Assessment of microbial loads of the Plankenburg and Berg Rivers and the survival of escherichia coli on raw vegetables under laboratory conditions

Barr, Alison ; Ackermann, Alison (2010-12)

Thesis (MSc Food Sc (Food Science))--University of Stellenbosch, 2010.

Thesis

ENGLISH ABSTRACT: Over the last decade, studies on the quality of the water in many of South Africa.s rivers revealed an increase in pollution levels (DWAF, 1996; DWAF, 2000). In agricultural areas of the Western Cape many farmers draw water for irrigation from nearby rivers without knowing what the microbial pollution level is. In order to investigate the current quality of river water in some of the Western Cape.s major rivers and to explore the possibility of pathogen carryover from water onto produce, this research project was initiated. In an exploratory study over a five month period, the microbiological and water chemistry of three selected sites from the upper Berg and two from the Plankenbrug Rivers were assessed. Studied organisms included Salmonella, Staphylococcus, Listeria, endosporeformers, coliforms, Escherichia coli and intestinal Enterococci, while the chemical analysis consisted of pH, alkalinity, conductivity and chemical oxygen demand (COD). Faecal coliform counts ranging from 540 to 1 700 000 cfu.100ml-1 and 490 to 160 000 cfu.100ml-1 were found for the Berg and Plankenbrug Rivers, respectively. The water temperature ranged from 12º to 21ºC with COD values always below 100 mg.L-1. Potential human pathogens such as Salmonella, Staphylococcus, Listeria, endosporeformers, E. coli and intestinal Enterococci were frequently isolated from all five sites that were sampled. These results are of great concern to farmers, fresh produce retailers and consumers alike as the river water is regularly drawn for irrigation of produce that is later consumed raw or after a minimal processing step. From the exploratory study it was concluded that the water from all the sites were not suitable for use in irrigation practices as they regularly exceeded the guidelines for faecal coliforms and E.coli as set out by South African authorities. Irrigation with faecally polluted river water is one way that fruit and vegetables can become contaminated with foodborne pathogens. The risk of disease transmission from potential pathogens present in the irrigation water is influenced by the microbial load present and the numbers carried over to the produce. In this study the carry-over and survival of Escherichia coli on green beans, sugar-snap peas and cocktail tomatoes was assessed under controlled laboratory conditions. The produce was exposed to E.coli under different combinations of exposure times (5, 15 or 30 min), drying times (30 or 120 min) and different inoculum concentration ranges (107, 105, 104, 10³ and 10ª). In all cases a reduction of at least one log value in original inoculum number was found with the 10ª inoculums showing no survivors. Follow-up studies with an exposure time of 60 min and increased drying times of 6 or 12 h. Neither of these parameter changes affected the variation in numbers for the same inoculum or the E.coli survivors. Similar E.coli loads to those detected on the green beans were detected on the sugar-snap peas. The number of survivors on the cocktail tomatoes was much lower than found for the beans and peas. The number of survivors on the cocktail tomatoes was much lower than found for the beans and peas. This was attributed the 'smooth'surface of the tomato skin probably making attachment of the E.coli bacteria difficult. With the exception of the 10ª inoculum range, all E.coli survivors detected on the three types of produce studied exceeded the guideline numbers set for fresh produce. If similar survival patterns are to be found in the environment then results from this study should serve as a warning that the Plankenburg river water is unsafe for use in the irrigation of fresh produce. Some farmers are already treating river water with chlorine prior to irrigation to eliminate the chance of pathogen transfer onto produce. However, this is not a feasible solution for most farmers due to the high cost of implementing a system such as this.

