Genetic diversity of community-associated methicillin-resistant Staphylococcus aureus in southern Stockholm, 2000–2005

This study investigated the molecular epidemiology of 104 community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) isolates from southern Stockholm during the period 2000–2005. The isolates were analysed by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, staphylococcal chromosomal cassette (SCC) mec typing and detection of genes encoding Panton–Valentine leukocidin (PVL). Overall, 28 distinct PFGE patterns and 13 sequence types (STs) were identified. ST80, ST8, ST88 and ST150 were the major CA-MRSA clones in the area, and these accounted for 75% (78/104) of all CA-MRSA isolates. ST150 isolates, which have, to date, been found only in Sweden, were isolated exclusively from a group of homeless individuals. Eighty-six (83%) of the 104 isolates in the study possessed SCC mec IV, found in ten different STs, while 16 isolates possessed SCC mec V. The PVL genes were detected in 56% (58/104) of the isolates. Strain ST80-MRSA-IV carrying PVL genes predominated over the 6-year period and accounted for 38% of all isolates. However, a polyclonal tendency was observed among the CA-MRSA isolates recovered in recent years.     

Epidemiology and outcomes of community-associated methicillin-resistant Staphylococcus aureus infection

Over a 2-year period (2003 to 2005) patients with community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) and community-acquired methicillin-susceptible Staphylococcus aureus (CA-MSSA) infections were prospectively identified. Patients infected with CA-MRSA (n = 102 patients) and CA-MSSA (n = 102 patients) had median ages of 46 and 53 years, respectively; the most common sites of infection in the two groups were skin/soft tissue (80 and 93%, respectively), respiratory tract (13 and 6%, respectively), and blood (4 and 1%, respectively). Fourteen percent of patients with CA-MRSA infections and 3% of patients with CA-MSSA infections had household contacts with similar infections (P < 0.01). Among the CA-MRSA isolates, the pulsed-field gel electrophoresis (PFGE) groups detected were USA300 (49%) and USA100 (13%), with 27 PFGE groups overall; 71% of the isolates were staphylococcal chromosome cassette mec (SCCmec) type IV, 29% were SCCmec type II, and 54% had the Panton-Valentine leucocidin (PVL) gene. Among the CA-MSSA isolates there were 33 PFGE groups, with isolates of the USA200 group comprising 11%, isolates of the USA600 group comprising 11%, isolates of the USA100 group comprising 10%, and isolates of the PVL type comprising 10%. Forty-six and 18% of the patients infected with CA-MRSA and CA-MSSA, respectively, were hospitalized (P < 0.001). Fifty percent of the patients received antibiotic therapy alone, 5% received surgery alone, 30% received antibiotics and surgery, 3% received other therapy, and 12% received no treatment. The median durations of antibiotic therapy were 12 and 10 days in the CA-MRSA- and CA-MSSA-infected patients, respectively; 48 and 56% of the patients in the two groups received adequate antimicrobial therapy, respectively (P < 0.001). The clinical success rates of the initial therapy in the two groups were 61 and 84%, respectively (P < 0.001); recurrences were more common in the CA-MRSA group (recurrences were detected in 18 and 6% of the patients in the two groups, respectively [P < 0.001]). CA-MRSA was an independent predictor of clinical failure in multivariate analysis (odds ratio, 3.4; 95% confidence interval, 1.7 to 6.9). In the community setting, the molecular characteristics of the S. aureus strains were heterogeneous. CA-MRSA infections were associated with a more adverse impact on outcome than CA-MSSA infections.     

Molecular epidemiology of hospital-onset methicillin-resistant Staphylococcus aureus infections in Southern Chile

