecular epidemiology and evolutionary nature of MRSA. Starting with the historical methods and continuing to the advanced whole-genome approaches, typing of collections of MRSA has shed light on the origin, spread, and evolutionary pathways of MRSA clones.

Diagnosis and management of Panton-Valentine leukocidin toxin associated Staphylococcus aureus infection: an update

The incidence of invasive Staphylococcus aureus (SA) infection has increased in the past decade and is associated with poor outcomes and high mortality rates. Of all the virulence factors, Panton-Valentine Leukocidin (PVL) has received the greatest attention. PVL producing SA strains are more likely to produce severe skin and soft tissue infections (SSTIs) and necrotizing pneumonia. This review focuses on the current evidence on PVL-SA virulence, epidemiology, clinical disease and treatment with relevance to healthcare in India.

Demography and Intercontinental Spread of the USA300 Community-Acquired Methicillin-Resistant Staphylococcus aureus Lineage

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) was recognized worldwide during the 1990s; in less than a decade, several genetically distinct CA-MRSA lineages carrying Panton-Valentine leukocidin genes have emerged on every continent. Most notably, in the United States, the sequence type 18-IV (ST8-IV) clone known as USA300 has become highly prevalent, outcompeting methicillin-susceptible S. aureus (MSSA) and other MRSA strains in both community and hospital settings. CA-MRSA bacteria are much less prevalent in Europe, where the European ST80-IV European CA-MRSA clone, USA300 CA-MRSA strains, and other lineages, such as ST22-IV, coexist. The question that arises is whether the USA300 CA-MRSA present in Europe (i) was imported once or on very few occasions, followed by a broad geographic spread, anticipating an increased prevalence in the future, or (ii) derived from multiple importations with limited spreading success. In the present study, we applied whole-genome sequencing to a collection of French USA300 CA-MRSA strains responsible for sporadic cases and micro-outbreaks over the past decade and United States ST8 MSSA and MRSA isolates. Genome-wide phylogenetic analysis demonstrated that the population structure of the French isolates is the product of multiple introductions dating back to the onset of the USA300 CA-MRSA clone in North America. Coalescent-based demography of the USA300 lineage shows that a strong expansion occurred during the 1990s concomitant with the acquisition of the arginine catabolic mobile element and antibiotic resistance, followed by a sharp decline initiated around 2008, reminiscent of the rise-and-fall pattern previously observed in the ST80 lineage. A future expansion of the USA300 lineage in Europe is therefore very unlikely.

To trace the origin, evolution, and dissemination pattern of the USA300 CA-MRSA clone in France, we sequenced a collection of strains of this lineage from cases reported in France in the last decade and compared them with 431 ST8 strains from the United States. We determined that the French CA-MRSA USA300 sporadic and micro-outbreak isolates resulted from multiple independent introductions of the USA300 North American lineage. At a global level, in the transition from an MSSA lineage to a successful CA-MRSA clone, it first became resistant to multiple antibiotics and acquired the arginine catabolic mobile element and subsequently acquired resistance to fluoroquinolones, and these two steps were associated with a dramatic demographic expansion. This expansion was followed by the current stabilization and expected decline of this lineage. These findings highlight the significance of horizontal gene acquisitions and point mutations in the success of such disseminated clones and illustrate their cyclic and sporadic life cycle.

Staphylococcus aureus-Associated Skin and Soft Tissue Infections: Anatomical Localization, Epidemiology, Therapy and Potential Prophylaxis

Skin and soft tissue infections (SSTIs) are among the most common infections worldwide. They range in severity from minor, self-limiting, superficial infections to life-threatening diseases requiring all the resources of modern medicine. Community (CA) and healthcare (HA) acquired SSTIs are most commonly caused by Staphylococcus aureus . They have variable presentations ranging from impetigo and folliculitis to surgical site infections (SSIs). Superficial SSTIs may lead to even more invasive infections such as bacteraemia and osteomyelitis. Here we describe the anatomical localization of the different SSTI associated with S. aureus, the virulence factors known to play a role in these infections, and their current epidemiology. Current prevention and treatment strategies are also discussed. Global epidemiological data show increasing incidence and severity of SSTIs in association with methicillin-resistant S. aureus strains (MRSA). CA-SSTIs are usually less morbid compared to other invasive infections caused by S. aureus, but they have become the most prevalent, requiring a great number of medical interventions, extensive antibiotic use, and therefore a high cost burden. Recurrence of SSTIs is common after initial successful treatment, and decolonization strategies have not been effective in reducing recurrence. Furthermore, decolonization approaches may be contributing to the selection and maintenance of multi-drug resistant strains. Clinical studies from the early 1900s and novel autovaccination approaches suggest an alternative strategy with potential effectiveness: using vaccines to control S. aureus cutaneous infections.

