Abstract:
Since the discovery of Escherichia coli O157:H7 in the early 1980s and the increased
association of foodborne outbreaks linked to fresh produce, a growing number of research
articles relating to this subject have been published. Although leaps in our understanding of
foodborne pathogen association with fresh produce have been made, our knowledge regarding
this subject remains limited, with many research findings being contradictory. The microbial
safety of commercially produced tomatoes in South Africa was investigated during 2012-
2014. Although no tomatoes tested were contaminated with either Salmonella enterica or
Escherichia coli O157:H7, the presence of Salmonella enterica in the packinghouse of the
first farm investigated in 2012 does indicate a potential risk associated with fresh tomatoes.
Rapid, sensitive, and accurate detection of foodborne pathogens is vital to ensure produce
safety. Conventional culturing techniques should be improved to reduce the analysis time,
increase the efficiency of recovery, improve the resurrection and growth of injured cells, and
to exclude other microorganisms present in the samples. The part of this dissertation therefore
aimed to investigate the application of EnBase® technology for the enhanced recovery of sublethally
injured E. coli O157:H7 from the environment and particularly surface water.
Limiting fermentable carbohydrate availability through enzymatic glucose release would
hypothetically prevent metabolic overload during enrichment cultivation, allowing enhanced
resuscitation and growth of target organisms. This was found to be the case when E. coli
O157:H7 was grown axenically under pristine conditions. EnPresso® B and variations thereof
performed sub-optimally compared to buffered peptone water when used for the enrichment
of E. coli O157:H7-spiked surface water in the presence of naturally occurring coliforms. The utilization of EnBase® technology for the selective and differential isolation and enumeration
of sub-lethally injured E. coli O157:H7 from spiked surface water on solid media were not
effective due to interference of the buffering capacity of EnPresso® B with the pH indicator
neutral red.
Understanding the biological and ecological factors enabling survival and persistence of
human enteric bacteria in fresh produce, as well as better detection and monitoring
techniques, are crucial in developing pre- and postharvest strategies to ensure safe produce in
the future.
