The distribution of bifidobacteria in the environment has been examined by using YN-6 medium. Although feces of humans, chickens, cows, dogs, pigs, horses, cats, sheep, beavers, goats, and turkeys were examined, bifidobacteria were isolated only from the feces of humans and swine. The frequency and distribution of component species of human fecal isolates were as in isolates from raw sewage. Bifidobacterium longum and B. adolescentis were most often isolated and in the highest densities. The levels of bifidobacteria in raw sewage were in the range of 106 organisms/100 ml, and the effect of primary and secondary sewage treatment on the number of viable organisms present was not significant. High densities of bifidobacteria were found in all samples from septic tanks. It was found that bifidobacteria did not survive as well as Escherichia coli in either fresh or marine waters. The ratio of bifidobacteria to E. coli is an indication of the age and of the effectiveness of treatment of sewage effluent.

The efficacy of powered air-purifying respirators, surgical masks, dust/mist respirators, and high-efficiency respirators were tested with a biological aerosol under simulated breathing conditions. Protective ability ranged from 67 to 99.95%. The majority of penetration in negative-pressure respirators occurred at the face-mask interface rather than through the filter material.

A membrane filter technique has been developed for the enumeration of bifidobacteria in natural aquatic environments. The technique is quantitative, selective, and differential. The medium (YN-6) contains: yeast extract, 2.0 g; agar, 1.5 g; polypeptone peptone, 1.0 g; vitamin-free Casamino Acids, 0.8 g; sodium chloride, 0.32 g; and L-cysteine hydrochloride, 0.003 g; in 100 ml of deionized water. The medium is adjusted to pH 7.0 before autoclaving. Nalidixic acid (80 micrograms/ml), neomycin sulfate (2.5 micrograms/ml), and bromcresol green (300 micrograms/ml) are included as selective and differential agents. After incubation for 48 h at 37 degrees C in an anaerobic environment, Gram-stained smears from green, glistening, smooth entire colonies are examined microscopically for typical bifidobacterial morphology. No significant difference in recoveries was observed when YN-6 was compared with reinforced clostridial agar, using bifidobacteria freshly isolated from feces and raw sewage. Using this technique with aquatic and fecal samples, less than 9% false-positive and 8% false-negative isolates were observed. These results indicated that the medium was able to satisfactorily recover organisms from a variety of situations.

Ligated ileal loops of adult rabbits were used to evaluate the prophylactic potential against cholera of a combined vaccine consisting of toxin-free crude flagella (CF) and glutaraldehyde-derived cholera toxoid (TV). The resulting fluid accumulation ratios were compared with those in rabbits immunized with saline (controls) and with CF and TV alone. Data for single vaccines confirmed the superior protection effect of CF over TV. In rabbits vaccinated with both CF and TV, maximal fluid accumulation ratios were not obtained with a challenge dose as high as 5 X 10(9) colony-forming units (CFU). Two rabbits similarly immunized failed to produce positive loops with challenges of 6.3 X 10(8) and 5 X 10(9) CFU, respectively. The vibriocidal titer of serum from rabbits immunized with a killed commercial vaccine in addition to those listed above was determined at intervals for a period of 164 days. No vibriocidal activity was detected in serum of control rabbits and of rabbits vaccinated with TV. Serum from animals given CF or commercial vaccine had similar vibriocidal titers even when the test bacteria were nonflagellated. Protection against challenge as evaluated by ileal loops did not, however, correlate with vibriocidal titer.