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D M Livermore

Publications and source records attributed to D M Livermore.

At least 127 records · Page 7Linked to original sources
PubMed1995

Resistance to extended-spectrum cephalosporins, caused by PER-1 beta-lactamase, in Salmonella typhimurium from Istanbul, Turkey.

Two Salmonella typhimurium isolates were studied, one as a representative from a series of neonatal meningitis cases treated at an Istanbul teaching hospital, the other from a gastro-enteritis case seen at a different Istanbul hospital. Both isolates were resistant to extended-spectrum cephalosporins, as well as penicillins, aminoglycosides and chloramphenicol. Cephalosporin resistance depended on production of PER-1 beta-lactamase, which is an extended-spectrum class A enzyme that is only distantly related to TEM and SHV enzymes, and which was previously known only from Pseudomonas aeruginosa isolates. The PER-1 gene was carried by an 81-MDa plasmid, which also determined resistance to aminoglycosides and chloramphenicol. Although it was not self-transmissible to Escherichia coli, this element did transfer if mobilised with plasmid pUZ8. The two S. typhimurium isolates gave indistinguishable DNA restriction patterns and, in addition to their 81-MDa plasmid, also contained 52- and 2.8-MDa plasmids, the last of these encoded TEM-1 enzyme. The two isolates were identical in serotype, antibiogram and plasmid-profile but nevertheless differed in phage type, and, therefore, represented distinct strains. The emergence of cefotaxime and ceftriaxone resistance in salmonellae is disturbing, since these agents are preferred therapy for neonatal meningitis caused by members of the genus.

Base Sequence↗
PubMed1995

Mechanisms of resistance to beta-lactam antibiotics amongst Pseudomonas aeruginosa isolates collected in the UK in 1993.

Antimicrobial resistance among 1991 Pseudomonas aeruginosa isolates collected at 24 UK hospitals during late 1993 was surveyed. Three-hundred and seventy-two of the isolates were resistant, or had reduced susceptibility, to some or all of azlocillin, carbenicillin, ceftazidime, imipenem and meropenem, and the mechanisms underlying their behaviour were examined. Only 13 isolates produced secondary beta-lactamases: six possessed PSE-1 or PSE-4 enzymes and seven had novel OXA enzyme types. Those with PSE types were highly resistant to azlocillin and carbenicillin whereas those with OXA enzymes were less resistant to these penicillins. Chromosomal beta-lactamase derepression was demonstrated in 54 isolates, most of which were resistant to ceftazidime and azlocillin although susceptible to carbenicillin and carbapenems. beta-Lactamase-independent "intrinsic" resistance occurred in 277 isolates and is believed to reflect some combination of impermeability and efflux. Two forms were seen: the classical type, present in 195 isolates, gave carbenicillin resistance (MIC > 128 mg/L) and reduced susceptibility to ciprofloxacin and to all beta-lactam agents except imipenem; a novel variant, seen in 82 isolates, affected only azlocillin, ceftazidime and, to a small extent, meropenem. Resistance to imipenem was largely dissociated from that to other beta-lactam agents, and probably reflected loss of D2 porin, whereas resistance to meropenem was mostly associated with intrinsic resistance to penicillins and cephalosporins. Comparison of the present results with those of a similar study in 1982 revealed significant increases in the proportions of isolates with intrinsic resistance or stable derepression (p < 0.01, chi 2 test).(ABSTRACT TRUNCATED AT 250 WORDS)

Carbapenems↗
PubMed1995

Characterization of an LysR family protein, SmeR from Serratia marcescens S6, its effect on expression of the carbapenem-hydrolyzing beta-lactamase Sme-1, and comparison of this regulator with other beta-lactamase regulators.

