Lower Viable Counts Research Articles

Effects of Chemical Preservatives on Storage and Nutrient Composition of Soybean Curd

ABSTRACTStorage and nutrient composition of soybean curd in immersion solutions were determined. Chemical preservatives (acetic acid or potassium sorbate + acetic acid) in soybean curd immersion solutions maintained low viable cell counts but had little effect on soybean curd nutritional quality during storage at 4–7°C for 21 days. Thiamin and riboflavin in soybean curd decreased (P<0.05) during storage, representing leaching of the vitamins into immersion solutions. After 14 days of storage, soybean curd protein decreased and carbohydrate increased (P<0.05). Decreases (P<0.05) in proline and arginine occurred following 14 days of storage, but no losses were found in remaining amino acids.

The role of H 2O 2 and the lactoperoxidaseSCN −H 2O 2 system on the interaction between two bacteria originating from human dental plaque, Streptococcus rattus (mutans) BHT and Streptococcus mitior LPA-1, grown on human teeth in an artificial mouth

Teeth were inoculated with either the organisms separately or with a freshly-prepared mixture of both. The apparatus was swept with 5 per cent ( v v ) CO 2 in either air or N 2, and incubated for 90 h. A nutrient supplement containing 1 per cent ( w v ) glucose was supplied for 1 h in every 6 h. Both organisms achieved similar numbers when grown aerobically in pure culture, yet in mixed culture there was pronounced inhibition of BHT ( p < 0.001). When the synthetic saliva was supplemented with catalase the strain BHT count in mixed culture was much higher ( p < 0.001). It was concluded, therefore, that the strain LPA-1 produced inhibitory levels of hydrogen peroxide (H 2O 2) on the tooth surface under aerobic conditions. This was supported by finding that a lower viable count of LPA-1 in pure culture was attained when lactoperoxidase (LPO) was included in the saliva ( p < 0.005), as all components of the LPOSCNH 2O 2 system were presumably present. With the N 2CO 2 mixture, conditions were not strictly anaerobic and both catalase and LPO increased all viable counts. Under these conditions, therefore, when H 2O 2 was limiting, LPO protected bacteria against its bactericidal effect.

Ciprofloxacin treatment of systemic salmonella infection in sensitive and resistance mice.

Five days therapy with ciprofloxacin (10 mg/kg bd) starting on day 6 after infection with Salmonella typhimurium, significantly reduced mortality in A/J and CBA mice. In CBA mice ciprofloxacin therapy also resulted in significantly lower viable counts of Salm. typhimurium in the livers and spleens of surviving mice at day 36 than was found in untreated mice or those given chloramphenicol. Ciprofloxacin failed to prevent fatal Salm. typhimurium disease in the majority of Balb/C mice, a strain that has no natural immunity to salmonella infection. Death was delayed in ciprofloxacin-treated mice and ciprofloxacin did control the multiplication of salmonellae in liver and spleen within 3 days of commencement.

Evaluation of Commercial Soybean Inoculants from South Carolina and Georgia1

AbstractSince poor quality inoculants could be one of the factors responsible for nodulation failures in soybeans [Glycine max (L.) Merr.], 93 planter‐box inocultants from commercial retail sources in South Carolina and Georgia were evaluated for numbers of viable Rhizobium japonicum on yeast extract mannitol agar. Spread plates were counted after incubation for 7 days at 28 C Two sub‐samples from each commercial inocultant were evaluated. Viable rhizobial counts ranged from 6.9 × 109 to ≤ 1.0 × 103/g of inoculant. Statistical differences were detected among brands. Inoculants which contained a fungicide and/or Mo were consistently and significantly lower in viable rhizobia than other brands. The low viable rhizobial counts were also reflected in poor nodulation of soybean roots under greenhouse conditions. A highly significant correlation was obtained between the log of viable rhizobia and the number of nodules per plant for 27 inoculants. Plate counts provided a relatively rapid and inexpensive method to assess the quality of commercial inoculants.

EFFECT OF PREPROCESS HOLDING ON THE QUALITY OF CANNED MAINE SARDINES

ABSTRACTThe effect of preprocess holding conditions (3 and 12% brine at 7.2 and 0.6°C) on the quality of canned sardines (Clupea harengus) was examined. The sardines appeared to have a relatively short shelf life and had to be canned within 36 hr when lightly salted (3% brine) and held at 7.2°C. At a lower temperature (0.6°C) and a higher salt concentration (12% brine) the sardines could be held up to 3 days. Low viable bacterial counts detected during storage experiments indicated spoilage not to be primarily due to bacterial activity. Sensory evaluation of the raw sardines could not be used with any accuracy to predict quality of the canned product, because raw sardines, which were still considered acceptable before canning, resulted in an unacceptable product. Of the objective quality tests performed on raw sardines (TMA, TBA, tyrosine and pH) only TMA‐N content appeared to possess high accuracy (P &lt; 0.001) in predicting quality of the canned products.

