SUSCEPTIBILITY OF RESPIRATORY STRAINS OF STAPHYLOCOCCUS-AUREUS TO 15 ANTIBIOTICS - RESULTS OF A COLLABORATIVE SURVEILLANCE STUDY (1992-1993)

As part of the Alexander Project during 1992 and 1993, 690 Staphylococ cus aureus strains isolated from community-acquired lower respiratory tract infections by clinical microbiology centres located in Europe an d the USA were analysed by a co-ordinating laboratory that determined minimal inhibitory concentrations of 15 antimicrobial agents using a s tandardised microdilution technique. The prevalence of penicillin-susc eptible microorganisms in this collection of pathogens was significant ly higher in Europe (21.2%) than it was in the USA(12.1%). Most isolat es (72.5%), however, were strains that had acquired the ability to syn thesise a beta-lactamase but which were sensitive to methicillin. The incidence of methicillin-resistance (9.1% overall) was highly variable depending on geographic location and year of isolation. Analysis of M IC(50), MIC(90), MIC range and modal MIC of the 15 antibiotics assayed disclosed no major differences between the datasets obtained during t he 2-year survey. Except for methicillin-resistant S. aureus, the acti vity of all the beta-lactams tested, with the exclusion of penicillin, amoxycillin and cefixime (that were completely inactive), was satisfa ctory. The effect of beta-lactamase synthesis was inhibited by the com bination of amoxycillin with clavulanate, and by cefuroxime and ceftri axone. Cefaclor was slightly less effective. Erythromycin, clarithromy cin and azithromycin showed identical cross-resistance rates (around 1 0%). Resistance to the macrolides was more frequent in the USA than in Europe and was the sole trait found to increase during the survey. Do xycycline, chloramphenicol, co-trimoxazole and the two fluoroquinolone s tested (ofloxacin and ciprofloxacin) were remarkably effective (resi stance lower than 1%). Only doxycycline and, to a lesser extent, co-tr imoxazole were partially active against methicillin-resistant strains.