MRSA Clones Research Articles

Genomic surveillance reveals low prevalence of livestock-associated methicillin-resistant Staphylococcus aureus in the East of England

Livestock-associated methicillin-resistant Staphylococcus aureus (LA-MRSA) is an emerging problem in many parts of the world. LA-MRSA has been isolated previously from animals and humans in the United Kingdom (UK), but the prevalence is unknown. The aim of this study was to determine the prevalence and to describe the molecular epidemiology of LA-MRSA isolated in the East of England (broadly Cambridge and the surrounding area). We accessed whole genome sequence data for 2,283 MRSA isolates from 1,465 people identified during a 12-month prospective study between 2012 and 2013 conducted in the East of England, United Kingdom. This laboratory serves four hospitals and 75 general practices. We screened the collection for multilocus sequence types (STs) and for host specific resistance and virulence factors previously associated with LA-MRSA. We identified 13 putative LA-MRSA isolates from 12 individuals, giving an estimated prevalence of 0.82% (95% CI 0.47% to 1.43%). Twelve isolates were mecC-MRSA (ten CC130, one ST425 and one ST1943) and single isolate was ST398. Our data demonstrate a low burden of LA-MRSA in the East of England, but the detection of mecC-MRSA and ST398 indicates the need for vigilance. Genomic surveillance provides a mechanism to detect and track the emergence and spread of MRSA clones of human importance.

Emergence of methicillin-resistant Staphylococcus aureus SCCmec type IV/V epidemic clones in a large teaching hospital in China

To investigate the staphylococcal cassette chromosome mec (SCCmec) genotype and molecular epidemiological characteristics of healthcare-associated methicillin-resistant Staphylococcus aureus (HA-MRSA) in a large teaching hospital in China. From January 2012 to December 2012, a total of 71 nonduplicate HA-MRSA were collected in a teaching hospital in Changsha, China. SCCmec types were determined by multiplex PCR, and Panton-Valentine leukocidin (PVL) gene was detected by PCR. The homology among the tested isolates was determined using pulsed-field gel electrophoresis (PFGE). Of the 71 HA-MRSA isolates, 49 (69.0%) carried SCCmec III, 10 (14.1%) carried SCCmec IV, 3 (4.2%) carried SCCmec V and 3 (4.2%) carried SCCmec II; the remaining 6 isolates were not typeable by PCR. Compared with patients having SCCmec I/II/III MRSA infections, those with SCCmec IV/V MRSA infections had a significantly younger age and a similar duration of hospital stay before the first MRSA-positive culture and total hospital stay. PVL genes were strongly associated with SCCmec type IV/V MRSA infections. HA-SCCmec IV/V MRSA strains showed a greater susceptibility to rifampicin, gentamicin, levofloxacin, ciprofloxacin, and tetracycline than HA-SCCmec I/II/III MRSA strains. The 13 HA-SCCmec IV/V MRSA isolates formed one large group at the 55% similarity level. Three PFGE clusters with a similarity index of 85% or more were identified, and unique PFGE profiles were observed in 4 isolates. This is the first report of HA-MRSA isolates carrying SCCmec V in Chinese hospitals. SCCmec types IV and V MRSA clones have emerged in Chinese hospitals, which urges more rigorous surveillance of their spread in healthcare facilities in China.

Dominance of community-associated methicillin-resistant Staphylococcus aureus clones in a maternity hospital.

