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Title: β-lactamase-mediated resistance in nosocomial Gram negative aerobic Bacilli
Author: Paton, Robert Hunter
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1994
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A survey of antibiotic resistance on Gram negative aerobic bacilli, which had been isolated from blood cultures during the period 1980-1991 from Edinburgh Royal Infirmary, was performed. All viable cultures were investigated for susceptibility to an extensive range of antibiotics including the newer carbapenems imipenem and meropenem. One hundred and sixty seven Gram negative, oxidase negative, aerobic bacilli, that were found to be resistant to cefuroxime (≥8.0μg/ml), were investigated further. The predominant species present were: enterobacter, serratia and acinetobacter. Isoelectric focusing (IEF) and conjugation studies were performed. None of the strains that transferred ampicillin resistance to Escherichia coli J62-2 co-transferred resistance to any of the later generation cephalosporins or to imipenem. It was apparent that inducible chromosomal β-lactamases were the main cause of cefuroxime resistance in these strains. Amongst the cefuroxime resistant strains an isolate of Acinetobacter baumannii was found to be resistant to all β-lactams including imipenem and meropenem. Isoelectric focusing revealed the presence of a chromosomal cephalosporinase and a novel β-lactamase of pI 6.65. Despite the fact that the original clinical isolate could be cured of its resistance to carbapenems and penicillins by growing in the presence of ethidium bromide with the concurrent loss of the enzyme of pI 6.65, no resistance plasmid was transferred. Plasmids were isolated but the physical loss of a plasmid in the cured strain could not be demonstrated. The enzyme hydrolysed penicillin, ampicillin and cephaloridine slowly during enzyme assay but inactivation of carbapenems could only be demonstrated by microbiological means. The enzyme was thus designated ARI 1 (Acinetobacter resistant to imipenem). The molecule size of the ARI 1 enzyme was 23 kDa. It was inhibited by BRL 42715 indicating that it was a serine active site β-lactamase. It was not inhibited by EDTA.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available