Discharge of inadequately treated sewage has been known to be conduits of these pathogens to surface water. This review assesses the impact of wastewater treatment plants as sources of contamination of receiving surface waters with Salmonella and Shigella species.
Overview of water in South Africa
Despite the uneven distribution of fresh or surface water, scarcity and heavy dependence on surface water to meet the ever-growing demand for water, it is alarming to note the increasing deterioration of surface water quality due to pollution (Chong et al., 2010); FAO, 2003; George et al., 2001; Pitman, 2011). During the past few decades, human development, population growth, extreme weather events, natural disasters and climate change have exerted very diverse pressures on both the quality and quantity of water resources, which in turn impact conditions that promote water-related diseases (Yang et al., 2012).
Wastewater effluent as a source of pathogenic microorganisms
Prevalence of Salmonella and Shigella species in treated wastewater effluents
However, the presence of Salmonella and Shigella species was detected at all points of the wastewater treatment plant, including the final effluent. Samie et al., (2009) regularly detected the presence of Salmonella and Shigella species among other pathogens at all stages of treatment at 14 different wastewater treatment plants in South Africa.
Implication of release of Salmonella and Shigella species on receiving water bodies Wastewater treatment plants are usually designed to efficiently remove biological oxygen
In a recent study, non-typhoidal Salmonella was described as the second leading cause of foodborne illness (11%) after norovirus (58%) and was the leading cause of hospitalization (35%) and death (28%) in the United States (Scallan et al ., 2011). The presence of these pathogenic bacteria in surface water can result in outbreaks of waterborne diseases (Musyoki et al., 2013).
Epidemiology of Salmonella and Shigella spp. in developing countries
Salmonella is a major cause of bacteremia in children and immunocompromised adults with an associated mortality of 20–25% (Sánchez-Vargas et al., 2011). Between 1996 and 2006, a survey in South Africa reported 50 cases of shigellosis affecting mostly children and immunocompromised patients (Davies and Karstaedt, 2008).
Pathogenicity of Salmonella and Shigella species
The TSS3 creates a channel through both the bacterial and epithelial cell periplasm, leading to a translocation of bacterial effectors into the cell cytoplasm ( Coburn et al., 2007 ). The secreted effectors interact with eukaryotic proteins to activate signal transduction pathways and rearrange the actin cytoskeleton, leading to membrane deformation and engulfment (Zou et al., 2011).
Antibiotic resistance development in Salmonella and Shigella species
Previous reports have suggested that resistant bacteria can once again become susceptible to an antibiotic after a period of withdrawal of that antibiotic from healthcare settings (Kariuki et al., 2006, Rahman et al., 2002).
Conclusion
Scope of the study
Hypothesis
It was hypothesized that the Durban sewage treatment plant is not efficient in removing the microbial load especially pathogenic organisms such as Salmonella and Shigella spp. It was further hypothesized that sewage effluents are a reservoir for antibiotic-resistant and virulent Salmonella and Shigella species.
Objectives
Aims
Occurrence of potentially pathogenic vibrations in the final effluent from a sewage treatment plant in a rural area of the Eastern Cape Province of South Africa. Occurrence and distribution of Listeria pathogens in the final effluent from a rural sewage treatment plant in the Eastern Cape Province of South Africa.
Introduction
These processes are associated with high operating and capital costs and are therefore beyond the reach of most developing countries (Wen et al., 2009). Also, previous reports from some provinces in South Africa have implicated treated sewage effluent as a point source of contamination of receiving watersheds with pathogenic and emerging pathogenic microorganisms (Odjadjare et al., 2012).
Materials and Methods
- Description of wastewater treatment plant investigated in this study
- Sample collection
- Physico-chemical analysis
- Microbial analysis
- Biochemical test of selected presumptive isolates
- Statistical Analysis
Where D1 = DO of the diluted sample immediately after preparation (mg/l) D2 = DO of the diluted sample after 5 days of incubation at 20°C (mg/l). Serial dilutions of water samples were made and standard membrane filtration using 0.45 µm pore and 47 mm diameter filter (Pall Corporation, USA) was used to concentrate 50 ml of properly diluted water sample.
