Cockroaches As Vectors of Salmonella : Laboratory and Field Trials

Studies were conducted to determine if individual American, German, or Oriental cockroaches could acquire a naladixic acid-resistant strain of Salmonella typhimurium from an infected food source and then infect noncontaminated colony members, food, and water. Cockroaches, food, and water were sampled after 24, 48, 72, and 96 h and assayed for S. typhimurium . Cockroaches, food, and water samples were positive for S. typhimurium at each 24-h sampling period. American and Oriental cockroaches were contaminated twice as often as German cockroaches. In a second study, the incidence of S. typhimurium cross-contamination between 1 or 5 infected cockroaches and 10 noninfected cockroaches was followed over 4 d. The highest frequency of cross-contamination occurred within 24 h and declined thereafter. Water sites were heavily contaminated throughout the 4-d test period. In a third study, the potential for contamination of table eggs via S. typhimurium -infected cockroaches was evaluated. Whole egg rinses of eggs exposed for 24 h to infected cockroaches contained a minimum of 75 S. typhimurium cells per egg. In a final study, American cockroaches captured from a commercial poultry feed mill and hatchery were assayed for salmonellae using an ELISA method. Five of 45 feed mill and eight of 45 hatchery cockroach samples were confirmed positive for salmonellae. These findings clearly suggest that cockroaches are capable of acquiring and infecting other cockroaches and objects, therefore implicating them as potential vectors of foodborne pathogens in poultry production and processing facilities.