RESISTANCE OF ACID-ADAPTED SALMONELLAE TO ORGANIC-ACID RINSES ON BEEF

Four strains of salmonellae, including three bovine isolates and an AT CC strain, were adapted to growth in acidic conditions by sequential t ransfer in tryptic soy broth with reduced pH values. The cultures were transferred until good growth (approximately log(10)7 CFU/ml) was obt ained within 24 h at 37 degrees C at pH 5.0. Lean beef tissue was inoc ulated by immersion into either the acid-adapted or the homologous par ent strain of each bacterium. The inoculated tissue was rinsed for 10s in 1.5% or 3.0% lactic acid solutions at 23 degrees C or 55 degrees C . Reductions in bacterial populations were compared between the parent and acid-adapted strains to determine if the acid-adapted strains wer e more resistant to the organic acid rinses. Acid-adapted strains had either equal or greater sensitivity to organic acid rinses than their homologous parent strains, indicating that acid adaptation did not res ult in bacteria which were resistant to organic acid rinses. Acid-adap ted strains had significantly lower D-55 degrees C?- values than their homologous parent strains.