Transfer of Plasmid-Borne Aminoglycoside-Resistance Determinants in Staphylococci

Abstract

SUMMARY. Aminoglycoside-resistance determinants in staphylococci are borne on conjugative and non-conjugative plasmids. The conjugative plasmids were found in methicillin-resistant strains of Staphylococcus aureus isolated recently in Darwin and Sydney, Australia and in Houston, Texas, USA. These plasmids and the class-2 conjugative plasmid reported by Archer and Johnston (1 983) had similar patterns of EcoR 1 restriction-endonuclease fragments, encoded resistance to gentamicin, kanamycin and neomycin, transferred to a non-lysogenic recipient in conditions that promoted close cell-to-cell contact and mobilised a small, non-conjugative plasmid. A further plasmid, pWG 14, encoding resistance to kanamycin, neomycin, streptomycin, erythromycin and lincomycin, also displayed conjugative properties but did not mobilise the small, non-conjugative plasmid. The transfer frequency of all conjugative plasmids was stimulated by the addition of polyethylene glycol, particularly at concentrations above 20%, to mixtures of donor and recipient broth cultures. Polyethylene glycol appeared to promote close cell-to-cell contact between donor and recipient cells. A representative of the most common aminoglycoside-resistance plasmids in Australian isolates of methicillin-resistant S. aureus was non-conjugative and transferred by a bacteriophage-mediated system to a lysogenic recipient. With the exception of plasmid pWG 14, the conjugative plasmids were also transferred by a bacteriophage-mediated system. Furthermore, cultural conditions that favoured conjugative transfer of plasmids inhibited bacteriophage-mediated transfer and vice versa. The efficacy of the two transfer systems for analysing the plasmids of gentamicin-resistant, methicillin-resistant isolates of S. aureus has been compared.

Methicillin-resistantStaphylococcus aureus: a 6-month survey in a Lisbon paediatric hospital

“…Examination of the plasmid profiles showed that although these MRSA strains are gentamicin resistant, they do not have the large gentamicin resistance plasmid usually present in the London and Australian isolates (Bradley et al 1985;Townsend et al 1985), suggesting that genes coding for aminoglycoside resistance are sited on the chromosome, as in some of the recent Dublin isolates (Cafferkey et at. 1985).…”

Intergeneric and interspecies gene exchange in gram-positive cocci

“…Antimicrobial resistance in staphylococci can arise by chromosomally mediated mechanisms, such as methicillin resistance; by mutation, such as resistance to rifampin, streptomycin, or fusidic acid; or by the acquisition of extrachromosomal DNA (38,54,64 (24), pGO4 and pUW3626 of Cohen et al (10), and pWG613 of Townsend et al (68) all appear to be similar to pAM899-1.…”

CONJUGATIVE, STAPHYLOCOCCAL PLASMIDS CARRYING HITCH‐HIKING TRANSPOSONS SIMILAR TO Tn554: INTRA‐AND INTERSPECIES DISSEMINATION OF ERYTHROMYCIN RESISTANCE

“…11). Transfer of some conjugative plasmids has not been detected under cultural conditions that favour phage-mediated conjugation (Townsend et al, 1985c(Townsend et al, , 1986, but in the case of plasmid pWG78 they appear to only inhibit transfer (Table 3, expts. 9, 11).…”

“…As described by Townsend et al (1985c and d); Sp** transductants were selected on BHIA containing 0-5% (w/v) Na citrate and 150 mg/1 Sp.…”

“…Transfer is independent of phage activity and the donor strain must carry a conjugative plasmid which may mobilise and transfer non-conjugative plasmids. Phage-mediated conjugation operates in broth cultures containing Ca + +, transfers most plasmids including conjugative plasmids and requires the presence of a lysogenic bacteriophage (Townsend et al, 1985c(Townsend et al, , 1986.…”