High prevalence of spa types associated with the clonal lineage CC398 among tetracycline-resistant methicillin-resistant Staphylococcus aureus strains in a Spanish hospital

Abstract

Objectives: The clonal lineages, resistance mechanisms and virulence traits of tetracycline-resistant (Tet(R)) methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in a Spanish hospital during 2009 and 2010 were investigated.

Methods: Fifty-two Tet(R) MRSA strains from unrelated patients were included in this study. Susceptibility to 26 antimicrobial agents was determined and 24 resistance genes were tested for by PCR. The sequences of the genes grlA and gyrA were analysed in all ciprofloxacin-resistant MRSA isolates. For all strains, spa, SCCmec and agr typing was implemented. Multilocus sequence typing was performed for 16 representative strains of the different spa types. The presence of the genes tst, lukF/lukS-PV, eta, etb, etd and cna was investigated by PCR.

Results: Fifteen different spa types, four of them new ones, were detected among the 52 strains, being associated with the following clonal complexes (CCs): CC398 (67.3%), CC1 (11.5%), CC5 (11.5%) and CC8 (9.6%). A novel sequence type (ST), ST2077, belonging to CC398 was identified. Most MRSA CC398 strains were typed as SCCmecV-agrI. In addition to β-lactam resistance, isolates showed resistance to (gene/number of strains): tetracycline [tet(K)/36, tet(L)/8 and tet(M)/48], macrolides and lincosamides [erm(B)/6, erm(C)/25, erm(T)/2, msr(A)/msr(B)/4 and mph(C)/4], aminoglycosides [aac(6')-Ie-aph(2')-Ia/8, ant(4')-Ia/13 and aph(3')-IIIa/15], trimethoprim [dfrS1/2 and dfrK/3] and mupirocin (mupA/3). Strains investigated for mutations mediating quinolone resistance revealed an S80F exchange in GrlA and different changes in GyrA. Three strains were Panton-Valentine leucocidin-positive (ST8 and ST94) and 41 strains were cna-positive. All MRSA isolates were negative for the genes tst, eta, etb and etd.

Conclusions: Tetracycline resistance could be a good marker for MRSA CC398, although this resistance can also be found in other lineages.