BackgroundMethicillin- resistant Staphylococcus aureus (MRSA) is a major pathogen causing healthcare- and community- acquired infections. The purpose of this study was to characterize MRSA isolated at the Maternity Hospital between 2006 and 2011 for their genetic relatedness.Materials and methodsThe MRSA isolates were investigated using a combination of antibiogram, Staphylococcal chromosome cassette mec (SCCmec) and spa typing to determine their relatedness to MRSA isolated in other Kuwait hospitals. The isolates were also investigated for the carriage of genes for Pantone valentine Leukocidin (PVL).ResultsA total of 103 MRSA obtained from 64 neonates, 17 adult patients and 12 healthcare workers. The isolates were resistant to Kanamycin (46.6%), gentamicin (40.8%), trimethoprim (32%), ciprofloxacin (22.3%), fusidic acid (16.5%), tetracycline (19.4%), erythromycin (15.5%), clindamycin (15.5%), streptomycin (11.6%) high-level mupirocin (2.9%) and chloramphenicol (0.9%). Twenty (19.4%) of the isolates were multiresistant. Thirty-one (30.0%) isolates were positive for PVL. Molecular typing revealed the presence of 11 clonal complexes and 23 clones with ST5-V-t002, (N = 22), ST22-IV-t223 (N = 18), ST22-IV-t852 (N = 10), ST80-IV-t044 (N = 7), ST5-V-t688 (N = 5), ST772-V-t657 (N = 5) and ST239-III-t860 (N = 4) constituting 66.9% of the isolates. Other clones were isolated sporadically. The number of MRSA isolates increased from two in 2006 to 22 in 2011 with a peak of 43 in 2008.ConclusionThe study revealed a high prevalence of community-associated MRSA Maternity hospital. The MRSA population consisted of known strains, such as ST239-III-t680, ST22-IV-t223/t852 and ST80-IV-t044, that were reported previously in Kuwait and novel strains such as ST5-V-t002, and several sporadic strains obtained for the first time in the Maternity hospital. This study has provided an initial data which will serve as a platform for future comparative studies on the distribution of MRSA clones in the Maternity hospital in Kuwait.

Infection Prevention Strategy in Hospitals in the Era of Community-Associated Methicillin-Resistant Staphylococcus aureus in the Asia-Pacific Region: A Review.

Community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has emerged as an important cause of healthcare-associated infection. CA-MRSA clones have replaced classic hospital MRSA clones in many countries and have shown higher potential in transmission and virulence than hospital MRSA clones. In particular, the emergence of CA-MRSA in the Asia-Pacific region is concerning owing to insufficient infection control measures in the region. The old strategies for infection prevention and control of MRSA comprised adherence to standard precaution and policy of active screening of MRSA carriers and decolonization, and it has been controversial which strategy is better in terms of outcome and cost-effectiveness. Epidemiological changes in MRSA has made the development of infection prevention strategy more complicated. Based on the literature review and the questionnaire survey, we considered infection prevention strategies for healthcare settings in the Asia-Pacific region in the era of CA-MRSA.

ST3268: a geographically widespread primate MRSA clone.

ST3268: a geographically widespread primate MRSA clone.

Molecular epidemiology of Staphylococcus aureus nasal colonization among patients and their parents /guardian in an Iranian referral hospital.

Carriage of Staphylococcus aureus in the nose appears to play a key role in the epidemiology and pathogenesis of infection. It is important to investigate the genetic relatedness of S.aureus and MRSA clones in different geographic regions. The aim of this study was to assess the nasal carriage rate of S.aureus, including MRSA strains in both hospitalized children and general adult population (parents/guardian). In addition, antibiotic susceptibility pattern and molecular diversity of S.aureus in both population was evaluated in an Iranian referral pediatrics Hospital. All samples were obtained through nasal screening of patients and general adult population at admission and discharge day. The prevalence, resistance, and molecular diversity of all S.aureus isolates were examined. In the current study, nasal carriage of S.aureus and Staphylococcus non aureus was identified in 384 (26%) and 1004 (68%) of the study population. The prevalence of MRSA nasal carriage in children and adults was 6.6% (29 out of 438) and 2.8% (29 out of 1046), respectively. Among S.aureus strains isolated obtained from patients and general adult population at admission day, high sensitivity to most of the antibiotics such as vancomycin (100%), rifampin (95%), linezolid (94%), quinupristin/dalfopristin (94%), minocycline (94%), chloramphenicol (89%), gentamycin (87%), amikacin (87%), clindamycin (86%) and moxifloxacin (83%) was seen. The most resistance antibiotics were penicillin (96-98%) and methicillin (44-47%). The susceptibility patterns of nasal S.aureus strains isolated at discharge day was not statistically different from S.aureus isolates obtained at admission day. Admission S.aureus isolated strains of 77 patients (64%) were similar to the isolated S.aureus strains of discharge, while S.aureus isolated strains of 43 patients (36%) was not similar to the strain of discharge (had similarity of less than 70%). High prevalence of nasal carriage of S.aureus and MRSA indicates the urgent need to improve strategies for management of S.aureus infections. Our findings are useful for understanding of S.aureus nasal colonization dynamics within the patients and general population. Surveillance for S.aureus in community settings can provide data on circulating strains and might help developing control measures for reducing of infection spread in hospitals.

