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Query: UMLS:C0348321 (Haemophilus)
 15,372 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A clinical isolate of Haemophilus parainfluenzae resistant to chloramphenicol and tetracycline transferred both cam and tet determinants to Escherichia coli K-12 during mixed cultivation on solid media irrespective of the selection employed. The doubly resistant transconjugant was found to contain levels of the enzyme chloramphenicol acetyltransferase (CAT) comparable to those found in R plasmid-bearing chloramphenicol-resistant enteric bacteria. Purification of CAT from the transconjugant was achieved by affinity chromatography, and the electrophoretically homogeneous protein was compared with previously characterized CAT variants specified by R plasmids. Although the CAT associated with cam from H. parainfluenzae was found to be distinct from the three types described previously, its N-terminal peptide amino acid sequence was identical with that determined for a type II CAT. Attempts to demonstrate covalently closed circular deoxyribonucleic acid in the H. parainfluenzae donor and the E. coli transconjugant were unsuccessful. The cam and tet determinants were nontransmissible from E. coli but could be cotransferred following the introduction of a suitable conjugative plasmid.
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PMID:Mechanism of transferable resistance to chloramphenicol in Haemophilus parainfluenzae. 64 51

A Haemophilus influenzae b (Hib) membrane protein with a molecular mass of 28 kDa bound polyclonal antisera raised against a highly purified Hib fimbrial subunit. We cloned the gene encoding this protein and found that the gene was expressed in Escherichia coli. DNA sequence analysis identified an 843-bp open reading frame which predicted a 26.78-kDa protein with an amino-terminal signal sequence and a mature protein with 70% similarity to the 28-kDa lipoprotein of E. coli (F. Yu, S. Inouye, and M. Inouye, J. Biol. Chem. 261:2284, 1986). Colony blot hybridization analysis with an intergenic probe of the cloned gene demonstrated that 29 of 32 H. influenzae strains hybridize with this gene. Insertion of a chloramphenicol acetyltransferase gene into the open reading frame inactivated expression of the 28-kDa protein in E. coli. Isogenic Hib strains were derived by marker exchange mutagenesis to generate mutants which no longer expressed the 28-kDa protein as recognized with Western immunoblot analysis. There was no difference in the rate of nasopharyngeal colonization of infant rats or monkeys by the isogenic mutants which lacked the 28-kDa protein compared with colonization by the wild-type strain. In contrast, the frequency of invasion and density of bacteremia in infant rats caused by the isogenic mutants were reduced relative to those caused by the wild-type Hib strain. We conclude that this 28-kDa outer membrane protein aids transepithelial invasion of type b strains but is not essential.
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PMID:Contribution of a 28-kilodalton membrane protein to the virulence of Haemophilus influenzae. 198 77

The ability of the College of American Pathologists Microbiology Surveys subscriber laboratories to perform antimicrobial susceptibility testing accurately has improved slightly since 1984. Currently (1989 surveys), the accuracies for disk diffusion and minimum inhibitory concentration antimicrobial susceptibility testing were 98.2% and 96.1%, respectively. Disk diffusion testing has recently (since 1986) become more popular, along with rapid automated systems, such as the AMS-Vitek System (St Louis, Mo). Rapid tests for beta-lactamase and chloramphenicol acetyltransferase have performed well. Quality control procedures have switched to a cost-effective weekly frequency pattern for nearly 70% of laboratories. Some antimicrobial susceptibility testing problems still exist among anaerobic bacterial methods, procedures for fastidious organisms (Haemophilus, Streptococcus species, Moraxella, pneumococci, gonococci), tests for oxacillin-resistant staphylococci, and the methods for use against nonenteric gram-negative or gram-positive bacilli. Antimicrobial susceptibility testing users subscribing to the College of American Pathologists surveys should strictly follow the National Committee for Clinical Laboratory Standards interpretive and quality control criteria to assure the best performance with the Clinical Laboratory Improvement Act, 1988, compliant College of American Pathologists proficiency sample program.
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PMID:Antimicrobial susceptibility testing trends and accuracy in the United States. A review of the College of American Pathologists Microbiology Surveys, 1972-1989. Microbiology Resource Committee of the College of American Pathologists. 202 10

