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L J Piddock

Publications and source records attributed to L J Piddock.

At least 55 records · Page 3Linked to original sources
PubMed1995

Quinolone resistance and Campylobacter spp.

Campylobacter are a frequent cause of diarrhoea in man. The in-vitro susceptibility of all species to the fluoroquinolones and the good response observed in early clinical trials has led to the proposal that these agents may be useful in the treatment of campylobacter enteritis and other more complicated campylobacter infections. However, fluoroquinolone-resistant campylobacters have been reported in up to 50% of isolates from man. The numbers of resistant isolates varies both between and within countries, factors associated with this include foreign travel, local usage of fluoroquinolones, especially in animal husbandry, and whether the microbiology laboratory tests for susceptibility to fluorinated agents, or just nalidixic acid. Fluoroquinolone-resistant campylobacter have emerged during therapy with fluoroquinolones and been responsible for treatment failure. The mechanism of resistance in most isolates is due to mutation in the gyrA (at threonine 86) gene which encodes the A subunit of DNA gyrase. The suggestion of cross resistance to non-quinolone antibiotics, such as tetracycline and/or erythromycin, is probably explained by coincidental occurrence in isolates already resistant to such drugs. The proposal that the veterinary use of fluoroquinolones has led to the selection of fluoroquinolone-resistant campylobacters in poultry which then enter the food-chain to infect man has been viewed as controversial. In the UK fluoroquinolone were only licensed for this use in 1993; it will be interesting to see whether resistant isolates increase the number, thereby lending support for this hypothesis.

Animals↗
PubMed1995

Mechanisms of resistance to fluoroquinolones: state-of-the-art 1992-1994.

This paper gives an update on the mechanisms of bacterial resistance to fluoroquinolones. The laboratory techniques currently used to determine the mechanism(s) of resistance are outlined, including the use of restriction fragment length polymorphism and single-stranded conformational polymorphism analysis of mutations in gyrA. Alterations in gyrA have continued to be the most reported cause of resistance, with high level resistance due to 2 or more mutations in this gene. Recently, mutations in gyrA of Mycobacterium tuberculosis and Campylobacter jejuni have been described. Complementation studies with plasmid encoded cloned gyrB from Escherichia coli suggest that high fluoroquinolone resistance (minimum inhibitory concentration = 32 mg/L) in Salmonella typhimurium can be due to mutation in both gyrA and gyrB. Decreased fluoroquinolone accumulation into E. coli has been shown to be due to mutations in a number of genes at different loci. Current interest has focused upon the marRAB and soxRS loci, with mutations in genes of either loci giving rise to decreased susceptibility to several unrelated drugs, including fluoroquinolones, tetracycline, chloramphenicol and some beta-lactams, and decreased expression of OmpF. The genetic characterisation of fluoroquinolone efflux from Staphylococcus aureus has shown that efflux occurs in both fluoroquinolone-susceptible and -resistant bacteria. The most likely cause of resistance is overexpression of NorA, giving rise to increased efflux. Recently, 2 efflux systems in Pseudomonas aeruginosa have been proposed, MexA-MexB-OprK and MexC-MexD-OprM, conferring decreased susceptibility to fluoroquinolones, tetracycline, chloramphenicol and some beta-lactams.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Quinolone resistance in veterinary isolates of Salmonella.

Twenty-seven nalidixic acid-resistant (MIC > or = 256 mg/L) isolates of salmonella from veterinary sources were also less susceptible to fluoroquinolones (range of MICs of ciprofloxacin, 0.12-2 mg/L). Six isolates were cross-resistant to one or more chemically unrelated antibacterial agents. The concentrations of enrofloxacin that inhibited DNA synthesis by 50% were similar to the MIC values for 23 of 27 isolates, suggesting a mutation in gyrA. Insertion of pNJR3-2 (gyrA) in nine of 20 isolates increased susceptibility to quinolones, suggesting that resistance was due to mutation in gyrA. Five of 27 isolates had reduced levels of accumulation of enrofloxacin. Two of the five also had increased susceptibility to quinolones when pNJR3-2 was introduced. None of the outer membrane protein profiles of the resistant isolates differed from those of sensitive control strains. Three of 27 isolates had differences in lipopolysaccharide profiles compared to control strains. Although the MIC of ciprofloxacin was less than the recommended UK break point concentrations for most isolates, the increasing incidence of quinolone-resistance in salmonella from veterinary sources is a matter of concern.

