Abstract
Healthy carriers of Staphylococcus aureus strains have an important role in the dissemination of this bacterium. To investigate the presence of S. aureus in the throat and anterior nares, samples from 1,243 healthy volunteers in a Mexican community were examined. The percentage of healthy carriers was 59.8%. Results showed that colonization of the throat occurred more frequently than that of the nares (46.5% versus 37.1%, P<0.0001). Of the S. aureus carriers, 22.2% were exclusive nasal carriers and 38% were exclusive throat carriers. A total of 1,039 strains were isolated; 12.6% were shown to be methicillin-resistant S. aureus (MRSA). Of MRSA strains, 32.1% were isolated from exclusive throat carriers. Most of the strains isolated from the anterior nares and throat of the same carriers were the same or related; however, some were different. Pulsed-field gel electrophoresis (PFGE) pattern analysis of the MRSA strains isolated from the exclusive nasal carriers or exclusive throat carriers showed that they belong to different clusters. A 6-year prospective study was performed to investigate the persistence of S. aureus in the throat. Results showed that 13% of subjects were persistent carriers. Most of them were colonized with the same clone of S. aureus throughout the time of the study, and just three had different clones. Antimicrobial susceptibility testing showed that 91.1% of the strains were penicillin resistant. The presence of mecA and nucA genes (in order to confirm methicillin resistance) and of thermostable nuclease of S. aureus was examined. This study showed that some strains of S. aureus regularly colonized the throats of healthy people and could persist for years.
Highlights
The epidemiology of S. aureus, in particular methicillin-resistant S. aureus (MRSA), has changed with the emergence of community-acquired MRSA (CA-MRSA) [6, 10]
Pulsed-field gel electrophoresis (PFGE) pattern analysis of the MRSA strains isolated from the exclusive nasal carriers or exclusive throat carriers showed that they belong to different clusters
The aim of this work was to determine the frequency and persistence of carriage of S. aureus, especially the MRSA strains, in the throat in relation to anterior nares in a Mexican open population and to determine the clonal relationships of nasal and throat strains by pulsed-field gel electrophoresis (PFGE) analysis as well as the persistence of carriage over the years, which has not been documented
Summary
The epidemiology of S. aureus, in particular methicillin-resistant S. aureus (MRSA), has changed with the emergence of community-acquired MRSA (CA-MRSA) [6, 10]. Recent studies confirmed the observation that the throat may be selectively colonized and escape current routine screening programs [1, 16, 18, 27, 33]. The persistence of single S. aureus clones in some of the carriers confirms previous reports on the exchange of S. aureus strains over time in nasal carriers [5, 13, 24]. It is unclear, whether throat carriers are a subgroup of the population who can maintain S. aureus in this anatomical site or whether the microorganisms are temporary residents
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