Naturally occurring penicillinase plasmids in Staphylococcus aureus

Incompatibility groups and the classification of fi - resistance factors

Incompatibility between R factors has been reported by several authors, and four incompatibility groups have already been described by Datta and Hedges among Rfi(-) factors. The stability of 12 plasmids in pairs was studied after 116 crosses, and five new groups were found, designated 5, 6, 7, 8, and 9. Each plasmid studied belongs to one single group. Incompatibility between plasmids in pairs is a clear-cut phenomenon, is easy to observe, and can provide a reliable method for recognizing and classifying resistance factors, and for tracing their spread among bacterial species.

Nature of the elimination of the penicillinase plasmid from Staphylococcus aureus by surface-active agents

Growth of Stapylococcus aureus in various ionic surface-active agents resulted in loss of the ability to produce penicillinase, whereas growth in nonionic surface-active agents had no effect on penicillinase production. The curing effect of various alkyl sulfates was found to be dependent upon the chain length. Curing by surface-active agents could be inhibited by magnesium. Reciprocal transduction experiments showed that curing by a surface-active agent was a property of the plasmid, not of the bacterial strain in which the plasmic resides.

Regulation of penicillinase synthesis: a mutation in Staphylococcus aureus unlinked to the penicillinase plasmid that reduced penicillinase inducibility

A mutant of Staphylococcus aureus strain 655 was isolated that is restricted in penicillinase induction. Wild-type plasmids that bear penicillinase determinants could not be fully induced in this mutant, 655par-1; hence, the responsible mutation is not located on the plasmid. Mutant plasmid PI(258)penI443, which produces penicillinase constitutively in wild-type cells, was fully constitutive for penicillinase production when it was harbored by mutant 655par-1. Therefore, the bacterial mutation does not interfere directly with the transcription of the penZ gene or translation of the penicillinase messenger ribonucleic acid. Mutant plasmid PII(147)penI220 was fully inducible in the mutant bacterium, even though the wild-type plasmid PII(147) was only partially inducible in the par-1 mutant. Thus, in the presence of inducer, complementation appears to occur between the product of the par-1 gene and the product of the penI220 gene. These results suggest that the par-1 gene codes for a penicillinase antire-pressor.

Effects of the recipient strain and ultraviolet irradiation on transduction kinetics of the penicillinase plasmid of Staphylococcus aureus

When the penicillinase plasmid of Staphylococcus aureus PS 81(P(81))(T(81)) was transferred to its cured derivative of PS 81(N(P))(T(81)), there was a fivefold increase in the transduction frequency of penicillinase plasmid markers after ultraviolet (UV) irradiation of the phage instead of the expected decrease typical for plasmid-borne markers. These results were independent of the transducing phage, the donor, and the method of curing the recipient and were also obtained with a cured derivative of PS 80(PI(80)). With PS 52, a naturally occurring penicillin-sensitive strain, and a cured transductant of PS 52 as the recipients, typical plasmid kinetics were observed. The plasmid location of penicillinase plasmid markers in transductants was confirmed by their instability in ethidium bromide (EB). In a cross between isogenic plasmids (PI(258)penZ cad x PI(258)penI asa ero), transductants were doubly selected for cadmium and erythromycin resistances. There was a twofold increase in transduction frequency after UV irradiation of the transducing phage and an increase in the proportion of recombinant type transductants. CsCl-EB density centrifugation revealed that plasmid deoxyribonucleic acid (DNA) was present in PS 81(P(81))(N(T)) and its cured derivative [PS 81(N(P))(N(T))], but not in PS 52. Sucrose gradient analysis of plasmid DNA showed that the penicillinase plasmid of PS 81(P(81))(N(T)) was larger than the plasmid in its cured derivative. Thus, the cured derivative contains plasmid DNA which appears to recombine with the incoming plasmid, causing the rise in transduction frequency noted after UV irradiation of transducing phage.

Stability of penicillinase plasmids in Staphylococcus aureus

The isolation of mutants of Staphylococcus aureus that are affected in the stability of penicillinase plasmids is described. One mutation is plasmid borne and results in nonreplication of the plasmid at 42 C. A second type of mutation is host-borne and gives rise to instability of both mcr(I) and mcr(II) penicillinase plasmids but not a tetracycline-resistant plasmid.

Evidence for genetic interaction between plasmid and chromosomal penicillinase linkage groups in Staphylococcus aureus

Spontaneous reciprocal recombination was detected between the regulator genes of penicillinase plasmids and chromosomal penicillinase linkage groups of Staphylococcus aureus. The frequency of recombination varied with different penicillinase linkage groups.

Differential depression of staphylococcal plasmid and chromosomal penicillinase genes by a class of unlinked chromosomal mutations (R2-)

We described previously a class of mutations (phenotypic designation R2(-)) in Staphylococcus aureus that were unlinked to penicillinase genes but nevertheless imposed constitutive synthesis of this enzyme upon wild-type plasmids. The plasmids affected by these mutations have been found to possess the same maintenance-compatibility type (I) and to form penicillinase of serotype A. Three plasmids that had a different maintenance-compatibility type (II) and formed penicillinase of serotype C were only slightly derepressed in R2(-) mutants. Three chromosomal penicillinase genes were variably derepressed, the range extending from negligible to nearly complete derepression. The differences in degree of derepression among the three types of penicillinase linkage groups were tentatively ascribed to position effects.

Penicillinase plasmid DNA from Staphylococcus aureus

A penicillinase plasmid from Staphylococcus aureus and three of its derivatives, all previously identified as extrachromosomal genetic elements, have been isolated in high yield as circular duplex DNA molecules. The wild-type plasmid was found by contour-length measurements of electron micrographs to have a molecular weight of 18.6 x 10(6) daltons. Two plasmids with deletions encompassing six and eight of the eleven known plasmid cistrons had molecular weights of 16.4 x 10(6) and 15.3 x 10(6) daltons, respectively. This information was used to establish approximate physical distances for the genetic map. A high-frequency transducing element also derived from the plasmid had a molecular weight of approximately 24 x 10(6) daltons. Although each plasmid preparation appeared homogeneous by ultracentrifugal analysis, electron micrographs always revealed the presence of a low percentage of complex oligomeric forms, particularly circular and catenated dimers.

Extrachromosomal inheritance in bacteria

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