To determine the safety of fresh-cut vegetables packaged in modified atmosphere, challenge studies using both nonproteolytic and proteolytic strains of Clostridium botulinum were performed with a variety of fresh-cut packaged salads and vegetables stored at different temperatures. When vegetables were inoculated with spores of C. botulinum and incubated in low-O 2 atmospheres, spore germination and growth and toxin production were observed. Botulinum toxin was produced by proteolytic types A and B on onion, butternut squash, rutabaga, salad, and stir-fry vegetables. Nonproteolytic C. botulinum produced toxin on butternut squash and salad. Nonproteolytic C. botulinum was capable of producing neurotoxin at temperatures as low as 5°C, whereas proteolytic strains produced neurotoxin at 15°C and higher. Although most samples were visibly spoiled before detection of botulinum toxin, samples of butternut squash and onion remained acceptable after detection of toxin. The strict maintenance of low temperatures (<5°C) is recommended in order to control the potential growth of C. botulinum on fresh-cut vegetables packaged in a modified atmosphere.

Challenge studies were carried out to evaluate the safety of a reformulated sous-vide processed spaghetti and meat-sauce product (a w 0.992–0.972, pH 4.5–6) inoculated with Clostridium botulinum types A and B spores. Following processing at 75°C for 36 min (equivalent to a 13 D process for Streptococcus faecium ), samples were stored at 15°C and analyzed at selected time intervals for toxin production and visible signs of spoilage. Toxin was detected in samples of pH > 5.5 after 14–21 days and in products of pH 5.25 after 35 days. Toxin was not detected in any samples of pH < 5.25 within 42 days storage at 15°C. All products of pH 5.75 and 6 were visibly spoiled, i.e., swollen due to CO 2 production, prior to toxigenesis. However, for products of pH 5.5 and 5.25, toxigenesis preceded spoilage. Subsequent studies were done to test the effect of additional salt (1–3% w/w) on the safety of a product of pH 5.5 at mild temperature-abuse storage conditions (i.e., 15°C). Toxin production was not delayed in samples containing < 1.5% added salt, while > 1.5% salt (w/w) prevented toxin production throughout the 42-day storage period at 15°C. Microwave heating of products for 5–10 min at full or half power in a domestic microwave (800 watts) inactivated the preformed toxin in all samples.

Adherence of gut microflora from Salmonella -free adult birds to the ceca of newly hatched chicks, and their role in protection against Salmonella was examined. The protective microflora remained attached to the cecal wall after four successive washings. Cultures of washed ceca taken from chicks 30 min to 1 h after treatment with fecal culture gave partial protection. Full protection was obtained with cultures from ceca taken 6 to 8 h after treatment.

Oral administration of defined mixtures of bacterial isolates from fecal and cecal contents of adult chickens protected young chicks against infection with Salmonella . One-day-old chicks were treated with mixtures containing 50, 40, 25 and 10 bacterial isolates and challenged 2 d later with 10 4 , 10 5 and 10 6 colony-forming units of nalidixic acid-resistant Salmonella typhimurium . The chicks were examined for infection 6 d after challenge. The mixture of 50 bacterial cultures gave protection comparable to that obtained with fecal or cecal cultures of unknown bacterial composition. Less protection was evident with mixtures containing fewer cultures.

Protection of chicks against Salmonella infection was obtained by oral administration of Nurmi cultures. The Nurmi cultures were prepared by inoculating adult chicken intestinal material (10 −1 to 10 −11 g) into anaerobic liquid medium and incubating for 3 d at 37°C. Excellent protection was obtained with cultures initiated with as little as 10 −7 g of fecal or cecal content; progressively less protection with 10 −8 to 5 × 10 −10 g; and none with cultures initiated with 10 −10 g. Protection was based on challenge of treated chicks with nalidixic acid-resistant (Nal + ) Salmonella and enumeration of the Nal + organisms in the chick cecal content 7 d later. To simplify the enumeration, a swab-plate method was developed. The method saves time and materials and gives relatively accurate (± 1 log 10 ) determinations of Nal + Salmonella over the range of 10 1 to 10 7 per g of cecal content.

Mixed treatment cultures obtained by inoculating anaerobic medium with chicken feces were administered to 0 to 1 d-old chicks in their drinking water. Three types of treatment cultures (all fourth passage) were compared: FFC (fresh fecal cultures started with inocula of fresh feces followed by four daily, uninterrupted serial subcultures), LFC (cultures started with inocula obtained by lyophilizing third-passage cultures), and FrFC (cultures started with inocula obtained by freezing third-passage cultures). Protection of treated chicks against infection by Salmonella typhimurium was assessed by challenging the chicks via their drinking water 2 d after treatment and culturing their ceca 8 to 9 d later, or at weekly intervals for 7 weeks. FFC protected chicks against infection more consistently than LFC or FrFC. However, some LFC and FrFC were as protective as FFC (α= .05). Treatment with cultures did not increase mortality or decrease weight gain.

Polymyxin B sulfate (PB) added to salt broth (SB) for selective enrichment of Vibrio parahaemolyticus was destroyed by autoclaving. Losses were about 49% at pH 7.4 and 97% at pH 8.8. Additionally, certain raw fish when added to salt polymyxin broth (SPB) caused a loss of PB, probably due to adsorption; vertebrate fish (red snapper and herring) caused a loss of about 72% of PB, but shellfish (oyster and clam) did not cause any loss.

Fecal suspensions and anaerobic fecal cultures prepared from adult chicken feces and administered by gavage into the crop or via drinking water were compared for their ability to protect newly hatched chickens against Salmonella infection. Good protection (decreased infection by ≥ 90%) was obtained with as little as 10 −4 g of feces or 10 −2 ml of a fourth serial fecal subculture. The two methods of administration were equally effective. Treatment of chicks with serially passaged fecal cultures via drinking water may provide adequate protection at a minimum cost, and with a low probability of transmitting viral or parasitic agents.

Day-old chicks ( Gallus domesticus ) were treated with cultured feces of adult chickens according to the Nurmi concept and were challenged 2 days later with Salmonella typhimurium . Treated chicks were less susceptible to infection than untreated chicks (16% vs. 79% infected). Those treated chicks that did become infected, contaminated their drinking water with fewer Salmonella than the untreated chicks (maximum of 10 4 /ml vs. ⩾ 10 7 /ml). Fecally contaminated water may be a major source for spreading Salmonella infection within a flock.

Chicks ( Gallus domesticus ) were treated per os with 24-h-old anaerobic cultures of feces from mature chickens 1 day after hatching, challenged with Salmonella typhimurium in the drinking water 2 days later, and sacrificed on day 11 or 12; then the lower third of the intestinal tract was examined for salmonellae. Cultures of feces inoculated directly into the crop or added to the drinking water, even after holding at −70 C for 21 days, protected chicks against infection by S. typhimurium . Cultures serially subcultured daily up to four times were protective, and dilution to 1:80 in drinking water containing 4 % skim milk powder did not decrease their protective effect. Treated chicks were about 1000-fold more resistant to infection by Salmonella than untreated chicks.