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Biomedical subjects

K Bush

Publications and source records attributed to K Bush.

At least 19 recordsLinked to original sources
PubMed1995

A model for recording the microcirculatory changes associated with standardized electrical injury of skeletal muscle.

The rate of major limb amputation following high voltage electrical injury remains high despite a decrease in mortality rate. Several theories about the pathophysiology of electrical injury have been discussed in the literature and different clinical regimens have been attempted to decrease the high amputation rate. However, to date, the overall tissue response after electrical injury remains incompletely understood with nothing new to offer these unfortunate patients. We have developed a rat gracilis muscle intravital microscopy preparation in order to better understand the mechanisms of this injury. A standardized 40-V stimulation of 10-sec duration was applied to the anterior belly of the gracilis muscle which translated into a current load of 30 mA. The current density was 750 mA/cm2. Sequential intravital assessment of microcirculatory changes before injury, as well as 5, 15, 30, 60, 120, 180 and 240 min after injury was performed. Consistent findings included initial cessation of blood flow in many capillary beds, focal flow reversal, venous and arterial vascular spasm. Restitution of microvascular flow varied from several minutes to 1 hr and was preceded by vasodilation at 5-15 min following the injury (+16.9 microns from baseline at 15 min). Starting at 30 min progressive vasoconstriction was noted (-0.8 micron from baseline at 30 min, -31.3 microns from baseline at 4 hr). High resolution observation of neutrophil behavior showed an increase in the number of these cells adherent to venular endothelium in areas exhibiting circulatory disturbances (+11.4 cells at 5 min, +15 cells at 4 hr). The standardization of this model allows a quantitative method of evaluating the microcirculatory changes associated with electrical injury and of studying ways to prevent tissue damage. The microcirculatory changes induced by electrical injury were similar to those reported in ischemia-reperfusion injury of skeletal muscle.

Animals↗
PubMed1995

Biochemical comparison of imipenem, meropenem and biapenem: permeability, binding to penicillin-binding proteins, and stability to hydrolysis by beta-lactamases.

Biological activities of biapenem, imipenem, and meropenem were compared with respect to permeability into Gram-negative bacteria, binding to penicillin-binding proteins (PBPs), and hydrolysis by beta-lactamases. Permeability for the three carbapenems was similar when measured in Serratia marcescens S6 producing a carbapenem-hydrolyzing beta-lactamase. Penetration of the carbapenems was comparable with cephaloridine and faster than piperacillin or the extended spectrum cephalosporin cefotaxime. All the carbapenems bound most strongly to PBP 2 of Escherichia coli and Pseudomonas aeruginosa, and to PBP 1 of Staphylococcus aureus. In addition, biapenem showed strong affinity with PBP 1a of E. coli and PBP 1b of P. aeruginosa. Selected serine beta-lactamases, including the extended spectrum plasmid-mediated beta-lactamases, hydrolyzed these carbapenems at rates < 0.1% that of cephaloridine. Metallo-beta-lactamases hydrolysed the carbapenems at measurable rates, with enzymes from Bacteroides fragilis and Xanthomonas maltophilia hydrolyzing biapenem at lower Vmax values than meropenem or imipenem. In conclusion, all the carbapenems exhibited good rates of penetration, bound strongly to PBPs in both Gram-negative and Gram-positive bacteria, and were stable to most Group 1 and Group 2 serine beta-lactamases, but were hydrolyzed by metallo-beta-lactamases.

Bacteria↗
PubMed1995

SHV-7, a novel cefotaxime-hydrolyzing beta-lactamase, identified in Escherichia coli isolates from hospitalized nursing home patients.

