Risk Assessment and Management of Escherichia coli in Local Vegetable Markets

Abstract

Fresh produce linked foodborne outbreaks have become a global concern. Nutritional value of vegetables and high prices of meat and meat originated food compel common people for consumption of plant originated food particularly salad vegetables. Microbial population of vegetable surfaces contains large number of pathogenic bacteria including members of Enterobactereace. Most promising pathogen among enteric microbes is Escherichia coli (E.coli) that is normally a nonpathogenic bacteria and becomes virulent due to several pathogenic factors like toxin production. Shigalike toxins are chief disease causing molecular structures produced by Shigalike toxin producing strains of E.coli possessing genes for shigalike toxin I and shigalike toxin II. It was intended to assess and manage the risk associated with these potential pathogens. This research was an effort to reduce faecal contamination of salad vegetables consumed in Pakistan and to provide clean nutritious food to public. A survey was conducted in three markets of Islamabad, Rawalpindi and Lahore and tomato, lettuce, cabbage and cucumber were collected from three shops of each market. Each vegetable was analysed as unwashed and washed for aeobic plate count (APC), total coliforms, faecal coliforms and E.coli. About two hundred and fifty E. coli isolates were preserved, serotyped and studied for presence of shigalike toxin genes. Results indicated a high APC on all vegetable samples. Total coliforms, faecal coliforms and E.coli count exceeded the permissible limits in most samples. Highest APC was associated with lettuce (6.6 log 10 cfu/g). Tomato was least contaminated by APC (5.6 log 10 cfu/g). E.coli was detected in tomato, lettuce, cucumber and cabbage. Washed samples showed significantly reduced bacterial population. Two hundred and fifty isolates of E.coli were biochemically characterized and serotyped for O and H antigens. Majority of strains could not be identified by serotyping. Polymerase chain reaction (PCR) results indicated presence of shigalike toxins in 55 E.coli isolates. Raw garlic proved to be most promising antibacterial spice extract with maximum zone of inhibition (29mm) and lowest MIC (3mg/ml). Ginger, cinnamon, mustard also indicated considerable antibacterial activity. Extracts xiprepared by using methanol, acetone and water as solvents showed variable antimicrobial efficiency. Solvent extraction reduced efficacy of extracts as compared to crude extracts. Acetic acid, citric acid and common salt also lowered growth of E.coli strains. A treatment solution of pH=2.7, consisting of 5 ml of raw extracts of garlic, ginger, mustard, cinnamon, 5 ml of 2% acetic acid, 2% citric acid and 1.5% common salt was prepared and directly applied on salad vegetables. This composite treatment solution significantly reduced APC and completely eliminated total coliforms, faecal coliforms and E.coli. These findings conclude with high potentially pathogenic microbial load on salad vegetables and urge for preventive action on priority basis. Raw spice extracts alongwith non toxic chemicals provide an excellent source for pathogens elimination from fresh produce.