Cryopreservation of Salmonella enterica in porcine fecal samples

Abstract

Fecal samples are normally tested for Salmonella soon after collection because storage at any temperature, mcluding refrigeration or freezmg, can reduce detect1on. To evaluate several cryopreservatlon techniques, autoclaved porcine feces with and without additives were inoculated with 103 CFU S. Derby (UW -9)/g with autoclaved feces pnor to freezing. The mixtures and % of the CFU inoculum that was recovered was as follows: Feces only, 11 %; 50% feces plus 50% glycerol, 45%, 25% feces, 50% glycerol, 25% tetrathionate broth, 63%, 25% feces, 50% glycerol, 25% buffered peptone water (BPW), 66%; 50% feces, 50% glycyceroi/Tris buffer, 58%; 50 % feces, 50% BPW, 30%. When fresh (not autoclaved) feces were used, inoculated with a nalidixic acid resistant S Typhimurium (WI-73), 4% of the inoculum was recovered from undiluted frozen feces wh1le the add1tlon of 50% BPW before freezmg mcreased recovery to 27% In a 2x2x2 fully randomized block factorial study, fresh fecal samples were inoculated with 103 CFU UW-73 /g feces. These samples were processed undiluted or with the addition of glycerol and/or BPW before freezmg. The addition of 20%-40% of each compound simultaneously resulted 1n mcreased recovery of UW-73 when compared with undiluted fecal samples (p<O 05). The addition of 40% BPW and 20% glycerol in combination resulted in the highest recovery (83%). It 1s concluded that the addition of 20-40% glycerol and 20-40% BPW before freezmg may be effective cryopreservat1ves for Salmonella m porc1ne fecal samples, allowing for simplified and more economical laboratory enumeration