Four ceftazidime-resistant Escherichia coli strains were isolated from elderly nursing home patients in a New York hospital during 1993. Strains MCQ-2, MCQ-3, and MCQ-4 were determined to be identical by pulsed-field gel electrophoresis and plasmid profiles, whereas strain MCQ-1 was unique. Strain MCQ-1 was determined to produce a TEM-10 beta-lactamase. Strains MCQ-2, MCQ-3, and MCQ-4 were also noted to be resistant to cefotaxime. These three strains produced two beta-lactamases with pIs of 5.4 (TEM-1) and 7.6. beta-Lactamase assays revealed that the pI 7.6 enzyme hydrolyzed cefotaxime faster (at a relative hydrolysis rate of 30% compared with that of benzylpenicillin) than either ceftazidime or aztreonam (relative hydrolysis rates of 13 and 3.3%, respectively). Nucleotide sequencing of the gene encoding the pI 7.6 beta-lactamase from strain MCQ-3 revealed a blaSHV-type gene differing from the gene encoding SHV-1 at four nucleotides which resulted in amino acid substitutions: phenylalanine for isoleucine at position 8, serine for arginine at position 43, serine for glycine at position 238, and lysine for glutamate at position 240. This novel SHV-type extended-spectrum beta-lactamase is designated SHV-7.

Amino Acid Sequence↗
PubMed1995

The expanded scapular flap.

The scapular fasciocutaneous flap is a very reliable free tissue transfer, but its size and/or thickness may limit its use in some patients. Scapular fasciocutaneous flaps were expanded for 6 to 12 weeks prior to transfer in 14 patients. The flaps ranged in size from 96 to 1885 cm2 and were used to cover chronic soft-tissue defects. Twelve were transferred as free flaps to distant sites, while two were transferred as pedicled flaps to the ipsilateral extremity. The pedicled flaps were designed across the entire back to incorporate both scapular territories but were rotated on a single vascular pedicle. All flaps survived, but three had marginal distal necrosis not related to the microvascular anastomoses. Two flaps transferred by microsurgical technique developed arterial thromboses requiring revision of the anastomoses. Three patients developed partial donor wound dehiscence after transfer of large flaps that healed by secondary intention in two cases and required a split-thickness skin graft for donor-site closure in the third. Flap expansion produces a delay phenomenon that augments blood supply and increases the area of skin that can survive on a single vascular pedicle. This technique may be useful in selected patients in whom a large, thin fasciocutaneous flap is required and there is sufficient time to allow flap expansion prior to transfer.

Adolescent↗
PubMed1994

Identification of TEM-26 beta-lactamase responsible for a major outbreak of ceftazidime-resistant Klebsiella pneumoniae.

An epidemic of nosocomial ceftazidime-resistant Klebsiella pneumoniae was correlated with production of a ceftazidime-hydrolyzing enzyme with an isoelectric point of 5.6 (BMH-1). BMH-1 was encoded on a large transferable plasmid conferring multiple antibiotic resistance. The gene that encodes BMH-1 was identical to the gene that encodes the TEM-26 extended-spectrum beta-lactamase.

Base Sequence↗
PubMed1994

Multiply resistant Klebsiella pneumoniae strains from two Chicago hospitals: identification of the extended-spectrum TEM-12 and TEM-10 ceftazidime-hydrolyzing beta-lactamases in a single isolate.

Ceftazidime-resistant Klebsiella pneumoniae strains began to appear when ceftazidime usage was increased in two unrelated Chicago hospitals. These strains produced a beta-lactamase with an isoelectric point of 5.6 (RP-5.6) and strong hydrolyzing activity against ceftazidime. Two different restriction digest profiles were associated with the ceftazidime resistance plasmids. A second beta-lactamase with a pI of 5.2 (RP-5.2) was coproduced in two representative strains. The second beta-lactamase hydrolyzed ceftazidime, cefotaxime, and aztreonam with relative hydrolysis rates of < 8% of that observed for benzylpenicillin. Both enzymes were inhibited by clavulanic acid and tazobactam. Nucleotide sequencing of the genes coding for RP-5.2 and RP-5.6 revealed sequences identical to those of the TEM-12 and TEM-10 beta-lactamase genes, respectively. Both genes were derived from a TEM-1 sequence related to that of the gene encoded on the Tn2 transposon. Single point mutations are required to progress from TEM-1 to TEM-12 and from TEM-12 to TEM-10. Extracts from broths grown from single cell isolates of the strain producing TEM-12 and TEM-10 were shown to contain both enzymes. Transconjugants producing either the TEM-12 or the TEM-10 beta-lactamase were obtained. A significant finding was that both enzymes were encoded by plasmids with identical restriction digest patterns. These studies show that mutations leading to extended-spectrum beta-lactamases can occur sequentially in the same organism, with the genes encoding both enzymes maintained stably.

