Biochemical and Genetic Basis of Tetracycline Resistance in Staphylococcus aureus

Abstract

Both the genetic and biochemical basis of tetracycline resistance in a number of staphylococcal strains was investigated. The strains examined could be classified into three groups: (i) those possessing a high basal level of resistance and in which resistance could be induced to higher levels (macro-inducible); (ii) those which had a high uninduced level of resistance, but which were virtually uninducible (macro-constitutive); (iii) one derivative which had a low basal level of resistance and was also uninducible (micro-constitutive). Resistance in macro-constitutive strains was plasmid mediated and typical of organisms possessing wild-type plasmids. The macro-constitutive pattern of resistance appeared to be correlated with a chromosomal location for the resistance genes, whereas the micro-constitutive pattern was correlated with loss of a region from the wild-type plasmid. Analysis of membrane proteins by sodium dodecyl sulfate polyacrylamide gel electrophoresis suggested that a number of membrane polypeptides became unstable in staphylococci possessing high-level tetracycline resistance. In particular, the absence of a polypeptide of 22,000 daltons was always associated with high-level resistance. There was no evidence that multiple gene copies are required for expression of tetracycline resistance in Staphylococcus aureus .

Minocycline Resistance in Staphylococcus aureus: Effect on Phage Susceptibility

“…In contrast to tmn R transductants obtained with donor strains susceptible to phages of the 83A/84/85, no detectable change in phage susceptibility was observed with tmn R transductants into strain RN 450 from two donor strains of phage type 42 E. Similar results were reported by Chopra et al (7) after transfer of chromosomal tetracycline resistance from a methicillin-resistant strain of phage type 53/77/ 84/88.…”

Effect of Plasmid Carriage on the Virulence of Staphylococcus Aureus

“…between approximately 15,000 and 120,000 daltons (in this system, polypeptide mobility is inversely related to molecular weight). As previously noted (Theodore and Panos, 1973 ;Chopra et al, 1974), membranes from a number of staphylococcal strains are characterised by the presence of a major polypeptide of M.W. c. 35,000 daltons (indicated by dotted lines in the figure).…”

“…This could occur by the selection of strains capable of maintaining stably a large amount of extrachromosomal DNA, or by integration into the chromosome of regions of plasmid DNA specifying antibiotic resistance and virulence. This process has probably already occurred for the genes coding for tetracycline resistance (Kayser, Wust and Corrodi, 1972;Chopra et al, 1974).…”

“…649 tet-r(P), which harbours a plasmid coding for tetracycline resistance; no. 649 tet-r(C), on the other hand, has chromosomal genes for tetracycline resistance (Chopra, Lacey and Connolly, 1974). Strain 649MR-tN was obtained from no.…”

Further Evolution of a Strain of Staphylococcus Aureus in Vivo: Evidence for Significant Inactivation of Flucloxacillin by Penicillinase

“…However, assessment of the growth rate of individual cultures may not be sufficiently sensitive to detect slight variations between different strains, because some environmental variables cannot be controlled. Accordingly, mixed cultures, comprising one lincomycin-resistant and one lincomycin-sensitive organism were monitored by the method of Lacey and Chopra (1974). In some experiments we used pairs of cultures, obtained directly from the patient, that were similar phenotypically except in lincomycin sensitivity.…”