Abstract
To date, the microbiological quality of river sediments and its impact on water resources are not included in the water quality monitoring assessment. Therefore, the aim of this study was to establish genetic relatedness between faecal coliforms and enterococci isolated from the river water and riverbed sediments of Apies River to better understand the genetic similarity of microorganisms between the sediment and water phases. Indicator bacteria were subjected to a molecular study, which consisted of PCR amplification and sequence analysis of the 16S rRNA and 23S rRNA gene using specific primers for faecal coliforms and enterococci, respectively. Results revealed that the Apies River had high faecal pollution levels with enterococci showing low to moderate correlation coefficient (r2 values ranged from 0.2605 to 0.7499) compared to the faecal coliforms which showed zero to low correlation (r2 values ranged from 0.0027 to 0.1407) indicating that enterococci may be better indicator than faecal coliforms for detecting faecal contamination in riverbed sediments. The phylogenetic tree of faecal coliforms revealed a 98% homology among their nucleotide sequences confirming the close genetic relatedness between river water and riverbed sediment isolates. The phylogenetic tree of the enterococci showed that Enterococcus faecalis and Enterococcus faecium are the predominant species found in both river water and riverbed sediments with bootstrap values of ≥99%. A high degree of genetic relatedness between sediment and water isolates indicated a possible common ancestry and transmission pathway. We recommend the microbial monitoring of riverbed sediments as it harbours more diverse microbial community and once resuspended may cause health and environmental problems.
Highlights
The South African government has implemented regulations and policies to deliver safe water to all; based on the figures given in the Millennium Development Goals (MDG) Report 2013, 3–5 million people in South Africa still lack access to an improved water source (UN 2013)
Faecal coliforms were more abundant than Enterococcus with mean concentrations of 7.60 log10 and 6.38 log10 colony forming unit (CFU)/100 mL respectively for riverbed sediment and mean concentration of 3.09 log10 CFU/100 mL and 3.97 log10 CFU/100 mL for river water
Concentration of faecal coliforms and Enterococcus spp. in water and sediments of Apies River demonstrates that the river receives high loads of external faecal pollution
Summary
The South African government has implemented regulations and policies to deliver safe water to all; based on the figures given in the Millennium Development Goals (MDG) Report 2013, 3–5 million people in South Africa still lack access to an improved water source (UN 2013). Increasing evidence indicates that many marine sediments (stream substrates) serve as reservoir of pathogenic microorganisms of faecal origin (e.g. Escherichia and Enterococcus), including pathogenic and virulent strains of bacteria (Alm et al 2003; Luna et al 2010). The presence of these faecal bacteria poses serious concerns for the quality of aquatic systems as well as for human health, especially when sediments undergo re-suspension due to both natural and anthropogenic disturbances (Luna et al 2012)
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