Minimal medium recovery of heated Salmonella typhimurium LT2.

SUMMARY: Exponential phase Salmonella typhimurium lt2, S. thompson and S. heidelberg grown in a glucose-salts medium (M-9), harvested at 37°C and heat-treated at 50°C exhibit a higher recovery on M-9 agar than on Trypticase Soy agar with yeast extract. This phenomenon is analogous to minimal medium recovery of irradiated bacteria. Supplementation of M-9 agar with yeast extract or Casamino acids resulted in lower viable counts of heat-treated bacteria than on M-9 agar alone. Heat-treated bacteria incubated at 37°C in M-9 broth or distilled water recovered their ability to grow on TSY agar. This recovery is inhibited by hydroxyurea.

The immunity conferred by effective BCG and vole bacillus vaccines, in relation to individual variations in induced tuberculin sensitivity and to technical variations in the vaccines

Summary An analysis of the ten-year incidence of tuberculosis in various subgroups of participants in the Medical Research Council trial of tuberculosis vaccines has confirmed that the (liquid) BCG and vole bacillus vaccines used were highly effective in preventing tuberculosis. The percentage efficacy of the BCG vaccine (Danish substrain) was 80%, and of the vole bacillus vaccines (four substrains) was 74%, 91%, 78% and 86% respectively. The immunity conferred by the BCG vaccine did not depend on the degree of tuberculin sensitivity induced in the individual, which varied widely even though the average level was high. The immunity conferred by the vole bacillus vaccines also did not depend on the degree of tuberculin sensitivity induced in the individual; this conclusion held equally for substrain I (which induced a low average level of sensitivity) and for substrains 2 to 4 (which induced much higher average levels of sensitivity, similar to that induced by BCG vaccine). The average level of tuberculin sensitivity induced by the BCG vaccine was greater for the batches with higher viable counts than for those with lower viable counts, but there was no definite association of the protective efficacy with viable count. The average level of tuberculin sensitivity induced by the BCG vaccine increased with two successive improvements in manufacturing and issuing technique, but protective efficacy was not definitely influenced thereby. The average level of tuberculin sensitivity induced by substrain 1 of the vole bacillus vaccine was greater after an increase in opacity standard (but still remained well below the level induced by substrains 2 to 4). The protective efficacy was not definitely influenced. It is concluded that with highly effective tuberculosis vaccines, the degree of protection conferred on the individual is independent of the degree of tuberculin skin sensitivity induced in that individual by the vaccination. Moreover, in this study technical variations between the various batches of vaccine, within the normal production range, affected the average level of induced tuberculin sensitivity, but did not have an important influence on the protective efficacy of the vaccine.

Pertussis Immunisation—Additional Factors Governing the Potency for Mice of Phase I Vaccines

Summary Under the conditions of these experiments, fluid cultures of H. pertussis have proved less virulent for mice than B-G. cultures. As on B-G. medium (Gray 1946) mouse virulence in fluid medium decreases with increasing physiological age, though less rapidly than on B-G. medium. Vaccines made from fluid cultures have proved less potent for mice than B-G. vaccines. When cultures of more than 72 hours' incubation are used for vaccine production, they are of little value as immunising agents. When fluid cultures are agitated continuously during the incubation, the yield is greatly increased. Marked alterations occur, however, in viable counts, in virulence and in immunising potency. The effects on potency are inconstant and not yet completely understood. The ratio of viable to total counts in standardised suspensions from solid or fluid cultures bears no constant relationship to either virulence by the intranasal route, or to immunsiing potency. An observation, intriguing in the light of current concepts of growth dynamics, was the common occurrence of lower viable counts at 48 hours than at either 24 hours or 72 hours in suspensions standardised to the same density. There appears to be little to choose between phenol, formalin, merthiolate and mild heat in producing H. pertussis vaccine. There is no evidence of autolytic loss of antigenic potency over a period of three months' storage in phenolised vaccine. No more efficient vaccine for mice, under the experimental conditions employed, has yet been evolved than one prepared from a 24 hr culture on B-G. medium of H. pertussis phase I.