Serratia marcescens S6 produces a chromosomally encoded carbapenem-hydrolyzing class A beta-lactamase, Sme-1 (T. Naas, L. Vandel, W. Sougakoff, D. M. Livermore, and P. Nordmann, Antimicrob. Agents Chemother. 38:1262-1270, 1994). Upstream from smeA we identified a second open reading frame (EMBL accession number Z30237). This encodes a 33.1-kDa protein, SmeR, which has a high degree of homology with NmcR, the LysR regulatory protein of the only other sequenced carbapenem-hydrolyzing class A beta-lactamase, NmcA from Enterobacter cloacae NOR-1. It is weakly related to AmpR of the chromosomal cephalosporinase regulatory systems described in E. cloacae, Yersinia enterocolitica, Citrobacter freundii, and Pseudomonas aeruginosa and is very weakly related to other LysR-type regulators of class A beta-lactamases. SmeR is a weakly positive regulator for Sme-1 expression in the absence of or in the presence of beta-lactam inducers. The -35 and -10 regions of smeR are in the opposite orientations and are face-to-face relative to the smeA promoter. SmeR acts similarly to NmcR and not as the AmpR regulators described for class C beta-lactamase systems. SmeR is a weak inducer in the absence or presence of beta-lactams. As was found for the AmpC-AmpR and NmcA-NmcR systems, a putative SmeR-binding site was present upstream from the beta-lactamase gene promoter regions. beta-Galactosidase activity from a smeR-lacZ translational fusion was expressed constitutively and decreased in the presence of SmeR from a coresident plasmid, suggesting that SmeR is autogeneously controlled. Finally, beta-lactams did not affect the expression of SmeR, which is the second regulator of a class A carbapenem-hydrolyzing beta-lactamase to be identified.

Amino Acid Sequence↗
PubMed1995

OXA-14, another extended-spectrum variant of OXA-10 (PSE-2) beta-lactamase from Pseudomonas aeruginosa.

Pseudomonas aeruginosa 455, isolated in Ankara, Turkey, produced a pI 6.2 beta-lactamase determined by plasmid pMLH53 and resisted all beta-lactams except carbapenems. This beta-lactamase, named OXA-14, corresponded to OXA-10 (PSE-2) except that aspartate replaced glycine at position 157 and thus is intermediate between OXA-10 and OXA-11, which has aspartate at position 157 and a further substitution at position 143.

Anti-Bacterial Agents↗
PubMed1995

beta-Lactamases in laboratory and clinical resistance.

beta-Lactamases are the commonest single cause of bacterial resistance to beta-lactam antibiotics. Numerous chromosomal and plasmid-mediated types are known and may be classified by their sequences or phenotypic properties. The ability of a beta-lactamase to cause resistance varies with its activity, quantity, and cellular location and, for gram-negative organisms, the permeability of the producer strain. beta-Lactamases sometimes cause obvious resistance to substrate drugs in routine tests; often, however, these enzymes reduce susceptibility without causing resistance at current, pharmacologically chosen breakpoints. This review considers the ability of the prevalent beta-lactamases to cause resistance to widely used beta-lactams, whether resistance is accurately reflected in routine tests, and the extent to which the antibiogram for an organism can be used to predict the type of beta-lactamase that it produces.

Enterobacteriaceae↗
PubMed1995

A one-year survey of Neisseria gonorrhoeae isolated from patients attending an east London genitourinary medicine clinic: antibiotic susceptibility patterns and patients' characteristics.