Sensitivity of enzymes to inhibition by thiol-reactive reagents is often presented as evidence for the possible involvement of cysteine residues in substrate binding and catalysis or to highlight possible important differences in structure and mechanism between closely related enzymes. The primary phenotypic distinction between the enterobacterial type II chloramphenicol acetyltransferase (CATII; typified by the enzyme encoded by the incW transmissible plasmid pSa) and the CATI and CATIII variants is the greatly enhanced susceptibility of CATII to inactivation by thiol-specific modifying reagents. Determination of the nucleotide sequence of the gene, catII, present on pSa and that of a related determinant, catIIH, isolated from Haemophilus influenzae indicates that sensitivity to such reagents cannot be due to the presence of additional reactive cysteine residues in CATII. Comparative analysis of the inactivation of CATII and CATIII by 5,5'-dithiobis-(2-nitrobenzoic acid) (DTNB), 4,4'-dithiodipyridine (DTDP) and methyl methanethiosulphonate (MMTS) suggests that (i) inactivation occurs as a result of chemical modification of the same residue (Cys-31) in each enzyme, (ii) reagents that inactivate via a pseudo-first-order process (DTNB and DTDP) appear to bind with a greater affinity to CATII, and (iii) the intrinsic reactivity of Cys-31 in CATII greatly exceeds that of the corresponding residue in CATIII. The results lead to the conclusion that a striking difference in chemical reactivity of a unique and conserved thiol group between closely related enzyme variants may not be easily explained even when a high-resolution tertiary structure is available for one of them. Plausible explanations include more favourable access of reagents to Cys-31 in CATII or an enhanced reactivity of its thiol group imposed by the side chains of residues that are not in immediate contact with it.
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PMID:Nucleotide sequences of genes encoding the type II chloramphenicol acetyltransferases of Escherichia coli and Haemophilus influenzae, which are sensitive to inhibition by thiol-reactive reagents. 226 78

Seven clinical isolates of chloramphenicol-resistant Haemophilus influenzae were studied. The products of chloramphenicol inactivation by chloramphenicol acetyltransferase (CAT) were identified by high performance liquid chromatography. The sole product in H. influenzae is a single monoacetyl compound, whereas variants of CAT isolated from other chloramphenicol-resistant bacteria usually produce both monoacetyl and diacetyl chloramphenicol metabolites. The chloramphenicol resistance gene was found to reside on a 65-kb plasmid which, in five of the six cases studied, appeared to be integrated into the host cell chromosome.
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PMID:Demonstration of a functional variant of chloramphenicol acetyltransferase in Haemophilus influenzae. 266 28

A total of 2,811 clinical isolates of Haemophilus influenzae were obtained during 1986 from 30 medical centers and one nationwide private independent laboratory in the United States. Among these, 757 (26.9%) were type b strains. The overall rate of beta-lactamase-mediated ampicillin resistance was 20.0%. Type b strains were approximately twice as likely as non-type b strains to produce beta-lactamase (31.7 versus 15.6%). The MICs of 12 antimicrobial agents were determined for all isolates. Ampicillin resistance among strains that lacked beta-lactamase activity was extremely uncommon (0.1%). Percentages of study isolates susceptible to cefamandole, cefaclor, cephalothin, and cephalexin were 98.7, 94.5, 87.3, and 43.3%, respectively. For 14 strains (0.5% of the total), chloramphenicol MICs were greater than or equal to 8.0 micrograms, and thus the strains were considered resistant. All of these resistant strains produced chloramphenicol acetyltransferase. In addition, all 14 strains were resistant to tetracycline; 11 produced beta-lactamase. The percentage of isolates susceptible to tetracycline was 97.7%. In contrast, erythromycin and sulfisoxazole were relatively inactive. The combination of erythromycin-sulfisoxazole (1/64) was more active than erythromycin alone but essentially equivalent in activity to sulfisoxazole alone. Finally, small numbers of clinical isolates of H. influenzae were resistant to trimethoprim-sulfamethoxazole and rifampin.
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PMID:National collaborative study of the prevalence of antimicrobial resistance among clinical isolates of Haemophilus influenzae. 325 21

Of 2458 isolates of Haemophilus influenzae examined in a recent British survey, 42 were resistant to chloramphenicol. Two resistant isolates were of type b and 40 were non-capsulate. Spectrophotometric assay showed that all the resistant isolates produced chloramphenicol acetyltransferase (CAT). CAT activity did not increase following growth on heated blood agar containing chloramphenicol 2 mg/L but was reduced by 84-98% when extracts were treated for 30 min with 5', 5'-dithiobis-2-nitrobenzoate. These data suggest that H. influenzae CATs resemble the Type-II CATs produced by enterobacteria. Extrachromosomal DNA was detected in five only of the 42 resistant isolates and cured derivatives of two plasmid-containing strains retained their chloramphenicol resistance. These results suggest that the CAT gene is located on the chromosome.
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PMID:Mechanisms of chloramphenicol resistance in Haemophilus influenzae in the United Kingdom. 326 60

