Recent techniques for detection of Salmonella typhimurium in camel minced meat, experimentally contaminated

Abstract

Fresh camel meat was obtained from slaughtered local Najdi camel sold at private butcher stores in Buraydah, Kingdom of Saudi Arabia. Red thigh meat was selected from sound inspected carcass and transferred, while cold, to the lab within 30 minutes to be processed immediately. Camel meat was minced using the meat grinder and divided into 25 g portions in sterile bags (Seward Medical Stomacher® 400 sterile bags). Minced meat portions were inoculated with 1 mL of (10, 103 or 105 ) of S. typhimurium colony forming units. At the same time, 25 g portions were left uninoculated to be used as salmonella-negative control. The inoculated and uninoculated portions were preserved refrigerated or frozen and processed at different time intervals. Detection of salmonella in inoculated meat by using conventional isolation, the VIT-Salmonella kit, the GLISA Singlepath® Salmonella detection kit, and Polymerase chain reaction. The obtained results concerning with detection of S. typhimurium in contaminated minced camel meat using conventional isolation revealed that, S. typhimurium could not be detected at zero time of inoculation from inoculated camel minced meat containing either 10 and ii 103 bacterial CFU. Meanwhile, S. typhimurium was detected in meat containing 105 bacterial CFU in count of 3.1 x 104 /g. After 2 days of chilling in refrigerator at 6 oC, S. typhimurium could not be detected in first dilution camel meat containing 10 CFU, while it was detected in meat containing 10 and 103 bacterial CFU in counts of 1.3 x 104 and 1 x 105 /g of the examined minced meat sample, respectively. Similar results of isolation were obtained after 4 days of chilling where S. typhimurium could be only isolated from meat containing 103 and 105 CFU in counts of 3 x 105 and 1.2 x 106 /g of the examined sample. It was observed that the count of the recovered salmonella CFU in minced camel meat was increased by increasing chilling time in meat containing 103 or 105 salmonella CFU. While, S. typhimurium could not be detected from inoculated camel minced meat containing either 10 and 103 bacterial CFU after one and four months of freezing at – 18 oC, respectively. Meanwhile, S. typhimurium was only detected in minced meat containing 103 bacterial CFU in count of 100/g after one week of freezing. Also, the inoculated S. typhimurium strain could be detected from camel minced meat containing 105 bacterial CFU after one week, one and four months of freezing at – 18 oC in counts of 25 x 103 , 18 x 103 and 16 x 103 /g of the examined sample, respectively. It was observed that the count of the recovered salmonella CFU in minced camel meat was relatively decreased by increasing freezing time in meat containing 105 salmonella CFU and the inoculated strain could not be detected after one and two months of freezing in minced meat containing 103 CFU. iii Concerning the detection of S. typhimurium in contaminated camel meat using salmonella-Singlepath kit . S. typhimurium was detected in all contaminated camel meat samples with different bacterial counts (10, 103 and 105 ) bacterial colony forming units (CFU). Also, S. typhimurium was detected by its all concentration at zero time (directly after inoculation), 2 days refrigeration, 4 days refrigeration, 1 week freezing, one months freezing, and 4 months freezing. Meanwhile, non-inoculated meat showed negative results. The results of detection of S. typhimurium in contaminated camel meat using VIT-salmonella kit showed that S. typhimurium was detected in all contaminated camel meat samples with different bacterial counts (10, 103 and 105 ) bacterial colony forming units (CFU). Also, S. typhimurium was detected by its all concentration at zero time (directly after inoculation), 2 days chilling, 4 days chilling, 1 week freezing, one months freezing, and 4 months freezing. Meanwhile, non-inoculated meat showed negative results. Detection of S. typhimurium in contaminated camel meat using polymerase chain reaction revealed that S. typhimurium DNA was detected in all contaminated camel meat samples with different bacterial counts (10, 103 and 105 ) bacterial colony forming units (CFU). Also, S. typhimurium DNA was detected by its all concentration at zero time (directly after inoculation), 2 days refrigeration, 4 days refrigeration, 1 week freezing, one months freezing, and 4 months freezing. Meanwhile, non-inoculated meat showed negative results. PCR positive products were obtained from samples taken from lactose broth culture of the contaminated camel meat i. e. after 24 hours. Positive results were indicated by obtaining the salmonella-specific PCR product (284 bp) using the specific primers. iv It can be concluded that the sensitivity of isolation decreased when the bacterial load decreased in the meat. On the other hand, GLISA Singlepath salmonella kit, VIT-Salmonella kit and PCR were more sensitive than conventional isolation as all of them could detect salmonella in camel meat with different bacterial loads and kept by chilling or freezing. However, PCR was able to detect salmonella in the pre-enrichment culture after 24 hours while Singlepath salmonella and VIT-Salmonella kits detected salmonella in the enrichment culture after 48 hours.