The Journal of Medical Microbiology, Vol 23, Issue 2 111-118, Copyright © 1987 by Society for General Microbiology
Antibiotic resistances and plasmids in Staphylococcus aureus from Italian hospitals
M. Gelmi, I. Foresti, G. Ravizzola, C. Bonfanti, R. Verardi, A. Caruso and A. Turano
A total of 473 Staphylococcus aureus isolates from six Italian hospitals
was examined for susceptibility to several antimicrobial agents and for
plasmid content. Methicillin-resistant S. aureus (MRSA) were characterised
by a plasmid of mol. wt (10(6)) 18-22 or 25 that carried the determinants
for penicillinase production, resistance to cadmium ions and resistance to
tetracycline. MRSA isolates usually harboured other smaller plasmids of
mol. wt (10(6)) 2.8, 2.6 and 1.65 that encoded resistance to tetracycline,
chloramphenicol and erythromycin, respectively, and cryptic plasmids of
mol. wt (10(6)) c. 2 and 1 were found frequently. Methicillin-sensitive S.
aureus (MSSA) that produced penicillinase often carried plasmids of mol. wt
(10(6)) 11 or 13. No particular difference was found in plasmid patterns of
strains from the various sources. Analysis of plasmids by EcoRI digestion
showed that plasmids of similar mol. wt and phenotypic characteristics may
have different restriction patterns, but often share one or more fragments
in common.