Staphylococcus aureus spa type t437: identification of the most dominant community-associated clone from Asia across Europe

Methicillin-resistant Staphylococcus aureus (MRSA) belonging to the multilocus sequence type clonal complex 59 (MLST CC59) is the predominant community-associated MRSA clone in Asia. This clone, which is primarily linked with the spa type t437, has so far only been reported in low numbers among large epidemiological studies in Europe. Nevertheless, the overall numbers identified in some Northern European reference laboratories have increased during the past decade. To determine whether the S. aureus t437 clone is present in other European countries, and to assess its genetic diversity across Europe, we analysed 147 S. aureus t437 isolates from 11 European countries collected over a period of 11 years using multiple locus variable number tandem repeat fingerprinting/analysis (MLVF/MLVA) and MLST. Additionally 16 S. aureus t437 isolates from healthy carriers and patients from China were included. Most isolates were shown to be monophyletic with 98% of the isolates belonging to the single MLVA complex 621, to which nearly all included isolates from China also belonged. More importantly, all MLST-typed isolates belonged to CC59. Our study implies that the European S. aureus t437 population represents a genetically tight cluster, irrespective of the year, country and site of isolation. This underpins the view that S. aureus CC59 has been introduced into several European countries, not being restricted to particular geographical regions or specific host environments. The European S. aureus t437 isolates thus bear the general hallmarks of a high-risk clone.

Panton-Valentine leukocidin (PVL)-positive health care-associated methicillin-resistant Staphylococcus aureus isolates are associated with skin and soft tissue infections and colonized mainly by infective PVL-encoding bacteriophages

The emergence of Panton-Valentine leukocidin (PVL)-positive methicillin-resistant Staphylococcus aureus (MRSA) is a public health concern worldwide. PVL is associated with community-associated MRSA and is linked to skin and soft tissue infections (SSTIs). However, PVL genes have also been detected in health care-associated (HA) MRSA isolates. The diseases associated with PVL-positive HA-MRSA isolates and the distributions of PVL-encoding bacteriophages in HA-MRSA have not been determined. In this study, a total of 259 HA-MRSA strains isolated between 2009 and 2012 in China from inpatients with SSTIs, pneumonia, and bacteremia were selected for molecular typing, including staphylococcal cassette chromosome mec typing, multilocus sequence typing, and staphylococcal protein A gene typing. The PVL genes and PVL bacteriophages in the MRSA isolates were characterized by PCR. Among the tested MRSA isolates, 28.6% (74/259) were PVL positive. The high prevalence of PVL-carrying HA-MRSA was observed to be associated with SSTIs but not with pneumonia or bacteremia. The PVL-positive HA-MRSA isolates were colonized mainly by infective PVL phages, namely, Φ7247PVL, ΦSLT, and ΦSa2958. The distribution of PVL-carrying bacteriophages differed geographically. Our study highlights the potential risk of the emergence of multidrug-resistant HA-MRSA strains with increased virulence.

Impact of psm-mec in the mobile genetic element on the clinical characteristics and outcome of SCCmec-II methicillin-resistant Staphylococcus aureus bacteraemia in Japan

Over-expression of alpha-phenol-soluble modulins (PSMs) results in high virulence of community-associated methicillin-resistant Staphylococcus aureus (MRSA). The psm-mec gene, located in the mobile genetic element SCCmec-II, suppresses PSMαs production. Fifty-two patients with MRSA bacteraemia were enrolled. MRSA isolates were evaluated with regard to the psm-mec gene sequence, bacterial virulence, and the minimum inhibitory concentration (MIC) of vancomycin and teicoplanin. Fifty-one MRSA isolates were classified as SCCmec-II, and 10 had one point mutation in the psm-mec promoter. We compared clinical characteristics and outcomes between mutant MRSA and wild-type MRSA. Production of PSMα3 in mutant MRSA was significantly increased, but biofilm formation was suppressed. Wild-type MRSA caused more catheter-related bloodstream infections (30/41 vs. 3/10, p 0.0028), whereas mutant MRSA formed more deep abscesses (4/10 vs. 3/41, p 0.035). Bacteraemia caused by mutant MRSA was associated with reduced 30-day mortality (1/10 vs. 13/41, p 0.25), although this difference was not significant. The MIC90 of teicoplanin was higher for wild-type MRSA (1.5 mg/L vs. 1 mg/L), but the MIC of vancomycin was not different between the two groups. The 30-day mortality of MRSA with a high MIC of teicoplanin (≥1.5 mg/L) was higher than that of strains with a lower MIC (≤0.75 mg/L) (6/10 vs. 6/33, p 0.017). Mutation of the psm-mec promoter contributes to virulence of SCCmec-II MRSA, and the product of psm-mec may determine the clinical characteristics of bacteraemia caused by SCCmec-II MRSA, but it does not affect mortality.

