Phenotypic and molecular characterisation of methicillin-resistant Staphylococcus aureus isolated from clinical samples in northern Chile

Abstract number: P529

Gahona J., Araya J., Silva J.

Objectives: Methicillin-resistant Staphylococcus aureus is a significant problem in healthcare settings around the world. The aim of this work was to study the phenotypic and molecular characteristics of methicillin resistant Staphylococcus aureus (MRSA) isolated from clinical samples in the north of Chile.

Methods: A total of 76 MRSA strains from skin and tissues infections samples isolated in Health Centers of Antofagasta, Chile (2007), were included in this study. The S. aureus strains were identified by biochemical tests, API Staph and typed by Phene-Plates. The susceptibility to antimicrobial drugs was determined by a dilution technique agar, the presence of beta-lactamase by phenotypic and molecular methods, and detection of mec and luk genes by PCR. Also, the presence of plasmids was investigated by gel electrophoresis and genotypes by PFGE.

Results: More of 80% of the assayed MRSA strains exhibited high resistance to ampicillin, penicillin, eritromycin, claritromycin, amikacine and ciprofloxacin; moderate resistance to cotrimoxazole (18.5%) and tetracycline (4.2%); and 100% of susceptibility to rifampin and vancomycin. Around 90% of the strains were resistant to methicillin and the 79% presented beta-lactamase. The Ph-phene method identified 7 biochemical phenotypes and the antibiotic resistance patterns shown 5 different antibiotypes. More of 60% of the strains exhibited multiple resistance to 9 or more antimicrobials. Different genotypes were identified by PFGE and one genotype was dominant. A plasmid of 7 kb in 8 MRSA strains, also two of them presented a plasmid of 20 kb. The PCR analysis revealed the presence of mecA gen in 97.3%, mecR1 MS gen in 52.6%, mecR1 PB gen in 36.8%, and mecI in 55.2% of the MRSA strains, and also in 44.5% of the strains was detected the luk gene. However, the mecA gen was found in 6 methicillin susceptible strains. In two MRSA strains, it was not possible to detect the presence of the mecA gen.

Conclusions: MRSA strains are present in a high percentage in Health Centers of Antofagasta Chile, the strains exhibited multiple resistance to antibiotics and presence of plasmids. Also, the MRSA strains presented beta-lactamase, mec and luk genes in prevalent phenotypes and genotypes of MRSA strains. These findings can contribute to understand and control the MRSA strains circulating in the Health Centers of Antofagasta.