An extracellular protease, which previously has been found to correlate with the appearance of bleblike evaginations on the cell wall of Pseudomonas fragi ATCC 4973, was purified 38-fold by ammonium sulfate precipitation and Sephadex chromatography to yield a single band by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Polyclonal rabbit antiserum raised against the purified enzyme had an enzyme-linked immunosorbent assay titer of 4 x 107. The peroxidase antiperoxidase method was used to localize the neutral protease in P. fragi at the ultrastructural level. Electron microscopy of cell sections of this organism revealed that high concentrations of positive immunoperoxidase reaction product were located near the cell wall, whereas control sections stained with preimmune or heterologous serum did not show similar deposits to be present. These results are consistent with the hypothesis that blebs appearing on P. fragi contain high concentrations of neutral protease.

No abstract

Pseudomonas fragi is one of several pseudomonads known to produce proteolytic enzymes. During growth of P. fragi in brain heart infusion broth (BHI) at 10°C, the bacterial population increased from 107 to over 1010 CFU/ml after 130 h, with a concurrent increase in pH from 7.4 to 8.5. Maximal extracellular protease activity occurred after 60 to 72 h. Ultrastructural examination of cells grown in BHI showed the presence of bleb-like evaginations of the cell wall. Similar structures were not detected when P. fragi was grown in Koser citrate broth, a medium which was unsuitable for supporting protease production by P. fragi.

Microbiological quality, as estimated from temperature and mesophilic aerobic plate counts of beef loaf, instant mashed potatoes and frozen peas, was determined at point of service to compare conduction, convection and microwave reheating in a hospital-type cook/chill foodservice system. Although reheated products were similar microbiologically (mean log CFU/g = 2.3 to 3.4), internal end temperatures, even under laboratory-controlled conditions, did not meet FDA recommended standards (≥74°C) for reheated products in up to 83% of situations observed. Such data demonstrate the potential for foodborne illness in hospital cook/chill foodservice systems.

Precooked slices of beef loaf, peas and potatoes were reheated individually or together as a meal by conduction, convection or microwave radiation. At point of service, products were compared for visual appeal and other sensory qualities by 12 taste panelists during four laboratory replications of a simulated hospital cook/chill foodservice system. Time and temperature measurements of food handling as well as moisture content and Hunter Color values of experimental products were also monitored. Best food temperature control was obtained after microwave reheating. When the experimental products were reheated as meals, panelists rated the food prepared in the conduction subsystem highest for sensory quality. Although differences in moisture of slices of beef loaf individually reheated were undetected by panelists, objective measurements generally indicated that microwave reheated products had the lowest moisture content. Under full load conditions, conduction reheat is recommended to optimize visual appeal and other sensory qualities of meals served in hospital cook/chill foodservice systems.