Abstract

Background:  A non-destructive method such as a cloacal swab is very important to the poultry industry because it allows the breeder companies to determine if Salmonella is present in the valuable breeder chicks without the necessity of sacrificing any birds. 

Objective:  To evaluate a nondestructive procedure to detect the presence of Salmonella in valuable breeder chicks. 

Methodology:  Day-of-age broiler chicks from a commercial hatchery were orally gavaged with a marker strain of Salmonella Typhimurium (ST), and then placed in isolation units with drinkers, mesh flooring and feeders. At 7 and 14 days, 10 birds were cloacally swabbed (shallow and deep). Swabs were inserted 1 cm (shallow) into the cloaca and 2 cm deep (into the colon).  Each swab was immersed in 5.0 ml of buffered peptone water (BPW), then streaked onto brilliant green sulfa agar plates with 200 ppm nalidixic acid (BGSN). Tubes and plates were incubated 24 h at 370C. When plates were negative, the pre-enriched tubes were vortexed and once again plated onto BGSN. The procedure for the frozen swabs was the same, except that 15% glycerol was added to the BPW and then frozen at -20C for 14 days. They were then thawed and analyzed as above. After swabbing, the chicks were sacrificed. The ceca was removed, placed in a stomacher bag, and macerated with a rubber mallet. Enumeration of the marker strain followed. 

Results:  When the level of the marker ST was greater than 106 CFU/g of ceca and cecal contents, detection with either shallow or deep swab was the same 94% (47/50). When the level of ST was less than 106 CFU/g, detection with either method fell to 63.3% (38/60). After 14 days freezing the swabs at -20C, the shallow method detected 50% (32/64), and the deep swab detected 64% (41/64).

Conclusion:  Regardless of the level of ST in the ceca, there was no difference in the detection rate between the shallow or the deep swab. Even when using low inoculum levels, a high rate of ST colonization in the ceca was reached, allowing both the shallow and deep swabs to almost all be positive at 7 days of age. Since the poultry companies may not be able to analyze the swab results on the same day as collection, we decided to evaluate if freezing the swabs for as long as 14 days would have any adverse effect on the recovery of ST. Freezing did not seem to make a difference in sensitivity. For frozen swabs the deep colonal swab yielded better results than the shallow swab. So you can freeze if you must, but doing the analysis the same day as the swabbing (unfrozen) techniques seems to be slightly more reliable.