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Biomedical subjects

G A Jacoby

Publications and source records attributed to G A Jacoby.

At least 19 recordsLinked to original sources
PubMed1998

Quinolone resistance from a transferable plasmid.

BACKGROUND: Bacteria can mutate to acquire quinolone resistance by target alterations or diminished drug accumulation. Plasmid-mediated resistance to quinolones in clinical isolates has been claimed but not confirmed. We investigated whether a multiresistance plasmid could transfer resistance to quinolones between bacteria. METHODS: We transferred resistance between strains by conjugation. The resistance plasmid was visualised in different hosts by agarose-gel electrophoresis. We determined the frequency of spontaneous mutations to ciprofloxacin or nalidixic-acid resistance in Escherichia coli strains, with or without the quinolone resistance plasmid. FINDINGS: A multiresistance plasmid (pMG252) from a clinical isolate of Klebsiella pneumoniae was found to increase quinolone resistance to minimum inhibitory concentrations (MICs) as high as 32 microg/mL for ciprofloxacin when transferred to strains of K pneumoniae deficient in outer-membrane porins. Much lower resistance was seen when pMG252 was introduced into K pneumoniae or E coli strains with normal porins. The plasmid had a wide host range and expressed quinolone resistance in other enterobacteriaceae and in Pseudomonas aeruginosa. From a plasmid-containing E coli strain with ciprofloxacin MIC of 0.25 microg/mL and nalidixic-acid MIC of 32 microg/mL, quinolone-resistant mutants could be obtained at more than 100 times the frequency of a plasmid-free strain, reaching MICs for ciprofloxacin of 4 microg/mL and for nalidixic acid of 256 microg/mL. INTERPRETATION: Transferable resistance to fluoroquinines and nalidixic acid has been found in a clinical isolate of K pneumoniae on a broad host range plasmid. Although resistance was low in wild-type strains, higher levels of quinolone resistance arose readily by mutation. Such a plasmid can speed the development and spread of resistance to these valuable antimicrobial agents.

Anti-Infective Agents↗
PubMed1997

Extended-spectrum beta-lactamases and other enzymes providing resistance to oxyimino-beta-lactams.

Bacteria have once again demonstrated their remarkably versatility in meeting the introduction of new classes of beta-lactam antibiotics by modifying available plasmid mediated beta-lactamases to expand their spectrum of action and by incorporating chromosomal beta-lactamase genes onto plasmids that permit their spread to new hosts. Such resistance is more common than presently is appreciated because current NCCLS breakpoints for resistance underestimate its prevalence. A number of risk factors for acquisition of ESBL-producing K. pneumoniae have been defined, but most will be no easier to control than those for infection by MRSA or VRE. More clinical and animal model studies are needed to evaluate options for treatment. Most strains remain susceptible to imipenem and other carbapenems, but carbapenem resistance has appeared either by spread of metallo-beta-lactamase or by production of an AmpC enzyme combined with loss of an outer membrane porin channel. Attack on our adversaries' latest biological weapons is likely to require enhanced versatility on our part as well.

Anti-Bacterial Agents↗
PubMed1996

In vivo selection of porin-deficient mutants of Klebsiella pneumoniae with increased resistance to cefoxitin and expanded-spectrum-cephalosporins.

Four Klebsiella pneumoniae isolates (LB1, LB2, LB3, and LB4) with increased antimicrobial resistance were obtained from the same patient. The four isolates were indistinguishable in biotype, plasmid content, lipopolysaccharide, and DNA analysis by pulse-field gel electrophoresis. Isolate LB1 made TEM-1 and SHV-1 beta-lactamases. Isolates LB2, LB3, and LB4 produced SHV-5 in addition to TEM-1 and SHV-1. MICs of cefoxitin, ceftazidime, and cefotaxime against LB1 were 4, 1, and 0.06 micrograms/ml, respectively. MICs of ceftazidime against K. pneumoniae LB2, LB3, and LB4 were > 256 micrograms/ml, and those of cefotaxime were 2, 4, and 64 micrograms/ml, respectively. MICs of cefoxitin against K. pneumoniae LB2 and LB3 were 4 micrograms/ml, but that against K. pneumoniae LB4 was 128 micrgrams/ml. K. pneumoniae LB4 could transfer resistance to ceftazidime and cefotaxime, but not that to cefoxitin, to Escherichia coli. Isolate LB4 and cefoxitin-resistant laboratory mutants lacked an outer membrane protein of about 35 kDa whose molecular mass, mode of isolation, resistance to proteases, and reaction with a porin-specific antiserum suggested that it was a porin. MICs of cefoxitin and cefotaxime reverted to 4 and 2 micrograms/ml, respectively, when isolate LB4 was transformed with a gene coding for the K. pneumoniae porin OmpK36. We conclude that the increased resistance to cefoxitin and expanded-spectrum cephalosporins of isolate LB4 was due to loss of a porin channel for antibiotic uptake.

