Flow characteristics of red cell containing fluids through pores. The effect of filter plugging, a mathematical model.

A mathematical model was developed that describes the effects of filter plugging on flow through 3 micron pore polycarbonate filters as a function of time, pressure, and cell concentration, both under stirring and nonstirring conditions. The mathematical constants for the model were derived from experimental data generated with a filtration apparatus, and were tested by using various concentrations of cells that are able to plug filter pores. A computer simulation program was written to test the model over a wide range of nonfilterable cell concentrations.

Thermotolerance of heat-shocked Listeria monocytogenes in milk exposed to high-temperature, short-time pasteurization.

The effect of prior heat shock (48 degrees C for 15 min) on the thermotolerance of Listeria monocytogenes at the minimal high-temperature, short-time (71.7 degrees C for 15 s) parameters required by the Pasteurized Milk Ordinance was examined. The mean D71.7 degrees C value for heat-shocked L. monocytogenes was 4.6 +/- 0.5 s (control D = 3.0 +/- 1.0 s); the ratio of D to control D was 1.5. The increased thermotolerance of heat-shocked Listeria cells was not significant and appeared unlikely to have practical implications, in terms of risk assessment, for the safety of pasteurized milk.

Thermotolerance of Listeria monocytogenes and Salmonella typhimurium after sublethal heat shock.

The effect of prior heat shock on thermotolerance of Listeria monocytogenes and Salmonella typhimurium in broth culture was determined. Bacteria were grown at the permissive temperature of 35 degrees C, sublethally heated at 35 (control), 42, 48, and 52 degrees C (nonpermissive control) for various times, and inactivated at either 57.8 or 52 degrees C. The induction of increased thermotolerance by heat shock, although consistent within each experiment, was generally not significant for L. monocytogenes; the increase was significant for S. typhimurium. Temperature shift experiments with L. monocytogenes suggested that induced thermotolerance was not long lived unless the shock temperature was maintained.

Comparative recovery of uninjured and heat-injured Listeria monocytogenes cells from bovine milk.

The standard selective enrichment protocols of the Food and Drug Administration (FDA) and U.S. Department of Agriculture (USDA) were compared with an experimental nonselective broth enrichment (NSB) protocol and variations of the standard cold-enrichment (CE) protocol for the recovery of heat-injured Listeria monocytogenes. Bacterial cells (10(7)/ml) were suspended in sterile milk and heated at 71.7 degrees C in a slug-flow heat exchanger for holding times ranging from 1 to 30 s. Surviving cells were determined (50% endpoint) by the given protocols, and the following D values were obtained: NSB, D = 2.0 +/- 0.5 s; FDA, D = 1.4 +/- 0.3 s; USDA, D = 0.6 +/- 0.2 s; CE, D less than or equal to 1.2 s. The respective direct-plating media used in these enrichments were also analyzed for recovery, and the following D values were calculated from the enumeration of surviving cells; NSB, D = 2.7 +/- 0.8 s; FDA, D = 1.3 +/- 0.4 s; USDA, D = 0.7 +/- 0.2 s. The low levels of heat-injured L. monocytogenes cells which were detected at inactivation endpoints on the optimal nonselective media (25 degrees C for 7 days) failed to recover and multiply during experimental CEs (4 degrees C for 28 days). Initial inactivation experiments in which raw whole milk was used as the heating menstruum gave much lower recoveries with all protocols. The detectable limits for uninjured cells that were suspended in raw milk were similar (0.35 to 3.2 cells per ml) for the standard CE, FDA, and USDA protocols.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemagglutination and adhesiveness of epidemiologically distinct strains of Vibrio parahaemolyticus.

Twelve strains of Vibrio parahaemolyticus from four epidemiologically distinct groups were examined for their ability to hemagglutinate human, bovine, chicken, guinea pig, and rabbit erythrocytes and to adhere to human buccal mucosal epithelial cells in the presence and absence of mannose. Four of six Kanagawa-positive but none of six Kanagawa-negative strains showed mannose-sensitive hemagglutination with erythrocytes of rabbits and of one or more additional species. Mannose-resistant hemagglutination was shown by one strain in each group with no apparent relationship to strain source or hemolytic capability. All strains adhered to human buccal mucosal cells, with but a single strain showing significant difference in adherence at the alpha = 0.05 level. The adherence pattern had no relationship to the four epidemiological groups. Although adhesive processes may well be involved in disease caused by V. parahaemolyticus, our results do not support a role for adherence as a predictor of pathogenicity.

Thermal resistance of Bacillus subtilis var. niger in a closed system.

The heat resistance of Bacillus subtilis var. niger has been measured from 85 to 125 degrees C using moisture levels of percent relative humidity (%RH) less than or equal to 0.001 to 100 in a closed system. Five curves have been presented to characterize the thermal destruction, using thermal death times defined as F values at a given combination of three moisture and temperature conditions. Reductions of 99.99% (4-log10 cycles) of the initial population were estimated for the three moisture conditions. At 110 degrees C, the expected time for a 4-log10 reduction was 1.1 h at %RH = 100, 3.1 h at %RH less than or equal to 0.1 and 54 h at %RH = 10.7. Goodness-of-fit tests to examine the adequacy of three polynomial models failed to indicate a trend. The linear model (from which estimates of D are obtained) was satisfactory for estimating the thermal death times (%RH less than or equal to 0.1) in the plate count range. The estimates based on observed thermal death times and D values for the %RH = 100 diverged so that D values generally gave a more conservative estimate over the temperature range 90 to 125 degrees C. Estimates of ZF and ZL ranged from 32.1 to 58.3 degrees C for the %RH less than or equal to 0.1 and 100. A ZD value of 30.0 was obtained for data observed at %RH less than or equal to 0.1. The ZF results were obtained from plotting observed log times to achieve a 99.99% reduction in the initial population versus temperature. Estimates of ZL and ZD were obtained by using linear estimates of L100 approximately equal to 4D and D values in a similar plot.