Panton-Valentine leukocidin-positive Staphylococcus aureus in Ireland from 2002 to 2011: 21 clones, frequent importation of clones, temporal shifts of predominant methicillin-resistant S. aureus clones, and increasing multiresistance

There has been a worldwide increase in community-associated (CA) methicillin-resistant Staphylococcus aureus (MRSA) infections. CA-MRSA isolates commonly produce the Panton-Valentine leukocidin toxin encoded by the pvl genes lukF-PV and lukS-PV. This study investigated the clinical and molecular epidemiologies of pvl-positive MRSA and methicillin-susceptible S. aureus (MSSA) isolates identified by the Irish National MRSA Reference Laboratory (NMRSARL) between 2002 and 2011. All pvl-positive MRSA (n=190) and MSSA (n=39) isolates underwent antibiogram-resistogram typing, spa typing, and DNA microarray profiling for multilocus sequence type, clonal complex (CC) and/or sequence type (ST), staphylococcal cassette chromosome mec type assignment, and virulence and resistance gene detection. Where available, patient demographics and clinical data were analyzed. The prevalence of pvl-positive MRSA increased from 0.2% to 8.8%, and that of pvl-positive MSSA decreased from 20% to 2.5% during the study period. The pvl-positive MRSA and MSSA isolates belonged to 16 and 5 genotypes, respectively, with CC/ST8-MRSA-IV, CC/ST30-MRSA-IV, CC/ST80-MRSA-IV, CC1/ST772-MRSA-V, CC30-MSSA, CC22-MSSA, and CC121-MSSA predominating. Temporal shifts in the predominant pvl-positive MRSA genotypes and a 6-fold increase in multiresistant pvl-positive MRSA genotypes occurred during the study period. An analysis of patient data indicated that pvl-positive S. aureus strains, especially MRSA strains, had been imported into Ireland several times. Two hospital and six family clusters of pvl-positive MRSA were identified, and 70% of the patient isolates for which information was available were from patients in the community. This study highlights the increased burden and changing molecular epidemiology of pvl-positive S. aureus in Ireland over the last decade and the contribution of international travel to the influx of genetically diverse pvl-positive S. aureus isolates into Ireland.

Clinical significance of methicillin-resistant Staphylococcus aureus colonization on hospital admission: one-year infection risk

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) nasal colonization among inpatients is a well-established risk factor for MRSA infection during the same hospitalization, but the long-term risk of MRSA infection is uncertain. We performed a retrospective cohort study to determine the one-year risk of MRSA infection among inpatients with MRSA-positive nasal polymerase chain reaction (PCR) tests confirmed by positive nasal culture (Group 1), patients with positive nasal PCR but negative nasal culture (Group 2), and patients with negative nasal PCR (Group 3).

METHODOLOGY/PRINCIPAL FINDINGS

Subjects were adults admitted to a four-hospital system between November 1, 2006 and March 31, 2011, comprising 195,255 admissions. Patients underwent nasal swab for MRSA PCR upon admission; if positive, nasal culture for MRSA was performed; if recovered, MRSA was tested for Panton-Valentine Leukocidin (PVL). Outcomes included MRSA-positive clinical culture and skin and soft tissue infection (SSTI). Group 1 patients had a one-year risk of MRSA-positive clinical culture of 8.0% compared with 3.0% for Group 2 patients, and 0.6% for Group 3 patients (p<0.001). In a multivariable model, the hazard ratios for future MRSA-positive clinical culture were 6.52 (95% CI, 5.57 to 7.64) for Group 1 and 3.40 (95% CI, 2.70 to 4.27) for Group 2, compared with Group 3 (p<0.0001). History of MRSA and concurrent MRSA-positive clinical culture were significant risk factors for future MRSA-positive clinical culture. Group 1 patients colonized with PVL-positive MRSA had a one-year risk of MRSA-positive clinical culture of 10.1%, and a one-year risk of MRSA-positive clinical culture or SSTI diagnosis of 21.7%, compared with risks of 7.1% and 12.5%, respectively, for patients colonized with PVL-negative MRSA (p = 0.04, p = 0.005, respectively).

CONCLUSIONS/SIGNIFICANCE

MRSA nasal colonization is a significant risk factor for future MRSA infection; more so if detected by culture than PCR. Colonization with PVL-positive MRSA is associated with greater risk than PVL-negative MRSA.