AFRIKAANSE OPSOMMING: Oor die afgelope tien jaar het studies oor die gehalte van die water in baie van Suid-Afrika se riviere 'n toename in besoedelingsvlakke getoon. Baie boere in landbou gebiede van die Wes-Kaap wat watertrek vir besproeiing uit die nabygelee riviere is onbewus van die mikrobiese besoedelingsvlak van die rivier. Hierdie navorsingsprojek is geinisieer ten einde die huidige gehalte van die water in sommige van die Wes-Kaap se riviere te monitor, asook die moontlikheid van patogeen oordrag van die water na vars produkte te ondersoek. Met behulp van 'n verkennende studie oor . vyf maande tydperk, is die mikrobiologiese en water chemie kenmerke van drie geselekteerde moniteringspunte uit die boonste Bergrivier, en twee uit die Plankenburgrivier bemonster. Die bestudeerde organismes het ingesluit: Salmonella, Staphylococcus, Listeria, endosporeformers, fekale kolivorme, Escherichia coli en intestinale Enterococci. Die chemiese parameters het bestaan uit pH, alkaliniteit, geleiding, temperatuur en chemiese suurstof behoeftes (CSB). Fekale kolivorme tellings het gewissel van 540 - 1 700 000 cfu.100ml-1 en 490 tot 160 000 cfu.100ml-1 is gevind vir die Berg- en Plankenburgriviere, onderskeidelik. Die water temperatuur het gewissel van 12 º tot 21ºC met die CSB-waarde altyd onder 100 mg.L-1. Potensiele menslike patogene soos Salmonella, Staphylococcus, Listeria, endosporeformers, E. coli en intestinale Enterococci is dikwels geisoleer uit al vyf die moniteringspunte. Hierdie resultate is van groot belang vir boere, kleinhandelaars en varsprodukte verbruikers omdat die riviere se water gereeld onttrek word vir besproeiing van produkte wat later gebruik word in rou of in minimale geprosesseerde vorm. Vanuit die verkennende en uit die langer termyn studie (12 maande) is die gevolgtrekking gemaak dat die water vanuit die riviere nie geskik is vir gebruik in besproeiingspraktyke waar die riglyne vir fekale kolivorme en E. coli, soos uiteengesit deur die Suid-Afrikaanse owerhede, gereeld oorskry word nie. Besproeiing met fekale besoedelde rivierwater is een manier waarop groente en vrugte besmet kan word met voedsel patogene. Die risiko vir die oordrag van moontlike patogene teenwoordig in die besproeiingswater word beinvloed deur die mikrobiese lading teenwoordig en die getalle wat oorgedra word na die produkte. In hierdie studie is die oordrag en oorlewing van E. coli op groenboontjies, ertjies en tamaties onder beheerde laboratoriumtoestande beoordeel. Die produkte is blootgestel aan E. coli onder verskillende kombinasies van blootstellingstydperke (5, 15 of 30 min), drogingstye (30 of 120 min) en verskillende inokulum konsentrasies (107, 105, 104, 10³ en 10ª). In elke geval is . afname van ten minste een log waarde van die oorspronklike inokulum konsentrasie gevind. Die 10ª inokulum reeks het geen oorlewende selle getoon nie. Opvolg studies is gedoen met 'n blootstellingstyd van 60 min en verlengde drogingstye van 6 of 12 uur. Daar is gevind dat hierdie parameter veranderings die variasie in getalle vir dieselfde inokulum of die oorlewende E. coli nie beinvloed het nie. Soortgelyke E. coli ladings wat op die groenbone aangetref is, is ook op die ertjies aangetref. Die aantal oorlewendes op die tamaties was heelwat laer as die resultate vir die boontjies en ertjies. Dit word toegeskryf aan die "gladde" oppervlak van die tamatie-vel wat waarskynlik die aanhegting van die E. coli selle bemoeilik. Met die uitsondering van die 10ª inokulum reeks, het al die E. coli oorlewende selle gevind op die drie tipes produkte, die riglyn getalle oorskry wat vir vars produkte gestel is. As soortgelyke oorlewingspatrone gevind word in die omgewing, behoort die resultate van hierdie studie as waarskuwing te dien dat die water van die Plankenburgrivier ongeskik is vir die besproeiing van vars produkte. Sommige boere is reeds besig met chloor behandeling van die rivierwater voor besproeiing, om die kans van patogeenoordrag na die produkte uit te skakel. Dit is egter nie 'n haalbare oplossing vir die meeste boere nie as gevolg van die hoe kostes verbonde aan die implementering van' n stelsel soos hierdie.

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