Novel type of staphylococcal cassette chromosome mec identified in community-acquired methicillin- … (original) (raw)
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Antimicrobial Agents and Chemotherapy, 2002
We identified a new type of staphylococcal cassette chromosome mec (SCCmec) from two communityacquired methicillin-resistant Staphylococcus aureus (MRSA) strains. The novel element, designated type IV SCCmec, had a unique combination of the class B mec gene complex and the type 2 ccr gene complex and was much smaller in size (21 to 24 kb) than previously identified SCCmec elements of hospital-acquired MRSA. Consistent with the strains' susceptibilities to various non--lactam antibiotics, the type IV SCCmec was devoid of any antibiotic resistance genes other than the mecA gene.
Antimicrobial Agents and Chemotherapy, 2011
The structures of staphylococcal cassette chromosome mec (SCC mec ) elements carried by 31 clonal complex 398 (CC398) methicillin-resistant Staphylococcus aureus (MRSA) strains isolated from the participants at a conference were analyzed. The SCC mec s were classified into novel types, namely, IX, X, V(5C2&5) subtype c, and IVa. Type V(5C2&5) subtype c, IX, and X SCC mec s carried genes conferring resistance to metals. The structures of SCC mec s from CC398 strains were distinct from those normally found in humans, adding to the evidence that humans are not the original host for CC398.
Journal of Antimicrobial Chemotherapy, 2004
Objectives: To determine the DNA relatedness of an outbreak of community-acquired fucidin-resistant methicillin-resistant Staphylococcus aureus (MRSA) and methicillin-susceptible S. aureus (MSSA) isolated from intravenous drug users (IVDUs). Materials and methods: Relatedness was determined by PFGE analysis of macro-restricted chromosome, together with a variety of PCR methods, to determine polymorphisms in the accessory gene regulator (agr) locus, the structure of the staphylococcal cassette chromosome (SCCmec) and the presence or absence of the gene encoding Panton-Valentine leucocidin (PVL). Results: Clonality of the MRSA and MSSA was established by PFGE, a finding further supported by agr analysis. By PCR, the MRSA contained the typical genetic organization of SCCmec type-1. However, the MSSA, though mecA-negative, contained certain fragments of the SCC. Genes encoding PVL were not detected. Conclusions: This outbreak involved a community-acquired fucidin-resistant MRSA and its methicillinsusceptible homologue. The MSSA did not contain the mecA gene but did contain elements of the mobile type-I SCC. The MSSA were associated with a change in PFGE pattern with a deletion in fragment size of~215-195 kb.
Journal of Clinical Microbiology, 2005
Staphylococcal cassette chromosome mec (SCCmec) typing is essential for understanding the molecular epidemiology of methicillin-resistant Staphylococcus aureus (MRSA). SCCmec elements are currently classified into types I to V based on the nature of the mec and ccr gene complexes, and are further classified into subtypes according to their junkyard region DNA segments. Previously described traditional SCCmec PCR typing schemes require multiple primer sets and PCR experiments, while a previously published multiplex PCR assay is limited in its ability to detect recently discovered types and subtypes such as SCCmec type V and subtypes IVa, b, c, and d. We designed new sets of SCCmec type-and subtype-unique and specific primers and developed a novel multiplex PCR assay allowing for concomitant detection of the methicillin resistance (mecA gene) (also serving as an internal control) to facilitate detection and classification of all currently described SCCmec types and subtypes I, II, III, IVa, b, c, d, and V. Our assay demonstrated 100% sensitivity and specificity in accurately characterizing 54 MRSA strains belonging to the various known SCCmec types and subtypes, when compared with previously described typing methods. Further application of our assay in 453 randomly selected local clinical isolates confirmed its feasibility and practicality. This novel assay offers a rapid, simple, and feasible method for SCCmec typing of MRSA, and may serve as a useful tool for clinicians and epidemiologists in their efforts to prevent and control infections caused by this organism.
PloS one, 2014
Clinical laboratories are increasingly using molecular tests for methicillin-resistant Staphylococcus aureus (MRSA) screening. However, primers have to be targeted to a variable chromosomal region, the staphylococcal cassette chromosome mec (SCCmec). We initially screened 726 MRSA isolates from a single UK hospital trust by recombinase polymerase amplification (RPA), a novel, isothermal alternative to PCR. Undetected isolates were further characterised using multilocus sequence, spa typing and whole genome sequencing. 96% of our tested phenotypically MRSA isolates contained one of the six orfX-SCCmec junctions our RPA test and commercially available molecular tests target. However 30 isolates could not be detected. Sequencing of 24 of these isolates demonstrated recombinations within the SCCmec element with novel insertions that interfered with the RPA, preventing identification as MRSA. This result suggests that clinical laboratories cannot rely solely upon molecular assays to reliably detect all methicillin-resistance. The presence of significant recombinations in the SCCmec element, where the majority of assays target their primers, suggests that there will continue to be isolates that escape identification. We caution that dependence on amplification-based molecular assays will continue to result in failure to diagnose a small proportion (,4%) of MRSA isolates, unless the true level of SCCmec natural diversity is determined by whole genome sequencing of a large collection of MRSA isolates.
Clinical Microbiology and Infection, 2008
The first methicillin-resistant Staphylococcus aureus (MRSA) strain originated when a staphylococcal cassette chromosome mec (SCCmec) with the gene mecA was integrated into the chromosome of a susceptible S. aureus cell. The SCCmec elements are common among the coagulase-negative staphylococci, e.g. Staphylococcus haemolyticus, and these are considered to be potential SCCmec donors when new clones of MRSA arise. An outbreak of MRSA occurred at a neonatal intensive-care unit, and the isolates were all of sequence type (ST) 45, as characterized by multilocus sequence typing, but were not typeable with respect to SCCmec types I, II, III or IV. During the same time period, methicillin-resistant S. haemolyticus (MRSH) isolates identified in blood cultures at the same ward were found to be genotypically homogenous by pulsed-field gel electrophoresis, and did not carry a type I, II, III or IV SCCmec either. Thus, the hypothesis was raised that an SCCmec of MRSH had been transferred to a methicillin-susceptible S. aureus strain and thereby created a new clone of MRSA that caused the outbreak. This study showed that MRSA from the outbreak carried a ccrC and a class C mec complex that was also found among MRSH isolates. Partial sequencing of the mec complexes showed more than 99% homology, indicative of a common type V SCCmec. This finding may provide evidence for a recent horizontal transfer of an SCCmec from MRSH to an identified potential recipient, an ST45 methicillinsusceptible S. aureus strain, thereby creating a new clone of MRSA that caused the outbreak.