Abstract
BackgroundA limitation of both culture-based and molecular methods of screening for staphylococcal infection is that current tests determine only the presence or absence of colonization with no information on the colonizing strain type. A technique that couples polymerase chain reaction to mass spectrometry (PCR/ESI-MS) has recently been developed and an assay validated to identify and genotype S. aureus and coagulase-negative staphylococci (CoNS).MethodsThis study was conducted to determine the rates, risk factors, and molecular genotypes of colonizing Staphylococcus aureus in adult patients presenting to an inner-city academic emergency department. Participants completed a structured questionnaire to assess hospital and community risks for infection with methicillin-resistant S. aureus (MRSA). Nasal swabs were analyzed by PCR/ESI-MS to identify and genotype S. aureus and CoNS.ResultsOf 200 patients evaluated, 59 were colonized with S. aureus; 27 of these were methicillin-resistant strains. Twenty-four of the 59 S. aureus carriers were co-colonized with a CoNS and 140 of the 200 patients were colonized exclusively with CoNS. The molecular genotypes of the 59 S. aureus strains were diverse; 21 unique molecular genotypes belonging to seven major clonal complexes were identified. Eighty-five of 200 patients carried strains with high-level mupirocin resistance. Of these eighty-five participants, 4 were colonized exclusively with S. aureus, 16 were co-colonized with S. aureus and CoNS, and 65 were colonized exclusively with CoNS.ConclusionThe prevalence of S. aureus and methicillin-resistant S. aureus colonization in a random sample of patients seeking care in Emergency Department was 29.5% and 13.5%, respectively. A substantial fraction of the S. aureus-colonized patients were co-colonized with CoNS and high-level mupirocin-resistant CoNS. Determining the molecular genotype of S. aureus during intake screening may prove valuable in the future if certain molecular genotypes become associated with increased infection risk.
Highlights
A limitation of both culture-based and molecular methods of screening for staphylococcal infection is that current tests determine only the presence or absence of colonization with no information on the colonizing strain type
Excellent agreement with multilocus sequence typing (MLST) and pulsedfield gel electrophoresis (PFGE) results [13] was reached using in the PCR/ESI-MS assay a set of eight primer pairs that target the same genes as those for MLST
The primer set used to analyze the nasal swabs contains a primer pair targeted to the highly conserved tufB gene that amplifies all species within the Staphylococcus genus but not other bacterial genera
Summary
A limitation of both culture-based and molecular methods of screening for staphylococcal infection is that current tests determine only the presence or absence of colonization with no information on the colonizing strain type. We have developed a rapid molecular surveillance assay based on PCR coupled to electrospray ionization mass spectrometry (PCR/ESI-MS) [10,11,12] that identifies and provides detailed information about S. aureus strains. Excellent agreement with multilocus sequence typing (MLST) and pulsedfield gel electrophoresis (PFGE) results [13] was reached using in the PCR/ESI-MS assay a set of eight primer pairs that target the same genes as those for MLST. This set of primer pairs was designed to optimize the information content of the amplicons and distinguished 99% of 710 distinct S. aureus sequence types [13].
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