Showing papers by "Ian Chopra published in 1987"
TL;DR: The in-vitro susceptibilities of several Providencia stuartii cell envelope enzymes, including ATPase, to chlor hexidine were compared and support the suggestion that bacterial membrane-bound ATPases are specific targets for chlorhexidine.
Abstract: The possibility that chlorhexidine is a specific inhibitor of membrane bound bacterial adenosine triphosphatase (ATPase) was addressed. The in-vitro susceptibilities of several Providencia stuartii cell envelope enzymes, including ATPase, to chlorhexidine were compared. The following concentrations of chlorhexidine were required to cause 50% inhibition of enzyme activity in preparations from chlorhexidine-sensitive strains (MIC 50 mg chlorhexidine/l): ATPase (160 mg/l), succinic dehydrogenase (greater than 300 mg/l), penicillin binding protein 7 (300 mg/l) and beta-lactamase (45 mg/l). Fifty per cent inhibition of the ATPase from a chlorhexidine-resistant strain (MIC 1600 mg/l) was achieved at an in-vitro concentration of 225 mg chlorhexidine/l. Our observations do not support the suggestion that bacterial membrane-bound ATPases are specific targets for chlorhexidine.
30 citations
TL;DR: The changes in the susceptibility of PBP 2a, 2b and 3 mutants to beta-lactam antibiotics imply that these PBPs are killing targets, consistent with the fact that thesePBPs are also important for shape determination and peptidoglycan synthesis.
Abstract: SUMMARY: Bacillus subtilis mutants with altered penicillin-binding proteins (PBPs), or altered expression of PBPs, were isolated by screening for changes in susceptibility to β-lactam antibiotics. Mutations affecting only PBPs 2a, 2b and 3 were isolated. Cell shape and peptidoglycan metabolism were examined in representative mutants. Cells of a PBP 2a mutant (UB8521) were usually twisted whereas PBP 2b (UB8524) and 3 (UB8525) mutants produced helices, particularly after growth at 41 °C. The PBP 2a mutant (UB8521) had a higher peptidoglycan synthetic activity than its parent strain whereas the opposite applied to the PBP 2b mutant UB8524. The PBP 3 mutant (UB8525) had a similar peptidoglycan synthetic activity to that of the parent strain when grown at 37 °C, but 40% higher activity after growth at 41°C. The PBP 2a mutant (UB8521) exhibited the same wall thickening activity as the parent, but the PBP 2b and 3 mutants (UB8524 and UB8525) were partially defective in this respect. The changes in the susceptibility of PBP 2a, 2b and 3 mutants to β-lactam antibiotics imply that these PBPs are killing targets, consistent with the fact that these PBPs are also important for shape determination and peptidoglycan synthesis.
23 citations
Journal Article•
TL;DR: It is suggested that characterisation of membrane proteins will be of value in the identification of C. diversus by their outer membrane polypeptide and inner membrane penicillin binding protein (PBP) profiles.
Abstract: Previous studies demonstrated that difficulties can occur in distinguishing Citrobacter diversus from Escherichia coli. In this paper we show that the two species can be distinguished from each other by their outer membrane polypeptide and inner membrane penicillin binding protein (PBP) profiles. We suggest that characterisation of membrane proteins will be of value in the identification of C. diversus.
TL;DR: The purity of the various P. stuartii cell envelope fractions was assessed by a combination of techniques that included one- and two-dimensional gel electrophoresis of proteins, enzyme assays and detection of penicillin-binding proteins.
Abstract: Cell envelopes (i.e. unfractionated inner and outer membranes) were obtained from Providencia stuartii by following procedures previously applied to the isolation of envelopes from Escherichia coli. The P. stuartii envelopes contained known inner membrane enzymes that included a variety of dehydrogenases and ATPase. The catalytic activity of the ATPase depended upon the concentration of magnesium ions, the substrate (ATP) level and the ratio of magnesium ions to ATP. Cell envelopes from P. stuartii were further fractionated to recover inner and outer membrane polypeptides by treatment with the detergent Sarkosyl. Proteins from the periplasmic region were recovered by a simple osmotic shock procedure also previously applied to E. coli. The purity of the various P. stuartii cell envelope fractions was assessed by a combination of techniques that included one- and two-dimensional gel electrophoresis of proteins, enzyme assays and detection of penicillin-binding proteins.
TL;DR: Synthesis of penP was more susceptible to inhibition by puromycin than the pBR322-encoded TEM1 β-lactamase, and the implications of these results for mechanisms of secretion and insertion of lipoproteins into the E. coli outer membrane are discussed.
Abstract: Plasmid pBR322 and penP-encoded β-lactamase activities were examined in cell fractions from wild-type and murein lipoprotein-deficient Escherichia coli strains. The specific activity of the Bacillus licheniformis penP gene product, a lipoprotein when expressed in E. coli, was increased in the outer membrane of a murein-lipoprotein deficient mutant. The activities of the 2 enzymes in wild-type E. coli exposed to the translational inhibitor puromycin were also investigated. Synthesis of penP was more susceptible to inhibition by puromycin than the pBR322-encoded TEM1 β-lactamase. The implications of these results for mechanisms of secretion and insertion of lipoproteins into the E. coli outer membrane are discussed.
TL;DR: The authors showed that the two species can be distinguished from each other by their outer membrane polypeptide and inner membrane penicillin binding protein (PBP) profiles, and suggested that characterisation of membrane proteins will be of value in the identification of C. diversus.
Abstract: Previous studies demonstrated that difficulties can occur in distinguishing Citrobacter diversus from Escherichia coli. In this paper we show that the two species can be distinguished from each other by their outer membrane polypeptide and inner membrane penicillin binding protein (PBP) profiles. We suggest that characterisation of membrane proteins will be of value in the identification of C. diversus.