Animals↗
PubMed1994

In-vitro activity of quinolones and macrolides against mycobacteria.

The activities of eight quinolones (ciprofloxacin, clinafloxacin, levofloxacin, ofloxacin, A-80556, sparfloxacin, temafloxacin and tosufloxacin) and three macrolides (azithromycin, clarithromycin and erythromycin) against 98 clinical isolates of Mycobacterium tuberculosis and 120 isolates of five different atypical mycobacterial species including 20 Mycobacterium kansasii, 25 Mycobacterium scrofulaceum, 25 Mycobacterium avium/intracellulare, 25 Mycobacterium chelonae and 25 Mycobacterium fortuitum were determined with the Middlebrook 7H9 broth macrodilution method. Sparfloxacin, clinafloxacin, levofloxacin, ciprofloxacin and ofloxacin were active against M. tuberculosis (MIC90 0.06-0.5 mg/L; MBC90 0.125-2.0 mg/L). However, higher MIC90S and MBC90S of these quinolones were obtained for strains of multi-drug resistant M. tuberculosis. The macrolides tested had poor activity against M. tuberculosis isolates (MIC90 > 8.0 mg/L). Furthermore, high MIC90S of the quinolones and macrolides (2.0 to 8.0 mg/L) were obtained for clinical isolates of atypical mycobacteria, with the exception of clarithromycin against M. kansasii (MIC90 = 1.0 mg/L) and sparfloxacin against M. scrofulaceum (MIC90 = 1.0 mg/L).

4-Quinolones↗
PubMed1994

Interaction of divalent cations, quinolones and bacteria.

The interaction between divalent cations and quinolones and the mechanism by which the former antagonizes the antimicrobial activities of the latter were investigated. In the presence of either magnesium or calcium chloride, the MICs of 18 quinolones for Gram-positive and Gram-negative bacteria increased. Accumulation of and inhibition of DNA synthesis by quinolones were decreased in the presence of magnesium chloride while, in the presence of EDTA, there was no increase in the concentration of accumulated quinolone for any of the agents tested. Only with nalidixic acid was there enhancement of the inhibition of DNA synthesis. Chelation of selected quinolones by magnesium was demonstrated with a fluorescence assay which showed that the extent to which fluorescence (consistent with chelation) was enhanced varied with the quinolone. Assessment of the strength of the magnesium-quinolone complexes with the chelating agent EDTA demonstrated that some of the complexes could be broken. Thin layer chromatography of quinolones and quinolone-magnesium complexes provided evidence that the components of the complex were probably combined in a ratio of 1:1 and that reduced intracellular accumulation of the quinolones in the presence of magnesium was unlikely to be due to a complex being too bulky to be taken through the porin channels. In contrast with permeabilizers which are known to utilize the self-promoted uptake pathway, none of the quinolones studied permeabilized Gram-negative bacteria to lysozyme, caused enhanced fluorescence to 1-N-phenyl-naphthylamine (NPN) or increased the leakage of periplasmic beta-lactamase into the culture medium. The reduced activities of the quinolones in the presence of divalent cations may be the result of the chelation of exogenous ions and, possibly, lipopolysaccharide- or lipoteichoic acid-associated magnesium ions, thereby resulting in less drug being available to enter the bacterium. Alternatively, reduced activity may be due to a fundamental effect on the interaction between quinolones and their target DNA gyrase.

4-Quinolones↗
PubMed1994

Activity of Bay y3118 against quinolone-susceptible and -resistant gram-negative and gram-positive bacteria.

