Purpose : To evaluate the behavior of Listeria monocytogenes and Salmonella spp. strains in sponges containing homogenates of chicken, mayonnaise and yogurt with and without detergent, after consecutive treatments with detergent or plain water simulating the household use.
Methods : Three strains of Listeria monocytogenes and Salmonella Typhimurium or Enteritidis were inoculated (104 - 105 CFU/ml) in homogenate of yogurt (5% w/v), mayonnaise (5% w/v) or chicken (1% w/v) of pH 4.5, 4.5 and 6.5, respectively. Then, aliquots (3 ml) of a homogenate were poured in commercial sponges and incubated at 20°C for up to 7 days. Inoculated sponges were treated with a commercial detergent (1% w/v) which proved to be the most effective among 4 detergents with different composition. Sponges were dipped and squeezed in tap water containing detergent (1% w/v) resulting in the sponge holding 10 ml of liquid. Successive treatments of sponges with water or detergent took place on days 1, 4 and 7 at 20°C.
Results : Both pathogens increased to 2.3 - 2.5 log CFU/g during incubation of sponges in the absence of detergent. After the first treatment with the detergent, L. monocytogenes reduced by 1.7–2.1 log CFU/g and Salmonella by 0.7-1.4 log CFU/g. Consecutive treatments with detergent caused further reductions (0.3-1.3 log CFU/g) within 7 days to those observed on the first day. In contrast, repeated treatments of sponges with water resulted in growth of up to 2.1 logs CFU/g of both microorganisms. Repeated treatments of sponges with detergents delivered 2.3 log CFU/g higher reductions than a single treatment on day 1, followed by storage without further treatments.
Significance : The survival and growth of pathogens in sponges suggest that sponges are critical vehicles of bacterial contamination in household environments.