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Heidi Segal

Publications and source records attributed to Heidi Segal.

6 recordsLinked to original sources
PubMed2005

Is IS(ABA-1) customized for Acinetobacter?

An insertion sequence (IS(ABA-1)) was identified in Acinetobacter spp., but not in Enterobacteriacea and Pseudomonas aeruginosa. Numerous copies of the IS were identified in Acinetobacter strains containing the element. In one of the Acinetobacter baumannii strains, IS(ABA-1) was identified adjacent to sulII and transcription of the resistance gene is presumed to be dependent on promoter sequences within the IS. Since the IS is adjacent to ampC and bla(OXA) in this A. baumannii strain, it may be that IS(ABA-1) plays an important role in the expression of antibiotic resistance genes in this genus.

Acinetobacter↗
PubMed2004

Role of class A penicillin-binding proteins in PBP5-mediated beta-lactam resistance in Enterococcus faecalis.

Peptidoglycan polymerization complexes contain multimodular penicillin-binding proteins (PBP) of classes A and B that associate a conserved C-terminal transpeptidase module to an N-terminal glycosyltransferase or morphogenesis module, respectively. In Enterococcus faecalis, class B PBP5 mediates intrinsic resistance to the cephalosporin class of beta-lactam antibiotics, such as ceftriaxone. To identify the glycosyltransferase partner(s) of PBP5, combinations of deletions were introduced in all three class A PBP genes of E. faecalis JH2-2 (ponA, pbpF, and pbpZ). Among mutants with single or double deletions, only JH2-2 DeltaponA DeltapbpF was susceptible to ceftriaxone. Ceftriaxone resistance was restored by heterologous expression of pbpF from Enterococcus faecium but not by mgt encoding the monofunctional glycosyltransferase of Staphylococcus aureus. Thus, PBP5 partners essential for peptidoglycan polymerization in the presence of beta-lactams formed a subset of the class A PBPs of E. faecalis, and heterospecific complementation was observed with an ortholog from E. faecium. Site-directed mutagenesis of pbpF confirmed that the catalytic serine residue of the transpeptidase module was not required for resistance. None of the three class A PBP genes was essential for viability, although deletion of the three genes led to an increase in the generation time and to a decrease in peptidoglycan cross-linking. As the E. faecalis chromosome does not contain any additional glycosyltransferase-related genes, these observations indicate that glycan chain polymerization in the triple mutant is performed by a novel type of glycosyltransferase. The latter enzyme was not inhibited by moenomycin, since deletion of the three class A PBP genes led to high-level resistance to this glycosyltransferase inhibitor.

Bacterial Proteins↗
PubMed2003

Outer membrane protein alterations and blaTEM-1 variants: their role in beta-lactam resistance in Klebsiella pneumoniae.

OBJECTIVES: The aim of the study was to characterize the genetic basis of resistance to selected beta-lactam antibiotics in two clinical isolates of Klebsiella pneumoniae. METHODS AND RESULTS: K. pneumoniae strains were isolated from two hospitalized patients. One of the strains was resistant to amoxicillin, co-amoxiclav, cefuroxime, piperacillin and cefoxitin but susceptible to all the other cephalosporins tested. The second strain displayed a similar phenotype except that it was resistant to piperacillin/tazobactam and susceptible to cefoxitin. PCR assays and DNA sequencing showed that the cefoxitin-susceptible strain contained a novel blaTEM-1 variant downstream of the strong Pa/Pb promoter. SDS-PAGE analysis of the outer membrane proteins (OMPs) did not identify OmpK35 and suggested reduced expression of OmpK36 in this strain. Following passage in non-selective media, expression of OmpK36 was restored with a concomitant increase in cefuroxime susceptibility. A similar experimental approach identified blaTEM-1C in the cefoxitin-resistant K. pneumoniae strain. This strain was deficient in OmpK35 and OmpK36; absence of the latter protein was due to the presence of IS1 in the ompK36 regulatory region. CONCLUSIONS: Resistance to selected beta-lactams in two clinical isolates of K. pneumoniae was due to interplay between the expression of OMPs and TEM-1.

Anti-Bacterial Agents↗
PubMed2003

Characterization of class 1 integron resistance gene cassettes and the identification of a novel IS-like element in Acinetobacter baumannii.

Based on hybridization studies, 21/32 multi-resistant clinical isolates of Acinetobacter baumannii contain class 1 integrons. Amplification products were obtained from 20 of the hybridization-positive strains. A single dfrA7 cassette was identified in 18 of the isolates and an integron with two cassettes (aadB-aadA4) was found in only one strain. Amplicons were not obtained from one of the hybridization positive strains. DNA sequence analysis of a 6.080-kb fragment, cloned from this strain, identified the remnant of an integron, following insertion of IS26 into the 5(')-end of intI1. The 6.080-kb sequence carries an aminoglycoside resistance gene, linked to a portion of IS1133, which in turn is linked to a sequence that has properties of IS elements, including sequences that could stimulate transcription, and ORFs encoding amino acid sequences with similarity to a transposase from Deinococcus radiodurans.

Acinetobacter baumannii↗