Anti-Bacterial Agents↗
PubMed1994

Cloning and expression of a cloxacillin-hydrolyzing enzyme and a cephalosporinase from Aeromonas sobria AER 14M in Escherichia coli: requirement for an E. coli chromosomal mutation for efficient expression of the class D enzyme.

Two beta-lactamase genes, asbA1 and asbB1, encoding AsbA1 and AsbB1, respectively, have been cloned from Aeromonas sobria AER 14M into Escherichia coli. AsbA1 was expressed at low but detectable levels in all E. coli laboratory cloning strains tested. AsbB1 was expressed well in the E. coli cloning strain DH5 alpha. However, no enzyme activity could be detected from the same clone when placed in E. coli MC1061. Ampicillin-resistant mutants of E. coli MC1061 were obtained that expressed high levels of enzymatically active AsbB1. Four independent mutants were examined. All four mutations mapped to one locus, designated blpA (beta-lactamase permissive). The blpA locus was distinct from other known loci that play a role in beta-lactamase expression, i.e., the two loci that affect expression of the Bacteroides fragilis metallo-beta-lactamase and the ampC regulatory genes, ampD, ampE, and ampG. Sequence analysis of asbA1 and asbB1 revealed that AsbA1 was a class C beta-lactamase most closely related to the Pseudomonas aeruginosa chromosomal cephalosporinase and probably represents the common A. sobria cephalosporinase. AsbB1 was a class D enzyme most closely related to the oxacillin-hydrolyzing enzyme OXA-1, with 34% amino acid sequence identity. Purified AsbA1 was a typical cephalosporinase with a substrate profile that reflected high rates of hydrolysis of cephaloridine compared with benzylpenicillin. Purified AsbB1 showed strong penicillinase activity, with hydrolysis rates for carbenicillin and cloxacillin 2 to 2.5 times that for benzylpenicillin. Hydrolysis of imipenem was < or = 1% of that for benzylpenicillin. Both clavulanic acid and tazobactam strongly inhibited AsbB1, while sulbactam inhibited the AsbB1 enzyme less effectively. None of the inhibitors worked well against the AsbA1 enzyme. The chelators EDTA and 1,10-o-phenanthroline did not affect the activity of either enzyme. A. sobria AER 14M was found to produce both a group 1 cephalosporinase and a novel group 2d cloxacillin-hydrolyzing beta-lactamase that has been designated here OXA-12.

Aeromonas↗
PubMed1994

Contribution of enzymatic properties, cell permeability, and enzyme expression to microbiological activities of beta-lactams in three Bacteroides fragilis isolates that harbor a metallo-beta-lactamase gene.

The metallo-beta-lactamase gene, ccrA, has been cloned from three clinical isolates of Bacteroides fragilis, TAL3636, QMCN3, and QMCN4. Although all three isolates harbored a gene encoding a potent beta-lactamase, the MICs of benzylpenicillin, piperacillin, cefotaxime, ceftazidime, imipenem, and biapenem for the three isolates varied from 4- to > 128-fold. QMCN4 was the most susceptible of the three isolates, followed by QMCN3. TAL3636 was resistant to all of the beta-lactams. Previous DNA sequence analysis of the three ccrA genes revealed that the enzymes differed at 5 amino acid residues (B. A. Rasmussen, Y. Gluzman, and F. P. Tally, Mol. Microbiol. 5:1211-1219, 1991). Biochemical characterization of the three enzymes revealed only small differences in kcat and Km values for the majority of beta-lactams tested. Thus, the 5 amino acid substitutions affected the hydrolyzing activity of the enzymes only modestly. Crypticity differences between the three isolates showed that QMCN4 was the least permeable of the isolates to cephaloridine, followed by TAL3636, and that QMCN3 was highly permeable to cephaloridine. Therefore, neither catalytic activity nor permeability was a major contributor to the dramatic differences in the MICs. Instead, microbiological susceptibility was closely related to the level of metallo-beta-lactamase present in each isolate. Both biochemical and physical studies indicated that TAL3636 produced 5- to 10-fold and 50- to 100-fold more metallo-beta-lactamase than QMCN3 and QMCN4, respectively. Therefore, the level of CcrA enzyme production is the dominant contributing factor to high-level resistance among strains harboring a ccrA gene.

