Molecular Characterization of Staphylococcus aureus Isolates Associated with Nasal Colonization and Environmental Contamination in Academic Dental Clinics

Abstract

Aim: To determine the genetic makeup of methicillin-sensitive/methicillin-resistant Staphylococcus aureus (MSSA/MRSA) from nasal colonization and environmental contamination in dental clinics. Materials and Methods: Nasal swabs from students and health care workers and environmental swabs were obtained at two academic dental clinics in the United Arab Emirates. The StaphyType DNA microarray-based assay was used for molecular characterization.

Results: Forty-eight S. aureus isolates were identified phenotypically (nasal: n = 43; environmental: n = 5), but 6 of these were assigned to S. argenteus by genotyping. These were CC(argenteus)2596, CC(arg)2250-MSSA, CC(arg)2250-MSSA-(Panton Valentine leukocidin [PVL]+) (n = 2), and CC(arg)2198-MSSA (n = 2). MRSA nasal colonization rate was 5.4% (n/N = 8/146) with the following strain affiliations: CC5-MRSA-[IV+fus+ccrAB], ‘‘Maltese Clone’’; CC6-MRSA-IV, ‘‘WA MRSA-51’’; CC22-MRSA-IV (PVL+/tst+); CC22-MRSA-[IV+ fus+ccrAA/(C)]; and two each of CC5-MRSA-[VI+fus] and CC97-MRSA-[V/VT+fus]. The SCC-borne fusidic acid resistance (fusC) gene was detected in MRSA (n = 5) and MSSA (n = 1). Some MSSA strains, CC1-MSSA- [fus+ccrAB1] and ST1278-MSSA-[ccrA1], harbored recombinase genes. A CC30-MSSA harbored ACME locus/arc-genes, while ST1278-MSSA-[ccrA1] had an ACME-III element. Enterotoxin genes were commonly carried, but tst-1 gene was found in only CC22, CC30, and CC34 strains, while pvl genes were identified in CC(arg)2250 and CC22-MRSA-IV. Of the 51 noncoagulase staphylococci (CoNS) identified, 18 were mecA positive.

Conclusion: The findings demonstrate the first report of rare strains (ST1278 MSSA, CC(arg)2198, CC(arg)2596, and PVL+CC(arg)2250) in our region. Detection of MSSA with recombinase genes and ACME loci alongside mecA-positive CoNS is of clinical significance as this could provide a milieu for acquisition and transfer of SCC-elements, either with different ACME types, with fusC or the mecA gene resulting in conversion of MSSA into MRSA.