MINIATURIZED MOST PROBABLE NUMBER AND ENRICHMENT SEROLOGY TECHNIQUE FOR THE ENUMERATION OF SALMONELLA SPP. ON POULTRY CARCASSES

The ability of two 8-tube most probable number (MPN) techniques to qua ntitatively recover Salmonella spp. from 26 fresh, naturally contamina ted chicken skin samples was compared. Individual macerated skin sampl es were tested in parallel using a traditional (tMPN) and a miniaturiz ed (mMPN) analytical procedure. In the tMPN assay, replicate aqueous p ortions from each macerated sample were preenriched individually in bu ffered peptone water, selectively enriched in Muller-Kauffmann tetrath ionate brilliant green broth (MKTBG), and plated on Rambach agar. Each MKTBG was also postenriched in M Broth, and the resulting postenrichm ent culture screened for the presence of Salmonella cells by enrichmen t serology (ES). Although a similar analytical approach was used in th e mMPN assay, it differed from the tMPN in the use of smaller test vol umes dispensed in microplates, and on a sedimented portion of skin mac erate as test material. Of the 26 Salmonella-contaminated samples exam ined in this study, the tMPN coupled to Rambach agar or ES identified 23 and 24 positive samples, respectively. Under homologous conditions, the mMPN detected all 26 positive Salmonella contaminated samples. Th e most probable numbers in 100-g skin samples analyzed by the tMPN ran ged from 18/100 g to 9,530,000/100 g with a median value of 570/100 g. Levels of contamination by the mMPN procedure ranged from 90/100 g to 556,000/100 g with a median value of 1,200/100 g. Statistical analysi s of experimental data underlined the equivalence of the tMPN and the mMPN procedures and nonequivalence of the Rambach plating and ES condi tions. It is suggested that the microplate mMPN coupled to ES offers a reliable and more cost-effective analytical approach for the quantita tive recovery of Salmonella on broiler carcasses.