Salmonella has been one of the major food-borne pathogens for animals and humans for last many years. Many food borne outbreaks and other sporadic cases occur due to Salmonella in many countries. Foods of animal origin are considered major sources of Salmonella. However, Salmonella infections due to consumption of raw vegetables have occurred numerously in recent past. 30% of sewage water is directly used for irrigation purposes in Pakistan for various crops including vegetables. It may be the cause of Salmonella contamination. Apart from conventional microbiological techniques, nucleic acid amplification technologies have provided the opportunity for rapid detection of Salmonella from various sources, providing better sensitivity and superior specificity, thereby refining the administration of outbreaks by more rapid confirmation.
Untreated wastewater is the major source of Salmonella contamination of vegetables. Vegetable sampling was done from field, wholesale and retail markets of Lahore city and wastewater sampling was done from River Ravi, Lahore Canal and other sources by using aseptic techniques and was transported at 4°C. Salmonella species was isolated by conventional methods and suspected colonies were confirmed by biochemical tests TSI and Urease Test. DNA was extracted through boiling and 10% chelex method. Molecular characterization of isolated strains was done through PCR. Antibiotic resistance of confirmed isolates were also checked.
A total of 320 (Vegetable n=160, Wastewater n=160) samples were taken for present study for screening of salmonella microbial contamination in it. Different types of vegetables including Coriander (n=40), Mint (n=40), Carrot (n=40), Radish (n=40) were used for analysis.
CHAPTER 6
SUMMARY
Summary
46
Wastewater samples were also collected from various sources like River Ravi (n=60), Lahore Branch Canal (n=60) and Kharak Nala (n=40).
Salmonella was found in 4/40 (10%) samples of Coriander, 3/40 (7.5%) of Mint, 5/40 (12.5%) of Carrot, 3/40 (7.5%) of Radish and 33/160 (20.63%) of wastewater samples through PCR detection. Many of the isolates were found multi-drug resistant.
This study revealed the presence of multi-drug resistant Salmonella species in vegetables and wastewater. All the vegetables studied were contaminated with Salmonella. This data was designed to find out the magnitude and real picture of the pathogen. It helped in drawing a relationship between Salmonella contamination of vegetables and irrigation of wastewater. As wastewater is the main reason for bacterial contamination of vegetables, measures should be adopted at governmental level for reduction of this contamination. Water disinfection practices and continuous water supply for irrigation can reduce the bacterial load.