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Biomedical subjects

G A Jacoby

Publications and source records attributed to G A Jacoby.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1991

Chromosomally mediated beta-lactamase production and gentamicin resistance in Enterococcus faecalis.

We have analyzed four distinct strains of multiply resistant, beta-lactamase-producing enterococci isolated during an outbreak of colonization with these strains on an infant-toddler surgical ward at The Children's Hospital in Boston, Mass. All four strains were resistant to erythromycin, penicillin, and tetracycline and to high levels of gentamicin and streptomycin. One strain was also resistant to chloramphenicol. Plasmid profiles revealed four different plasmid patterns, with the number of identified plasmids ranging from zero to three. The gene coding for beta-lactamase production could be transferred at low frequency (less than 10(-8)) to an enterococcal recipient from one strain in conjunction with all of the other resistance determinants. Probes derived from the staphylococcal beta-lactamase gene and gentamicin resistance gene failed to hybridize with any of the detectable plasmids, but both genes were present on restriction fragments of genomic DNA in all strains. Our results indicate that the beta-lactamase genes and gentamicin resistance genes in these strains are integrated into the bacterial chromosome. The cotransmissibility of the resistance determinants raises the possibility of their incorporation into a multiresistance transposable genetic element.

Conjugation, Genetic↗
PubMed1990

Outbreak of ceftazidime resistance caused by extended-spectrum beta-lactamases at a Massachusetts chronic-care facility.

During a 4-month period in late 1988, we isolated ceftazidime-resistant strains of Klebsiella pneumoniae and other members of the family Enterobacteriaceae from 29 patients at a chronic-care facility in Massachusetts. Ceftazidime resistance resulted from two distinct extended-spectrum beta-lactamases of the TEM type which efficiently hydrolyzed the cephalosporin: YOU-1 with a pI of 5.57 and YOU-2 with a pI of 5.2. Genes encoding these enzymes were present on different but closely related high-molecular-weight, multiple antibiotic resistance plasmids of the H12 incompatibility group and were transferable by conjugation in vitro. Agarose gel electrophoresis of extracts from clinical isolates indicated that this outbreak arose from plasmid transmission among different strains of the family Enterobacteriaceae rather than from dissemination of a single resistant isolate. Isolation rates of ceftazidime-resistant organisms transiently decreased after use of this drug was restricted, but resistant isolates continued to be recovered 7 months after empiric use of ceftazidime ceased.

Ceftazidime↗
PubMed1990

Novel plasmid-mediated beta-lactamase (MIR-1) conferring resistance to oxyimino- and alpha-methoxy beta-lactams in clinical isolates of Klebsiella pneumoniae.

Klebsiella pneumoniae isolates from 11 patients at the Miriam Hospital were identified as resistant to cefoxitin and ceftibuten as well as to aztreonam, cefotaxime, and ceftazidime. Resistance could be transferred by conjugation or transformation with plasmid DNA into Escherichia coli and was due to the production of a beta-lactamase with an isoelectric point of 8.4 named MIR-1. In E. coli, MIR-1 conferred resistance to aztreonam, cefotaxime, ceftazidime, ceftibuten, ceftriaxone, and such alpha-methoxy beta-lactams as cefmetazole, cefotetan, cefoxitin, and moxalactam. In vitro, MIR-1 hydrolyzed cephalothin and cephaloridine much more rapidly than it did penicillin G, ampicillin, or carbenicillin. Cefotaxime was hydrolyzed at 10% the rate of cephaloridine. Cefoxitin inactivation could only be detected by a microbiological test. The inhibition profile of MIR-1 was similar to that of chromosomally mediated class I beta-lactamases. Potassium clavulanate had little effect on cefoxitin or cefibuten resistance and was a poor inhibitor of MIR-1 activity. Cefoxitin or imipenem did not induce MIR-1. The gene determining MIR-1 was cloned on a 1.4-kb AccI-PstI fragment. Under stringent conditions, probes for TEM-1 and SHV-1 genes and the E. coli ampC gene failed to hybridize with the MIR-1 gene. However, a provisional sequence of 150 bp of the MIR-1 gene proved to be 90% identical to the sequence of ampC from Enterobacter cloacae but only 71% identical to that of E. coli, thus explaining the lack of hybridization to the E. coli ampC probe. Plasmid profiles of the 11 K. pneumoniae clinical isolates were not identical, but each contained a plasmid from 40 to 60 kb that hybridized with the cloned MIR-1 gene. Both transfer-proficient and transfer-deficient MIR-1 plasmids belonged to the N incompatibility group. Thus, the resistance of these K. pneumoniae strains was the result of plasmid acquisition of a class I beta-lactamase, a new resistance determinant that expands the kinds of beta-lactam resistance capable of spread by plasmid dissemination among clinical isolates.

