Analysis of plasmids mediating gentamicin resistance in methicillin-resistant Staphylococcus aureus

Abstract

Gentamicin-resistance plasmids in methicillin-resistant Staphylococcus aureus isolated from four Australian hospitals have been studied. All the plasmids conferred resistance to gentamicin, tobramycin, kanamycin and all but one conferred resistance to quarternary ammonium compounds. Plasmids which only carried these resistance determinants were ca 15.3 megadaltons and were only found in isolates from one hospital. The most common plasmid was ca 18.0 megadaltons and in addition encoded trimethoprim resistance. Two plasmids, one of ca 19.6 megadaltons and one of ca 28.5 megadaltons were found to carry the penicillinase determinant. However only the larger of these encoded heavy metal ion resistance and was sensitive to quaternary ammonium compounds. EcoR1 analysis indicated that all but the ca 28.5 megadalton plasmid were closely related. The EcoR1 analysis of the ca 28.5 megadalton plasmid indicated that it could have resulted from recombination between a gentamicin resistance determinant and a penicillinase plasmid.

Susceptibility to Antimicrobial Agents and Analysis of Plasmids in Gentamicin- And Methicillin-Resistant Staphylococcus Aureus From Dublin Hospitals

“…This resistance marker is usually chromosomal in S. aureus (Lewis and Lacey, 1973;Lacey, 1975) although such plasmids have been found in MGRSA strains in Australia (Townsend et al, 1984a). Furthermore, in Australian strains, tetracycline resistance was usually chromosomal (Gillespie et al, 1984).…”

Evolution of Austalian Isolates of Methicillin-Resistant Staphylococcus Aureus: A Problem of Plasmid Incompatibility?

“…The discovery of NAB-resistance plasmids belonging to IncI means that this is the first group of staphylococcal plasmids to be shown to contain plasmids with unrelated phenotypes. Moreover, plasmids pWG51, pWG53, pWG54 and pWGll5 do not appear to be related to pase plasmids when examined in an EcoR 1 -restriction-enzyme analysis (Townsend et al, 1984a and b), a method which has previously been used to establish relatedness amongst IncI plasmids .…”

“…Another example of a naturally occurring recombinant plasmid is pWG50, isolated from MRSA strain WG526 (Townsend et al, 19836). This is also an IncI plasmid (Table 111) and has been previously characterised as a recombinant plasmid based on phenotype and restriction-enzyme analysis (Townsend et al, 1984a). A more detailed study is necessary before one can conjecture about the selective pressures that have influenced the emergence of these plasmids.…”

“…The (14-6-22) x lo6 mol. wt plasmids determine resistance to quaternary ammonium compounds (Townsend et al, 1983a and1984a;Grubb et al, 1983), propamidine isethionate (Townsend et al, 1984b), ethidium bromide and a range of compounds (Emslie et al, 1985, and in press) which share a common property of being nucleic acid-binding compounds (NAB). Consequently, resistance to these agents will be referred to as NAB resistance.…”

“…Consequently, resistance to these agents will be referred to as NAB resistance. The NAB-resistance plasmids also carry one or more of the determinants for pase, gentamicin (Gm) resistance or trimethoprim (Tp) resistance (Townsend et al, 1983a(Townsend et al, , 1984a(Townsend et al, and 1984b.…”