Limited value of routine spa typing: a cross-sectional study of methicillin-resistant Staphylococcus aureus-positive patients in an Austrian hospital

BACKGROUND

We investigated whether spa typing is useful for indicating the setting of methicillin-resistant Staphylococcus aureus (MRSA) acquisition (community or health care acquired), the clinical relevance (colonization or infection), the type of infection (invasive or noninvasive), and the clinical outcome.

METHODS

Between August 2006 and December 2009, 381 routinely diagnosed culture-confirmed MRSA-positive patients were included into a cross-sectional study at an 800-bed hospital.

RESULTS

Out of 159 patients with colonization, 27 (17%) acquired MRSA in the community (CA-MRSA) and 123 (77.4%) in health care settings (HA-MRSA), and, of the 222 patients with infections, 119 (53.6%) had HA-MRSA and 103 (46.4%) had CA-MRSA. The 10 most frequent spa types accounted for 68.2% of the 346 typed MRSA isolates: t190 (28.3%), t032 (16.5%), t041 (9.4%), t008 (8.4%), t001 (3.4%), t002 (2.9%), t044 (3.1%), t223 (2.1%), t015 (2.1%), t127 (1.3%).

CONCLUSION

Spa typing of routinely identified MRSA isolates is unsuitable to predict the likeliness of an infection, of an invasive infection, and the clinical outcome. Molecular criteria such as spa type or Panton-Valentine leukocidin positivity used for classifying MRSA as either belonging to a community or hospital clone are of limited value to indicate the setting, where the MRSA strain was actually acquired according to epidemiologic criteria.

Multiplex real-time PCR assay for the detection of meticillin-resistant Staphylococcus aureus and Panton-Valentine leukocidin from clinical samples

The control and prevention of meticillin-resistant Staphylococcus aureus (MRSA) is a major challenge for healthcare establishments, especially as this pathogen continues to evolve. The emergence and spread of community associated MRSA producing Panton-Valentine leukocidin (PVL) causing severe, sometimes fatal, infections in otherwise healthy people is a significant cause of concern. Patient screening to detect MRSA is now widely used as part of an effective control program to limit the spread of this pathogen. Real-time PCR targeting specific MRSA markers offers a rapid alternative to conventional methods enabling earlier intervention, such as patient isolation and decolonization treatment. Herein we describe a multiplex real-time assay that combines primers and probes to detect MRSA and the genes for PVL to provide a rapid and informative assay.

Frequency and clinical association of Panton-Valentine leukocidin-positive Staphylococcus aureus isolates: a study from Kuwait

OBJECTIVE

This study was undertaken to determine the frequency of Panton-Valentine leukocidin (PVL)-producing Staphylococcus aureus among strains isolated in our laboratory and to study the association of PVL-positive strains with clinical disease.

MATERIALS AND METHODS

A total of 291 S. aureus isolates obtained from different clinical specimens from June 1, 2009, to March 31, 2010, at the Farwania Hospital Laboratory were investigated for antimicrobial susceptibility, carriage of genes for PVL, and SCCmec elements. Antimicrobial susceptibility testing was performed by standard methods. The presence of mecA genes for PVL SCCmec typing was determined by PCR.

RESULTS

Of the 291 S. aureus isolates, 89 (30.6%) were methicillin-resistant S. aureus (MRSA), whereas 202 (69.4%) were methicillin susceptible (MSSA). Genes for PVL were detected in 13 (14.6%) and 24 (12.0%) of the MRSA and MSSA isolates, respectively. The majority of the PVL-producing MRSA and MSSA were isolated from 12 (30.7%) and 19 (21.8%) cases of skin and soft tissue infections (SSTI), respectively. Although both MSSA and MRSA strains were uniformly susceptible to rifampicin, teicoplanin, and vancomycin, multidrug resistance was observed among PVL-producing and nonproducing MRSA isolates. Both MRSA types carried SCCmec type III, IV, IVc, and V genetic elements.

CONCLUSION

This study revealed the presence of genes for PVL in both MSSA and MRSA, associated mostly with SSTI and respiratory tract infections, supporting previous observations that PVL production is widespread among S. aureus strains obtained from different clinical sources.

Association of a lukM-positive clone of Staphylococcus aureus with fatal exudative dermatitis in red squirrels (Sciurus vulgaris)

Fatal exudative dermatitis (FED) is a recently described condition affecting red squirrels (Sciurus vulgaris) on the Isle of Wight and Jersey (Simpson et al., 2010a). Staphylococcus aureus strains isolated from skin lesions in cases of FED were characterised by molecular and phenotypic approaches. The strains were found to belong to a single MLST clonal complex (CC49) representing either ST49 or a novel single locus variant thereof (ST1957), were closely related by other molecular typing approaches, and all possessed the leukotoxin M encoding gene (lukM). In contrast S. aureus was either not isolated from none-FED cases or belonged to distinct and diverse molecular types that, with one exception, did not encode lukM. All isolates from FED cases were susceptible to all antimicrobials tested, including penicillin, and all proved negative for mecA and mecC as well as 14 other staphylococcal toxin genes. As all squirrels affected by FED were infected with S. aureus of the same lineage and encoded the lukM gene, it is possible that strains of this lineage may be involved in the pathogenesis of the dermatitis.