RESULTS
Physicochemical parameters of treated wastewater effluent and receiving surface waters
In NWWTW, BOD5 was stable at each sampling point in each month, ranging from 1.03 mg/l to 9.42 mg/l throughout the study period. While at the NGWTP, BOD5 was stable at all sampled points in each month, but varied from 2.20 mg/l to 11.04 mg/l throughout the study period.
Microbial profile of treated wastewater effluent and receiving river
Statistical analysis
Discussions
This high variation has been reported in previous studies in the Eastern Cape province of South Africa (Igbinosa et al., 2009; Odjadjare and Okoh 2010). Biochemical oxygen demand (BOD5), the amount of oxygen required by bacteria to oxidize organic matter present in water, is a basic tool for measuring the degree of water pollution (Allan et al., 2000). There are no South African guidelines for BOD in the final wastewater stream; however, the European Union (EU) recommends a discharge limit of 3 to 6 mg/l for aquatic ecosystems (Momba et al., 2006).
High levels of COD observed upstream can be attributed to runoff, agricultural activities and anthropogenic activities upstream (Igbinosa et al., 2009).
Prevalence of potentially pathogenic vibrios in final effluents from a wastewater treatment facility in a rural community of the Eastern Cape. 2011) Detection of potential risk of wastewater effluent for transmission of antibiotic resistance of Vibrio species as a reservoir in a suburban community in South Africa. Urban wastewater treatment plants as hotspots for the release of antibiotics into the environment: A review. The impact of inadequate wastewater treatment on the receiving water bodies - Case study: Buffalo City and Nkokonbe Municipalities of the Eastern Cape Province, Water SA.
Pseudomonas species in the final wastewater from three municipal wastewater treatment plants in South Africa.
Introduction
SPI-1 and 2 contain the invA and spiC genes are essential for systemic pathogenesis because they encode a type III secretion system (T3SS) required for invasion (Hensel 2004, Miki et al., 2004). The T3SS system is used by the pathogen to deliver virulence factors to the host cell and interfere with or subvert normal host cell signaling pathways (Marcus et al., 2000). SPI-4 is a 25 kb pathogenicity island that contains the orfL gene, thought to encode a type 1 secretion system (an autotransporter protein) that mediates the secretion of toxins and is required for macrophage survival (Gassama-sow et al., 2006; Sánchez-Jiménez et al., 2010).
Olaniran et al., 2012) leading to public health risks for those who rely on these waters for socio-economic activities.
Materials and Methods .1 Sample collection
- Microbial analysis
- Biochemical confirmation of presumptive Salmonella spp
- Molecular confirmation of presumptive Salmonella spp
- Virulence gene detection
- Antibiotics susceptibility test
Template DNA was prepared from fresh cultures of the isolates on nutrient agar using the boiling method as previously described (Akinbowale et al., 2007) with modifications. The antibiotic susceptibility of the isolates was determined using the Kirby-Bauer disc diffusion method described by Tao et al. The standardized culture of the isolates was inoculated onto Mueller-Hinton agar using sterile inoculums for confluent growth and allowed to dry for 10 minutes.
The diameter of the inhibition zone was measured and recorded to the nearest millimeter as recommended by the Clinical and Laboratory Standards Institute (2007).
Results
Distribution and Confirmation of presumptive Salmonella spp. recovered from treated wastewater and receiving surface waters
Antibiogram profile of Salmonella spp. in treated effluent and receiving surface water Antibiogram profile of the confirmed isolates from New Germany wastewater treatment plant is
Distribution of virulence signatures in Salmonella spp. recovered from treated wastewater and receiving surface waters
Lane M contains 100bp marker, lanes 1 to 6 contain environmental isolates, lane 7 contains negative control, and lane 8 contains Salmonella typhimurium ATCC 13317 as positive control. Lane M contains 100 bp marker, lanes 1 to 6 contain environmental isolates, lane 7 contains negative control and lane 8 contains Salmonella typhimurium ATCC 13317 as positive control. Lane M contains marker, lanes 1 to 16 contain environmental isolates, lane 17 contains negative control and lane 18 contains Salmonella tyhimurium as positive control.