Amidohydrolases↗
PubMed1994

Gene sequence and biochemical characterization of FOX-1 from Klebsiella pneumoniae, a new AmpC-type plasmid-mediated beta-lactamase with two molecular variants.

Klebsiella pneumoniae BA32, a clinical isolate from Buenos Aires, Argentina, was found to produce a plasmid-encoded beta-lactamase (FOX-1) which conferred resistance to broad-spectrum cephalosporins and cephamycins. Resistance could be transferred by conjugation or transformation into Escherichia coli K-12 via a 48.5-kb plasmid (pGLK1) that produced two FOX-1 molecular variants with isoelectric points of 6.8 and 7.2 and apparent molecular sizes of 37 and 35 kDa, respectively. The kinetic study revealed that the two variants had very similar substrate and inhibition profiles. These values resemble those of chromosomally mediated class C (group 1) cephalosporinases. The structural gene of FOX-1 (blaFOX-1) was cloned into a 2,270-bp PstI-PstI fragment and was expressed in E. coli TG1. The deduced 382-amino-acid sequence of FOX-1 exhibited a high degree of similarity with chromosomally encoded AmpC beta-lactamases of Pseudomonas aeruginosa, Serratia marcescens, Enterobacter cloacae, E. coli, and Citrobacter freundii. These findings suggest that FOX-1 is a plasmid-mediated AmpC-type beta-lactamase that is encoded by a single gene and that has two molecular variants.

Aged↗
PubMed1993

Antimicrobial resistance in Bacteroides.

Antimicrobial resistance in Bacteroides species has a direct impact on the selection of chemotherapy for anaerobic infections. Multiple studies have documented differences in susceptibility patterns related to individual hospitals, geographic areas, and antibiotic-prescribing practices. Resistance to beta-lactam antibiotics, tetracycline, clindamycin, and metronidazole has been documented in Bacteroides species. The prime mechanism for beta-lactam resistance is the production of beta-lactamases, including penicillinases, cephalosporinases, and the metallo-beta-lactamases that can hydrolyze imipenem. Resistance to tetracycline is mediated by ribosomal protection by the tetQ class. Resistance to clindamycin is mediated by ribosomal modification. Metronidazole resistance may be caused by a combination of decreased antibiotic uptake, decreased nitroreductase activity, and decreased pyruvate:ferredoxin oxidoreductase activity accompanied by increased lactate dehydrogenase activity. Most disturbing is the appearance of resistance to multiple agents in the same organism. Understanding the mechanisms of resistance and the mechanisms of action of these drugs not only will lead to the design of new antimicrobial agents but will permit informed selection of therapy for bacteroides infections.

Anti-Bacterial Agents↗
PubMed1993

Kinetic interactions of tazobactam with beta-lactamases from all major structural classes.

Tazobactam was shown to be a potent inhibitor of group 1, 2a, 2b, and 2b' beta-lactamases. Extended kinetic studies with class A and C serine beta-lactamases showed that the PC1, TEM-2, and P99 enzymes all were reversibly inhibited prior to inactivation of the enzymes. The CcrA metallo-beta-lactamase was less well inhibited, with a 50% inhibitory concentration at least 3 orders of magnitude less favorable than those for most serine beta-lactamases. The numbers of hydrolytic turnovers of tazobactam before inactivation were 2 for PC1, 125 for TEM-2, 50 for P99, and 4,000 for the CcrA enzyme. In spectral studies, transient intermediates were formed after reaction of tazobactam with the PC1, TEM-2, and CcrA beta-lactamases, corresponding to enzyme-associated intermediates responsible for hydrolysis of tazobactam. Chromophores absorbing at 270 nm (CcrA) and 288 nm (TEM-2 and PC1) were observed for these reaction intermediates. The P99 cephalosporinase formed a stable complex with a UV maximum at 295 nm. Incubation of tazobactam with all of the enzymes resulted in accumulation of a tazobactam reaction product with a short-wavelength absorbance. This product has characteristics similar to those of the major eucaryotic metabolite of tazobactam. Possible reaction mechanisms are presented to explain the findings. In conclusion, both serine-based and metallo-beta-lactamases were irreversibly inactivated by tazobactam following an initial transient inhibition phase.