The activity of Bay y3118 against laboratory strains of bacteria, including those with mutations in gyrA, with decreased expression of outer membrane proteins, and/or that are multiply resistant, and 121 selected clinical isolates, including highly fluoroquinolone-resistant bacteria from Spain and Argentina, was determined. Bay y3118 was extremely active (MICs, < or = 1 microgram/ml) against all bacteria, including quinolone-resistant laboratory strains. However, Bay y3118 was less active against 46 of 121 quinolone-resistant clinical isolates, such that > or = 16 micrograms of Bay y3118 per ml was required to inhibit 3 isolates. The concentration of Bay y3118 required to inhibit DNA synthesis by 50% correlated well with the MIC. Bay y3118 had accumulation kinetics similar to those of previously studied fluoroquinolones, e.g., ciprofloxacin, and there was a 50% decrease in the steady-state concentration in those members of the family Enterobacteriaceae that lacked porin proteins. Magnesium chloride at 20 mM apparently abolished the accumulation of Bay y3118 into Escherichia coli and reduced the level of accumulation into other gram-negative bacteria and Staphylococcus aureus. Carbonyl cyanide m-chlorophenylhydrazone at 100 microM enhanced the accumulation of Bay y3118 into E. coli, but it had a minimal effect on accumulation into S. aureus.

Anti-Infective Agents↗
PubMed1993

Activity of 13 beta-lactam agents combined with BRL 42715 against beta-lactamase producing gram-negative bacteria compared to combinations with clavulanic acid, tazobactam and sulbactam.

The activity of six cephalosporins, six penicillins and one monobactam combined with BRL 42715, clavulanic acid, sulbactam or tazobactam at 0.1, 0.5, 1, 2, 5 and 10 mg/L was determined for 45 beta-lactamase producing Gram-negative bacteria. The combination of BRL 42715 with any of the agents was more active than any of the other inhibitor and beta-lactam combinations. Unlike the other beta-lactamase inhibitors, BRL 42715 enhanced the activity of the beta-lactams for strains that constitutively expressed Richmond & Sykes Class I beta-lactamase and against strains expressing extended-spectrum plasmid-mediated beta-lactamases.

Anti-Bacterial Agents↗
PubMed1993

Comparison of the mechanism of action and resistance of two new fluoroquinolones, rufloxacin and MF961 with those of ofloxacin and fleroxacin in gram-negative and gram-positive bacteria.

For rufloxacin MF961, ofloxacin and fleroxacin the inhibition of DNA synthesis, intracellular accumulation, optimum bactericidal concentration (OBC) and killing kinetics at the OBC for Enterobacteriaceae, Pseudomonas aeruginosa and staphylococci and induction of recA in Escherichia coli were determined. All agents had good activity against all the strains and inhibited DNA synthesis by 50% at concentrations correlating with the MIC. The maximum recA inducing concentrations after 60 min exposure to the quinolones in E. coli were 0.5 mg/L of rufloxacin, MF961, ofloxacin and 0.05 mg/L of fleroxacin. Accumulation of all quinolones was rapid; however, higher concentrations of all agents were accumulated within staphylococci than in Gram-negative bacteria. Rufloxacin was accumulated to higher concentrations in all bacteria than the other three agents. Laboratory mutants with decreased susceptibility to the four drugs were selected from each strain. All agents selected mutants with decreased susceptibility to quinolones alone, with phenotypes suggesting mutations in gyrA. Multiply-resistant mutants were also selected; however, as few had decreased expression of OmpF, the mutated gene is unlikely to be an allele of marA. All mutants had MICs > or = 2 mg/L, a typical breakpoint concentration for most quinolones.

Anti-Infective Agents↗
PubMed1993

Accumulation and killing kinetics of fifteen quinolones for Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa.