OBJECTIVES: To collect epidemiological data on gonococcal infection in an east London genitourinary medicine (GUM) clinic; to perform antibiotic susceptibility testing on Neisseria gonorrhoeae isolates and relate results to patient data; to assess the efficacy of current first-line antibiotic therapy for treating gonorrhoea. METHODS: Gonococcal isolates were collected from 113 patients attending the GUM clinic at Newham General Hospital over a one year period. Isolates (104) were tested for susceptibility to various antibiotics. Plasmid profiles were obtained for penicillinase producing gonococci (PPNG) and isolates exhibiting high-level tetracycline resistance (TRNG). Epidemiological information was collected from clinic attenders by routine note-taking. RESULTS: PPNG (16) accounted for 15% of isolates tested, only three being acquired outside the United Kingdom (U.K.). Plasmid typing showed three types of beta-lactamase-encoding plasmids were represented (2.9 MDa, 3.2 MDa and 4.4 MDa). Amongst the non-PPNG isolates, high-level chromosomal resistance to penicillin (CMRNG) was found in 3.5%, intermediate resistance in 57.5% and full susceptibility in 39%. One isolate showed decreased susceptibility to ciprofloxacin (MIC = 0.06 mg/l). Three PPNG isolates also possessed a 25.2 MDa plasmid and expressed high-level tetracycline resistance encoded by tetM. All isolates were susceptible to cefixime, cefotaxime, azithromycin and spectinomycin. Most gonorrhoea (90%) was seen in local residents. The male:female case ratio was 2:1 with homosexually-acquired gonorrhoea accounting for only 3.5% of the total. Most patients (96%) had acquired gonorrhoea in the U.K.. A past history of gonorrhoea was more frequent in male patients. Concurrent chlamydial infection was seen in 31% females and 16% males. CONCLUSIONS: The high PPNG rate supports a previous decision to change first-line therapy from amoxycillin with probenecid to ciprofloxacin. There was no evidence of clinical treatment failure with ciprofloxacin. Cefixime, cefotaxime, azithromycin and spectinomycin all appear to be suitable alternative therapies. Acquisition of gonorrhoea abroad was associated with isolates exhibiting penicillin resistance but such isolates were also obtained from patients infected locally and without a history of foreign travel.

Adult↗
PubMed1994

Evolution of beta-lactamase inhibitors.

beta-Lactamases present the greatest single challenge to beta-lactam antibiotics, including piperacillin. beta-Lactamase-mediated resistance to supposedly beta-lactamase stable agents such as second- and third-generation cephalosporins is now emerging and inhibitor combinations provide an alternative strategy to overcome this problem. The success of this strategy depends on 1) how efficiently the inhibitor inhibits important beta-lactamases, 2) on how much beta-lactamase the bacteria produce, 3) on the drug that is to be protected, 4) on the permeability and intrinsic susceptibility of the organisms and 5) on the conditions, notably the pH. Tazobactam inhibits most of the clinically important beta-lactamases that give piperacillin resistance, except for the Class I types. Piperacillin itself is a relatively easy drug to protect, particularly against the TEM-type enzymes. The result is that tazobactam greatly extends the activity of piperacillin, notably against enterobacteria, but also against staphylococci and anaerobes. The survey confirmed the very broad spectrum of activity of piperacillin/tazobactam. Resistance occurred in about 17% of the Enterobacter, Citrobacter, Serratia group, where we believe it to have been caused by derepressed Class I enzymes since these strains were cross-resistant to third-generation cephalosporins. Otherwise, resistance was largely confined to such organisms as E. faecium and methicillin-resistant staphylococci, which have piperacillin insensitive penicillin-binding proteins. Finally, some question remains on the antistaphylococcal activity of piperacillin/tazobactam, where MIC tests gave a more favorable impression than disc tests. Nevertheless, early clinical results against staphylococcal infection appear good, with a response rate of nearly 90% [15].

Anti-Bacterial Agents↗
PubMed1994

Inoculum effects on Etests and agar dilution minimum inhibitory concentrations. Piperacillin and piperacillin-tazobactam against Staphylococcus aureus.

Inoculum effects notoriously occur with beta-lactamase-positive staphylococci in dilution susceptibility tests with substrate beta-lactams. Etests, like dilution experiments, demonstrated such effects with piperacillin and, to a lesser extent, with its tazobactam combinations. When Etests were used with the recommended inoculum of approximately 10(6) colony-forming units (CFU/plate, the minimum inhibitory concentrations (MICs) of piperacillin-tazobactam found for beta-lactamase-positive Staphylococcus aureus isolates resembled those found by agar dilution for inocula of 10(4) CFU/spot but were two- to eightfold below those found by agar dilution for inocula of 10(6) CFU/spot; MICs of piperacillin itself by Etest were about fourfold below even those found by agar dilution with inocula of 10(4) CFU/spot. Inoculum effects for beta-lactamase-negative S. aureus were minimal by both methods.

Bacteriological Techniques↗
PubMed1994

Susceptibility of Moraxella catarrhalis isolates to beta-lactam antibiotics in relation to beta-lactamase pattern.