A total of 601 clinical isolates of Haemophilus influenzae isolated in six different regions of Sweden were tested for chloramphenicol susceptibility by using agar dilution MIC determinations and disk diffusion tests. For seven strains MICs were 4 micrograms/ml or higher, and for one strain the MIC was 2 micrograms/ml. All eight strains produced chloramphenicol acetyltransferase. For the remaining 593 strains, MICs were less than or equal to 1 microgram/ml, and the MICs for 50% and 90% of the strains were both 0.5 microgram/ml. Disk diffusion tests carried out by using revised interpretive criteria introduced in 1984 by the Swedish Reference Group for Antibiotics correctly identified the 593 strains as susceptible and the 8 strains as resistant. Quality assessments were performed in 29 clinical microbiology laboratories. The revised criteria for chloramphenicol disk diffusion testing gave rise to false resistance results in some laboratories. The interpretive accuracy improved when the interlaboratory variation was compensated for by using adjusted breakpoints. Such revision was possible through peak correction, single-strain regression analysis, and standard curve regression analysis. Peak-corrected breakpoints improved the accuracy from an overall incidence of false-resistant isolates of 4.4% to 2.3%. Single-strain regression analysis and standard curve regression analysis provided laboratory- and species-specific breakpoints which reduced false resistance rates of 0.14% and 0%, respectively.
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PMID:Laboratory- and species-specific interpretive breakpoints for disk diffusion tests of chloramphenicol susceptibility of Haemophilus influenzae. 326 31

Haemophilus influenzae, Streptococcus pneumoniae, and Aerococcus species were tested for susceptibility to chloramphenicol by standard broth microdilution and disk-diffusion methods. MICs and zone diameter breakpoints were correlated with production of chloramphenicol acetyltransferase (CAT). A comparison of MICs and zone diameters indicated that the interpretative criteria for H. influenzae and S. pneumoniae should be an MIC of less than or equal to 4 micrograms/ml or a zone diameter greater than or equal to 25 mm for susceptible strains and an MIC of greater than or equal to 8 micrograms/ml or a zone diameter of less than or equal to 20 mm for resistant strains; for Aerococcus species, interpretative criteria should be an MIC of less than or equal to 8 micrograms/ml or a zone diameter of greater than or equal to 20 mm for susceptible strains and an MIC of greater than or equal to 32 micrograms/ml or a zone diameter of less than or equal to 12 mm for resistant strains. All but four strains of H. influenzae and one strain of S. pneumoniae that were resistant to chloramphenicol by these criteria produced CAT. For Aerococcus species, however, chloramphenicol-resistant strains were negative for CAT as determined by a commercially available disk test. When comparing susceptibility results with CAT production, thiamphenicol was a better indicator of the presence of the enzyme than chloramphenicol and may be useful in assaying resistance to chloramphenicol.
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PMID:Relationship between in vitro susceptibility test results for chloramphenicol and production of chloramphenicol acetyltransferase by Haemophilus influenzae, Streptococcus pneumoniae, and Aerococcus species. 326 21

Eighty-eight strains of Haemophilus influenzae were examined for resistance to chloramphenicol by various techniques. Methods compared were a rapid chemical assay for chloramphenicol acetyltransferase (CAT), an agar dilution minimum inhibitory concentration (MIC) method, disc diffusion tests with 10, 30, and 50 micrograms discs, and a microbiological technique for detecting CAT. Fifty-eight chloramphenicol-sensitive strains had MICs less than or equal to 0.5 mg/l, while 30 resistant strains had MICs greater than or equal to 4 mg/l. The chemical CAT assay clearly distinguished resistant from sensitive strains, was simple to perform and provided results within 30 min. By disc diffusion, the lower the disc content the clearer the distinction between sensitive and resistant populations. Difficulties were encountered in interpretating the microbiological CAT assays as some sensitive strains appeared resistant. The chemical CAT assay is recommended for use when a rapid result is required. Rare chloramphenicol-resistant, CAT-negative strains have been described in the USA and these strains would only be detected by a disc diffusion or MIC test.
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PMID:The reliability of methods for detecting chloramphenicol resistance in Haemophilus influenzae. 326 22


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