Human exposure to antibiotic resistant-Escherichia coli through irrigated lettuce

Antibiotic resistant bacteria (ARB) have been found on fresh fruit and vegetables globally. These types of ARB infections are spreading rapidly and are a major human health threat. A quantitative human exposure assessment model was created using scenario analysis to investigate the potential human exposure to antibiotic resistant Escherichia coli (AR-E. coli) through the consumption of lettuce irrigated with surface water. Scientific literature and site specific data were collected to model each process from farm to fork to calculate the concentration of AR-E. coli on the lettuce at the point of human consumption. The processes examined were the adhesion, colonisation and viability of bacteria on the lettuce; the effect of different post-harvest cleaning processes; the effect of consuming the lettuce before, on or after the expiry date; and the effect of the consumer washing the lettuce. The results show the mean human exposure levels ranged between 1.00 × 10−2 and 1.35 × 106 colony forming units (CFU) of AR-E. coli per 100 g of surface water irrigated lettuce for the different scenarios investigated. The mean probability of illness from consuming 100 g of lettuce contaminated with potential pathogenic antibiotic-sensitive E. coli was between 1.46 × 10−9 to 1.88 × 10−2. A back calculation revealed that in order for the EC No 1441/2007 regulation to be exceeded (≥1000 CFU/g of E. coli on lettuce at the manufacturing stage), the mean contamination levels required in the irrigation water would need to be 2.7, 3.1 or 4.8 log CFU/ml using the post-harvest treatments of washing with water, rapid cooling with water and washing with a chlorine solution respectively. The information generated from this model could help to set guidelines for producers on maximum permissible AR-E. coli contamination levels in irrigation water and provides recommendations on the best post-harvest treatment to use. Keywords: Antibiotic resistance, Escherichia coli, Irrigation, Human exposure, Lettuc

The potential human exposure to antibiotic resistant-Escherichia coli through recreational water

It is important that bathing water sites are free as possible from antibiotic resistant bacteria (ARB) to prevent the spread of difficult to treat infections throughout the population. This study examines the possible human exposure to antibiotic resistant Escherichia coli (AR-E. coli) through recreational activities at two different bathing water sites located near wastewater treatment plants (WWTPs). A quantitative risk assessment model was created to model the pathway of the AR-E. coli from the WWTPs effluent water through to the bathing water sites. Both sampling data and data from scientific literature were used. The main steps considered for the model were: the dilution and decay of the AR-E. coli from the WWTPs effluent water into the river; the dilution of the river into the bathing water sites and the human exposure to AR-E. coli through recreational activities at the bathing water sites (as a result of water ingestion). The results show the mean predicted human exposure levels ranged between 0.45 and 345.09 cfu/100 ml. A back calculation method determined that in accordance with the European Bathing Water Directive (2006/7/EC) (BWD) to be considered “poor” water quality, the concentration of AR-E. coli in WWTP effluent water would need to exceed 2.45 log cfu/ml at site 1 and exceed 2.71 log cfu/ml at site 2. This study provides valuable information for regulatory bodies and policy makers on the possible human exposure levels to AR-E. coli and the maximum permissible concentrations in WWTP effluent water to ensure compliance with relevant bathing water legislation