Submitted to: Journal of Applied Microbiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/15/2000
Publication Date: 5/15/2000
Citation: Davies, P.R., Turkson, P.K., Funk, J.A., Nichols, M.A., Ladely, S.R., Cray, P.J. 2000. Comparison of methods for isolating salmonella bacteria from faeces of naturally infected pigs. Journal of Applied Microbiology. 89: 169-177. Interpretive Summary: Bacteriologic culture is often the only means available to isolate and identify bacterial strains of interest. However, there are many methods available and results often differ between methods making comparisons difficult. We compared 2 different methods that are routinely used in the 2 laboratories. The media, temperature and time differed. We determined that overall both methods were comparable. However, the amount of sample as well as the temperature and time of incubation can influence the outcome. These data indicate that laboratories should consider comparing their methods to determine the sensitivity of their methods. Optimization of bacteriology culture methods is possible.
Technical Abstract: We conducted a series of 1 experiments on fecal samples collected from commercial swine farms to evaluate the effects of some methodologic factors on detection of Salmonella. The studies included comparison of two enrichment protocols used in our respective laboratories (Method 1: 10 g feces, buffered peptone water (BPW) preenrichment - selective enrichment in Rappaport Vassiliadis (RV) broth; Method 2 : ~1 g feces, primary enrichments in tetrathionate and Hajna GN broths/secondary enrichment in RV broth) and evaluation of enrichment temperatures in RV broth (37C vs 42C) and delayed secondary enrichment. Direct comparison of Method 1 and Method 2 indicated comparable results, although Method 2 yielded significantly better detection with fecal samples of equal weight. Enrichment in RV at 42C was superior to 37C, particularly for samples that were preenriched in BPW. Delayed secondary enrichment significantly increased detection of Salmonella from swine fees. These results highlight the imperfect sensitivity of culture methods and the need for researchers to consider the sensitivity of bacteriologic methods in the design and interpretation of epidemiologic studies based on fecal culture.