Methicillin-resistant Staphylococcus aureus (MRSA) is a pathogen of public health importance. In Chile, the Cordobes/Chilean clone was the predominant healthcare-associated MRSA (HA-MRSA) clone in 1998. Since then, the molecular epidemiological surveillance of MRSA has not been performed in Southern Chile. We aimed to investigate the molecular epidemiology of HA-MRSA infections in Southern Chile to identify the MRSA clones involved, and their evolutionary relationships with epidemic international MRSA lineages. A total of 303 single inpatient isolates of S. aureus were collected in the Valdivia County Hospital (2007–2008), revealing 33 % (100 MRSA/303) prevalence for HA-MRSA infections. The SCCmec types I and IV were identified in 97 % and 3 % of HA-MRSA, respectively. All isolates lacked the pvl genes. A random sample (n = 29) of all MRSA was studied by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), SCCmec subtyping, agr and spa typing, and virulence genes profiling. PFGE analysis revealed the predominance (89 %, 26/29) of pulsotype A and three additional pulsotypes, designated H1, I33, and G1. Pulsotype A (ST5-SCCmecI-spa-t149) is clonally related to the Cordobes/Chilean clone. Pulsotype H1 (ST5-SCCmecIVNT-spa-t002) is genetically related to the Pediatric clone (ST5-SCCmecIV). Pulsotype I33 (ST5-SCCmecIVc-spa-t002) is clonally related by PFGE to the community-associated MRSA (CA-MRSA) clone spread in Argentina, I-ST5-IVa-PVL⁺. The G1 pulsotype (ST8-SCCmecIVc-spa-t024) is clonally related to the epidemic USA300 CA-MRSA. Here, we demonstrate the stability of the Cordobes/Chilean clone over time as the major HA-MRSA clone in Southern Chile. The identification of two CA-MRSA clones might suggest that these clones have entered into the healthcare setting from the community. These results emphasize the importance of the local surveillance of MRSA infections in the community and hospital settings.     

Epidemiology of invasive methicillin-resistant Staphylococcus aureus clones collected in France in 2006 and 2007

We conducted a prospective multicenter study of methicillin-resistant Staphylococcus aureus (MRSA) isolates, including the first five consecutive clinical isolates, collected between September 2006 and February 2007 in 23 hospitals located throughout France (Fig. 1). The 111 isolates were tested for their antibiotic susceptibility patterns and were extensively characterized by screening for drug resistance and agr alleles, multilocus sequence typing (ST), staphylococcal cassette chromosome mec (SCCmec) typing, spa typing, and PCR profiling of 21 toxin genes. Clones were designated by their ST followed by their SCCmec type (I to VI). The Lyon clone ST8-IV or ST8-IV(variant) (n = 77; 69.4%) was widely distributed. Four minor clones were also detected, namely, the "classical" Pediatric clone ST5-IV (n = 9; 8.1%), the "new" Pediatric clone ST5-VI (n = 8; 7.2%), the clone Geraldine ST5-I(truncated) (n = 7; 6.3%), and the European clone ST80-IV (n = 4; 3.6%). The six other isolates were related to five rare clones. Relative to that of other European countries, the situation in France is marked by the predominance of a specific major clone and the worrying emergence of minor clones with enhanced virulence and new antibiotic susceptibility profiles.     

Epidemiology,evolution and cryptic susceptibility of methicillin-resistant Staphylococcus aureus in China: a whole-genome-based survey

ObjectivesThe aim of this study was to investigate the genomic epidemiology of methicillin-resistant Staphylococcus aureus (MRSA) in China to identify predominant lineages and their associations with clinical data and antimicrobial resistance profiles.MethodsWe performed a national prevalence study of patients with S. aureus infections in 22 tertiary hospitals in China from 2015 to 2017. Clinical data from patients and the antimicrobial phenotypes were collected for each isolate. Genome sequencing was performed on a proportion of isolates and a phylogenetic analysis was undertaken. Genotypic and phenotypic β-lactam susceptibilities were compared.ResultsA total of 1900 patients with S. aureus infections were included, of which 40% involved MRSA. Community-associated MRSA (CA-MRSA) infections were 24% of the total isolates. Genomic data showed that more than three-quarters of the MRSA were from three dominant lineages CC239 (25%, 116/471), CC5 (21%, 96/471) and CC59 (33%, 154/471) with CC59 accounting for more than half of the CA-MRSA isolates. Penicillin susceptibility genomic features were observed in 53% (251/470) of MRSA, including almost all of the CC59 (152/154) lineage, and 96% (242/251) of these isolates demonstrated in vitro susceptibility to penicillin or amoxicillin combined with clavulanic acid. Phylogenetic analysis indicated that the CC59 lineage can be divided into six lineages with all Asian CC59 isolates likely arising from an ancestral Mainland China lineage.ConclusionsThis study showed a high prevalence of CA-MRSA in China, largely due to the widespread presence of CC59. As almost all isolates in this lineage possess genetic variants leading to increased β-lactam susceptibility, we suggest that to improve antibiotic stewardship combinations of penicillins and β-lactamase inhibitors should be included in the antibiotic susceptibility testing panels used to inform treatment decisions and research undertaken on this combination therapy.     

