The Rcs phosphorelay is a cell envelope stress response activated by peptidoglycan stress and contributes to intrinsic antibiotic resistance. (17/94)

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Growth of Escherichia coli: significance of peptidoglycan degradation during elongation and septation. (18/94)

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In vitro interaction between mecillinam and piperacillin-tazobactam in the presence of azithromycin against members of the Enterobacteriaceae family and Pseudomonas aeruginosa. (19/94)

Mecillinam was tested in vitro alone or in combination with piperacillin-tazobactam and azithromycin against representative species of the Enterobacteriaceae family and Pseudomonas aeruginosa to extend its antibacterial spectrum, and to protect mecillinam from inactivating enzymes taking advantage of the presence of tazobactam. Drug interactions were studied by microdilution method, by selection of spontaneous resistant mutants on agar plates containing the drugs in combination and by time kill experiments. Against Enterobacteriaceae mecillinam and piperacillin-tazobactam showed synergistic interaction in 24/60 tests carried out by microdilution technology, in 4/16 by selecting resistant mutants and in 5/9 by time-kill experiments. P. aeruginosa reacted indifferently to the drug combinations, with few exceptions, when azithromycin was present a reduction of the MICs were recorded. Mecillinam reacted favourably in vitro in combination with piperacillin-tazobactam against not only strains included in its antibacterial spectrum but also against resistant Morganella morganii, Proteus spp and P. aeruginosa. The addition of azithromycin (8 mg/L) was beneficial for the drug combination increasing the bactericidal effect in the great majority of the cases. Only systematic in vivo studies may establish the clinical significance and benefits of the present observations.  (+info)

Buoyant density studies of several mecillinam-resistant and division mutants of Escherichia coli. (20/94)

The buoyant density of wild-type Escherichia coli cells has previously been reported not to vary with growth rate and cell size or age. In the present report we confirm these findings, using Percoll gradients, and analyze the recently described lov mutant, which was selected for its resistance to mecillinam and has been suggested to be affected in the coordination between mass growth and envelope synthesis. The average buoyant density of lov mutant cells was significantly lower than that of wild-type cells. Similarly, the buoyant density of wild-type cells decreased in the presence of mecillinam. The density of the lov mutant, like that of the wild type, was invariant over a 2.8-fold range in growth rate. In this range, however, the average cell volume was also constant. Analysis of buoyant density as a function of cell volume in individual cultures revealed that smaller (newborn) lov mutant cells had higher density than larger (old) cells; however, the density of the small cells never approached that of the wild-type cells, whose density was independent of cell size (age). A pattern similar to that of lov mutant cells was observed in cells carrying the mecillinam-resistant mutations pbpA(Ts) and rodA(Ts) and the division mutation ftsI(Ts) at nonpermissive temperatures as well as in wild-type cells treated with mecillinam, but not in mecillinam-resistant crp or cya mutants.  (+info)

Activity of mecillinam against Escherichia coli resistant to third-generation cephalosporins. (21/94)

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Growth properties of mecillinam-resistant bacterial variants in urine. (22/94)

Resistant variants are often formed when susceptible Enterobacteriaceae are grown in media containing mecillinam. These variants have not yet been detected in patients or identified as a cause of treatment failure in limited clinical trials. Mecillinam-resistant organisms were formed by 5 out of 13 urinary isolates of Enterobacteriaceae incubated in urine containing mecillinam. The mean generation time of these five variants in urine containing therapeutic concentrations of mecillinam was 3.2 times that of normal organisms in antibiotic-free urine. When three of these five resistant variants were subcultured in antibiotic-free urine, the generation time, morphology, and antibiotic susceptibility returned to normal. On antibiotic-free agar medium, all five mecillinam-resistant variants readily reverted to the "susceptible" form and were therefore more likely to be phenotypic rather than genotypic mutants. In a second series of experiments, the flushing effect of the bladder on the clearance of organisms was partly simulated by frequent subculture in urine. Under these conditions, the cell density of cultures of all bacteria remained high during 10 subcultures over 52 h. However, bacterial populations progressively decreased in urine containing mecillinam until none could be detected at 28 h or thereafter. The slow growth rate of mecillinam-resistant variants may explain why detectable numbers of these organisms fail to colonize the urinary tract during treatment. Other factors may reinforce the postulated effect of the reduced growth rate in vivo.  (+info)

Mapping of the mecillinam-resistant, round morphological mutants of Escherichia coli. (23/94)

Genes responsible for round morphology in mecillinam-resistant, round morphological mutants of Escherichia coli have been mapped. Three mutants, called rodX, mapped at around 14 min, and two, called rodY, mapped at around 70 min by P1 transduction. These are either the same or very close to the loci reported, respectively, for the rodA (H. Matsuzawa, K. Hayakawa, T. Sato, and K. Imahori, J. Bacteriol. 115:436-442, 1973) and envB genes (B. Westling-Haggstrom and S. Normark, J. Bacteriol. 123:75-82, 1975). This suggests that mecillinam can be used very efficiently to select for found morphological mutants of rodA and envB after nitrosoguanidine treatment.  (+info)

Penicillin-binding protein 2 is essential for the integrity of growing cells of Escherichia coli ponB strains. (24/94)

Analysis of Escherichia coli pbpA(Ts) or rodA(Ts) strains defective for penicillin-binding protein (PBP) 1A or PBP 1B indicated that the activity of PBP 2 is essential to prevent cell lysis in PBP 1B(-) strains and suggested that PBP 2 is active or activatable in rodA(Ts) mutants under restrictive conditions.  (+info)