Profiling of potential pathogens from Plankenburg river water used for the irrigation of fresh produce

[摘要] ENGLISH ABSTRACT: The increased consumption of fresh produce has been shown to be related to increases infoodborne disease outbreaks and these have in many cases been ascribed directly to carry-over ofpathogens from contaminated irrigation water. In South Africa, rivers are the main source ofirrigation water but many have been found to be unsuitable for irrigation of fresh produce becauseof the unacceptably high levels of faecal contamination.The main aim of this study was to do a baseline evaluation of the microbiological quality ofthe Plankenburg and Eerste Rivers and to determine which bacterial contaminants are present.Two sampling sites were selected for the Plankenburg (Plank-1 and -3) and one for the EersteRiver (Eerste-1). The microbiological analysis included aerobic colony count (ACC), aerobic andanaerobic sporeformers, Staphylococcus, Salmonella, Listeria, enterococci, coliforms, faecalcoliforms and E. coli using standard methods. The faecal contamination levels for both riversexceeded the DWAF and WHO guidelines of <1 000 E. coli per 100 mL water for irrigation of freshproduce intended to be consumed raw. The Plankenburg River sites always had higher coliformcontamination levels (1 200 - 13 000 000 MPN per 100 mL water) than the Eerste River site (230 -79 000 MPN per 100 mL water). There was also a high incidence of index organisms includingSalmonella, Staphylococcus, Listeria and endosporeformers. The isolation of intestinalenterococci suggested the presence of potential pathogens that can cause disease outbreaks.The baseline data also showed large variations in microbial loads over the 15 month study with thefaecal coliform counts ranging for Plank-1 from 1 200 to 7 000 000 MPN.100mL-1, Plank-3 from 10to 460 000 MPN.100mL-1 and Eerste-1 from 28 to 79 000 MPN.100mL-1. The water temperaturesat all three sites ranged from 12.1° to 21.7°C with COD values in most cases below 100 mg.L-1.As the baseline study showed large variations in microbial loads over the 15 month studyperiod an assessment using the Colilert-18 system of the weekly, daily and hourly variations, for 6weeks over a period of 4 months was conducted at site Plank-2. This site was specifically used asit is an irrigation source point for nearby fresh produce farmers and is about 2 km furtherdownstream from an informal settlement. The weekly variation trend for total coliforms (TC)showed a decrease over the entire sampling period with the highest count of 3 200 000 MPN.100mL-1 during the warmer period. The E.coli (Ec) counts showed a similar trend with the highestcount of 440 000 MPN.100 mL-1 also in March. The daily variation trends were the same for boththe TC and Ec and counts found to increase from Monday to Thursday followed by a decrease toSunday. The highest counts were on Thursday with average TC and Ec counts of 1 900 000 and160 000 MPN.100 mL-1, respectively. The hourly variation trends were similar for both TC and Ecwith counts increasing from 06h00 to 12h00 followed by a decrease to 18h00. The increases in TCand Ec counts found during the weekly, daily and hourly variation trend studies clearly suggeststhat the 15 month sampling that was done once a month on Mondays at 08h00 could beconsidered an underestimation of the contamination levels of the Plankenburg and Eerste Rivers.The overall weekly variation trend for the water temperature showed a decrease over thesampling period while the daily and hourly variation trends showed an increase from 06h00 to18h00. The overall weekly trend for pH differed from that of the temperature with an increase overthe sampling period. The analysis of covariance showed no correlation (p < 0.05) between thephysico-chemical (temperature and pH) and the microbial variables (TC and Ec). Therefore it wasconcluded that temperature and pH had no direct impact on either the total coliform or E. colicounts.Both the Plankenburg and Eerste Rivers were found to be unsuitable for the irrigation offresh produce intended to be consumed raw due to the high levels of faecal contamination thatexceeded DWAF and WHO guidelines. Irrigation with such water could pose a health risk becauseof presence of potential pathogens that could be carried-over to fresh produce.

[发布机构] Stellenbosch University