Community-associated meticillin-resistant Staphylococcus aureus: the case for a genotypic definition

BACKGROUND

New distinct strains of community-associated meticillin-resistant Staphylococcus aureus (CA-MRSA) have emerged as a cause of infection in previously healthy individuals in community settings. It is important to identify CA-MRSA for clinical management, epidemiological analysis, infection prevention and control, and regulatory reporting, but definitions and nomenclature of these strains are confused.

AIM

To review attempts to define CA-MRSA and propose a new definition.

METHODS

Non-systematic review.

FINDINGS

Epidemiological definitions were useful for differentiating CA-MRSA and healthcare-associated (HA)-MRSA strain types in the past. However, although HA-MRSA strain types are rarely transmitted in the community, CA-MRSA strains have started to be transmitted in healthcare facilities, so epidemiological definitions are breaking down. CA-MRSA are community strains of S. aureus that have acquired the meticillin resistance gene, mecA. They are distinct from HA-MRSA and should be defined genetically. This may be done by combining genotypic typing by multi-locus sequence or spa with analysis of the staphylococcal cassette chromosome mec. Carriage of Panton-Valentine leukocidin or antimicrobial susceptibility profiles can be useful indicators of CA-MRSA but should not be used for their definition.

CONCLUSION

For full assessment of their epidemiology, MRSA infections should be characterized as: (1) caused by HA- or CA-MRSA strain types; (2) acquired in community or healthcare settings; and (3) onset in the community or healthcare facility.

Molecular characterization and panton-valentine leucocidin typing of community-acquired methicillin-sensitive Staphylococcus aureus clinical isolates

Limited comprehensive molecular typing data exist currently for Panton-Valentine leucocidin (PVL)-positive, methicillin-sensitive Staphylococcus aureus (PVL-MSSA) clinical isolates. Characterization of PVL-MSSA isolates by multilocus sequence typing (MLST) and spa typing in this study showed a genetic similarity to PVL-positive, methicillin-resistant S. aureus (PVL-MRSA) strains, although three novel spa types and a novel MLST (ST1518) were detected. Furthermore, the detection of PVL phages and haplotypes in PVL-MSSA identical to those previously found in PVL-MRSA isolates highlights the role these strains may play as precursors of emerging lineages of clinical significance.

Spread of epidemic MRSA-ST5-IV clone encoding PVL as a major cause of community onset staphylococcal infections in Argentinean children

BACKGROUND

Community-associated methicillin-resistant Staphylococcus aureus-(CA-MRSA) strains have emerged in Argentina. We investigated the clinical and molecular evolution of community-onset MRSA infections (CO-MRSA) in children of Córdoba, Argentina, 2005-2008. Additionally, data from 2007 were compared with the epidemiology of these infections in other regions of the country.

METHODOLOGY/PRINCIPAL FINDINGS

Two datasets were used: i) lab-based prospective surveillance of CA-MRSA isolates from 3 Córdoba pediatric hospitals-(CBAH1-H3) in 2007-2008 (compared to previously published data of 2005) and ii) a sampling of CO-MRSA from a study involving both, healthcare-associated community-onset-(HACO) infections in children with risk-factors for healthcare-associated infections-(HRFs), and CA-MRSA infections in patients without HRFs detected in multiple centers of Argentina in 2007. Molecular typing was performed on the CA-MRSA-(n: 99) isolates from the CBAH1-H3-dataset and on the HACO-MRSA-(n: 51) and CA-MRSA-(n: 213) isolates from other regions. Between 2005-2008, the annual proportion of CA-MRSA/CA-S. aureus in Córdoba hospitals increased from 25% to 49%, P<0.01. Total CA-MRSA infections increased 3.6 fold-(5.1 to 18.6 cases/100,000 annual-visits, P<0.0001), associated with an important increase of invasive CA-MRSA infections-(8.5 fold). In all regions analyzed, a single genotype prevailed in both CA-MRSA (82%) and HACO-MRSA(57%), which showed pulsed-field-gel electrophoresis-(PFGE)-type-"I", sequence-type-5-(ST5), SCCmec-type-IVa, spa-t311, and was positive for PVL. The second clone, pulsotype-N/ST30/CC30/SCCmecIVc/t019/PVL(+), accounted for 11.5% of total CA-MRSA infections. Importantly, the first 4 isolates of Argentina belonging to South American-USA300 clone-(USA300/ST8/CC8/SCCmecIVc/t008/PVL(+)/ACME(-)) were detected. We also demonstrated that a HA-MRSA clone-(pulsotype-C/ST100/CC5) caused 2% and 10% of CA-MRSA and HACO-MRSA infections respectively and was associated with a SCCmec type closely related to SCCmecIV(2B&5).

