Genetic background and antibiotic resistance of Staphylococcus aureus strains isolated in the Republic of Georgia

Abstract

The genetic composition and antibiotic sensitivities of 50 clinical isolates of Staphylococcus aureus obtained from various clinics in the Republic of Georgia were characterized. S. aureus strains ATCC 700699 and ATCC 29737 were included as reference standards in all analyses. All 52 strains had identical 16S rRNA profiles. In contrast, pulsed-field gel electrophoresis (PFGE) identified 20 distinct PFGE types among the 52 strains examined, which indicates that PFGE is more discriminating than is 16S rRNA sequence analysis for differentiating S. aureus strains. The results of our PFGE typing also suggest that multiple genetic subpopulations (related at the ca. 85% similarity level, based on their SmaI PFGE patterns) exist among the Georgian S. aureus strains. Twenty-two of the 50 Georgian strains were methicillin resistant and PCR positive for mecA, and 5 strains were methicillin sensitive even though they possessed mecA. None of the strains were vancomycin resistant or contained vanA. The nucleotide sequences of mecA fragments obtained from all mecA-containing strains were identical. Our data indicate that the population of S. aureus strains in Georgia is fairly homogeneous and that the prevalence of methicillin-resistant, mecA-positive strains is relatively high in that country.

FIG. 1.

PFGE patterns of SmaI-digested DNA of S. aureus strains. Lanes 1 and 24, MidRange II PFG marker (New England Biolabs, Ipswich, Mass.); lanes 2 and 23, λ ladder PFG marker (New England Biolabs); lanes 3 to 15, representative PFGE types from P1 to P13, respectively; lane 16, PFGE type P18; lanes 17 to 22, PFGE types P14, P15, P16, P17, P19, and P20, respectively.

FIG. 2.

UPGMA dendrogram of S. aureus strains.