Methicillin resistance and biofilm production in clinical isolates of Staphylococcus aureus and coagulase negative Staphylococcus in Mexico

Introduction. Infections associated with health care caused by S. aureus and coagulase-negative Staphylococci (SCN) multi-resistant to antibiotics, cause a high epidemiological impact due to their high morbidity and mortality; and it may be related to biofilm formation, which also is related to antimicrobial resistance. Objective. Determine methicillin resistance and quantify the biofilm production to establish if there is a relationship in clinical isolates of S. aureus and SCN. Material and methods. 11 strains of S. aureus and 12 SCN were studied. Methicillin resistance was determined with cefoxitin discs and reference values as CLSI, 2018. Biofilm production was quantified with crystal violet method. The mecA and icaADBC genes were identified by PCR. A bivariate analysis was performed with the Chi-square (X2) and V de Cramer statistical tests, using the SPSS V 20.0 program. Results. Nine strains of S.aureus were methicillin-resistant (MR), two strains were methicillin-sensitive (MS). Eight SCN strains were MR and four were MS. The mecA + genotype was found in eight of the nine S. aureus MR strains and six of eight MR SCN. All strains formed biofilm. 10 strains of S.aureus and 11 of SCN presented the icaADCB+ genotype. No association was found between methicillin resistance and biofilm formation. Conclusions. Cefoxitin is enough to define the MR phenotype and is associated with the mecA + genotype. All strains formed biofilm and were related to the presence of the icaADCB operon. Biofilm formation and methicillin resistance were independent features on the two groups of strains.