CONCLUSIONS/SIGNIFICANCE

The dissemination of epidemic MRSA clone, ST5-IV-PVL(+) was the main cause of increasing staphylococcal community-onset infections in Argentinean children (2003-2008), conversely to other countries. The predominance of this clone, which has capacity to express the h-VISA phenotype, in healthcare-associated community-onset cases suggests that it has infiltrated into hospital-settings.

Do differences in Panton-Valentine leukocidin production among international methicillin-resistant Staphylococcus aureus clones affect disease presentation and severity?

Panton-Valentine leukocidin (PVL) production by methicillin-resistant Staphylococcus aureus (MRSA) was determined in vitro using the enzyme-linked immunosorbent assay (ELISA), and associations with clinical presentation and bacterial genetic characteristics were examined. PVL production ranged from 0.02 to 4.865 μg/ml and correlated with a multilocus sequence type (MLST) clonal complex associated with specific PVL phage types. A relationship between PVL production and clinical presentation or patient demographics could not be demonstrated.

Meticillin-resistant Staphylococcus aureus (MRSA): global epidemiology and harmonisation of typing methods

This article reviews recent findings on the global epidemiology of healthcare-acquired/associated (HA), community-acquired/associated (CA) and livestock-associated (LA) meticillin-resistant Staphylococcus aureus (MRSA) and aims to reach a consensus regarding the harmonisation of typing methods for MRSA. MRSA rates continue to increase rapidly in many regions and there is a dynamic spread of strains across the globe. HA-MRSA is currently endemic in hospitals in most regions. CA-MRSA clones have been spreading rapidly in the community and also infiltrating healthcare in many regions worldwide. To date, LA-MRSA is only prevalent in certain high-risk groups of workers in direct contact with live animals. CA-MRSA and LA-MRSA have become a challenge for countries that have so far maintained low rates of MRSA. These evolutionary changes have resulted in MRSA continuing to be a major threat to public health. Continuous efforts to understand the changing epidemiology of S. aureus infection in humans and animals are therefore necessary, not only for appropriate antimicrobial treatment and effective infection control but also to monitor the evolution of the species. The group made several consensus decisions with regard to harmonisation of typing methods. A stratified, three-level organisation of testing laboratories was proposed: local; regional; and national. The functions of, and testing methodology used by, each laboratory were defined. The group consensus was to recommend spa and staphylococcal cassette chromosome mec (SCCmec) typing as the preferred methods. Both are informative in defining particular strain characteristics and utilise standardised nomenclatures, making them applicable globally. Effective communication between each of the different levels and between national centres was viewed as being crucial to inform and monitor the molecular epidemiology of MRSA at national and international levels.

A field guide to pandemic, epidemic and sporadic clones of methicillin-resistant Staphylococcus aureus

In recent years, methicillin-resistant Staphylococcus aureus (MRSA) have become a truly global challenge. In addition to the long-known healthcare-associated clones, novel strains have also emerged outside of the hospital settings, in the community as well as in livestock. The emergence and spread of virulent clones expressing Panton-Valentine leukocidin (PVL) is an additional cause for concern. In order to provide an overview of pandemic, epidemic and sporadic strains, more than 3,000 clinical and veterinary isolates of MRSA mainly from Germany, the United Kingdom, Ireland, France, Malta, Abu Dhabi, Hong Kong, Australia, Trinidad & Tobago as well as some reference strains from the United States have been genotyped by DNA microarray analysis. This technique allowed the assignment of the MRSA isolates to 34 distinct lineages which can be clearly defined based on non-mobile genes. The results were in accordance with data from multilocus sequence typing. More than 100 different strains were distinguished based on affiliation to these lineages, SCCmec type and the presence or absence of PVL. These strains are described here mainly with regard to clinically relevant antimicrobial resistance- and virulence-associated markers, but also in relation to epidemiology and geographic distribution. The findings of the study show a high level of biodiversity among MRSA, especially among strains harbouring SCCmec IV and V elements. The data also indicate a high rate of genetic recombination in MRSA involving SCC elements, bacteriophages or other mobile genetic elements and large-scale chromosomal replacements.

Methicillin-resistant Staphylococcus aureus in Northeastern Scotland in 2003 to 2007: evolving strain distribution and resistance patterns

This study explored strain distribution and resistance patterns of methicillin-resistant Staphylococcus aureus (MRSA) over a 5-year period in northeastern Scotland. We noted a shift in the relative rates of epidemic strains and an increase in community-associated strains. Use of oral antibiotics to eradicate throat carriage may have contributed to trimethoprim resistance, which was observed to increase 10-fold.

