Evolution of nasal carriage of methicillin-resistant coagulase-negative staphylococci in a remote population.

Nasal carriage of methicillin-resistant coagulase-negative staphylococci (MR-CoNS) is highly prevalent in community subjects, but its dynamic has been little investigated. Nasal swabbing was performed in 2006 and 2008 in 154 Amerindians living isolated in French Guiana. MR-CoNS strains were identified and characterized by non-ß-lactam susceptibility testing and staphylococcal cassette chromosome mec element (SCCmec) typing, characterizing the associations of ccr and mec gene complex allotypes, and for MR Staphylococcus epidermidis (MRSE), multilocus variable number of tandem repeats analysis (MLVA) was used. The impact of sociodemographic and medical characteristics on the persistence of MR-CoNS carriage was assessed by bivariate analysis. Prevalence of MR-CoNS carriage was 50.6% in 2006 and 46.8% in 2008. The 274 MR-CoNS isolates, including S. epidermidis (n = 89, 62 MLVA patterns), Staphylococcus haemolyticus (n = 78), and Staphylococcus hominis (n = 72), exhibited 41 distinct ccr and mec gene complex associations. Persistent carriage (in 2006 and 2008), intermittent carriage (either in 2006 or 2008), and noncarriage were documented in 25.3, 47.4, and 27.3% of the participants, respectively. Persistent carriage of a given MRSE isolate was rarely observed (n = 8 isolates). Furthermore, no epidemiological factor, including antibiotic exposure, was associated with persistent carriage. The high diversity of MRSE clones and their ccr and mec gene complex associations contrasted with the high carriage rates in this isolated community, which might reflect the occurrence of SCCmec rearrangement and the generation of new MR-CoNS strains.

High prevalence of the arginine catabolic mobile element in carriage isolates of methicillin-resistant Staphylococcus epidermidis.

BACKGROUND: the arginine catabolic mobile element (ACME) associated with staphylococcal cassette chromosome mec (SCCmec) in the USA300 clone of community-acquired methicillin-resistant Staphylococcus aureus enhances its fitness and ability to colonize the host. Staphylococcus epidermidis may act as a reservoir of ACME for S. aureus. We assessed the diffusion of ACME in methicillin-resistant S. epidermidis (MRSE) isolates colonizing outpatients. METHODS: seventy-eight MRSE strains isolated in outpatients from five countries were characterized by multilocus sequence typing (MLST) and SCCmec typing and screened for the arcA and opp3AB markers of ACME. ACME-arcA and ACME-opp3AB were sequenced. ACME type I from MRSE and USA300 were compared by long-range PCR (LR-PCR). RESULTS: fifty-three (67.9%) MRSE strains carried an ACME element, including 19 (24.4%), 32 (41.0%) and 2 (2.6%) with ACME type I (arcA+/opp3AB+), II (arcA+/opp3AB-) and III (arcA-/opp3AB+), respectively. The prevalence of ACME did not differ between clonal complex 2 (42/60 strains) and other sequence types (11/18 strains, P = 0.7), with MLST data suggesting frequent intraspecies acquisition. ACME-arcA sequences were highly conserved, whereas ACME-opp3AB displayed 11 distinct allotypes. ACME was found in 14/29, 9/11 and 30/37 strains with type IV, type V and non-typeable SCCmec, respectively (P = 0.01). ACME was more frequently associated with ccrC than with ccrAB2 (82.4% versus 60.0%, P = 0.048). LR-PCR indicated structural homologies of ACME I between MRSE and USA300. CONCLUSIONS: ACME is widely disseminated in MRSE strains colonizing outpatients and may contribute to their spread in a community environment with low antibiotic exposure, as suggested for USA300.

Methicillin-resistant coagulase-negative staphylococci in the community: high homology of SCCmec IVa between Staphylococcus epidermidis and major clones of methicillin-resistant Staphylococcus aureus.

BACKGROUND: Data on community spread of methicillin-resistant coagulase-negative staphylococci (MR-CoNS) are scarce. We assessed their potential role as a reservoir of staphylococcal cassette chromosome mec (SCCmec) IVa, the leading SCCmec subtype in community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA). METHODS: Nasal carriage of MR-CoNS was prospectively investigated in 291 adults at hospital admission. MR-CoNS were characterized by SCCmec typing, long-range polymerase chain reaction (PCR) for SCCmec IV, and multiple-locus variable-number tandem repeat analysis (MLVA) for Staphylococcus epidermidis (MRSE) strains. Three SCCmec IVa elements were fully sequenced. RESULTS: The carriage rate of MR-CoNS was 19.2% (25.9% and 16.5% in patients with and patients without previous exposure to the health care system, respectively; P = .09). MR-CoNS strains (n = 83, including 58 MRSE strains with highly heterogeneous MLVA patterns) carried SCCmec type IVa (n = 9, all MRSE), other SCCmec IV subtypes (n = 9, including 7 MRSE), other SCCmec types (n = 15), and nontypeable SCCmec (n = 50). Long-range PCR indicated structural homology between SCCmec IV in MRSE and that in MRSA. Complete sequences of SCCmec IVa from 3 MRSE strains were highly homologous to those available for CA-MRSA, including major clones USA300 and USA400. CONCLUSIONS: MR-CoNS are probably disseminated in the community, notably in subjects without previous exposure to the health care system. MRSE, the most prevalent species, may act as a reservoir of SCCmec IVa for CA-MRSA.

The carriage population of Staphylococcus aureus from Mali is composed of a combination of pandemic clones and the divergent Panton-Valentine leukocidin-positive genotype ST152.

Staphylococcus aureus is an important human pathogen, but it appears more commonly in asymptomatic colonization of the nasopharynx than in cases of invasive disease. Evidence concerning the global population structure of S. aureus is limited by the overrepresentation in the multilocus sequence testing database of disease isolates recovered from Western Europe, the Americas, Australia, and Japan. We address this by presenting data from the S. aureus carriage population in Mali, the first detailed characterization of asymptomatic carriage from an African population. These data confirm the pandemic spread of many of the common S. aureus clones in the carriage population. We also note the high frequency (approximately 24%) of a single divergent genotype, sequence type 152 (ST152), which has not previously been recovered from nasal carriage isolates but corresponds to a sporadic Panton-Valentine leukocidin (PVL)-positive, community-acquired methicillin-resistant S. aureus clone noted mostly in Central Europe. We show that 100% of the ST152 isolates recovered from nasal carriage samples in Mali are PVL positive and discuss implications relating to the emergence and spread of this virulent genotype.