Carriage and molecular-genetic features of meticillin-resistant Staphylococcus aureus among medical students
Long-term carriage of Staphylococcus aureus is detected on average in 30% of the population and plays an important role in the development of infectious diseases. Molecular typing and analysis of S. aureus strains colonizing the human population is important for identifying strains with particular virulence and antibiotic resistance. The aim of the work is to study the level of carriage and molecular genetic characteristics of MRSA circulating among students. 2503 students of 1-3 courses of medical university were examined for the presence of S. aureus, including MRSA in 2008-2017. Anterior nasal swabs were examined bacteriologically. Antibiotic sensitivity was determined by the disk diffusion method, serial dilutions in Mueller-Hinton agar, the E-test method. The strains were typed - PFGE, MLST, spa, agr, SCCmec, coagulase typing. 49 virulence genes were identified by PCR. For detection the level of SEA toxin production we used latex agglutination reaction. Colonization of S. aureus was detected in students in 21.5% of cases, the proportion of MRSA carriage was 0.04%. The incidence of MDR strains among MSSA was 13.9%. The isolated MRSA strain belonged to ST8/spat008/SCCmecIV.3.1.1./CoaIII/agr1/sea, resistant to ciprofloxacin, levofloxacin, chloramphenicol. The level of production of enterotoxin SEA is 1.024 ng/ml. It was genetically similar to ST8 strains isolated from patients during the first hours of hospitalization. After 7 years, the MRSA strain was re-isolated, belonging to the same genetic variant. Thus, a long-term (7 years) carriage of one genetic variant of MRSA was revealed. Over time, the strain changed towards an increase in MIC to vancomycin and to hVISA, and chloramphenicol resistance developed.