| Summary: | Water is considered the most vital resource on earth and its quality is deteriorating. Not all
residents living in South Africa‘s rural areas have access to treated drinking water, and use
water from rivers, dams, and wells. The quality of these resources is unknown, as well as the
effects of the bacteria in the water on human health. The heterotrophic plate count (HPC)
method is a globally used test to evaluate microbial water quality. According to South African
water quality guidelines, water of good quality may not contain more than a 1 000 coliforming
units (CFU)/mℓ. There is mounting evidence that HPC bacteria may be hazardous to humans
with compromised, underdeveloped, and weakened immune systems.
In this study the pathogenic potential of HPC bacteria was investigated. Samples were collected
from boreholes in the North West Province and HPCs were enumerated with a culture-based
method. Standard physico-chemical parameters were measured for the water. Different HPC
bacteria were isolated and purified and tested for α- or β-haemolysis, as well as the production
of extracellular enzymes such as DNase, proteinase, lecithinase, chondroitinase, hyaluronidase
and lipase, as these are pathogenic characteristics. The isolates were identified with 16S rRNA
gene sequencing. The model for the human intestine, Hutu-80 cells, were exposed to the
potentially pathogenic HPC isolates to determine their effects on the viability of the human cells.
The isolates were also exposed to different dilutions of simulated gastric fluid (SGF) to evaluate
its effect on the viability of bacteria. Antibiotic resistant potential of each isolate was determined
by the Kirby-Bauer disk diffusion method. Three borehole samples did not comply with the
physico-chemical guidelines. Half of the samples exceeded the microbial water quality guideline
and the greatest CFU was 292 350 CFU/mℓ. 27% of the isolate HPC bacteria were α- or β-
haemolytic. Subsequent analysis revealed the production of: DNase in 72%, proteinase in 40%,
lipase and lecithinase in 29%, hyaluronidase in 25% and least produced was chondroitinase in
25%. The HPC isolates identified included: Alcaligenes faecalis, Aeromonas hydrophila and A.
taiwanesis, Bacillus sp., Bacillus thuringiensis, Bacillus subtilis, Bacillus pumilus, Brevibacillus
sp., Bacillus cereus and Pseudomonas sp. All the isolates, except Alcaligenes faecalis, were
toxic to the human intestinal cells to varying degrees. Seven isolates survived exposure to the
most diluted SGF and of these, four isolates also survived the intermediate dilution but, only one
survived the highest SGF concentration. Some isolates were resistant to selected antibiotics,
but none to neomycin and vancomycin. Amoxillin and oxytetracycline were the least effective of
the antibiotics tested. A pathogen score was calculated for each isolate based on the results of
this study. Bacillus cereus had the highest pathogen index with declining pathogenicity as follows:
Alcaligenes faecalis > B. thuringiensis > Bacillus pumilus >
Pseudomonas sp. > Brevibacillus > Aeromonas taiwanesis > Aeromonas hydrophila > Bacillus
subtilis > Bacillus sp. The results of this study prove that standard water quality tests such as
the physico-chemical and the HPC methods are insufficient to provide protection against the
effects of certain pathogenic HPC bacteria. === MSc (Environmental Sciences), North-West University, Potchefstroom Campus, 2014
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