Moraxella catarrhalis isolates (n = 413) were collected from 20 clinical laboratories in England and Scotland in 1991 and were examined for beta-lactamase production by isoelectric focusing. beta-Lactamases were found in 375 isolates of which, 349 (93.1%) had BRO-1 enzyme and 26 (6.9%) had BRO-2. Minor variation in electrofocusing pattern occurred within both enzyme types. Ampicillin MICs for BRO-1 producers were 25-fold higher than for non-producers, but those for BRO-2 producers were raised only four-fold. MICs of cefaclor, cefixime, loracarbef, co-amoxiclav and cefetamet generally were two- to four-fold higher for BRO-1 producers than for BRO-2 producers and enzyme non-producers. Similarly, the inhibition zones of discs containing cefaclor, cefixime, loracarbef or co-amoxiclav were smaller for BRO-1 producers than for non-producers. Amongst the compounds tested, cefetamet seemed the least affected by beta-lactamase production in both MIC and disc tests. Overall, these results indicate that BRO-1 enzyme predominates amongst M. catarrhalis isolates from the UK, as in other countries, and suggest that BRO-1 production gives slight protection against many of the newer oral beta-lactams as well as causing ampicillin resistance.

Anti-Bacterial Agents↗
PubMed1994

Comparative in-vitro activity of biapenem against enterobacteria with beta-lactamase-mediated antibiotic resistance.

The effects of enterobacterial beta-lactamases were studied for biapenem (L627), a new carbapenem. Susceptibility tests were performed for isogenic mutant series of Citrobacter freundii, Enterobacter cloacae, Morganella morganii, Serratia marcescens and Proteus vulgaris which varied only in chromosomal beta-lactamase expression. beta-Lactamase-derepressed organisms in these series were as susceptible as beta-lactamase-inducible strains to biapenem; beta-lactamase-basal mutants were up to eight-fold more susceptible. Similar patterns of relative activity against the different expression types were noted for imipenem and biapenem. These data were related to direct induction and hydrolysis assays: biapenem, like imipenem, was a strong inducer of several Class I enzymes and of the P. vulgaris cefuroximase and, like the other carbapenems, was only very slowly hydrolysed by these enzymes. Moreover, like meropenem, biapenem reversibly deactivated these beta-lactamases. Piperacillin and the cephalosporins, tested as comparators, were more labile than carbapenems to the Class I enzymes, were weak inducers below their MICs and lacked deactivator function. In consequence their MICs were higher for derepressed organisms than for those with inducible or basal beta-lactamase expression. Unlike the carbapenems, they selected derepressed mutants from inducible populations. Biapenem, like imipenem and meropenem, retained full activity against most transconjugants of Escherichia coli K-12 that produced plasmid-mediated beta-lactamases, including extended-spectrum TEM mutants. Only production of OXA-10 (previously PSE-2) enzyme gave a slight reduction in susceptibility to the new carbapenem. Biapenem resistance (MIC 16 mg/L) did, however, occur in S. marcescens S6, which produced a chromosomal carbapenemase. This enzyme hydrolysed biapenem. Overall, our findings indicate that biapenem shares the favourable properties of imipenem and meropenem in its interactions with the most important beta-lactamases of enterobacteria.

Drug Resistance, Microbial↗
PubMed1994

beta-Lactamase types amongst Staphylococcus aureus isolates in relation to susceptibility to beta-lactamase inhibitor combinations.

Relationships between beta-lactamase type and antimicrobial susceptibility were investigated for Staphylococcus aureus isolates collected recently at UK and Irish hospitals, and for reference producers of types A, B, C and D enzymes. Producers of types A and C beta-lactamases predominated amongst the isolates. Tazobactam and clavulanate combinations were studied, as previous observation showed that these inhibitors incompletely reversed the in-vitro amoxycillin and piperacillin resistance of beta-lactamase-positive staphylococci. Further penicillins and cephalosporins served as controls. Organisms with type C beta-lactamase were less susceptible than those with type A enzyme to piperacillin/tazobactam and amoxycillin/tazobactam in disc and MIC tests, and to co-amoxiclav in disc tests only. Conversely, producers of type A enzyme were less susceptible to cephazolin than those with type C enzyme. Kinetic assays showed that type A enzymes bound piperacillin and amoxycillin less tightly than did type C enzyme (higher Kmapp), and were more susceptible to inhibition by clavulanate and tazobactam (lower I50s). However, the susceptibility to beta-lactamase inhibitor combinations for the few producers of types B and D enzymes tested could not be similarly explained by Kmapp and I50 data. It therefore seems that other factors besides beta-lactamase affinity co-determine the susceptibility of the staphylococci. Possible variables include the exact chemistry of the enzyme-inhibitor interaction, and the degree of beta-lactamase induction. Both tazobactam and clavulanate induced staphylococcal types A and C penicillinases.