Cefoxitin↗
PubMed1996

Detection of extended-spectrum beta-lactamases in clinical isolates of Klebsiella pneumoniae and Escherichia coli.

Forty clinical isolates of Escherichia coli and 141 isolates of Klebsiella pneumoniae that either transferred ceftazidime resistance or showed sulbactam enhancement of oxyimino-beta-lactam susceptibility were tested by disk diffusion methodology for susceptibility to aztreonam, cefotaxime, ceftazidime, and cefoxitin. With standard 30 micrograms antibiotic disks, the fraction of these extended-spectrum beta-lactamase (ESBL)-producing isolates testing resistant by National Committee for Clinical Laboratory Standards criteria was lowest (24%) with cefotaxime disks. Forty percent of the E. coli and 29% of the K. pneumoniae isolates appeared susceptible with at least one oxyimino-beta-lactam disk. Ceftazidime and aztreonam disks were equivalent in differentiating ESBL production, and both were superior to cefotaxime disks. Over half the E. Coli and 29% of the K. pneumoniae isolates tested cefoxitin resistant. In 30 isolates, cefoxitin resistance was transmissible and due to a plasmid-mediated AmpC-type beta-lactamase. With a 5-micrograms ceftazidime disk, a breakpoint could be chosen with high sensitivity and specificity for ESBL-producing organisms. Present disk diffusion criteria underestimate the prevalence of ESBL-producing strains.

Anti-Bacterial Agents↗
PubMed1996

Antimicrobial-resistant pathogens in the 1990s.

Streptococcus pneumoniae, Enterococcus faecalis, Enterococcus faecium, Staphylococcus aureus, and Klebsiella pneumoniae have become increasingly resistant to antimicrobial agents. This chapter reviews the epidemiology of this resistance, its detection in the laboratory, the mechanisms of resistance, and the options for therapy and infection control.

Anti-Bacterial Agents↗
PubMed1994

Genetics of extended-spectrum beta-lactamases.

Bacteria have adapted to the introduction of aztreonam, cefotaxime, ceftazidime, ceftriaxone and other oxyimino-beta-lactams by altering existing plasmid-mediated class A and class D beta-lactamases so as to expand their spectrum of activity. In the TEM and SHV families of extended-spectrum beta-lactamases, relative activity toward oxyimino-substrates increases with the number of amino acid substitutions but at the price of lowered intrinsic efficiency, so that compensatory up-promoter events are often associated with increased enzyme expression. Another new mechanism of resistance is the capture on plasmids of normally chromosomal genes from Enterobacter cloacae, Citrobacter freundii or Pseudomonas aeruginosa, which upon transfer can provide Klebsiella pneumoniae or Escherichia coli with resistance to alpha-methoxy-beta-lactams, such as cefoxitin or cefotetan, as well as to oxyimino-beta-lactams.

Bacteria↗
PubMed1994

Extrachromosomal resistance in gram-negative organisms: the evolution of beta-lactamase.

beta-Lactamases are the major defense used by bacteria to overcome the effects of penicillins, cephalosporins and related beta-lactam antibiotics. In the antibiotic era, the enzymes have evolved to become more prevalent, to appear in new hosts, to be expressed at higher levels, to be acquired by plasmids and to change catalytic properties to increase affinity for what were meant to be nonhydrolysable substrates or to reduce affinity for beta-lactamase inhibitors.

Genes, Bacterial↗
PubMed1994

Prevalence and resistance mechanisms of common bacterial respiratory pathogens.

Organisms causing common infections of the respiratory tract are becoming increasingly resistant to antimicrobial agents. In 1990-1991 between 15% and 20% of isolates of Streptococcus pneumoniae from the United States had MICs of penicillin G of > or = 0.1 microgram/mL and 2%-3% had MICs of > or = 1.0 microgram/mL. The percentage of isolates that are resistant is even higher in other parts of the world. Although most penicillin-resistant strains of S. pneumoniae are susceptible to broad-spectrum cephalosporins, a few isolates resistant to cefuroxime, cefotaxime, and ceftriaxone have appeared. Unlike other respiratory pathogens in which the production of beta-lactamase is responsible for resistance, S. pneumoniae exhibits resistance that is caused by alterations in penicillin-binding proteins. Consequently, beta-lactam/beta-lactamase inhibitor combinations have no particular value against resistant pneumococci. Furthermore, penicillin-resistant pneumococci are often coresistant to macrolides, sulfa-based drugs, and tetracycline. Knowledge of how resistance is attained presumably will further the development of new strategies for treatment. The mechanisms of resistance of pneumococci and other common respiratory pathogens (particularly Haemophilus influenzae and Moraxella catarrhalis) to standard antimicrobial agents are examined in this report.

