Short (6 h) enrichment under five different selective conditions adversely affected the isolation of Salmonella from pre-enriched samples of naturally contaminated foods. Of the 109 high moisture and 18 low moisture foods found to contain salmonellae following conventional (24 h) enrichment, combined results of the abbreviated enrichment procedures identified only 99 (90.8%) and 13 (72.2%) contaminated samples, respectively. The productivities of tetrathionate brilliant green (TBG 43 ) and Muller-Kauffman tetrathionate (MKTBG 43 ) broths consistently exceeded that obtained with the modified Rappaport (RV 43 ), tetrathionate brilliant green (TBG 35 ), and selenite cystine (SC 35 ) media after 6 and 24 h of incubation. Semi-quantitative analyses of growth under all enrichment conditions indicated that short (6 h) enrichment negatively affected method sensitivity through reduced numbers of Salmonella colonies and heavy growth of nonsalmonellae on bismuth sulfite (BSA) and brilliant green sulfa (BGS) plating media. These findings raise concerns on the dependability of commercial diagnostic schemes that incorporate abbreviated (6 h) enrichment in TBG 35 and/or SC 35 in their analytical protocol.
One hundred and fifty-three samples of tofu, related products, and environmental samples comprising 346 sample units were collected from 14 manufacturers across Canada. They were analyzed for coliforms, Salmonella , Yersinia , Staphylococcus aureus , and psychrotrophs. Although S. aureus counts were generally less than 250 cells per g and Salmonella was not detected, levels of psychrotrophs exceeded 10 6 per g in more than 45% of finished tofu and okara samples, and levels of coliforms exceeded 10 3 per g in more than 35% of these samples. Yersinia enterocolitica was also isolated from four samples of finished tofu.
Polymyxin B sulfate (PB) added to salt broth (SB) for selective enrichment of Vibrio parahaemolyticus was destroyed by autoclaving. Losses were about 49% at pH 7.4 and 97% at pH 8.8. Additionally, certain raw fish when added to salt polymyxin broth (SPB) caused a loss of PB, probably due to adsorption; vertebrate fish (red snapper and herring) caused a loss of about 72% of PB, but shellfish (oyster and clam) did not cause any loss.