Hi all…it is widely assumed that an important waterborne pathogen, Escherichia coli (E. coli) O157:H7, is shed from warm blooded animals and in some instances is transported to a drinking water treatment plant intake/source. As far as we’ve understood to date, it could not grow and reproduce in the environment (unlike some non pathogenic E. coli). Some recent food studies have shown that it can grow inside plants that are consumed by humans. Now a study has shown that E. coli O157:H7 can not only survive but can reproduce in soil as well! This may have implications for drinking water treatment but studies/assessments will need to be conducted to confirm if conditions exist whereby this increases risk, affects the timing of the risk, or is treated as a new unrecognized source of risk.
In the discussion the authors write: “E. coli is not thought to survive for long periods outside the host intestine, so produce-associated outbreaks have widely been ascribed to recent fecal contamination. The suspected sources of produce contamination include soil amendments (manure or compost), irrigation water contaminated with cattle feces, or contaminated surface runoff (Ongeng et al., 2015). Our results showed that E. coli O157 can grow using nutrients available in soils (Figure 1). There have been countless studies reporting numbers of E. coli O157 in soils over time, and some have suggested growth in soil. Survival of E. coli in soil has been reported by many researchers; more than 200 d under natural environmental conditions and 500 d in frozen soil and on plant roots (Gagliardi and Karns, 2002; Islam et al., 2004). This is the first report showing definitively that E. coli O157 is able to grow using water soluble nutrients in soil.”
The article is open access so if you’re interested you can download it at: https://www.frontiersin.org/journals/microbiology#articles
Bill
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Growth and Extended Survival of Escherichia coli O157:H7 in Soil Organic Matter
Gitanjali NandaKafle, Amy A. Christie, Sébastien Vilain and Volker S. Brözel
Frontiers in Microbiology, April 23, 2018 Vol 9, article 762
Abstract
“Enterohaemorrhagic Escherichia coli, such as serotype O157:H7, are a leading cause of food-associated outbreaks. While the primary reservoir is associated with cattle, plant foods have been associated as sources of human infection. E. coli is able to grow in the tissue of food plants such as spinach. While fecal contamination is the primary suspect, soil has been underestimated as a potential reservoir. Persistence of bacterial populations in open systems is the product of growth, death, predation, and competition. Here we report that E. coli O157:H7 can grow using the soluble compounds in soil, and characterize the effect of soil growth on the stationary phase proteome. E. coli 933D (stxII\u8722 –) was cultured in Soil Extracted Soluble Organic Matter (SESOM) and the culturable count determined for 24d. The proteomes of exponential and stationary phase populations were characterized by 2D gel electrophoresis and protein spots were identified by MALDI-TOF mass spectrometry. While LB controls displayed a death phase, SESOM grown population remained culturable for 24d, indicating an altered physiological state with superior longevity. This was not due to decreased cell density on entry to stationary phase as 24 h SESOM populations concentrated 10-fold retained their longevity. Principal component analysis showed that stationary phase proteomes from SESOM and LB were different. Differences included proteins involved in stress response, motility, membrane and wall composition, nutrient uptake, translation and protein turnover, and anabolic and catabolic pathways, indicating an altered physiological state of soil-grown cells entering stationary phase. The results suggest that E. coli may be a soil commensal that, in absence of predation and competition, maintains stable populations in soil.”