Hospital clones of methicillin-resistant Staphylococcus aureus are carried by medical students even before healthcare exposure

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) strains are prevalent in healthcare and the community. Few studies have examined MRSA carriage among medical students.The aim of this study is to examine Staphylococcus aureus (SA) carriage, and particular MRSA, over time in cohort medical studentsMethodsProspective collection of nasal swabs from medical students in Israel and assessment of SA carriage. Three samples were taken per student in preclinical and clinical parts of studies. Antibiotic susceptibilities were recorded and MRSA typing was performed by staphylococcal cassette chromosome mec (SCCmec) types, Panton Valentine Leukocidin (PVL) encoding genes, and spa types. Clonality was assessed by pulsed-field gel electrophoresis.ResultsAmong 58 students, SA carriage rates increased from 33% to 38% to 41% at baseline (preclinical studies), 13 and 19 months (clinical studies), respectively (p = 0.07). Methicillin-susceptible SA (MSSA) carriage increased in the clinical studies period (22 to 41%, p = 0.01). Overall, seven students (12%) carried 13 MRSA isolates. MRSA isolates were PVL negative and were characterized as SCCmecII-t002, SCCmecIV-t032, or t12435 with untypable SCCmec. MRSA carriage during the pre-clinical studies was evident in 4/7 students. Two students carried different MRSA clones at various times and persistent MRSA carriage was noted in one student. Simultaneous carriage of MRSA and MSSA was not detected.ConclusionsMSSA carriage increased during the clinical part of studies in Israeli medical students. Compared with previous reports, higher rates of MRSA carriage were evident. MRSA strains were genotypically similar to Israeli healthcare-associated clones; however, carriage occurred largely before healthcare exposure, implying community-acquisition of hospital strains.

Prevalence of nasal colonisation by methicillin-sensitive and methicillin-resistant Staphylococcus aureus among healthcare workers and students in Madagascar.

BackgroundMethicillin-resistant Staphylococcus aureus (MRSA) clones pose a significant threat to hospitalised patients because the bacteria can be transmitted by asymptomatic carriers within healthcare facilities. To date, nothing is known about the prevalence of S. aureus and MRSA among healthcare workers in Madagascar.The objective of our study was to examine the prevalence and clonal epidemiology of nasal S. aureus and MRSA among healthcare workers and non-medical University students in Antananarivo, Madagascar.MethodsThis cross sectional study screened nasal swabs taken from students and healthcare workers for S. aureus. Multiplex PCR was performed to identify S. aureus-specific (nuc), MRSA-specific mecA and mecC genes, Panton-Valentine leukocidin (PVL) (lukF-PV), and toxic shock syndrome toxin-1 (TSST-1) specific genes in methicillin-sensitive S. aureus (MSSA) and MRSA isolates. Staphylococcus protein A gene (spa) typing was performed for all confirmed MRSA isolates. The frequency distribution of nasal S. aureus and MRSA of healthcare workers and non-medical students was compared using Pearson’s χ2 test.ResultsOf 1548 nasal swabs tested, 171 (11 %) were positive for S. aureus; 20 (1.3 %) of these isolates were identified as MRSA. S. aureus was detected in 91 of 863 healthcare workers (10.4 %) and in 80 (11.8 %) of 685 students; however, 14 (1.5 %) healthcare workers carried MRSA compared with six (0.9 %) students. Nasal carriage of S. aureus and MRSA was more prevalent in women than in men, and 21 (11.7 %) S. aureus isolates were PVL-positive and 36 (21 %) were TSST-1 positive. The mecC gene was not detected in any isolates. Five different spa types were identified, with spa type t186 being the predominant MRSA clone (16/20).ConclusionThe results of the present study reveal a low frequency of S. aureus and MRSA nasal carriage in both students and healthcare workers from Antananarivo, Madagascar. The predominant MRSA clone (t186) was previously described in hospitalised patients in Madagascar.Electronic supplementary materialThe online version of this article (doi:10.1186/s12879-016-1733-6) contains supplementary material, which is available to authorized users.

