Evolution of Plasmids In Vivo In a Strain of Staphylococcus Aureus

Variation in the Properties of a Strain of Staphylococcus Aureus Isolated Over Three Months from a Single Hospital

“…In Staphylococcus aureus, experiments in vitro demonstrate that mutation to resistance to a few antibiotics can occur at frequencies of 10 -7-10 -10, and that a variety of plasmids may be lost from or gained by the cell, although there seems to be ;a limit to the number of plasmids that an organism can maintain stably (Lacey and Chopra, 1974). We have found that plasmid genome can also be lost from a strain in vivo at high frequency (Lacey, Lewis, and Grinsted, 1973;Lacey, Lewis, and Rosdahl, 1974) and that one plasmid has been gained by several different staphylococci in nature . Rather few clinical strains appear to have gained resistance to antibiotics by mutation, apart from resistance to streptomycin (Lacey and Chopra, 1972).…”

Biochemical and Genetic Basis of Tetracycline Resistance in Staphylococcus aureus

“…Examples of regulatory changes in the production of staphylococcal penicillinases, which may be due to partial loss of plasmid DNA, have recently been reported (22,23). Loss of small fragments of plasmid genomes therefore appears to be common in S. aureus.…”

“…For example, in some erythromycin-resistant staphylococci, subinhibitory concentrations of antibiotic produce at least a 100-fold increase in resistance (22,38), whereas incubation of tetracycline-resistant strains with subinhibitory concentrations of tetracycline produced at the most a fivefold increase in resistance (34).…”

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

“…Between Aug. 1972 and May 1973, flucoxacillin, clindamycin and fusidic acid were prescribed successively, and most of the isolates were still penicillin resistant (see Lacey et al, 1974). From May 1973 to 12 Nov. 1973 all antibiotic therapy ceased, and during this interval the proportion of isolates producing penicillinase macroconstitutively and the proportion producing it microconstitutively fell ( fig.…”

“…In some experiments we used pairs of cultures, obtained directly from the patient, that were similar phenotypically except in lincomycin sensitivity. In other experiments, one-step mutants (see Lacey et al, 1974) resistant to lincomycin were monitored with their lincomycin-sensitive counterparts. The relative doubling time of the lincomycin-resistant cells was marginally longer than that of the lincomycinsensitive cells, the time for the resistant cell being 100-1 10 % longer (mean 103 %)…”