The accumulation of fifteen quinolone antimicrobial agents (nalidixic acid, eight mono-fluorinated agents, three di-fluorinated agents and three tri-fluorinated agents) by Escherichia coli KL16, Staphylococcus aureus NCTC 8532 and Pseudomonas aeruginosa NCTC 10662 was studied. The concentration of quinolones accumulated varied with the quinolone and the bacterial species, and was not affected by the number of fluorine atoms on the quinolone nucleus. There was also no direct relationship between the hydrophobicity or the molecular size of each drug and accumulation or activity. The killing of the three strains by the fifteen quinolones at a concentration of 10 mg/L was determined in broth and phosphate buffer to mimic the conditions of the accumulation assay. The bactericidal activity varied with the agent and the strain, and usually reflected the in-vitro activity of the drug. Despite most agents causing a decrease in the viable count of the three strains there was no detectable effect on the pattern of accumulation of the quinolones.

Anti-Infective Agents↗
PubMed1993

The accumulation of five antibacterial agents in porin-deficient mutants of Escherichia coli.

A library of isogenic mutants containing Mud9-induced deletions of the structural and regulatory genes for the porin proteins OmpF and OmpC of Escherichia coli was constructed. The accumulation of norfloxacin, tetracycline, chloramphenicol, cephalothin and cefoxitin was measured with each strain, and shown to be reproducible with low experimental standard deviations, such that the roles of OmpF, OmpC and PhoE in the accumulation of these agents were determined. All data were statistically analysed to determine whether the differences observed between the data for each mutant compared with those for the other mutants and for the wild-type strain were significant. The loss of OmpF reduced accumulation of norfloxacin, tetracycline, cephalothin and cefoxitin by 16-60% compared to the wild-type parent strain, but reduced accumulation of chloramphenicol by < 10%. The loss of OmpC reduced accumulation of cephalothin and cefoxitin by 13 and 34%, respectively, compared to the wild-type parent strain, but had little effect on the accumulation of norfloxacin, chloramphenicol and tetracycline (< 3%). The loss of both OmpF and OmpC (ompR) reduced accumulation of norfloxacin, chloramphenicol, tetracycline, cephalothin and cefoxitin by 36-68%. However, the presence of PhoE in the absence of both OmpF and OmpC, enhanced accumulation to 52-119% of the concentrations of these five agents accumulated by the wild-type strain. These data suggest that OmpF is the preferred route of entry for three of the antibiotics studied, but not for chloramphenicol and tetracycline which utilize both porins equally well. The high levels of accumulation (30-64%) of all five antibiotics in the absence of all major porins suggest that an alternative mechanism(s) of accumulation is available.

Anti-Infective Agents↗
PubMed1993

High-level quinolone resistance amongst clinical isolates of Escherichia coli and Klebsiella pneumoniae from Spain.

A recombinant plasmid containing gyr A encoding wild-type Escherichia coli quinolone susceptible DNA gyrase A subunits has been used as a broad host range gene probe. Strains expressing gyr A-mediated quinolone resistance become susceptible to quinolones upon insertion of the plasmid, whereas the plasmid without gyrA (pLA2917, vector) has no effect. Fifteen highly ciprofloxacin-resistant E. coli and three Klebsiella pneumoniae (MICs 2-64 mg/L) were isolated from clinical specimens in the Hospital de la Princesa, Madrid, Spain. Plasmid pNJR3-2 and pLA2917 were introduced into the clinical isolates by conjugation, and transconjugants selected with tetracycline or kanamycin (for which the plasmids encode resistance). Ten transconjugants from each mating, the original isolates, the gene probe and vector control were screened for susceptibility to nalidixic acid, ciprofloxacin, ofloxacin, norfloxacin, tetracycline, chloramphenicol, cefoxitin and trimethoprim. Lower MICs of quinolones were seen for the transconjugants of two K. pneumoniae isolates in the presence of the gene probe, suggesting that these isolates harboured mutations in gyr A. Plasmid profiles confirmed the presence of the probe. The susceptibility of the third K. pneumoniae strain and all E. coli isolates were unaffected by insertion of the plasmid, suggesting another mechanism was responsible for quinolone resistance.

4-Quinolones↗
PubMed1993

Ciprofloxacin resistance in clinical isolates of Salmonella typhimurium obtained from two patients.

