Epidemiologic study of Staphylococcus strains isolated from clinical material in 24 Italian hospitals

A nationwide epidemiologic study of clinical Staphylococcus isolates was performed in Italy by 24 operative units distributed throughout the country. A total of 7,017 Staphylococcus strains were examined according to a standard protocol. Three species of acknowledged importance in human infections (namely S. aureus, S. epidermidis, and S. saprophyticus) were identified singly, whereas the other staphylococci were considered as a whole and designated Staphylococcus spp. S. aureus totalled 55% of total isolates and was reported by most operative units as the predominant species among isolates both from various inpatient departments and from outpatients. S. saprophyticus was twofold more frequent among isolates from out- than from inpatients. Susceptibility to methicillin varied considerably from hospital to hospital, but a general tendency toward an increasing spread of resistance was noted. The overall incidence of methicillin resistance (29%) resulted from a wide range of values generally higher in isolates from inpatients (35%) than from outpatients (21%). Particularly high percentages of resistance (45%) were recorded in isolates from intensive care departments. Susceptibility testing to four additional beta-lactams (cefoxitin, cefuroxime, cefotaxime, and piperacillin) and to four aminoglycosides (gentamicin, tobramycin, amikacin, and netilmicin) indicated that antibiotic resistance was widespread and in all species more frequent among methicillin-resistant than among methicillin-sensitive staphylococci. Netilmicin proved more active than the other antibiotics tested; its greater activity was most evident against methicillin-resistant strains. Coagulase-negative staphylococci were more resistant than S. aureus to methicillin and most of the other antibiotics, suggesting their increasing involvement in human infections.