Fusidic acid and clindamycin resistance in community-associated, methicillin-resistant Staphylococcus aureus infections in children of Central Greece

Introduction

In Greece, fusidic acid and clindamycin are commonly used for the empiric therapy of suspected staphylococcal infections.

Methods

The medical records of children examined at the outpatient clinics or admitted to the pediatric wards of the University General Hospital of Larissa, Central Greece, with community-associated staphylococcal infections from January 2003 to December 2009 were reviewed.

Results

Of 309 children (0-14 years old), 21 (6.8%) had invasive infections and 288 (93.2%) skin and soft tissue infections (SSTIs). Thirty-five patients were ≤30 days of age. The proportion of staphylococcal infections caused by a community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) isolate increased from 51.5% (69 of 134) in 2003-2006 to 63.4% (111 of 175) in 2007-2009 (P = 0.037). Among the CA-MRSA isolates, 88.9% were resistant to fusidic acid, 77.6% to tetracycline, and 21.1% to clindamycin. Clindamycin resistance increased from 0% (2003) to 31.2% (2009) among the CA-MRSA isolates (P = 0.011). Over the 7-year period, an increase in multidrug-resistant CA-MRSA isolates was observed (P = 0.004). One hundred and thirty-one (93.6%) of the 140 tested MRSA isolates were Panton-Valentine leukocidin-positive. Multilocus sequence typing of 72 CA-MRSA isolates revealed that they belonged to ST80 (n = 61), ST30 (n = 6), ST377 (n = 3), ST22 (n = 1), and ST152 (n = 1). Resistance to fusidic acid was observed in ST80 (58/61), ST30 (1/6), and ST22 (1/1) isolates.

Conclusion

In areas with high rate of infections caused by multidrug-resistant CA-MRSA isolates, predominantly belonging to the European ST80 clone, fusidic acid and clindamycin should be used cautiously as empiric therapy in patients with suspected severe staphylococcal infections.

Distinct bacteriophages encoding Panton-Valentine leukocidin (PVL) among international methicillin-resistant Staphylococcus aureus clones harboring PVL

Genetically diverse community-associated methicillin resistant Staphylococcus aureus (CA-MRSA) can harbor a bacteriophage encoding Panton-Valentine leukocidin (PVL) lysogenized into its chromosome (prophage). Six PVL phages (ΦPVL, Φ108PVL, ΦSLT, ΦSa2MW, ΦSa2USA, and ΦSa2958) are known, and single-nucleotide polymorphisms (SNPs) in the PVL genes have been reported. We sought to determine the distribution of lysogenized PVL phages among MRSA strains with PVL (PVL-MRSA strains), the PVL gene sequences, and the chromosomal phage insertion sites in 114 isolates comprising nine clones of PVL-MRSA that were selected for maximal underlying genetic diversity. The six PVL phages were identified by PCR; ΦSa2USA was present in the highest number of different lineages (multilocus sequence type clonal complex 1 [CC1], CC5, CC8, and sequence type 93 [ST93]) (n = 37 isolates). Analysis of 92 isolates confirmed that PVL phages inserted into the same chromosomal insertion locus in CC22, -30, and -80 but in a different locus in isolates of CC1, -5, -8, -59, and -88 and ST93 (and CC22 in two isolates). Within the two different loci, specific attachment motifs were found in all cases, although some limited inter- and intralineage sequence variation occurred. Overall, lineage-specific relationships between the PVL phage, the genes that encode the toxin, and the position at which the phage inserts into the host chromosome were identified. These analyses provide important insights into the microepidemiology of PVL-MRSA, will prove a valuable adjunct in outbreak investigation, and may help predict the emergence of new strains.

Molecular epidemiology of Panton-Valentine leukocidin-positive Staphylococcus aureus in Spain: emergence of the USA300 clone in an autochthonous population

We characterized all of the Panton-Valentine leukocidin (PVL)-positive Staphylococcus aureus isolates collected between 2005 and 2008 in the Bilbao, Spain, area. For the first time, the USA300 clone is reported as predominant among PVL-positive clones in a European autochthonous population, requiring active monitoring of the incidence of USA300 in Spain and throughout Europe.

Utility of antimicrobial susceptibility-based algorithms for the presumptive identification of genotypically-defined community-associated methicillin-resistant Staphylococcus aureus at a London teaching hospital

PURPOSE

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) strains are classically characterised by susceptibility to most non-β-lactam antimicrobial agents. We sought to determine whether antimicrobial susceptibility (AMS)-based algorithms could be used to presumptively identify CA-MRSA in a hospital MRSA collection.

