Antibiotic Resistance in Staphylococcus Aureus Isolated at an Australian Hospital between 1946 and 1981

Abstract

SUMMARY.A total of 517 strains of Staphylococcus aureus isolated at a hospital in Melbourne, Australia between 1946 and 198 1 was examined for resistance to a range of antimicrobial agents and for the presence of plasmid DNA. The use of mixed-culture transfer and restriction endonuclease analysis showed that the determinants for resistance to penicillin and to the heavy metals were carried by several related plasmids of (15-23) x lo6 mol. wt, and that tetracycline resistance was encoded on a plasmid of 2.8 x 1 O6 mol. wt in strains isolated before 1970. These phenotypes were chromosomally encoded in the majority of strains isolated thereafter. Resistance to chloramphenicol throughout the study period was plasmid-mediated. Of five aminoglycoside-resistance phenotypes, one was plasmid-mediated and three were chromosomally encoded. The remaining phenotype, specifying low-level gentamicin resistance, was found to be located on the chromosome of early isolates, but in later strains was borne by an 18 x lo6 mol. wt plasmid which also encoded resistance to quaternary ammonium compounds.

The Plasmidome of Firmicutes: Impact on the Emergence and the Spread of Resistance to Antimicrobials

“…The rapid emergence in Firmicutes of genes coding for AbR, Met R , and Bc R immediately after their introduction and significant (often massive) use in different settings has been demonstrated for chloramphenicol (catA), tetracyclines (tetL), macrolides (ermB), neomycin (aad), gentamicin (aac6aph2), trimethoprim (dfr), betalactams (blaZ), and antiseptics (qac) in hospitals during the 1950s to 1970s, and for tylosin (ermC, ermT), phenicols (fex), pleuromutilins (cfr), and zinc-bacitracin in animals during the 1990s, thus supporting the hypothesis of the existence of a previous gastrointestinal reservoir of genes that were selected for the first time as AbR genes (gene exaptation) (84,88,91).…”

“…Rep_3 plasmids play a relevant role as vehicles of AbR among staphylococci. Plasmids from S. aureus are overrepresented by closely related variants containing Rep 5 , which are associated with genes coding for penicilinase and resistance to heavy metals (cadmium and arsenic) (51,53,66,84). Staphylococcal plasmids within this group include AbR plasmids from coagulasenegative strains of animal origin, some of them with RIPs that would not be detected by current typing systems (97,98).…”

“…5) (9,(211)(212)(213). Comprehensive reviews address the essentially clonal population structure of S. aureus (214)(215)(216) and other staphylococcal species (207) and also the impact of HGT in the evolutionary history of staphylococcal populations (9,(217)(218)(219), with emphasis on the description of the plasmids associated with AbR genetic elements (9,51,84,220) and their influence on the variability of lineages (217,219,(221)(222)(223)(224).…”

“…All these are compatible and can be identified as the rep 19 , rep 20 , and rep 15 families, respectively, according to Jensen's plasmid typing system (59,127,128). The pSK41 family (rep 15 ) is the largest group of conjugative plasmids in staphylococci, traditionally represented by pSK41, pG01, and pJE1, which emerged in the early 1980s associated with resistance to gentamicin due to the presence of Tn4001 (84,129). They often confer resistance to other antibiotics such as neomycin, tobramycin and kanamycin (due to the integration of pUB110 plasmids that harbor the aadD gene), antiseptics (due to the presence of qac genes) (130), and eventually trimethoprim (mediated by Tn4001), penicillins (due to the presence of Tn552::blaZ), and others.…”

“…5 and 7), some plasmid chimeras being fixed and persistently recovered for years. For example, emblematic mosaics theta/RCR plasmids of staphylococci (e.g., cointegrates of RepA_N/pSK41 and Rep_1/ pUB110, which encode resistance to gentamicin) and E. faecalis (e.g., pAMα1) have both been selected in those lineages since the early 1970s (7,71,84).…”