DISCUSSION
In the Eastern Cape Province of South Africa, Momba et al. 2006) observed the presence of Salmonella spp. The results obtained in this study further emphasize the need for careful use of fluoroquinolones and other commonly used antibiotics to prevent the emergence of resistant phenotypes (Jin et al., 2012). In another study Oliveira et al. 2012) reported that 21.12% of the isolates in the study were completely resistant to Nalidixic acid.
It is also worth noting that the invA gene used to positively confirm the identity of the isolates is a virulence gene located on SP-1 (Dione et al., 2011).
A review of the ecology, colonization and genetic characterization of Salmonella enterica serovar Sofia, a productive but avirulent poultry serovar in Australia. Prevalence, antimicrobial resistance and relationship to indicator and pathogenic microorganisms of Salmonella enterica isolated from surface water in an agricultural landscape. Salmonella pathogenicity islands encoding type III secretion systems. 2004) Evolution of pathogenicity islands of Salmonella enterica.
Characterization of Salmonella pathogenicity island 1 type III secretion-dependent hemolytic activity in Salmonella enterica serovar Typhimurium.
Research in perspective
This indicates that the discharge of treated wastewater from these treatment plants could lead to contamination of the receiving surface water with Salmonella and suspected Shigella spp. Biochemical and molecular tests showed that none of the suspected Shigella were actually Shigella spp. Resistance to nalidixic acid suggests possible resistance or reduced susceptibility to more potent quinolones such as norfloxacin and ciprofloxacin (CLSI, 2007).
Molecular testing for the presence of virulence signatures revealed that of the 200 isolates tested in this study, 93% contained the spiC gene, 84% contained the misL gene, and 87.5% contained the orfL gene, while 87% contained the pipD gene.
Potential for future development of the study
Therefore, it is recommended to use pulsed field gel electrophoresis for further molecular analysis and genotyping of the obtained isolates to determine their type and subtypes. Bacteria are known to have and carry genes that confer resistance to certain types of antibiotics and virulence. Due to the myriad of possible genes, DNA microarray techniques can be used to detect these genes (Ma et al., 2007; Frye et al., 2010).
Future studies should also determine the mechanism of pathogenicity and antibiotic resistance, as well as the ability of isolates to acquire and transfer virulence and resistance genes in order to remedy the public health threats posed by these pathogens.
BOD values for treated sewage effluent and receiving surface water at Norther treatment plant. BOD values for treated wastewater and receiving surface water at the new German wastewater treatment plant. CORRELATIONS /VARIABLES=pH Turbidity BOD COD Temperatures SalmonellaT ShigellaT /PRINT=TOHALE NOSIG /STATISTICAL DESCRIPTION /MISSING=PAIR WEIGHT.
CORRELATIONS /CHANGES=pHr TurbidityT BODt CODr TempR SalmonellaT ShigellaT /PRESSURE=TWO TAIL NOSE /STATISTICAL DESCRIPTIONS /ONTEND=PURPLE SIGHT. CORRELATIONS /VARIABLES=pH BOD COD TurbidityT temperatureR SalmonellaT ShigellaT /PRESSURE=TWO TAIL NOSE /STATISTICAL DESCRIPTIONS /ONTEND=PURPLE SIGHT. CORRELATIONS /CHANGES=pH COD TurbidityT BODt TempR SalmonellaT ShigellaT /PRESSURE=TWO TAIL NOSE /STATISTICAL DESCRIPTIONS /ONTEND=PURPLE SIGHT.
