Characterization of Clostridium spp. isolated from selected surface water systems and aquatic sediment
Fourie, Johannes Cornelius Jacobus
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Clostridium are ubiquitous in nature and common inhabitants of the gastrointestinal track of humans and animals. Some are pathogenic or toxin producers. These pathogenic Clostridium species can be introduced into surface water systems through various sources, such as effluent from wastewater treatment plants (WWTP) and surface runoff from agricultural areas. In a South African context, little information is available on this subject. Therefore, this study aimed to characterize Clostridium species isolated from surface water and aquatic sediment in selected river systems across the North West Province in South Africa. To achieve this aim, this study had two main objectives. The first objective focused on determining the prevalence of Clostridium species in surface water of the Schoonspruit, Crocodile and Groot Marico Rivers and evaluate its potential as an indicator of faecal pollution, along with the possible health risks associated with these species. The presence of sulphite-reducing Clostridium (SRC) species were confirmed in all three surface water systems using the Fung double tube method. The high levels of SRC were correlated with those of other faecal indicator organisms (FIO). WWTP alongside the rivers were identified as one of the major contributors of SRC species and FIO in these surface water systems. These findings supported the potential of SRC species as a possible surrogate faecal indicator. However, limitations of SRC species as FIO were noticed in this study. Furthermore, the results showed that the physico-chemical parameters such as temperature, dissolved oxygen, chemical oxygen demand, nitrates, phosphates and sulphates present in the water had a great effect in the Clostridium spp. levels during the warm-rainy season. This was possibly due to non-point source pollution such as surface runoff which promoted eutrophication in parts of these river systems. The second objective of the study was to investigate antibiotic resistance in Clostridium species isolated from both surface water and aquatic sediment and the presence of antibiotic resistance gene in these isolates. A total of 67 Clostridium isolates obtained from the Schoonspruit and Crocodile Rivers showed resistance against Ampicillin, Tetracycline or Clindamycin. No antibiotic resistant isolates were obtained from the Groot Marico River. The minimum inhibitory concentration (MIC) of 6 antibiotics were determined using the recommended agar dilution method. MIC values of Ampicillin (AMP) ranged from 0.25-2 μg/ml, 0.5 to >256 μg/ml for Tetracycline (TE), 0.25 to >256 μg/ml for Clindamycin (DA), 0.5-16 μg/ml for Amoxicillin (AMX), 0.5-32 μg/ml for Chloramphenicol (C) and 0.5-64 μg/ml for Metronidazole (MTZ). Using these MIC values, resistance profile could be generated for each antibiotic resistant Clostridium isolate. These results revealed that Antibiotics such as Amoxicillin and Chloramphenicol were the most effective in inhibiting the growth of antibiotic resistant Clostridium species. Whereas the majority of the isolates showed resistance against Ampicillin and Tetracycline. None of the antibiotics tested for in this study were 100% effective against the Clostridium isolates. Furthermore, ten different multi-antibiotic resistant (MAR) phenotypes were also observed across these isolates. The most prevalent one being AMP-TE-DA-MTZ-C-AMX. All the isolates that presented this phenotype were obtained from aquatic sediment, suggesting that aquatic sediment may be a reservoir for antibiotic resistance and MAR Clostridium species. Additionally, the presence of several antibiotic resistance genes was also screened for using PCR. One of the genes encoding for macrolide-lincosamide-streptogramin (MLS) (ermF), and β-lactam (blaTEM) resistance were not found to be present in any Clindamycin and Ampicillin resistant isolates, respectively. However, several Clindamycin resistant Clostridium isolates were found to harbour the ermB gene, which also encodes for MLS resistance. Two genes encoding for efflux mechanisms against Tetracycline (tetK and tetL) were found in the genomes of some of the Tetracycline resistant isolates. Using both Gram and endospore staining, alongside DNA sequencing, 7 Clostridium species were identified throughout both studies, which included Clostridium bifermentans, C. perfringens, C. sordellii, C. baratii, C. ghonii, C. lituseburense and C. dakarense. Several of these Clostridium species are known pathogens and have been associated with severe gastrointestinal diseases, botulism and necrotising gas-gangrene in both humans and animals. To conclude, the data generated revealed the presence of potentially pathogenic Clostridium species in both surface water and sediment. The presence of antibiotic resistant genes in environmental Clostridium species are also a cause for concern. The expression of these genes could contribute to MAR in these potential pathogenic bacteria. Furthermore, these results highlighted the necessity to screen for other antibiotic resistant pathogens in the aquatic environment and to further investigate the potential sources. Additionally, it is recommended that SRC species should be used as an additional indicator of faecal pollution in surface water systems. Lastly, all these findings indicate that the surface water systems in the North West Province are exposed to various pollutants such as antibiotics and faecal contaminants from runoff and WWTP. This is cause for concern, considering that many rural and informal communities are directly dependent on these water sources and as a result affecting the health of its users, particularly the immune-compromised individuals and livestock.