Thesis submitted in fulfillment for the requirements for the degree Doctor Technologiae: Environmental Health in the Faculty of Applied Sciences, Cape Peninsula University of Technology, 2012 / Water related issues such as water treatment and distribution have become extremely important
all over the world due to population growth, growing urbanization, health and environmental
pollutions. Contamination of water bodies especially in Africa with antibiotic resistant bacteria
strains is a cause for concern. Escherichia coli O157 H:7, and various strains of non O157 E.
coli and Acinetobacter spp. are known for antibiotic resistance. Both bacteria are
environmental organisms found coexisting together with high potentials of exchange of
resistance genes. Despite the stress conditions confronting these bacteria in water, food and
the human body, in the form of disinfectants, antibiotics, salts and the innate immunity, they
appear to develop adaptive mechanisms that enable them survive and cause infection. This
therefore necessitates the need for investigation of effective virulence factor-targeted control
measures.
Culture of 62 water samples on Brilliance E. coli/coliform selective medium (BECSM, Oxoid),
Eosin Methylene Blue (EMB) agar, or Baumann’s enrichment medium (BEM) and Leeds
Acinetobacter Medium (LAM) for the isolation of E. coli and Acinetobacter spp. was carried
out. Isolates were investigated for virulence factors, antibiotic resistance and transformation of
resistance genes. The effect of oxidative stress exerted by 0.3% Crystal violet, 0.3% Bile salt,
4.0% NaCl, and 8% ethanol on some of the multi-drug resistant strains as well as the effect of
stem back extracts of Curtisia dentata on verotoxin production by the verotoxic strains was
also investigated.
Out of the 69 isolates of E. coli (including O26:H11, O55, O111:NM, 72 O126, O44, O124,
O96:H9, O103:H2, O145:NM and O145:H2.) and 41 isolates of Acinetobacter spp. with 26
(53.06%) of the E. coli and 6 (14.63%) of the A. haemolyticus isolates producing verotoxins,
and no A. lwoffii isolate produced the toxins. Twenty five - 25(35.23%), 14(20.30%) and
28(40.58%) of the E. coli isolates were positive for VTx1&2, Vtx1 and Vtx2 respectively,
49(71.015%), were positive for extended-spectrum beta-lactamases (ESBLs), 7(77.78%) for
serum resistance, 57(82.61%) for cell surface hydrophobicity, 48(69.57%) for gelatinase
production and 37(53.62%) for haemolysin production. While transformation occurred among
the E. coli and Acinetobacter isolates (transformation frequency: 13.3 x 10-7- 53.4-7), there was
poor curing of the plasmid genes, a confirmation of presence of stable antibiotic resistant genes
(DNA concentration between 42.7-123.8 μg) and intra-genetic transfer of multidrug resistant
genes among isolates.
Oxidative stress due to chemicals, salts, alcohol or freeze-thawing (blow temperature stress)
exerted various degrees of lethality on E. coli isolates with some bacterial strains losing their
potential to express virulence factors with time. There was however, generally insignificant (t
test; P≤0.05) lethal effect against all the A. haemolyticus isolates, but crystal violet exerted the
highest lethal effect on some individual isolates followed by ethanol, bile salt and NaCl.
Isolates from wastewater demonstrated the highest rate of resistance compared to isolates from
river water. The cell kill index (CKI) increased as temperature stress (-5; -18; and -28ºC)
increased with time. But the rate of loss of expression of virulence factors or viability was
slower in isolates from wastewater and abattoir compared to those from river water. Sixty
percent of the E. coli isolates showed various levels of resistance to different antibiotics
(ampicillin (10 μg), cefuroxime, cephalexin, ceftazidime and tetracycline (30 95 μg in each case))
(multidrug resistance index (MDRI) values 4.20-5.60%). Relative inhibition zone diameters
(RIZD) of C. dentata extracts against E. coli serotypes ranged between 8-28% (MIC, 100-2500
μg/ml), while against A. lwoffii and A. haemolyiticus, the RIZD values ranged between 10-28%
(MIC, 100-850 μg/ml) and 6-28% (MIC 150-2500 μg/ml) respectively. However, higher MICs
(MIC, 70-2500 mg/ml) were recorded for isolates with high MDRI values. Extracts
demonstrated inhibitory action against the expression of both Vtx1 and Vtx2 genes in E. coli,
A. haemolyticus and A. lwoffii. Saponins, tannins, glycosides, anthraquinones, flavonoids,
steroids, phenols quinones, anthocyanins, amines and carboxylic acids were present in C.
dentata. Ethanol root bark extracts consistently showed the highest DPPH radical scavenging
activity (62.43%), total phenol content (TPH) (57.62 26 mg GAE/g) and reducing power (RP)
(41.32%), followed by those of the stem bark and leaf extracts with the respective values of
54.68%, 37.77 mg GAE/g and 21.83%. The extracts also induced the leakage of Na+ and K+ 107
ions from both test bacteria.
Detection of virulence factors, antibiotic resistance genes and transformation among these
isolates is a very significant outcome that will influence approaches to proactive preventive
and control measures and future investigations. Resistant verotoxic A. haemolyticus could
further complicate treatment in verotoxic food-borne or nosocomial infections. Induction of
cationic leakage by extracts of C. dentata is an indication of one of its mechanism of action on
bacterial cells. The plant can therefore be a good source of antibiotic substances for
composition as antioxidants or antimicrobials with novel mechanism of action for the
treatment of verotoxic bacterial infections.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/808 |
| Date | January 2012 |
| Creators | Hamuel, James Doughari |
| Contributors | Venter, A., Mrs |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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