Significance of bacteria associated with invertebrates in drinking water distribution networks.

The implication of invertebrates found in drinking water distribution networks to public health is of concern to water utilities. Previous studies have shown that the bacteria associated with the invertebrates could be potentially pathogenic to humans. This study investigated the level and identity of bacteria commonly associated with invertebrates collected from the drinking water treatment systems as well as from the main pipelines leaving the treatment works. On all sampling occasions bacteria were isolated from the invertebrate samples collected. The highest bacterial counts were observed for the samples taken before filtration as was expected. There were, however, indications that optimal removal of invertebrates from water did not always occur. During the investigation, 116 colonies were sampled for further identification. The isolates represent several bacterial genera and species that are pathogenic or opportunistic pathogens of humans. Diarrhoea, meningitis, septicaemia and skin infections are among the diseases associated with these organisms. The estimated number of bacteria that could be associated with a single invertebrate (as based on average invertebrate numbers) could range from 10 to 4000 bacteria per organism. It can, therefore, be concluded that bacteria associated with invertebrates might under the worst case scenario pose a potential health risk to water users. In the light of the above findings it is clear that invertebrates in drinking water should be controlled at levels as low as technically and economically feasible.

Evaluation of a rapid polymerase chain reaction based identification technique for Vibrio cholerae isolates.

Rapid and accurate identification of waterborne pathogens, such as Vibrio cholerae, in drinking-water sources is important to enable effective resource management and public health protection. Phenotypic systems currently being used for the identification of Vibrio cholerae isolates are time-consuming and the need exists for the development of suitable molecular techniques that can offer both fast and reliable identification. During this study, isolates identified as Vibrio cholerae by means of two different biochemical test systems (API 20E and VITEK 32) were analysed with the polymerase chain reaction (PCR) to compare the reliability of the various identification systems. The selected PCR technique amplified a sequence within the outer membrane protein of Vibrio cholerae, a gene specific for V. cholerae. It was found that out of 243 isolates biochemically identified as V. cholerae with either the API or VITEK system, 21 isolates did not give a positive result with the PCR detection method. Sequencing the 16S rDNA of more than half of these isolates and comparison of the sequences with Internet databases indicated that most of the isolates belonged to the genus Aeromonas. The results indicated that the rapid PCR procedure was more accurate than the API or VITEK systems currently being used for the phenotypic identification of Vibrio cholerae isolates.

Potentially pathogenic features of heterotrophic plate count bacteria isolated from treated and untreated drinking water.

Heterotrophic plate counts (HPCs) are commonly used to assess the general microbiological quality of drinking water. Drinking water quality specifications worldwide recommend HPC limits from 100 to 500 cfu ml(-1). A number of recent studies revealed evidence that these bacteria may not be as harmless as generally accepted. It appears that immuno-compromised individuals are particularly at risk. This would include the very young and very old patients with diseases such as AIDS and patients on therapy for purposes such as organ transplantation and cancer treatment. In this study, 339 bacterial colonies were isolated at random from selected treated and untreated drinking water in South Africa using routine heterotrophic plate count tests. In a first step to screen for potentially pathogenic properties, 188 (55.5%) of the isolates showed alpha- or beta-haemolysis on human- and horse-blood agar media. Subsequent analysis of the haemolytic isolates for enzymatic properties associated with pathogenicity revealed the presence of chondroitinase in 5.3% of the isolates, coagulase in 16.0%, DNase in 60.6%, elastase in 33.0%, fibrinolysin in 53.7%, gelatinase in 62.2%, hyaluronidase in 21.3%, lecithinase in 47.9%, lipase in 54.8% and proteinase in 64.4%. Fluorescein and pyocyanin were not produced by any of the isolates. Among the haemolytic isolates, 77.7% were resistant to oxacillin 1 microg, 59.6% to penicillin G 2 units, 47.3% to penicillin G 10 units, 54.3% to ampicillin 10 microg and 43.1% to ampicillin 25 microg. Cell culture studies revealed that 96% of haemolytic isolates were cytotoxic to HEp-2 cells, and 98.9% of the 181 cytotoxic isolates adhered to HEp-2 or Caco-2 cells. HEp-2 cells were invaded by 43.6%, and Caco-2 cells by 49.7%, of the 181 cytotoxic isolates. The invasion index on HEp-2 cells ranged from 1.9 x 10(-1) to 8.9 x 10(-6), whereas the invasion index on Caco-2 cells varied between 7.7 x 10(-2) and 8.3 x 10(-6). The most commonly isolated genera with these potentially pathogenic features were Aeromonas, Acinetobacter, Aureobacterium, Bacillus, Chryseobacterium, Corynebacterium, Klebsiella, Moraxella, Pseudomonas, Staphylococcus, Tsukamurella and Vibrio. The results obtained in this study support earlier findings on potentially pathogenic features of bacteria detected by routine HPCs on drinking water. These findings are in agreement with some epidemiological studies, which indicated an association between HPCs in drinking water and the incidence of gastroenteritis in consumers. However, the extent of the health risk concerned needs to be defined in more detail for meaningful revision of quality guidelines for HPCs in drinking water.