Researchers from the University of Pretoria and the Water Research Commission are tracking multi-drug resistant bacteria in South Africa's water sources to assess how they affect food safety when used for irrigating crops.
Water is a critical input in fresh produce cultivation and processing, but it can also carry pathogens and other contaminants. Irrigation water contaminated with bacteria such as Escherichia coli can transfer to fruit and vegetables. Consuming raw or insufficiently washed produce can result in illness.
The research team has been investigating bacterial pathogens in water for the past 20 years. Their work includes identifying contamination hotspots, testing microbiological quality along fresh produce supply chains, and monitoring irrigation water. They have documented the transfer of Salmonella and E. coli from irrigation water to soil and vegetables on smallholder and commercial farms.
Rainwater harvesting is often used in rural areas, but poorly maintained storage tanks can accumulate biofilms that support microbial growth, including potential pathogens. Surface water sources such as rivers and dams are another risk, frequently showing high levels of E. coli and multi-drug resistant bacteria.
Current water quality guidelines in South Africa focus largely on indicator organisms such as E. coli. According to the researchers, these standards do not address multidrug-resistant bacteria or emerging pathogens, creating gaps in food safety oversight.
Contamination often begins upstream, where untreated or partially treated sewage enters rivers and dams. These waters are then used for irrigation by small-scale farmers who supply fresh produce to informal markets. At the retail level, further contamination risks can occur, for example, when spinach is placed in unclean water to prevent wilting. Research has also found bacterial pathogens with antimicrobial resistance on produce at the point of sale.
The team stresses the need for more real-time data and updated water quality guidelines that extend beyond E. coli testing to include Salmonella and toxin-producing E. coli strains. Continuous surveillance is recommended in areas with known water quality challenges, alongside monitoring of produce to check for contamination.
The researchers are currently monitoring antibiotic resistance in rivers, intending to develop practical actions for safer irrigation practices and improved hygiene. They highlight the importance of coordinated efforts between government, scientists, farmers, and communities. They also recommend a comprehensive national food safety policy, aligned with a continental food safety framework.
Source: Daily Maverick