Molecular epidemiology of methicillin resistant Staphylococcus aureus bacteremia in a teaching hospital from Argentina

DI GREGORIO, S.; GULONE, L.; PERAZZI, B.; MARTINEZ ORDOÑEZ, A.; MOLLERACH, M.; FAMIGLIETTI, A.

Buenos Aires

Congreso; International Congress of Traslational Medicine. Cellular and Molecular Pathways as Therapeutic Targets; 2014

IMBS. Facultad de Farmacia y Bioquimica. UBA.

Introduction: Community acquired methicillin resistant Staphylococcus aureus (CA-MRSA) is a relevant pathogen that produces non-complicated and complicated infections in patients without healthcare associated risk factors. Traditionally different genetic lineages have been described in the community and in hospital settings but nowadays community associated strains are replacing typical hospital associated strains (HA-MRSA). CA-MRSA strains usually carry SCCmecIV, PVL genes and are more virulent than HA-MRSA strains. Methods: Antimicrobial susceptibility of a collection of S. aureus isolates recovered from bloodstream infections at Hospital de Clínicas José de San Martín, between August 2009 and November 2010 was characterized by phenotypic methods according to CLSI guidelines. Panton Valentine Leukocidin coding genes (luk-SF/PV) and macrolide resistance genes were studied by PCR. Additionally, strains were genotyped by SCCmec typing, agr group, PFGE, spa typing and MLST. Results: Forty-eight out of the 92 (52.2 %) patients with S. aureus bacteremia included in the study were infected by MSSA, whereas 44 (47.8%) were infected by MRSA. MRSA isolates were more likely to be resistant to gentamicin, erythromycin/clindamycin, and ciprofloxacin (p<0.0001). As revealed by the D-Test, in the MSSA group, 9/9 erythromycin-resistant isolates displayed inducible clindamycin resistance. By contrast, in the MRSA group, only 5/26 erythromycin-resistant isolates displayed the inducible phenotype, 1/26 was negative by the D-Test, and the remaining isolates (20/26) showed constitutive clindamycin resistance (MLSc). Macrolide resistance genes detected in 15/20 MLSc isolates included: ermA (7), ermB (2), ermTR (6), ermC (5). None of them carried lnuA or lnuB genes. All isolates were susceptible to linezolid, tigecycline, vancomycin, and teicoplanin. The molecular characterization of the MRSA group revealed 43/44 isolates harboring the mecA gene. The most frequent SCCmec types were SCCmec I and IV (41.8 and 39.5% respectively) and the most frequent agr group among them was the agr group II (53.5%). Only 13/44 (29.5%) harbored the PVL coding genes (lukS/F-PV), and all PVL-positive isolates also harbored SCCmec IVc or SCCmec IVa. PFGE and MLST analysis revealed that 14/18 MRSA isolates carrying SCCmec I corresponded to the Cordobés clone (pulsotype D-ST5-SCCmec I). Most isolates carrying SCCmec IV were related to the main community-acquired MRSA (CA-MRSA) clones described in Argentina: pulsotype C (ST30-SCCmec IVc) and pulsotype A (ST5-SCCmec IVa) (nine and five isolates respectively). Conclusions: MRSA represented almost half of bacteremia cases in the study and are more likely to be resistant to other antimicrobial families than MSSA. Our results showed the spread of CA-MRSA into hospital settings. The ST30-SCCmec IVc-pulsotype C clone, recently described as the main cause of CA-MRSA infections in Argentina, was the most frequent CA-MRSA clone recovered in this study.