Prevalence of Salmonella in broiler flocks: effect of litter water activity, house construction, and watering devices.

Litter samples from 24 flocks of broilers and four flocks of broiler breeders were evaluated for Salmonella contamination, water activity (Aw), and total moisture content (MC). The drag swab (DS) monitoring system was used to collect samples to detect Salmonella contamination. Simultaneously, representative samples of the uppermost surfaces of dry (loose) litter and wet (caked) litter were collected for Aw and MC analyses. On dry litter surfaces, high Aw values (0.90-0.95) were associated with flocks Salmonella-positive using DS; low Aw values (0.79-0.84) were associated with flocks Salmonella-negative by DS; and transition Aw values (0.85-0.89) were associated with flocks having an increased risk for the presence of Salmonella. The association of high Aw values with Salmonella risk was not observed for wet (caked) litter surfaces. Observations suggest that limiting Aw in the litter base of broiler houses may create a less favorable environment for the multiplication of Salmonella and thus a more hygienic environment for broiler production.

Evaluation of possible alternatives to double-strength skim milk used to saturate drag swabs for Salmonella detection.

The drag-swab Salmonella screening technique was evaluated using less expensive alternatives to double-strength skim milk (2 x SM) as a saturating medium for drag swabs. Ten pre-determined Salmonella-positive poultry houses were studied. In the first phase, Salmonella screening efficiency of drag swabs impregnated with 2 x SM and commercially available canned Carnation evaporated skim milk (CESM) were compared. Results showed CESM to be a less efficient alternative. In the second phase of the study, the Salmonella screening efficiency of drag swabs impregnated with 2% buffered peptone water (BPW), physiological saline (PS), and distilled water (DW) were evaluated along with an unimpregnated drag swab (dry drag swab) (DD) as possible alternatives to 2 x SM. The efficiency of Salmonella detection using various impregnation treatments were in the following order: 2 x SM > PS > BPW > DW > DD.

Correlation of water activity and other environmental conditions with repeated detection of Salmonella contamination on poultry farms.

Three flocks on 13 different broiler farms were monitored for Salmonella over three consecutive growout periods using the drag swab (DS) technique. One house was consistently negative for Salmonella contamination (7.7%); four houses were consistently positive (30.8%); and eight houses (61.5%) alternated between either a DS Salmonella-negative or -positive status. Simultaneously, numerous environmental parameters of the litter surface were measured, including water activity (Aw), ammonia, temperature, pH, moisture content (MC), ash content, and volatile solids. Analysis of these data as a corollary to either Salmonella-negative or -positive DS results revealed significant correlation coefficients for some of the parameters, especially Aw. The results suggest that there should be further exploration of remedial intervention based on control of some of the physical features of litter (e.g., controlling litter Aw and possibly MC and pH levels) in poultry houses.

The effect of exposure, storage times, and types of holding media on the drag-swab monitoring technique for Salmonella.

Four maintenance media were compared for the preservation of the sensitivity of drag swabs and to assess the survival of Salmonella spp. on drag swabs at reduced temperatures. The effects of Difco double-strength skim milk (2 x SM), 2% buffered peptone water (BPW), a modified liquid Cary-Blair transport medium (LCB), and lactose broth holding medium were compared, as were storage periods of various lengths. The results with enzyme-linked immunosorbent antigen capture assay and highly selective plating media detection systems showed that 2 x SM had the highest level of recovery of salmonellae after prolonged storage, both under refrigeration at 4 C for 3 days and under frozen conditions of -15 C for 2 weeks.