Strain differentiation in methicillin-resistant Staphylococcus aureus

Three different systems were used to test 236 isolates of methicillin-resistant Staphylococcus aureus in an attempt to ascertain if more than one strain is responsible for the current problem of cross-infection by this organism in N.S.W. hospitals. The biochemical tests used were of little assistance. Phage typing, using the Basic International Set of typing phages at 100 x routine test dilution (RTD), provided evidence of the presence of several different strains. Phage type 83A/85/95/90/88 was the typing pattern of the predominant strain and the nest most frequent group was not typable. These results were often difficult to read. Five new phages were therefore isolated and found to be valuable as they produced easily identifiable patterns at RTD.     

Gentamicin resistance in methicillin-resistant Staphylococcus aureus

Gentamicin resistance has been studied in methicillin-resistant Staphylococcus aureus (MRSA) strains, from Royal Melbourne Hospital (RMH) and Sydney. Gentamicin resistance was transferred in mixed cultures to a plasmid free strain, and the determinants were examined. The Sydney strain had high level resistance to gentamicin, tobramycin, kanamycin and neomycin which was carried on a c.34 megadalton plasmid. The gentamicin resistant RMH isolates all had a determinant which conferred low level resistance to gentamicin, tobramycin and kanamycin and appeared to be chromosomal in one isolate, on a plasmid of c.28.5 megadaltons in another and on a plasmid of c.18 megadaltons in the other isolates. It is suggested that a gentamicin resistance transposon is being transferred in the MRSA at RMH.     

Mechanism of beta-lactam-resistance in methicillin-resistant Staphylococcus aureus

The role of penicillin-binding protein (PBP) 2' in the expression of beta-lactam-resistance was investigated using methicillin-resistant Staphylococcus aureus (MRSA) strains with different level of resistance. Both high- and moderate-level MRSA produced very similar PBP 2' with low affinities for beta-lactam antibiotics. Affinities of antibiotics for PBP 2' (I50, concentration which inhibits [14C] benzylpenicillin-binding by 50%) correlated well with their antibacterial activities (MIC) in a high-level MRSA, but did not in a moderate-level MRSA. High-level MRSA contained a larger amount of PBP 2' than moderate-level MRSA, and the amount of PBP 2' decreased by increasing the temperature of the culture; the extent of decrease was larger in a strain which was sensitive at 37 degrees C than a strain which exerted relatively high level resistance even at 40 degrees C. A cephamycin-resistant, methicillin-sensitive strain began to synthesize PBP 2' by adding cephamycin-type antibiotics to the medium and consequently acquired resistance to methicillin. Latent MRSA producing no PBP 2' generated clones which produced PBP 2' constitutively and were highly resistant to all beta-lactams. These results suggest that the presence of PBP 2' is critical for the expression of beta-lactam-resistance in MRSA and the degree of the resistance depends mainly on the amount of PBP 2' which differs from strain to strain and is influenced by environments such as temperature and the presence of inducer.     

Management of methicillin-resistant Staphylococcus aureus infections

This review addresses selected aspects of the management of severe healthcare-associated infections due to methicillin-resistant Staphylococcus aureus (MRSA), including the limitations of current therapy, potential alternative agents, new therapeutic options, clinical approaches to MRSA bacteraemia/endocarditis and ventilator-associated pneumonia, and strategies to improve outcomes in patients with severe MRSA infections.     

