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.Staphylococcus aureus remains one of the most frequently occurring community-acquired as well as hospital-acquired pathogens, with high rates of hospital-acquired infections (11).Recently, 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). Reports from different parts of the world indicate that CA-MRSA has emerged as a new pathogen (3,26,32).S. aureus is a transient or persistent part of the resident flora in the anterior nares of the population (15). The anterior nares are considered to be the primary colonization site, and approximately 30% of healthy people carry this bacterium (15).The human throat is less well studied than the nares as a carriage site; nevertheless, some isolations have been reported (19,22,25). Colonization of the throat but not of the nares may be more common than is currently acknowledged. Recent studies confirmed the observation that the throat may be selectively colonized and escape current routine screening programs (1,16,18,27,33). Unrecognized carriers may spread MRSA and render infection control programs futile (18,19,27).Three main carriage patterns have been described when individuals are repeatedly sampled in the anterior nares for S. aureus over longer periods of time: the so-called noncarriers, ...

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The pathogenicity of Escherichia coli strains that cause cervico-vaginal infections (CVI) is due to the presence of several virulence genes. The objective of this study was to define the variability regarding the genotype of antibiotic resistance, the transcription profiles of virulence genes after in vitro infection of the vaginal cell line A431 and the phylogroup composition of a group of cervico-vaginal E. coli strains (CVEC). A total of 200 E. coli strains isolated from Mexican women with CVI from two medical units of the Mexican Institute of Social Security were analysed. E. coli strains and antibiotic resistance genes were identified using conventional polymerase chain reaction (PCR), and phylogroups were identified using multiplex PCR. Virulence gene transcription was measured through reverse-transcriptase realtime PCR after infection of the vaginal cell line A431. The most common antibiotic resistance genes among the CVEC strains were aac(3)II, TEM, dfrA1, sul1, and qnrA. The predominant phylogroup was B2. The genes most frequently transcribed in these strains were fimH, papC, irp2, iroN, kpsMTII, cnf1, and ompT, mainly in CVEC strains isolated from chronic and occasional vaginal infections. The strains showed a large diversity of transcription of the virulence genes phenotype and antibiotic resistance genotype, especially in the strains of phylogroups, B2, A, and D. The strains formed 2 large clusters, which contained several subclusters. The genetic diversity of CVEC strains was high. These strains have a large number of transcription patterns of virulence genes, and one-third of them carry three to seven antibiotic resistance genes.

CA-MRSA strains were detected in the nose and throat of healthy people. We identified a high level of genetic diversity among CA-MRSA strains in healthy people of Mexico City, which were different from the USA and pandemic clone profiles.