Epidemiological study of Staphylococcus aureus resistant to methicillin responsible for nosocomial infections in nine French hospitals

A number of European studies found that nosocomial infections were caused b y a limited number of methicillin-resistant Staphylococcus aureus (MRSA) st rains. A study was undertaken to determine the number of MRSA clones respon sible for nosocomial infections in France. Strains responsible for nosocomi al infections meeting CDC criteria were collected one week every month from June to October 1997 in nine French hospitals. Strains that were positive by the oxacillin-resistance screening test were studied for the IS 431, fem A, and mecA genes, Strain type was identified using pulsed-field gel electo phoresis of fragments produced by SmaI digestion, Susceptibility to antimic robials was evaluated based on inhibition zone diameters and minimal inhibi tory concentrations determined using the agar dilution method. The 83 strai ns studied were distributed across four pulsotypes, Eleven resistance pheno types were identified by ascending hierarchical classification based on inh ibition zone diameters. MRSAs responsible for nosocomial infections belong to a limited number of clones that express variable levels of resistance to antimicrobials.