Thermal resistance of intracellular Listeria monocytogenes cells suspended in raw bovine milk.

The thermal resistance of Listeria monocytogenes associated with a milk-borne outbreak of listeriosis was determined in parallel experiments by using freely suspended bacteria and bacteria internalized by phagocytes. The latter inoculum was generated by an in vitro phagocytosis reaction with immune-antigen-elicited murine peritoneal phagocytes. The heat suspension medium was raw whole bovine milk. Both suspensions were heated at temperatures ranging from 52.2 to 71.7 degrees C for various periods of time. Mean D values for each temperature and condition of heated suspension revealed no significant differences. The extrapolated D71.7 degrees C (161 degrees F) value for bacteria internalized by phagocytes was 1.9 s. Combined tube and slug-flow heat exchanger results yielded an estimated D71.7 degrees C value of 1.6 s for freely suspended bacteria. The intracellular position did not protect L. monocytogenes from thermal inactivation.

Melanogenesis in murine B16 cells exposed to Aeromonas hydrophila cytotoxic enterotoxin.

Specific markers (growth, melanogenesis) of B16 murine melanoma cells in culture were used as indicators of toxin production by Aeromonas hydrophila. Cytotonic enterotoxinlike activity (inhibited growth, raised tyrosinase activity, and melanin accumulation) occurred at cytotoxic end points of purified beta-hemolysin and several culture filtrates. Antihemolysin rabbit serum inhibited this activity. A hemolysin-neutralized culture filtrate concentrate (10X) failed to elevate tyrosinase relative to untreated and cholera toxin treated controls. Similar dilution profiles using Chinese hamster ovary cells showed limited cell extension only at cytotoxic end points with antihemolysin inhibiting this activity. Cytotoxicity of Chinese hamster ovary cells and B16 cells was proportional to hemolytic activity, with B16 cells showing about 100-fold greater sensitivity on a per cell basis. Cell culture cytotoxicity attributed to beta-hemolysin correlated with reactivity in rabbit ileal loop assays. The ADP-ribosyl transferase activity of concentrated (10X) A. hydrophila culture filtrates and fractions thereof was negative. Apparently sublethal doses of A. hydrophila beta-hemolysin can nonspecifically stimulate cyclic adenosine monophosphate mediated events in melanoma and Chinese hamster ovary cell assays, producing lower activities than cholera toxin with shorter lag times.

Thermal inactivation of Listeria monocytogenes within bovine milk phagocytes.

Thermal resistance of intracellular and freely suspended Listeria monocytogenes that was associated with a milkborne outbreak of listeriosis was studied by using the sealed tube and slug flow heat exchanger methods. Test temperatures for the former method were 57.8, 62.8, 66.1, and 68.9 degrees C (136, 145, 151, and 156 degrees F, respectively); whereas those for the latter method were 66.1, 68.9, 71.7, and 74.4 degrees C (151, 156, 161, and 166 degrees F, respectively). The heating menstruum was sterile, whole milk. The intracellular inoculum was generated from an in vitro phagocytosis reaction by using endotoxin-induced bovine milk phagocytes. The phagocyte population consisted of 88% neutrophils, 8% macrophages, and 4% lymphocytes. Neutrophils harbored the majority of intracellular L. monocytogenes. The mean level of infectivity in the phagocyte population was 43%, and there were 26.1 +/- 19.3 bacteria per cell (10(4) viable cells per ml of test milk). Initial bacterial counts for the freely suspended and intracellular experiments (the latter was based on a sonically disrupted sample) were 10(6) L. monocytogenes cells per ml. Heat-stressed bacteria were recovered by direct plating in parallel with recovery from an enrichment broth; both methods gave comparable results. The predicted D62.8 degrees C (145 degrees F) value for intracellular sealed tube studies was 53.8 s (ZD = 5.6 degrees C [10.0 degrees F]), indicating a safe 33.4 D margin of inactivation for vat pasteurization (62.8 degrees C for 30 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Heat resistance of bacillus spores at various relative humidities.

The thermal resistance characteristics of spores from strains of five different Bacillus species were determined in phosphate buffer and at relative humidities ranging from <0.001 to 100% in a closed-can system. Spores tested in the closed-can system showed a marked increase in heat resistance over those in phosphate buffer, with the greatest increases occurring at relative humidities between 1 and 50%. When estimates of the time to reduce the initial spore concentration 99.99% (F value) at eight different relative humidities were plotted against temperature, three different types of heat resistance profiles were obtained, with maximum resistances at relative humidities of 1, 7, and 30%. When the various strains of spores were heated at the relative humidity of their maximum heat resistance, their relative order of heat resistance was different from that seen in buffer. Spores from the soil isolate were most resistant under these conditions (F(121.1) = 99.5 h).

The contribution of assays for lymphocyte capping and creatine kinase to detection of the Becker-type dystrophy trait.

Members of three unrelated families with the mild Becker type of muscular dystrophy were subjected to lymphocyte capping tests and measurements of serum creatine kinase activity. Both tests correctly identified all nine affected males, but only the capping test was abnormal in seven of eight obligate carriers. The number of capped cells in carriers and affected persons with the Becker-type dystrophy was generally intermediate between those observed for individuals with the Duchenne trait and normal controls, thus potentially aiding in the differential diagnosis between the two myopathies. The lack of sensitivity of measurements of serum creatine kinase activity in identifying carriers is further complicated by the difficulty of establishing reliable reference intervals for this enzyme in 204 healthy controls. Detailed directions for the performance of the capping test are presented.