Bacteria↗
PubMed1994

Detection of Klebsiella pneumoniae and Escherichia coli strains producing extended-spectrum beta-lactamases.

Plasmids encoding extended-spectrum beta-lactamases of the TEM, SHV, and AmpC families were introduced into common Escherichia coli and Klebsiella pneumoniae hosts to create a homogeneous panel for evaluating the abilities of five test systems to detect resistance to eight beta-lactam antibiotics. Although MICs, as determined by agar dilution or E test strips, were increased and disk diffusion zone diameters were diminished, breakpoints for resistance were often not reached, and neither approach was sensitive in detecting resistance to oxyimino-beta-lactams. The MicroScan 18-h microdilution or Vitek rapid automated procedures were similarly insensitive. Ceftazidime was the best single test antibiotic for detecting extended-spectrum beta-lactamase production. beta-Lactamases TEM-7 and TEM-12 were particularly difficult to detect. Because of such difficulties, the prevalence of extended-spectrum beta-lactamases is likely to be greater than is currently appreciated.

Drug Resistance, Microbial↗
PubMed1993

Evaluation of five different methods to prepare bacterial extracts for the identification of beta-lactamases by isoelectric focusing.

The X-PRESS, osmotic shock, chloroform treatment, lysozyme treatment and ultrasonic disruption methods to release five different plasmid-mediated beta-lactamases from Escherichia coli and one chromosomal beta-lactamase from Enterobacter cloacae were compared. The main activities of TEM-1, SHV-1, OXA-1, OXA-2, PSE-4 and chromosomal P99 beta-lactamases were found at the same isoelectric point irrespective of the method used. However, additional satellite bands were found with TEM-1, OXA-1, OXA-2 and PSE-4 beta-lactamases released by the lysozyme method. In addition, beta-lactamase released by osmotic shock treatment was found to be unstable during storage at -20 degrees C or during the 18 h period of iso-electric focusing at +4 degrees C. Chloroform treatment produced similar band patterns and at least as good an enzyme yield as ultrasonic disintegration and was equally simple and fast to perform.

Bacteria↗
PubMed1993

Sequences of MGH-1, YOU-1, and YOU-2 extended-spectrum beta-lactamase genes.

Genes for MGH-1, YOU-1, and YOU-2 extended-spectrum beta-lactamases have been cloned and sequenced. The gene for MGH-1 has the sequence of blaTEM-10, YOU-2 has that of blaTEM-12, and YOU-1 has that of blaTEM-26. All have evolved from blaTEM-1b but have the strong dual promoter sequence of blaTEM-2.

Amino Acid Sequence↗
PubMed1991

Properties of plasmids responsible for production of extended-spectrum beta-lactamases.

The extended-spectrum beta-lactamases are believed to arise by mutations which alter the configuration around the active site of TEM- and SHV-type enzymes so as to increase their efficiency with otherwise nonhydrolyzable cephalosporins and monobactams. This hypothesis predicts that the genes for these new enzymes should be found on the same wide variety of plasmids that encode TEM-1, TEM-2, and SHV-1 beta-lactamases and that at least some of them should be mediated by transposons. Fifteen plasmids, each encoding an extended-spectrum beta-lactamase, were examined. Unlike the average TEM plasmid, all were large, ranging in size from 80 to 300 kb. All determined resistance to multiple antimicrobial agents, ranging from 5 to 11, and some conferred resistance to heavy metals and UV radiation as well. The plasmids belonged to a limited number of incompatibility (Inc) groups, including IncC, IncFI, IncHI2, and IncM. Because most of the mutations giving rise to extended-spectrum activity are G.C----A.T transitions and some of the mutant genes have as many as four base substitutions, a plasmid-determined mutator gene was searched for, but no such property was found. Several techniques were used to detect transposition of the extended-spectrum beta-lactamase genes, but a mobile genetic element could not be demonstrated even though eight of the plasmids hybridized with a DNA probe derived from the tnpR gene of Tn3. The genesis of extended-spectrum beta-lactamases may not be as simple as has been supposed.

DNA Transposable Elements↗
PubMed1991

Sequence of the PSE-1 beta-lactamase gene.

The nucleotide sequence of the PSE-1 beta-lactamase gene from Tn1403 indicates that it is contained in an integron and encodes a class A enzyme differing from PSE-4 and CARB-3 by single amino acid substitutions.

Amino Acid Sequence↗