Two patients (patients A and B) infected with Salmonella typhimurium failed ciprofloxacin therapy, and the posttherapy isolates had reduced susceptibilities to quinolones; 6 of 11 isolates from patient B were also cross-resistant to chemically unrelated agents. No transferable resistance, chloramphenicol-acetylating enzymes, or beta-lactamases were detected. For 13 of 14 isolates, the concentrations of ciprofloxacin that inhibited DNA synthesis by 50% were similar to the MICs, suggesting a mutation in gyrA. Insertion of pNJR3-2 (gyrA) in the posttherapy isolate from patient A and 5 of 11 of the posttherapy isolates from patient B resulted in lower quinolone MICs, also suggesting that resistance was due to a mutation in gyrA. Three of the five isolates also had reduced levels of accumulation of quinolones. All six cross-resistant isolates from patient B had reduced levels of accumulation of quinolones, but only one isolate had increased susceptibility when pNJR3-2 was inserted. Despite the lack of OmpF seen in five isolates from patient B, there was no correlation with decreased levels of quinolone accumulation. All isolates had identical smooth lipopolysaccharide profiles. The mechanism of apparently reduced accumulation has yet to be determined.

Anti-Infective Agents↗
PubMed1992

Activity of meropenem against imipenem-resistant bacteria and selection in vitro of carbapenem-resistant Enterobacteriaceae.

The activity of meropenem against 106 imipenem-resistant (MIC > or = 8 mg/l) clinical isolates, and the frequency of resistance to meropenem and imipenem among 24 Enterobacteriaceae was determined. Both agents selected colonies on agar but 20-80% were susceptible after one subculture and 72% of the mutants reverted to susceptibility 1 to 6 months after selection. All isolates and stable mutants were inhibited by > 1 mg/l meropenem, although the MIC of imipenem was 4-16 mg/l. Three of six Xanthomonas maltophilia isolates were susceptible to meropenem (MICs 2-4 mg/l). Pseudomonas aeruginosa lacking outer membrane protein D2 were resistant to meropenem, although isolates with substantially reduced expression of this protein were susceptible. None of the imipenem-resistant gram-positive bacteria were susceptible to meropenem. There was no clear correlation between altered outer membrane protein expression and decreased susceptibility to carbapenems, and there was no apparent involvement of plasmid or chromosomal beta-lactamase.

Bacteria↗
PubMed1992

Activity of cefpirome combined with beta-lactamase inhibitors and affinity for the penicillin-binding proteins of methicillin-resistant Staphylococcus aureus.

The susceptibility of 47 clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) to cefpirome, ceftazidime and methicillin was determined with Isosensitest media, with/without 5% NaCl and incubation at 30 degrees, 37 degrees and 44 degrees C for 24 and 48 h. At 24 h the MIC50 of cefpirome was 8 mg/l compared to 64 mg/l ceftazidime; at 48 h this increased to 32 mg/l cefpirome. The addition of 10 mg/l clavulanic acid or sulbactam lowered the MIC of cefpirome (at 48 h) by greater than four-fold in 23% and 11% of the strains, respectively. Cefpirome had primary affinity for penicillin-binding protein (PBP) 1 and 2 in five MRSA and one methicillin-susceptible Staphylococcus aureus. PBP 2a was present in all MRSA and was not saturated by 64 mg/l cefpirome. Clavulanic acid at a concentration of 10 mg/l bound to PBP 2 by greater than 50% in all strains, and when combined with cefpirome, the density of PBP 2a was also reduced but not completely abolished. The data from this study suggests that the mechanism of synergy of a beta-lactamase inhibitor plus a cephalosporin for MRSA may be due to an additive effect against PBPs and not just inhibition of a beta-lactamase. No cefpirome-resistant mutants could be selected from a methicillin-susceptible Staphylococcus aureus, but mutants were selected from an MRSA (expressing homogeneous methicillin resistance) for which MICs of cefpirome were 8 to 32 mg/l.

Bacterial Proteins↗