METHODS

Over a three-month period, all MRSA were tested for AMS, staphylococcal cassette chromosome mec (SCCmec) type, presence of the Panton-Valentine leukocidin (PVL) genes and spa type. CA-MRSA isolates were defined genotypically using a combination of spa and SCCmec type. AMS based algorithms were developed and tested for their sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV).

RESULTS

Ciprofloxacin susceptibility (p < 0.001) and fusidic acid resistance (p  = 0.044) were independent predictors of CA-MRSA in a multivariate model. Although 98.5% of HA-MRSA were ciprofloxacin resistant, so too were 36.6% of CA-MRSA. Algorithms based on ciprofloxacin-susceptibility and fusidic acid resistance performed best, with specificity and NPV >90% and sensitivity and PPV >70%.

CONCLUSIONS

Our data indicate that while ciprofloxacin-susceptible isolates are likely to be CA-MRSA, the use of ciprofloxacin-susceptibility as a marker of CA-MRSA would miss approximately one third of CA-MRSA isolates. Therefore, AMS patterns have limited utility for the identification of genetically-defined CA-MRSA in our setting.

Evaluation of the BD GeneOhm assay using the rotor-gene 6000 platform for rapid detection of methicillin-resistant Staphylococcus aureus from pooled screening swabs

As health services move toward universal methicillin-resistant Staphylococcus aureus (MRSA) screening for hospital admissions, the most cost-effective approach is yet to be defined. In this study, one of the largest to date, we evaluated the performance of the BD GeneOhm MRSA assay on the Rotor-Gene 6000 thermal cycler, using samples taken directly from pooled MRSA screens. Results were compared with the same assay performed on the Smart-Cycler II platform and overnight broth culture. Samples yielding discrepant results were subjected to detailed analysis with an in-house PCR and patient note review. A total of 1,428 pooled MRSA screens were tested. Sensitivities and specificities of 85.3% and 95.8% for the Rotor-Gene and 81% and 95.7% for the Smart-Cycler were obtained, compared with broth enrichment. The sensitivity of the BD GeneOhm assay was increased to 100% when the results of in-house PCR and patient note review were taken into account. This study demonstrates that the Rotor-Gene 6000 thermal cycler is a reliable platform for use with the BD GeneOhm assay. It also proves that commercial PCR can be performed direct on pooled samples in selective broth, without the need for overnight incubation.

Community-associated methicillin-resistant Staphylococcus aureus: epidemiology and clinical consequences of an emerging epidemic

Staphylococcus aureus is an important cause of skin and soft-tissue infections (SSTIs), endovascular infections, pneumonia, septic arthritis, endocarditis, osteomyelitis, foreign-body infections, and sepsis. Methicillin-resistant S. aureus (MRSA) isolates were once confined largely to hospitals, other health care environments, and patients frequenting these facilities. Since the mid-1990s, however, there has been an explosion in the number of MRSA infections reported in populations lacking risk factors for exposure to the health care system. This increase in the incidence of MRSA infection has been associated with the recognition of new MRSA clones known as community-associated MRSA (CA-MRSA). CA-MRSA strains differ from the older, health care-associated MRSA strains; they infect a different group of patients, they cause different clinical syndromes, they differ in antimicrobial susceptibility patterns, they spread rapidly among healthy people in the community, and they frequently cause infections in health care environments as well. This review details what is known about the epidemiology of CA-MRSA strains and the clinical spectrum of infectious syndromes associated with them that ranges from a commensal state to severe, overwhelming infection. It also addresses the therapy of these infections and strategies for their prevention.

Community-associated methicillin-resistant Staphylococcus aureus infections

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has been recognized for over a decade, and usually refers to MRSA identified in previously healthy individuals with no recognized MRSA risk factors. Infections range from minor skin and soft tissue infections, through to severe pneumonia and necrotizing fasciitis. This review summarizes the current data on the epidemiology and molecular features of CA-MRSA, in addition to diagnosis and therapeutic measures. We also refer to current national guidelines for the management of these infections. Areas of agreement include the important genotypic and phenotypic differences of community MRSA strains compared with hospital strains. Areas of controversy include the precise epidemiological definition of community-acquired/associated MRSA. Fortunately, true CA-MRSA can be differentiated from hospital MRSA by molecular techniques, as discussed herein. Recent interest has focused on the changing epidemiology of CA-MRSA. Worldwide, CA-MRSA is now seen outside of the initial specific population groups, and in the USA, the successful USA300 community strain is beginning to spread back into hospitals. Reasons why USA300 remains relatively uncommon in Europe are unclear. Topics timely for research include the investigation of the epidemiology of infections and evolutionary genomics.