Molecular genetics of methicillin-resistant Staphylococcus aureus

A large and growing proportion of Staphylococcus aureus clinical isolates are methicillin resistant, and are resistant to practically all beta-lactam antibiotics. Methicillin-resistant S. aureus (MRSA) strains harbor mecA, which is carried by a unique mobile genetic element, staphylococcal cassette chromosome mec (SCCmec) integrated into the S. aureus chromosome. The mecA gene encodes a methicillin-insensitive transpeptidase, the production of which confers resistance to otherwise inhibitory concentrations of beta-lactam antibiotics. Several distinct clones have been identified among MRSA that apparently have been generated by integration of distinct types of SCCmec. While MRSA are primarily nosocomial pathogens, recent observations indicate that other MRSA clones are colonizing a significant proportion of healthy individuals in the community as well. Community-acquired MRSA (C-MRSA), may become a new threat to humans, and international cooperation of researchers and clinicians will be of cardinal importance in addressing this problem.     

Lectin typing of methicillin-resistant Staphylococcus aureus

This study reports the patterns of agglutination of 77 clinical isolates of methicillin-resistant Staphylococcus aureus by 32 commercially available lectins. Cell suspensions were not pre-treated. Each isolate was cultured on three media: Columbia blood agar, trypticase-soy agar and Chapman Stone agar. The lectins agglutinating each isolate varied widely depending on culture medium; only five isolates were agglutinated by the same set of lectins regardless of the culture medium used. Lectin typing could be a useful epidemiological tool, but it is necessary to standardise assay conditions (notably culture medium) to enable meaningful comparison of the results produced by different research groups or centres.     

Community-acquired methicillin-resistant Staphylococcus aureus in Taiwan.

Staphylococcus aureus is a major cause of infections in both hospitals and communities, and is exhibiting increasing resistance to methicillin (methicillin-resistant S. aureus, MRSA) and related beta-lactams. MRSA is usually considered a nosocomial pathogen, but increasingly it is acquired in the community. In Taiwan, MRSA was colonized in a substantial proportion of healthy children and accounted for 25% to 75% of childhood community-acquired (CA) S. aureus infections. From the preliminary data, the isolates of sequence type (ST) 59 by multilocus sequence typing method appeared to be the major clone of CA-MRSA in northern Taiwan. Compared with those reported from the US and other countries, CA-MRSA isolates in Taiwan did not always harbor type IV staphylococcal cassette chromosome (SCCmec) and were resistant to multiple non-beta-lactam antibiotics, including clindamycin and macrolides. Molecular evidence suggested transmission of the community strain of MRSA into the hospital setting, and that the community strain had became a health care-associated pathogen. The treatment of putative CA S. aureus infection should be stratified according to the severity and the disease entity.     

Characterization of methicillin-resistant Staphylococcus aureus from Ulaanbaatar, Mongolia

In order to expand current knowledge of the types of methicillin-resistant Staphylococcus aureus (MRSA) strains circulating in central Asia, six MRSA strains collected from hospitals in Ulaanbaatar, Mongolia during 2000–2002 were examined. Three strains possessed a staphylococcal cassette chromosome mec (SCCmec) element of type IV c, were sequence type (ST) 154 according to multilocus sequence typing (MLST), and contained lukS–lukF (Panton–Valentine leukocidin). Another three strains contained a SCCmec element of type III and were MLST type ST 239. Using automated ribotyping, the six MRSA strains were divided into four different EcoRI ribotypes, and two groups of isolates were distinguished by means of SmaI-macrorestriction patterns. In comparison to other countries, the incidence of MRSA in Mongolia is low.     

Nosocomial infection with methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) isolated in our hospital between 1986 and 1989 were mainly examined for their susceptibility to various antibiotics and coagulase types. The isolation frequency of MRSA among S. aureus isolated from clinical specimens has been steadily increasing; 37.8% in 1986, 49.8% in 1987, 60.6% in 1988 and 63.2% in 1989. This trend was particularly noticeable in the specimens associated with the respiratory tracts. The isolation rate of MRSA in the surgery and pediatrics wards was higher than that in the internal medicine ward. More than 80% of MRSA were coagulase type II, which were multi-resistant to penicillins, cephems, aminoglycosides and macrolides, and sensitive to MINO, new quinolones and VCM. These epidemic strains were also isolated from the nose of medical staff and from air samples in the wards. These findings suggest that the hospital environment including the patients and hospital personnel is extensively contaminated with multi-resistant MRSA of coagulase type II. Measures should be taken for prevention and control of nosocomial infection with MRSA in the whole hospital.     