Amoxicillin↗
PubMed1994

In-vitro activity of biapenem, compared with imipenem and meropenem, against Pseudomonas aeruginosa strains and mutants with known resistance mechanisms.

The activity of biapenem (L-627, LJC-10627), a new carbapenem, was investigated against Pseudomonas aeruginosa strains, mutants and isolates with known resistance mechanisms to other beta-lactams. The behaviour of biapenem closely resembled that of imipenem, although it showed minor differences compared with meropenem, Inducible (i.e. normal) or derepressed chromosomal beta-lactamase expression gave slight protection against biapenem and imipenem, but insufficient to raise the MICs above clinically significant limits. This behaviour correlated with the slight lability of these compounds to the purified enzyme and with their strong capacity to induce beta-lactamase synthesis. Inducible or derepressed enzyme gave no protection against meropenem, possibly reflecting this compound's particular ability to deactivate the enzyme. Biapenem also has some ability to reversibly deactivate the enzyme. None of several plasmid-mediated beta-lactamases (TEM-2, PSE-1, -3 or -4; OXA-3,-6,-10,-11; NPS-1 or LCR-1) introduced into a P. aeruginosa PU21 recipient strain reduced susceptibility to biapenem or other carbapenems. Amongst permeability mutants, those lacking the D2 'carbapenem-specific' porin had reduced susceptibility to biapenem as well as to imipenem and meropenem. Biapenem and imipenem insusceptibility in these D2 porin-deficient mutants required continued expression of the chromosomal beta-lactamase, although this did not apply to meropenem. P. aeruginosa isolates and mutants with broad-spectrum insusceptibility ('intrinsic resistance') to penicillins, cephalosporins and unrelated drugs remained fully susceptible to biapenem and imipenem, whilst showing slightly reduced susceptibility to meropenem. Overall, these findings suggest that biapenem, like the earlier carbapenems, should prove to be a useful antipseudomonal agent, overcoming the mechanisms that commonly confer resistance to other classes of antipseudomonal beta-lactams.

Carbenicillin↗
PubMed1994

Effect of inoculum size on the in-vitro susceptibility to beta-lactam antibiotics of Moraxella catarrhalis isolates of different beta-lactamase types.

The effect of inoculum size on the results of agar dilution MIC tests was assessed for 20 Moraxella catarrhalis isolates with BRO-1 enzyme, 20 with BRO-2 enzyme and 15 isolates that did not produce beta-lactamase. The compounds tested were ampicillin, coamoxiclav, cefaclor, cefixime and cefetamet, and the inocula were 10(4), 10(5), 10(6) and 10(7) cfu/spot. The MICs of ampicillin for BRO-1 and BRO-2 producers were consistently higher than those for non-producers at inocula of 10(7) cfu/spot but overlapped with those for non-producers at lower inocula. A small beta-lactamase-related inoculum effect was seen with coamoxiclav; small inoculum effects also occurred with cefaclor and cefixime but were not related to enzyme presence or type. MICs of cefetamet were the least affected by the inoculum size. For all the compounds, the degree of correlation between MICs and the inhibition zones observed in disk diffusion tests was independent of the inoculum used in the MIC tests. These data suggest that high inocula should be used to determine MICs of ampicillin for M. catarrhalis but that this precaution is unnecessary with the cephalosporins tested or with coamoxiclav.

Amoxicillin↗
PubMed1994

Cloning and sequence analysis of the gene for a carbapenem-hydrolyzing class A beta-lactamase, Sme-1, from Serratia marcescens S6.