Bacterial Proteins↗
PubMed1993

Genetically diverse ceftazidime-resistant isolates from a single center: biochemical and genetic characterization of TEM-10 beta-lactamases encoded by different nucleotide sequences.

Ceftazidime-resistant isolates of Escherichia coli and Klebsiella pneumoniae produced a plasmid-mediated beta-lactamase with a pI of 5.6 with biochemical characteristics comparable to those of the TEM-10 beta-lactamase. Plasmids from the two strains were nonidentical. Both TEM-10 sequences differed from TEM-1 by substitutions of Ser-162 and Lys-237. The nucleotide sequences of the two genes were identical except for three silent nucleotide substitutions corresponding to the nucleotide differences in the Tn2 TEM-1 or Tn3 TEM-1 genes. The original TEM-10 plasmid was identical to that found in the E. coli isolate and coded for a gene that corresponded to the TEM-10 beta-lactamase from Tn2.

Ceftazidime↗
PubMed1992

The natural history of sciatica: a prospective radiological study.

This prospective study was set up to record the changes in the intervertebral disc accompanying resolution of sciatica following conservative treatment. Patients presenting with sciatica (n = 165) were examined by computed tomography (CT) of the lumbar spine. Disc lesions were classified into the following groups: herniation, sequestration, generalized bulge and focal bulge. Follow-up CT of the pathological disc was performed in 106 of the 165 patients after 1 year and identical anatomical sections were compared. All patients were initially treated conservatively by the injection of steroid and local anaesthetic at the intervertebral disc/nerve root interface. Of 84 cases of disc herniation and sequestration 64 (76%) showed either complete or partial resolution on follow-up CT examination. Of 22 cases with either a generalized or focal bulge of the disc 18 (82%) were unchanged on follow up. The classical disc herniation in a young patient is the type of disc lesion most likely to show greatest improvement at follow-up CT.

Adolescent↗
PubMed1992

The natural history of sciatica associated with disc pathology. A prospective study with clinical and independent radiologic follow-up.

The purpose of this study was to assess the natural history of sciatica due to lumbosacral nerve root compromise and to evaluate the pathomorphologic changes that accompany the natural resolution of the disease. One hundred sixty-five consecutive patients, 114 males and 51 females, with an average age of 41 years (range, 17-72) and an average duration of symptoms of 4.2 months (range, 1-72) presenting with sciatica thought to be due to lumbosacral nerve root compromise were admitted to the study. The cornerstone of treatment was the serial epidural administration of steroid and local anesthetic by the caudal route on an outpatient basis. Lumbar epidural injection or periradicular infiltration at the appropriate level, confirmed under image intensifier, was the next step before considering surgical decompression. An average of three injections (range, 0-8) was received by each patient. Patients underwent clinical examination and computed tomography. Twenty-three patients (14%) underwent surgical decompression. The remainder were clinically assessed at 1 year after presentation, and 111 were rescanned at the appropriate levels. All conservatively managed patients made a satisfactory clinical recovery: average reduction of pain on the visual analog scale was 94% (range, 45-100), and 64 (76%) of the 84 disc herniations and 7 (26%) of the 27 disc bulges showed partial or complete resolution (chi-square = 20.27, P = 0.0001). Thus a high proportion of patients with discogenic sciatica make a satisfactory recovery with aggressive conservative management, and this recovery is accompanied by resolution of disc herniations in a significant number. Only a small proportion of patients needed surgical decompression.

Adult↗