A variant of the Southern German clone of methicillin-resistant Staphylococcus aureus is predominant in Croatia

The aim of the present study was to investigate the antibiotic susceptibility patterns and molecular epidemiology of clinical methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered in 24 hospitals in 20 cities in Croatia from October to December 2004. A total of 1815 consecutive S. aureus isolates were recovered, 248 of which were MRSA. The MRSA isolates were analysed using spa typing, multilocus sequence typing and SCCmec typing. Furthermore, the presence of Panton–Valentine leukocidin (PVL) genes was determined as a genetic marker for community-associated MRSA. The MRSA prevalence was 14%. Ninety-six per cent of the MRSA isolates were resistant to ciprofloxacin, 95% to clindamycin and azithromycin, 94% to gentamicin, and 93% to erythromycin. The majority of the MRSA isolates (78%) was associated with the ST111-MRSA-I clone. In addition, various other endemic MRSA clones were observed, such as the ST247-MRSA-I (4%), the ST45-MRSA-IV (2%), the ST5-MRSA-I (2%), the ST239-MRSA-III (2%), the ST5-MRSA-II (1%), the ST8-MRSA-IV (1%) and the ST5-MRSA-IV (<1%) clones. Furthermore, we observed one PVL-negative ST80-MRSA-IV isolate. Four PVL-positive MRSA isolates were found, associated with ST8-MRSA-IV, ST80-MRSA-IV and ST80-MRSA-I. The ST111-MRSA-I clone was predominant in Croatia. Future surveillance studies of MRSA are important to elucidate whether changes in the clonal distribution of MRSA will occur, and if the minor endemic MRSA clones observed in the present study will replace the ST111-MRSA-I clone on a large scale.     

Lysogenicity of methicillin-resistant strains of Staphylococcus aureus

The lysogenic status of 23 strains of methicillin-resistant Staphylococcus aureus, isolated at the Royal Prince Alfred Hospital, Sydney, since 1980, was studied. Twenty strains, belonging to the four predominant phage types isolated in this hospital, carried the same lysogenic phage which we have designated C. Three other phages were isolated from five strains belonging to phage type 84/85/90. The presence of phage C had little effect on the phage-typing pattern of the strains. Similarly, lysogenization with the other three phages did not result in a significant change in phage-typing patterns. However, when strain 1489, isolated in 1969, was lysogenized with these three phages, there was a change in phage-typing pattern. Lysogenization of this strain with phage 47T resulted in a marked loss of sensitivity to both group-I and group-III phages. The lysogenic status of these methicillin-resistant strains of S. aureus was compared with that of strains isolated between 1967 and 1970. There was no evidence that the strains isolated recently were either related to, or derived from, the earlier ones.     

Transmission events and antimicrobial susceptibilities of methicillin-resistant Staphylococcus argenteus in Stockholm

ObjectivesStaphylococcus argenteus has been increasingly reported since the species was defined as a novel staphylococcal species in 2015. This study aims to investigate genetic epidemiological links and antimicrobial susceptibilities of methicillin-resistant S. argenteus isolates recovered in Stockholm.MethodsSixteen methicillin-resistant S. argenteus isolates were identified from a collection of methicillin-resistant Staphylococcus aureus in Stockholm 2007–2018, by using whole-genome sequencing and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). The genomes of the isolates were investigated by pulsed-field gel electrophoresis, single-nucleotide polymorphism (SNP)-based phylogeny, k-mer analysis, core-genome multi-locus sequence typing (cgMLST), resistance traits and virulence factors. The MICs of 19 antimicrobial agents for each isolate were determined by using the broth microdilution method.ResultsOf the 16 isolates, seven, seven and two isolates were assigned to ST1223, ST2250 and ST2793, respectively, with the S. aureus MLST-scheme. Analyses based on SNPs and cgMLST revealed a likely clonal spread of methicillin-resistant S. argenteus in 2007. Four isolates were found to be resistant to non-β-lactams in antimicrobial susceptibility testing.ConclusionsA transmission event of methicillin-resistant S. argenteus in family was identified by this study. Among our limited number of isolates, non-β-lactam resistance was detected, which highlights the necessity of a continued surveillance on this emerging pathogen. S. argenteus could be correctly identified by MALDI-TOF MS with the updated database, enabling its detection also in clinical laboratories.