Anti-Bacterial Agents↗
PubMed1990

Appearance of amikacin and tobramycin resistance due to 4'-aminoglycoside nucleotidyltransferase [ANT(4')-II] in gram-negative pathogens.

Following the use of amikacin as the principal aminoglycoside at a Denver hospital, amikacin resistance appeared first in Pseudomonas aeruginosa and then in Escherichia coli, Klebsiella pneumoniae, and other enteric organisms from debilitated and compromised patients who had spent time in intensive care units and who had been treated with multiple antibiotics, usually including amikacin. In a P. aeruginosa isolate, resistance to amikacin and tobramycin was transferable by the IncP-2 plasmid pMG77, while in E. coli and K. pneumoniae resistance was carried by the transmissible plasmids pMG220, pMG221, and pMG222 belonging to the IncM group. Isolates and transconjugants produced an enzyme with adenyltransferase activity with substrates having a 4'-hydroxyl group, such as amikacin, kanamycin, neomycin, Sch 21768, isepamicin (Sch 21420), or tobramycin, but not with aminoglycosides lacking this target, such as dibekacin, netilmicin, sisomicin, or gentamicin C components. Genes encoding the 4'-aminoglycoside nucleotidyltransferase [ANT(4')] activity were cloned from pMG77, pMG221, and pMG222. A DNA probe prepared from the ANT(4') found in P. aeruginosa hybridized with the ANT(4') determinant found in E. coli. A probe for the ANT(4') from Staphylococcal spp., which differs in its modification of substrates, like dibekacin, that have a 4"- but not a 4'-hydroxyl group, failed to hybridize with the gram-negative ANT(4') determinant, which consequently has been termed ANT(4')-II.

Amikacin↗
PubMed1990

Activities of beta-lactam antibiotics against Escherichia coli strains producing extended-spectrum beta-lactamases.

Seven extended-spectrum beta-lactamases related to TEM and four enzymes derived from SHV-1 were transferred to a common Escherichia coli host so that the activity of a variety of beta-lactams could be tested in a uniform genetic environment. For most derivatives, penicillinase activity was 10% or less than that of strains making TEM-1, TEM-2, or SHV-1 beta-lactamase, suggesting that reduced catalytic efficiency accompanied the broader substrate spectrum. Despite this deficit, resistance to aztreonam, carumonam, cefdinir, cefepime, cefixime, cefmenoxime, cefotaxime, cefotiam, cefpirome, cefpodoxime, ceftazidime, ceftibuten, ceftizoxime, ceftriaxone, cefuroxime, and E1040 was enhanced. For strains producing TEM-type enzymes, however, MICs of carumonam, cefepime, cefmenoxime, cefotiam, cefpirome, and ceftibuten were 8 micrograms/ml or less. Susceptibilities of cefmetazole, cefotetan, cefoxitin, flomoxef, imipenem, meropenem, moxalactam, temocillin, FCE 22101, and Sch 34343 were unaffected. FCE 22101, imipenem, meropenem, and Sch 34343 were inhibitory for all strains at 1 microgram/ml or less. In E. coli an OmpF- porin mutation in combination with an extended-spectrum beta-lactamase enhanced resistance to many of these agents, but generally by only fourfold. Hyperproduction of chromosomal AmpC beta-lactamase increased resistance to 7-alpha-methoxy beta-lactams but not that to temocillin. When tested at 8 micrograms/ml, clavulanate was more potent than sulbactam or tazobactam in overcoming resistance to ampicillin, while cefoperazone-sulbactam was more active than ticarcillin-clavulanate or piperacillin-tazobactam, especially against TEM-type extended-spectrum beta-lactamases.

Anti-Bacterial Agents↗
PubMed1989

Pseudomonas cepacia susceptibility to sulbactam.

For 25 of 32 Pseudomonas cepacia isolates, predominantly from sputum of adult patients, agar dilution MICs of sulbactam were 2.5 micrograms/ml, and for only one was the MIC more than 80 micrograms/ml. Susceptibility was reliably predicted by response to a commercial sulbactam-ampicillin disk.

Humans↗