Foodborne disease outbreaks linked to contaminated irrigation water and fresh produce are a public health concern. The presence of Escherichia coli isolates from irrigation water and leafy green vegetables in different food production systems (large commercial farms, small-scale farms, and homestead gardens) was investigated. The prevalence of antibiotic resistance and virulence in these isolates was further assessed, and links between water source and irrigated crops were identified using antimicrobial and genotypic analyses. Presumptive E. coli isolates were identified by matrix-assisted laser desorption ionization time-of-flight mass spectroscopy, and identities were confirmed by PCR using the uidA gene. Antimicrobial susceptibility was evaluated with the Kirby Bauer disk diffusion test; the presence of virulence genes was determined with enterobacterial repetitive intergenic consensus PCR assays. Of the 130 E. coli isolates from water (n =60) and leafy green vegetables (n =70), 19 (14.6%) were resistant to one antibiotic (tetracycline) and 92 (70.7%) were resistant to various antibiotics (including ampicillin, cefoxitin, and nalidixic acid). All E. coli isolates were susceptible to ceftriaxone and gentamicin. The virulence gene stx was detected in E. coli isolates from irrigation water (8 [13.3%] of 60 isolates) and cabbages (3 [7.5%] of 40), but the virulence genes eae and stx were not detected in any tested isolates from irrigation water and fresh produce samples. The prevalence of multidrug-resistant E. coli was lower in isolates from GLOBALG.A.P.-certified farms than in isolates from noncertified commercial and small-scale farms and homestead gardens. A link between the E. coli isolates from irrigation water sources and leafy green vegetables was established with phenotypic (antimicrobial) and genotypic (DNA fingerprinting) analyses. However, a link between virulence genes and the prevalence of antimicrobial resistance could not be established.

Access to large sources of quality water for irrigation is fundamental to the hygienic cultivation of fresh produce. However, due to factors such as contamination of water bodies, access to clean uncontaminated water is fast becoming an ever increasing global challenge. The unavailability of quality source water increases the risk of contamination of fresh produce with human pathogenic microorganisms, which may compromise public health. Over the past few years, there has been a decline in the microbiological quality of surface water and other sources used for irrigation. This is mainly due to upstream faecal contamination. Therefore, the assessment and subsequent suitability of alternative water sources for irrigation such as roof harvested rainwater should be considered. Contrasting views regarding the quality of roof harvested rainwater (RHRW) have been published. Pathogens such as Salmonella and Campylobacter species and Listeria monocytogenes have been reported in RHRW. Leafy green vegetables such as cabbage, spinach and lettuce are produced across a wide range of farming systems from 2 regulated formal (commercial farms) to informal (small-scale and homestead gardens) setups. This review will discuss global water challenges associated with irrigation water, microbial quality of source water for irrigation, crop contamination, and pathogen detection and characterization methodologies.

Foodborne disease outbreaks associated with fresh produce irrigated with contaminated water are a constant threat to consumer health. In this study, the impact of irrigation water on product safety from different food production systems (commercial to small‐scale faming and homestead gardens) was assessed. Hygiene indicators (total coliforms, Escherichia coli), and selected foodborne pathogens (Salmonella spp., Listeria monocytogenes, and Escherichia coli O157:H7) of water and leafy green vegetables were analyzed. Microbiological parameters of all irrigation water (except borehole) exceeded maximum limits set by the Department of Water Affairs for safe irrigation water. Microbial parameters for leafy greens ranged from 2.94 to 4.31 log CFU/g (aerobic plate counts) and 1 to 5.27 log MPN/100g (total coliforms and E. coli). Salmonella and E. coli O157:H7 were not detected in all samples tested but L. monocytogenes was present in irrigation water (commercial and small‐scale farm, and homestead gardens). This study highlights the potential riskiness of using polluted water for crop production in different agricultural settings. Practical applications These results show that the microbial quality of surface water is deteriorating in different agricultural settings. This may be a possible preharvest source of contamination of leafy green vegetables, which may then constitute a health risk to consumers. The presence of Listeria monocytogenes along the food supply chain is a potential health risk if the pathogen proliferates leading to high quantities suitable for onset of listeriosis. The absence of Salmonella and Escherichia coli O157:H7 in the samples tested is an encouraging result. Food safety protocols should be extended to the informal sectors and homestead gardens.

The study aimed at assessing the microbiological quality and suitability of roof-harvested rainwater (RHRW) for crop irrigation and domestic use. In total, 80 rain water tanks (246 samples) across three rural villages (Ga-Molepane, Jericho and Luthngele) were visited. Culture based techniques were used to isolate bacterial microbes and identities were confirmed using matrix assisted laser desorption/ ionization time of flight (MALDITOF MS). Uncultured fungal populations were also identified using pyrosequencing. Salmonella spp. (3%), L. monocytogenes (22%), total coliforms (57.7%), Escherichia coli (E. coli) (30.5%), Enterococcus spp. (48.8%), Pseudomonas spp. (21.5%) were detected in RHRW samples after rainfall. Fungal sequences belonging to species known to cause fever, coughing and shortness of breath in humans (Cryptococcus spp.) were identified. This study indicates that RHRW quality can be affected by external factors such as faecal material and debris on the rooftops. The use of untreated RHRW could pose a potential health risk if used for irrigation of crops or domestic use, especially in the case of a relative high population of immunocompromised individuals. This study does not dispute the fact that RHRW is an alternative irrigation water source but it recommends treatment before use for domestic purposes or for watering crops.

Nine morphologically distinct halophilic yeasts were isolated from Makgadikgadi and Sua pans, as pristine and extreme environments in Botswana. Screening for biosurfactant production showed that Rhodotorula mucilaginosa SP6 and Debaryomyces hansenii MK9 exhibited the highest biosurfactant activity using Xanthocercis zambesiaca seed powder as a novel and alternative inexpensive carbon substrate. Chemical characterization of the purified biosurfactants by Fourier Transform Infra-Red spectroscopy suggested that the biosurfactant from R. mucilaginosa SP6 was a rhamnolipid-type whereas the biosurfactant from D. hansenii MK9 was a sophorolipid-type. The two biosurfactants exhibited antimicrobial activities against eight pathogenic bacteria and fungal strains (Proteus vulgaris, Escherichia coli, Klebsiella pneumoniae, Staphylococcus aureus, Micrococcus luteus, Cryptococcus neoformans, Candida albicans and Aspergilus niger). The sophorolopid-type biosurfactant was found to be the most potent among the antimicrobial drug resistant strains tested. The findings open up prospects for the development of environmentally friendly antimicrobial drugs that use an inexpensive source of carbon to reduce the costs associated with the production of biosurfactants.