Identification of source and sink populations for the emergence and global spread of the East-Asia clone of community-associated MRSA.

BackgroundOur understanding of the factors influencing the emergence, dissemination and global distribution of epidemic clones of bacteria is limited. ST59 is a major epidemic clone of community-associated MRSA in East Asia, responsible for extensive morbidity and mortality, but has a much lower prevalence in other parts of the world. The geographic origin of ST59 and its international routes of dissemination are unclear and disputed in the literature.ResultsTo investigate the origin and spread of the ST59 clone, we obtained whole genome sequences of isolates from four continents, sampled over more than a decade, and carried out a time-scaled phylogeographic analysis. We discover that two distinct ST59 clades emerged concurrently, in East Asia and the USA, but underwent clonal expansion at different times. The East Asia clade was strongly enriched for gene determinants associated with antibiotic resistance, consistent with regional differences in antibiotic usage. Both clones spread independently to Australia and Europe, and we found evidence of the persistence of multi-drug resistance following export from East Asia. Direct transfer of strains between Taiwan and the USA was not observed in either direction, consistent with geographic niche exclusion.ConclusionsOur results resolve a longstanding controversy regarding the origin of the ST59 clone, revealing the major global source and sink populations and routes for the spread of multi-drug resistant clones. Additionally, our findings indicate that diversification of the accessory genome of epidemic clones partly reflects region-specific patterns of antibiotic usage, which may influence bacterial fitness after transmission to different geographic locations.Electronic supplementary materialThe online version of this article (doi:10.1186/s13059-016-1022-0) contains supplementary material, which is available to authorized users.

MRSA Causing Infections in Hospitals in Greater Metropolitan New York: Major Shift in the Dominant Clonal Type between 1996 and 2014.

A surveillance study in 1996 identified the USA100 clone (ST5/SCCmecII)–also known as the “New York/Japan” clone—as the most prevalent MRSA causing infections in 12 New York City hospitals. Here we update the epidemiology of MRSA in seven of the same hospitals eighteen years later in 2013/14. Most of the current MRSA isolates (78 of 121) belonged to the MRSA clone USA300 (CC8/SCCmecIV) but the USA100 clone–dominant in the 1996 survey–still remained the second most frequent MRSA (25 of the 121 isolates) causing 32% of blood stream infections. The USA300 clone was most common in skin and soft tissue infections (SSTIs) and was associated with 84.5% of SSTIs compared to 5% caused by the USA100 clone. Our data indicate that by 2013/14, the USA300 clone replaced the New York/Japan clone as the most frequent cause of MRSA infections in hospitals in Metropolitan New York. In parallel with this shift in the clonal type of MRSA, there was also a striking change in the types of MRSA infections from 1996 to 2014.

Heterogeneous oxacillin-resistant phenotypes and production of PBP2A by oxacillin-susceptible/mecA-positive MRSA strains from Africa

Recent surveillance of MRSA colonizing patients and healthcare workers in two African countries (Angola and São Tomé and Príncipe) reported the frequent recovery of oxacillin-susceptible MRSA (OS-MRSA): Staphylococcus aureus strains that gave positive results with the mecA DNA probe, but had low oxacillin MIC values characteristic of susceptible S. aureus. This apparent dissociation of the drug-resistant phenotype from mecA-the primary genetic determinant of resistance-prompted us to perform a more detailed analysis on nine of the African OS-MRSA strains. Oxacillin MIC values were determined by Etest and population analysis profiles with and without induction of the stringent stress response by mupirocin. Biochemical profiling using SDS-PAGE followed by western blotting was used for the detection of PBP2A protein produced. Cultures of the African MRSA strains (ST88-IVa and ST8-V) showed heterogeneous oxacillin resistance in which the majority of cells exhibited low oxacillin MICs (≤0.75 mg/L), but highly resistant subpopulations were also present with oxacillin MIC values up to several hundred mg/L and with frequencies of 10(-4) to 10(-6). The same strains after induction of the stringent stress response by mupirocin 'converted' the heterogeneous phenotypes into a more homogeneous and higher level resistance. After induction by oxacillin and mupirocin, each of the nine African OS-MRSA strains produced PBP2A-the protein product of mecA. The resistant phenotype of OS-MRSA resembles the phenotypes of historically early MRSA clones. The nature of genetic determinants responsible for the heterogeneous phenotypes of OS-MRSA remains to be determined.

