Biography: Douglas E. Cosby
Statement of the Problem: No single enrichment broth or temperature is used consistently throughout the research, regulatory or industry laboratories for the detection of Salmonella. This lack of a single methodology leads to confusion and possible bias both for and against Salmonella serotypes. The objective was to evaluate four selective enrichment broths [selenite cystine (SC), tetrathionate Hajna (TT), GN broth (GN) and Rappaport-Vassialiadis (RV)] at two temperatures (37℃ and 42℃) to determine the best for growth of four Salmonella serovars.
Methodology: Four Salmonella serovars [Enteritidis (SE), Heidelberg (SH), Kentucky (SK) and Typhimurium (ST)] were
inoculated individually (101 cfu) into duplicate tubes containing 10 mL of each of four enrichment broths at each temperature. After overnight enrichment, serial dilutions were plated onto brilliant green sulfa (BGS) agar plates for enumeration. Counts were made and recorded after 24 h incubation. Three replicates were conducted.
Conclusion & Significance: All four enrichment broths were significantly (P<0.05) more effective for recovery at 37℃ than at 42℃. When incubated at 37℃, recovery in SC was log10 4.4, 7.7, 7.6 and 7.5 for SE, SH, SK and ST, respectively; recovery in GN was log10 8.2, 8.4, 8.5 and 8.4 for SE, SH, SK and ST, respectively; recovery in TT was log10 6.9, 7.6, 8.1, and 7.3 for SE, SH, SK and ST, respectively; and recovery in RV was log10 8.1, 8.2, 8.2 and 7.9 for SE, SH, SK and ST respectively. At 37℃, significant differences were observed between TT/GN; TT/RV; SC/GN; and SC/RV and none observed between SC/TT or GN/RV. At 42℃, no significant difference was observed between three broths (SC, TT and RV) when Salmonella was recovered. Recovery of Salmonella strains can unintentionally be biased by on the incubation temperature or the enrichment broth selected simply because of laboratory preference or regulatory protocol.