Use this URL to cite or link to this record in EThOS:
Title: Glycopeptide resistance in lactic acid bacteria
Author: Humphreys, S.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
Availability of Full Text:
Full text unavailable from EThOS.
Please contact the current institution’s library for further details.
The glycopeptide antibiotics vancomycin and teicoplanin are used to treat infections caused by Gram positive bacteria. The formation of nascent peptidoglycan chains and cross linking of the cell wall is inhibited because the drugs bind specifically to the D-alanyl-D-alanine portion of the pentapeptide chain in peptidoglycan precursors. Plasmid-mediated, high-level resistance to both antibiotics in Enterococcus sp. is associated with production of a novel D-alanine:D-alanine (D-Ala:D-Ala) ligase of altered substrate specificity. This enzyme, VanA, synthesises the depsipeptide D-alanyl-D-lactate (D-Ala-D-Lac), which is incorporated into cell wall precursors, instead of D-Ala-D-Ala. Vancomycin has a 1000 fold lower affinity for cell wall precursors terminating in the hydroxyacid. VanA and other plasmid-borne van genes essential for high-level glycopeptide resistance in enterococci lie within the inverted repeats of a transposon; Tn1546, which has a distinctly different G+C ratio to enterococcal DNA, suggesting an exogenous origin. Lactic acid bacteria such as Lactobacillus sp. and Leuconostoc sp. are intrinsically resistant to glycopeptide antibiotics. Analysis of their cell wall precursors reveals that they terminate in D-Lac, suggesting a similar mechanism of resistance to that of the enterococci. The mechanism of cell wall synthesis in vancomycin-sensitive and resistant lactic acid bacteria and VanA-type enterococci was investigated. The D-Ala:D-Ala ligase from the glycopeptide-sensitive lactic acid bacterium, Lactobacillus delbrueckii, was purified directly from cell extracts and characterised. No D-Ala:D-hydroxyacid ligase activity was detected in extracts from the glycopeptide-resistant Lactobacillus brevis. Subsequently, the ligase of Leuconostoc mesenteroides (Lmddl), which had already been sequenced, was cloned and overexpressed, to allow purification and characterisation of the enzyme.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available