Antimicrobial resistances and virulence markers in Methicillin-resistant Staphylococcus aureus from broiler and turkey: A molecular view from farm to fork

Little is known about the characteristics of MRSA occurring along the broiler and turkey production chains. The aim of this study was to characterise and compare MRSA of turkey and broiler origin sampled on different production levels using a DNA microarray and antimicrobial susceptibility testing. Main differences could be observed in the prevalence of the resistance genes erm(C), aacA-aphD and tet(K) and the number of non-wild type strains with minimum inhibitory concentration values (MICs) above the epidemiological cut-off values (ECOFFs) for gentamicin and kanamycin. Overall, MRSA with non-wild type phenotype for the macrolide-lincosamide-streptogramin group, tetracycline, and trimethoprim were found in more than 70% of poultry isolates. Non-wild type isolates carrying the qacC gene conferring resistance to quaternary ammonium compound disinfectants were found at all production stages in similar frequencies. Regarding the presence of enterotoxin genes in poultry-derived MRSA the enterotoxin gene cluster (egc) was only found in Non-CC (clonal complex) 398 strains. Three CC398 strains harboured the genes sed (from turkey at slaughter and broiler meat) and sea-N315 (from a chicken carcass). One Non-CC398 strain isolated from turkey meat was found positive for the seb gene and also enterotoxin production. Similarity analysis based on selected resistance and virulence markers revealed a high clonality among Non-CC398 isolates. Isolates of the same clonal complex clustered together according to their common virulence and resistance profiles. Strains of CC9 were grouped in two subclusters due to different resistance genes. Our results underline, that there are other poultry associated clones of MRSA (mainly CC9 and CC5) besides the predominant CC398 which are similar in both poultry species.

Molecular characterization and clonal diversity of meticillin-resistant Staphylococcus aureus isolated from the community in Spain: emergence of clone sequence type 72

Sequence type 72 meticillin-resistant Staphylococcus aureus (ST72 MRSA) was recently detected in our hospital. Although in Europe this clone is rarely isolated, it is the leading cause of community-associated MRSA infections in Korea, spreading also into hospitals, where it has also emerged as the main MRSA clone recovered from raw meat. We studied MRSA isolated from outpatients in Spain during a nine-year period. More than 70% of the isolates belonged to predominant clones found in hospitals. There was a significant increase in the ST72 prevalence. It appears that boundaries of dominance among MRSA clones have become blurred, demanding continuous surveillance.

Rapid Emergence and Evolution of Staphylococcus aureus Clones Harboring fusC-Containing Staphylococcal Cassette Chromosome Elements.

The prevalence of fusidic acid (FA) resistance among Staphylococcus aureus strains in New Zealand (NZ) is among the highest reported globally, with a recent study describing a resistance rate of approximately 28%. Three FA-resistant S. aureus clones (ST5 MRSA, ST1 MSSA, and ST1 MRSA) have emerged over the past decade and now predominate in NZ, and in all three clones FA resistance is mediated by the fusC gene. In particular, ST5 MRSA has rapidly become the dominant MRSA clone in NZ, although the origin of FA-resistant ST5 MRSA has not been explored, and the genetic context of fusC in FA-resistant NZ isolates is unknown. To better understand the rapid emergence of FA-resistant S. aureus, we used population-based comparative genomics to characterize a collection of FA-resistant and FA-susceptible isolates from NZ. FA-resistant NZ ST5 MRSA displayed minimal genetic diversity and represented a phylogenetically distinct clade within a global population model of clonal complex 5 (CC5) S. aureus. In all lineages, fusC was invariably located within staphylococcal cassette chromosome (SCC) elements, suggesting that SCC-mediated horizontal transfer is the primary mechanism of fusC dissemination. The genotypic association of fusC with mecA has important implications for the emergence of MRSA clones in populations with high usage of fusidic acid. In addition, we found that fusC was colocated with a recently described virulence factor (tirS) in dominant NZ S. aureus clones, suggesting a fitness advantage. This study points to the likely molecular mechanisms responsible for the successful emergence and spread of FA-resistant S. aureus.

