W.B. Grubb

Dissemination of New Methicillin-Resistant Staphylococcus aureus Clones in the Community

ABSTRACT Multiple methicillin-resistant Staphylococcus aureus (MRSA) clones carrying type IV staphylococcal cassette chromosome mec were identified in the community-acquired MRSA strains of both the United States and Australia. They multiplied much faster than health-care-associated MRSA and were resistant to fewer non-beta-lactam antibiotics. They seem to have been derived from more diverse S. aureus populations than health-care-associated MRSA strains.

Genetic analysis of community isolates of methicillin-resistant Staphylococcus aureus in Western Australia☆

Methicillin-resistant Staphylococcus aureus (MRSA) obtained from patients who had not been hospitalized outside Western Australia (WA) were studied for antimicrobial resistance and plasmid content and by pulsed-field gel electrophoresis. They were found to be of several types, none of which appeared to be related to MRSA which have been previously studied. It appears that new MRSA strains have emerged in communities in the far north of WA and are being isolated at an increasing frequency in Perth hospitals 2000 km south.

Diversity among Community Isolates of Methicillin-Resistant Staphylococcus aureus in Australia

ABSTRACT Community methicillin-resistant Staphylococcus aureus (CMRSA) strains are being isolated with increasing frequency around the world. In Western Australia CMRSA are endemic in geographically remote communities and have been found to belong to five different contour-clamped homogeneous electric field (CHEF) electrophoretic patterns. Representatives of each of these CHEF patterns have been compared to CMRSA representative of CHEF patterns from other Australian states and New Zealand. With one exception, all of the isolates were nonmultiresistant and were not resistant to many antimicrobial agents other than the β-lactams. With one exception, which is not believed to be a CMRSA, all of the isolates harbored a β-lactamase plasmid. Erythromycin resistance was associated with a 2-kb plasmid. One of the β-lactamase plasmids was found to be able to acquire additional resistance determinants to become a multiple resistance plasmid. There were 10 multilocus sequence types belonging to eight distantly related clonal complexes of S. aureus. One new sequence type was found. Although most of the CMRSA harbored the type IVa SCCmec, a type IV structural variant was found and two new SCCmec types were identified. Protein A gene (spa) typing revealed two new spa types and, with two exceptions, corresponded to multilocus sequence typing. In contrast to other reports on CMRSA, most of the CMRSA strains studied here did not contain the Panton-Valentine leukocidin genes. The results also demonstrate that nonmultiresistant hospital strains such as UK EMRSA-15 may be able to circulate in the community and could be mistaken for CMRSA based on their resistance profiles.

The international spread of methicillin-resistant Staphylococcus aureus

A genetic analysis of representative methicillin-resistant Staphylococcus aureus (MRSA) being isolated in London and Dublin hospitals has demonstrated that the epidemic strains from two London hospitals are different from the Dublin strains, but indistinguishable from the epidemic strains of eastern Australia. The possibility that some strains of MRSA are more likely than others to spread within hospitals is discussed.

Methicillin-resistant Staphylococcus aureus clones, Western Australia.

The emergence of multiple multidrug-resistant Panton-Valentine leukocidin–positive MRSA clones in the community is a major public health concern.

Are all community methicillin‐resistant Staphylococcus aureus related? A comparison of their mec regions

Aims: To compare the relationship of community‐acquired, methicillin‐resistant Staphylococcus aureus (CMRSA) from five Australian States and New Zealand. Methods: Contour‐clamped homogeneous electric field (CHEF) electrophoresis and analysis of the mec complex and ccr gene complex by PCR were used to compare 22 CMRSA isolates from Western Australia (WA), South Australia (SA), Victoria (VIC), New South Wales (NSW) and New Zealand (NZ) and three hospital‐acquired epidemic MRSA (EMRSA). Results: Sixteen community isolates were found to carry Class B mec complex and Type 2 ccr gene complex. Two WA isolates carried the Class B1 mec complex and three VIC and one SA isolate carried a previously unreported mec complex, which has been labelled E. The ccr gene type of the Class B1 and Class E isolates could not be determined. These isolates may carry previously unreported ccr gene complexes. The relatedness of the CHEF patterns of the CMRSA was dependent on their geographical origin. A similar CHEF pattern was found in some WA MRSA, VIC and SA isolates. NSW and NZ CMRSA had the same CHEF patterns and were similar to three VIC isolates and EMRSA‐16. Two SA CMRSA isolates had CHEF patterns similar to the English EMRSA‐15 strain. A multiply resistant, nosocomial EMRSA from Australia had a class A mec complex, and a CHEF pattern, which was unrelated to any of the CMRSA. Conclusion: Most of the CMRSA isolated from five Australian states and New Zealand had unrelated CHEF patterns. However, the majority of them carried the Type IV SCCmec cassette (Class B mec and Type 2 ccr gene complexes), which indicates that they may have acquired their mec complex from the same source or that they have evolved from the same progenitor. Some of the CMRSA had a previously undescribed SCCmec cassette.

Gentamicin resistance in methicillin-resistant Staphylococcus aureus

Summary 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.

Emergence of high-level mupirocin resistance in methicillin-resistant Staphylococcus aureus in Western Australia

Six mupirocin-resistant Staphylococcus aureus were isolated from patients living in the northern part of Western Australia (WA). They were all resistant to methicillin, tetracycline, trimethoprim and cadmium and harboured similar 41.4 kb plasmids. Transfer and curing experiments with one of the isolates, WBG7569, demonstrated that the 41.4 kb plasmid encoded resistance to mupirocin, tetracycline, trimethoprim and cadmium. The isolates were compared by pulsed-field gel electrophoresis with methicillin-resistant S. aureus (MRSA) previously isolated from the Kimberley region in the northern-most part of WA (WA MRSA). The mupirocin-resistant isolates were found to be closely related to WA MRSA suggesting that they were WA MRSA which had acquired a new multiple-resistance plasmid encoding high-level mupirocin resistance.

Methicillin-resistant Staphylococcus aureus, Western Australia

Endemic MRSA persists in Western Australia despite control measures.

Evolutionary dynamics of methicillin-resistant Staphylococcus aureus within a healthcare system

BackgroundIn the past decade, several countries have seen gradual replacement of endemic multi-resistant healthcare-associated methicillin-resistant Staphylococcus aureus (MRSA) with clones that are more susceptible to antibiotic treatment. One example is Singapore, where MRSA ST239, the dominant clone since molecular profiling of MRSA began in the mid-1980s, has been replaced by ST22 isolates belonging to EMRSA-15, a recently emerged pandemic lineage originating from Europe.ResultsWe investigated the population structure of MRSA in Singaporean hospitals spanning three decades, using whole genome sequencing. Applying Bayesian phylogenetic methods we report that prior to the introduction of ST22, the ST239 MRSA population in Singapore originated from multiple introductions from the surrounding region; it was frequently transferred within the healthcare system resulting in a heterogeneous hospital population. Following the introduction of ST22 around the beginning of the millennium, this clone spread rapidly through Singaporean hospitals, supplanting the endemic ST239 population. Coalescent analysis revealed that although the genetic diversity of ST239 initially decreased as ST22 became more dominant, from 2007 onwards the genetic diversity of ST239 began to increase once more, which was not associated with the emergence of a sub-clone of ST239. Comparative genomic analysis of the accessory genome of the extant ST239 population identified that the Arginine Catabolic Mobile Element arose multiple times, thereby introducing genes associated with enhanced skin colonization into this population.ConclusionsOur results clearly demonstrate that, alongside clinical practice and antibiotic usage, competition between clones also has an important role in driving the evolution of nosocomial pathogen populations.