Serratia marcescens S6 produces a pI 9.7 carbapenem-hydrolyzing beta-lactamase that is probably encoded by the chromosome (Y. Yang, P. Wu, and D. M. Livermore, Antimicrob. Agents Chemother. 34:755-758, 1990). A total of 11.3 kb of genomic DNA from this strain was cloned into plasmid pACYC184 in Escherichia coli. After further subclonings, the carbapenem-hydrolyzing beta-lactamase gene (blaSme-1) was sequenced (EMBL accession number Z28968). The gene corresponded to an 882-bp open reading frame which encoded a 294-amino-acid polypeptide. This open reading frame was preceded by a -10 and a -35 region consistent with a putative promoter sequence of members of the family Enterobacteriaceae. This promoter was active in E. coli and S. marcescens, as demonstrated by primer extension analysis. N-terminal sequencing showed that the Sme-1 enzyme had a 27-amino-acid leader peptide and enabled calculation of the molecular mass of the mature protein (29.3 kDa). Sequence alignment revealed that Sme-1 is a class A serine beta-lactamase and not a class B metalloenzyme. The earlier view that the enzyme was zinc dependent was discounted. Among class A beta-lactamases, Sme-1 had the greatest amino acid identity (70%) with the pI 6.9 carbapenem-hydrolyzing beta-lactamase, NMC-A, from Enterobacter cloacae NOR-1. Comparison of these two protein sequences suggested a role for specific residues in carbapenem hydrolysis. The relatedness of Sme-1 to other class A beta-lactamases such as the TEM and SHV types was remote. This work details the sequence of the second carbapenem-hydrolyzing class A beta-lactamase from an enterobacterial species and the first in the genus Serratia.

Amino Acid Sequence↗
PubMed1994

Role of efflux pump(s) in intrinsic resistance of Pseudomonas aeruginosa: resistance to tetracycline, chloramphenicol, and norfloxacin.

Most strains of Pseudomonas aeruginosa are significantly more resistant, even in the absence of R plasmids, to many antimicrobial agents, including beta-lactams, tetracycline, chloramphenicol, and fluoroquinolones, than most other gram-negative rods. This broad-range resistance has so far been assumed to be mainly due to the low permeability of the P. aeruginosa outer membrane. The intrinsic-resistance phenotype becomes further enhanced in "intrinsically carbenicillin-resistant" isolates, which were often assumed to produce outer membranes of even lower permeability. It has been shown, however, that this hypothesis cannot explain the beta-lactam resistance of these isolates (D.M. Livermore and K.W.M. Davy, Antimicrob. Agents Chemother. 35:916-921, 1991). In this study, we examined the uptake of tetracycline, chloramphenicol, and norfloxacin by intact cells using strains showing widely different levels of intrinsic resistance. Their accumulation and the response to the addition of a proton conductor showed that even relatively susceptible strains of P. aeruginosa actively pump out these compounds from the cell and that the efflux activity becomes much stronger in strains showing higher levels of intrinsic resistance. We conclude that the efflux mechanism(s) are likely to contribute significantly to the intrinsic resistance of P. aeruginosa isolates to tetracycline, chloramphenicol, and fluoroquinolones, as does the low permeability of the outer membrane. This conclusion is supported by the observation that the hypersusceptibility to various agents of the mutant K799/61 (W. Zimmermann, Antimicrob. Agents Chemother. 18:94-100, 1980) was apparently caused by the lack of active efflux. Although the hypersusceptibility of this mutant has hitherto been assumed to be solely due to its higher outer membrane permeability, its outer membrane was shown to have a coefficient of permeability to cephaloridine that was not significantly different from that of the parent, resistant strain K799/WT. The strains with elevated intrinsic resistance overproduced two cytoplasmic membrane proteins and one outer membrane protein; at least two of these proteins appeared different from the proteins overproduced in the recently described mutant with a derepressed multidrug efflux system, MexA-MexB-OprK (K. Poole, K. Krebes, C. McNally, and S. Neshat, J. Bacteriol. 175:7363-7372, 1993).

Chloramphenicol↗