Analysis of MRSA clones with POT derived from outpatients in our hospital

Analysis of MRSA clones with POT derived from outpatients in our hospital

The Type I Restriction Enzymes as Barriers to Horizontal Gene Transfer: Determination of the DNA Target Sequences Recognised by Livestock-Associated Methicillin-Resistant Staphylococcus aureus Clonal Complexes 133/ST771 and 398.

The Type I DNA restriction-modification (RM) systems of Staphylococcus aureus are known to act as a significant barrier to horizontal gene transfer between S. aureus strains belonging to different clonal complexes. The livestock-associated clonal complexes CC133/771 and CC398 contain Type I RM systems not found in human MRSA strains as yet but at some point transfer will occur. When this does take place, horizontal gene transfer of resistance will happen more easily between these strains. The reservoir of antibiotic resistance, virulence and host-adaptation genes present in livestock-associated MRSA will then potentially contribute to the development of newly evolving MRSA clones. The target sites recognised by the Type I RM systems of CC133/771 and CC398 were identified as CAG(N)5RTGA and ACC(N)5RTGA, respectively. Assuming that these enzymes recognise the methylation state of adenine, the underlined A and T bases indicate the unique positions of methylation. Target methylation points for enzymes from CC1 were also identified. The methylation points for CC1-1 are CCAY(N)5TTAA and those for CC1-2 are CCAY(N)6 TGT with the underline indicating the adenine methylation site thus clearing up the ambiguity noted previously (Roberts et al. 2013, Nucleic Acids Res 41:7472-7484) for the half sites containing two adenine bases.

Prevalence and Trends of Staphylococcus aureus Bacteraemia in Hospitalized Patients in South Africa, 2010 to 2012: Laboratory-Based Surveillance Mapping of Antimicrobial Resistance and Molecular Epidemiology.

IntroductionWe aimed to obtain an in-depth understanding on recent antimicrobial resistance trends and molecular epidemiology trends of S. aureus bacteraemia (SAB).MethodsThirteen academic centres in South Africa were included from June 2010 until July 2012. S. aureus susceptibility testing was performed on the MicroScan Walkaway. Real-time PCR using the LightCycler 480 II was done for mecA and nuc. SCCmec and spa-typing were finalized with conventional PCR. We selected one isolate per common spa type per province for multilocus sequence typing (MLST).Results S. aureus from 2709 patients were included, and 1231 (46%) were resistant to methicillin, with a significant decline over the three-year period (p-value = 0.003). Geographical distribution of MRSA was significantly higher in Gauteng compared to the other provinces (P<0.001). Children <5 years were significantly associated with MRSA with higher rates compared to all other age groups (P = 0.01). The most prevalent SCCmec type was SCCmec type III (531 [41%]) followed by type IV (402 [31%]). Spa-typing discovered 47 different spa-types. The five (87%) most common spa-types were t037, t1257, t045, t064 and t012. Based on MLST, the commonest was ST612 clonal complex (CC8) (n = 7) followed by ST5 (CC5) (n = 4), ST36 (CC30) (n = 4) and ST239 (CC8) (n = 3).ConclusionsMRSA rate is high in South Africa. Majority of the isolates were classified as SCCmec type III (41%) and type IV (31%), which are typically associated with hospital and community- acquired infections, respectively. Overall, this study reveals the presence of a variety of hospital-acquired MRSA clones in South Africa dominance of few clones, spa 037 and 1257. Monitoring trends in resistance and molecular typing is recommended to detect changing epidemiological trends in AMR patterns of SAB.

Community and hospital acquired methicillin resistant Staphylococcus aureus efficiently retain the Van A determinant

