Membrane filtration for enumeration of salmonellae from processed broilers.

摘要

A membrane filter (MF) method to rapidly quantify Salmonella for processed postchill broilers was developed. Carcasses were sampled by whole carcass rinse procedure using 100 mL of 0.1% peptone plus 1% Tween 80. Recovered rinse samples were mixed with 10% trypsin at the ratio of 5:1 (v/v) and were incubated at 40 C for 30 min. The entire volume of the enzyme-treated sample was filtered using an ISO-GRID hydrophobic grid membrane filter (HGMF). The filter was placed on xylose lysine desoxycholate agar supplemented with sodium novobiocin (20 ppm) and sodium pyruvate (1%) and was incubated at 42 C. After 24 to 30 hr, Salmonella colonies developing on the filter were counted. Representative positive colonies were biochemically screened and serologically confirmed.;This MF method (100 mL of sample volume utilized for analysis) was compared in sensitivity and accuracy to a conventional cultural standard three-tube most probable number (MPN) procedure (10 mL, 1 mL, 0.1 mL, and 0.01 mL, totaling 34 mL) for artificially contaminated broiler carcasses. The MF method recovered Salmonella from 75% (18/24) of the samples, whereas the standard MPN procedure produced only 50% (12/24) positives. However, Salmonella levels recovered were lower with the MF method than with the standard MPN procedure for samples determined as positive by both methods.;Another comparison was made between the MF method and a modified three-tube MPN procedure in which sensitivity was improved by increasing utilized volumes to 30 mL, 3 mL, 0.3 mL and 0.03 mL. Carcass rinse samples were pooled and inoculated with temperature stressed Salmonella. The MF method was not capable of recovering 100% of inoculated Salmonella from 100 mL of carcass rinse fluid. The modified MPN procedure recovered significantly higher levels of inoculated Salmonella than did the MF method. However, the precision of the MPN procedure was limited.