A total of 396 food samples (ready-to-eat meat and poultry products; shellfish and finfish products; some raw shell and finfish and meat products; salads and coleslaws; baked confectionary) was purchased from local retail outlets and examined for the presence of motile aeromonads. Of the food categories tested, shellfish had the highest incidence, with 66% positive. Vegetable products, luncheon meat, salami, paté, and poultry products had very low incidences, and no motile aeromonads were found in baked confectionary, some of which contained whipped cream. Beef, pork, lamb, sausage, and finfish products had incidences above 20%. Most of the strains isolated were Aeromonas hydrophila. Given the reported distribution, a public health problem may exist if motile aeromonads do cause gastrointestinal disease.

No abstract

The effect of salt (NaCl) on the efficacy of nisin in preventing outgrowth of Bacillus licheniformis spores was determined in Plate Count Agar (PCA). An equivalent liquid medium was used for heat activation. Nisin and salt were added to the heat‐activation medium, the PCA, or both. The spores were extremely sensitive to nisin; outgrowth were completely inhibited in salt‐free media when 10 iu/ml of nisin was present in both the heat‐activation and the growth media or when 100 iu/ml nisin was present in either the heat‐activation and the growth medium. In media supplemented with 1% salt, outgrowth occurred from 1% of spores exposed to 100 iu/ml nisin in either the heat‐activation or the growth medium. A 3% salt supplement was necessary before detectable outgrowth occurred when both the heat‐activation and the growth media contained 100 iu/ml nisin. Salt appears to antagonize the sporicidal action of nisin by interfering with nisin adsorption onto the spore.

The shelf life at 25°C of chub‐packed luncheon meat was inversely related to oxygen (O2) availability within the casing. With fibrous casings that are freely permeable to O2, shelf life was less than 3 d. With plastic casings of low O2 permeability, the shelf life was 7 d when air was trapped in the emulsion during the casing filling process, 14 d when air was not trapped (normal vacuum‐stuffing) and greater than 28 d when vacuum‐stuffed chubs were stored in hydrogen (H2). The initial spoilage bacteria, Bacillus spp., grew only at the surface unless air was trapped in the emulsion when growth occurred throughout the luncheon meat. Bacillus spp. failed to grow on luncheon meat stored under H2. Oxygen availability within the casing determined both the site and rate of microbial spoilage of chub‐packed luncheon meat.

The presence of NaCl in the heating medium provided some protection from lethal heat damage for cells of a Streptococcus faecium strain isolated from luncheon meat whereas the presence of NaNO2 either alone or in addition to NaCl, had no significant effect on cell survival. Subsequent recovery and growth of heat-damaged cells was retarded by the presence of NaCl. When NaNO2 was present in addition to NaCl the inhibitory effect of the latter was reduced. These principal components of the luncheon-meat-cure are apparently opposed in their activities on post-heating recovery and growth of Strep. faecium. Product stability, i.e. duration of the lag before growth occurs, is directly related to the severity of the heat treatment and to the concentration of NaCl in the product. Therefore the resistance of pasteurized chub-packed luncheon meat to streptococcal spoilage during storage at temperatures conducive to microbial growth results from a prolonged heat-induced salt-maintained pre-growth adjustment phase rather than to any inherent inhibitory property of the luncheon meat to the growth of non-heat-damaged Strep. faecium cells.