Dissemination of vancomycin resistance from hospital to community strains is a serious threat to public health. Our study aimed to provide evidence for transmission of Van A type resistance from the hospital to the community. Wild-type community and hospital associated methicillin resistant Staphylococcus aureus strains were studied in vitro and in a model that mimicked a natural environment to ascertain their ability to acquire and maintain the vancomycin resistance determinant (Van A gene) from vancomycin resistant Enterococcus faecalis. Fitness was assessed and the cost of Van A acquisition and retention was estimated. In vitro mating experiments were carried out using a filter mating technique and a model of a natural water body environment. Transfer of resistance was carried out in two different conditions: restricted and favorable. Transconjugants were confirmed by E test and PCR using specific primer sets. Growth kinetics and fitness measurements were done by spectrometric analysis. Using the in vitro filter mating technique, high transfer frequencies that ranged from 0.7 × 10–3(0.0006) to 3.1 × 10–4(0.00011) were recorded, with the highest transfer frequencies for CA MRSA (thermosensitively homogenous) (0.7 × 10–3), and 1.2 × 10–4 to 2.4 × 10–6 in the model. HA MRSA (homogenous) showed a greater capacity (3.6 × 10–4) to receive the Van A gene, while CA MRSA showed a reduced ability to maintain the gene after serial subcultures. CA and HA thermosensitively heterogeneous MRSA transconjugants exhibited higher growth rates. The present study provides evidence for the enhanced ability of CA and HA MRSA clones to acquire and maintain Van A type resistance.

Staphylococcus aureus ST121: a globally disseminated hypervirulent clone.

Staphylococcus aureus is a leading cause of bacterial infections in hospitals and communities worldwide. With the development of typing methods, several pandemic clones have been well characterized, including the extensively spreading hospital-associated meticillin-resistant S. aureus (HA-MRSA) clone ST239 and the emerging hypervirulent community-associated (CA) MRSA clone USA300. The multilocus sequence typing method was set up based on seven housekeeping genes; S. aureus groups were defined by the sharing of alleles at ≥ 5 of the seven loci. In many cases, the predicted founder of a group would also be the most prevalent ST within the group. As a predicted founder of major S. aureus groups, approximately 90 % of ST121 strains was meticillin-susceptible S. aureus (MSSA). The majority of ST121 strains carry accessory gene regulator type IV, whereas staphylococcal protein A gene types for ST121 are exceptionally diverse. More than 90 % of S. aureus ST121 strains have Panton-Valentine leukocidin; other enterotoxins, haemolysins, leukocidins and exfoliative toxins also contribute to the high virulence of ST121 strains. Patients suffering from S. aureus ST121 infections often need longer hospitalization and prolonged antimicrobial therapy. In this review, we tried to summarize the epidemiology of the S. aureus clone ST121 and focused on the molecular types, toxin carriage and disease spectrum of this globally disseminated clone.

Clonal variation in high- and low-level phenotypic and genotypic mupirocin resistance of MRSA isolates in south-east London.

Both low-level mupirocin resistance (LMR) and high-level mupirocin resistance (HMR) have been identified. The aim of this study was to determine the epidemiology of LMR and HMR in MRSA isolates at five hospitals that have used mupirocin for targeted decolonization as part of successful institutional control programmes. All MRSA identified in three microbiology laboratories serving five central and south-east London hospitals and surrounding communities between November 2011 and February 2012 were included. HMR and LMR were determined by disc diffusion testing. WGS was used to derive multilocus sequence types (MLSTs) and the presence of HMR and LMR resistance determinants. Prevalence of either HMR or LMR amongst first healthcare episode isolates from 795 identified patients was 9.69% (95% CI 7.72-11.96); LMR was 6.29% (95% CI 4.70-8.21) and HMR was 3.40% (95% CI 2.25-4.90). Mupirocin resistance was not significantly different in isolates identified from inpatients at each microbiology laboratory, but was more common in genotypically defined 'hospital' rather than 'community' isolates (OR 3.17, 95% CI 1.36-9.30, P = 0.002). LMR was associated with inpatient stay, previous history of MRSA and age ≥65 years; HMR was associated with age ≥65 years and residential postcode outside London. LMR and HMR varied by clone, with both being low in the dominant UK MRSA clone ST22 compared with ST8, ST36 and ST239/241 for LMR and with ST8 and ST36 for HMR. V588F mutation and mupA carriage had high specificity (>97%) and area under the curve (>83%) to discriminate phenotypic mupirocin resistance, but uncertainty around the sensitivity point estimate was large (95% CI 52.50%-94.44%). Mutations in or near the mupA gene were found in eight isolates that carried mupA but were not HMR. Mupirocin resistance was identified in <10% of patients and varied significantly by clone, implying that changes in clonal epidemiology may have an important role in determining the prevalence of resistance in conjunction with selection due to mupirocin use.