Thesis (MScMedSc (Pathology. Medical Microbiology))--University of Stellenbosch, 2009. / Water is used for various purposes and contamination can have severe implications if
untreated. One of the most common and cost effective water disinfectants, especially used
in developing countries, is chlorine. However, microorganisms have developed different
mechanisms in response to environmental stress conditions, such as the viable but nonculturable
(VBNC) effects possibly displayed in this study, enabling them to survive.
Chlorine may also exert several effects on microorganisms, such as the expression of
multi-substrate efflux pumps, decreased membrane permeability and transport inhibition
that may lead to chlorine tolerance and antimicrobial resistance. In a descriptive and
comparative study, the molecular characteristics of E. coli strains isolated from
environmental waters in the Western Cape and the possible relationship between
chlorination and antimicrobial resistance were investigated.
Water and biofilm samples were exposed to chlorine, as well as efflux pump inhibitor (EPI)
concentrations, and surviving E. coli strains were tested for their phenotypic characteristics
including antimicrobial susceptibility profiles and morphological types. Candidate genes
possibly involved in resistance to antimicrobials, disinfection and efflux pumps were
detected with polymerase chain reaction (PCR) and sequenced. Sequencing analysis and
homology searches were done and E. coli strains were typed as either Enteropathogenic
E. coli strains (EPEC) or Enterotoxigenic E. coli strains (ETEC) on the presence of
virulence genes.
All water and biofilm sources examined were heavily polluted with E. coli, and a high
enumeration level of this indicator organism of faecal contamination was recorded.
Chlorine tolerance was found to be associated with antimicrobial resistance. Addition of
EPI with exposure to chlorine decreased enumeration levels of these organisms,
suggesting that efflux pumps may play a role in tolerance to chlorine. Several
morphological patterns were described amongst the E. coli strains and a change in this
was recorded after exposure to chlorine. Highly resistant antibiograms displayed by the
isolated strains included ampC β-lactamase producing E. coli strains and extended
spectrum β-lactamases (ESBLs). Amplification of the candidate genes selected for heatshock,
oxidative stress genes and efflux pump were most frequently detected while the
structural genes involved in fluoroquinolones (FQs) resistance were detected less
frequently in the selected strains. Sequencing of these amplified candidate genes
demonstrated various changes in amino acid sequences, including one common
mutational pathway taken by E. coli when exposed to stress conditions. Further homology
searches of the sequenced candidate genes illustrated similarities in 19 pathogenic and 14
non-pathogenic E. coli as well as 3 Shigella strains. Detection of virulence genes found
three EPEC strains (bfpA, eaeA), two EPEC (eaeA), ten EPEC (bfpA) and one ETEC
strain (st) amongst the isolates.
This study underlines the need for monitoring our water sources, which poses a public
health risk due to incomplete chlorination, antimicrobial resistance and the spread of
clinically relevant pathogenic strains.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2779 |
| Date | 03 1900 |
| Creators | Krige, Marilyn |
| Contributors | Wasserman, Elizabeth, University of Stellenbosch. Faculty of Health Sciences. Dept. of Pathology. Medical Microbiology. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | University of Stellenbosch |
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