RESUMO

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1. The effect on feed efficiency of two probiotics, one prepared with Saccharomyces boulardii and the other with Bacillus cereus var. toyoii, was tested in broilers infected with Salmonella enteritidis. 2. One-day-old chicks were divided at random into three groups and fed commercial feed devoid of antibiotics: group 1 was fed with non-supplemented feed, group 2 was supplemented with S. boulardii and group 3 with B. cereus. At 14 d of age the animals were challenged by the oral route with 1 x 10(7) viable S. enteritidis. 3. At d 47, average live weights were: group 1, 1.77 kg, group 2, 1.89 kg and group 3, 2.06 kg, and were significantly different. Feed conversion rates were 2.61 for group 1, 2.35 for group 2 and 2.30 for group 3. 4. We conclude that both probiotics improved feed efficiency in broilers.

Bacillus cereus CenBiot fulfilled the requirements to be used as probiotic. The spores showed D 80 of 14 hs, inhibited Escherichia coli and Yersinia pseudotuberculosis after 24 hs in associative culture, were innocuous for suckling and adult mice and were not inhibited by antibiotics at low concentrations. Revista de Microbiologia (1999) Probiotics are "viable mono or mixed cultures of microorganisms which, applied to animal or man, beneficially affect the host by improving the properties of the indigenous flora" (10). They must promote growth, improve feed conversion and inhibit enteropathogens, without causing any undesirable effect. In addition, they must survive the stress produced during manufacturing, storage and administration at farm conditions. Key words: probiotic, Bacillus cereusThe search for new probiotic strains has increased in recent years due to the necessity to find economic and effective substitutes for antibiotics used as feed additives. Several strains of Lactobacillus, Pediococcus, Bacteroides, Bifidobacterium, Bacillus, Streptococcus and Escherichia coli, alone or consortiated, have been used as probiotics (8), giving controversial results. Among the various species of probiotics, those belonging to the genus Bacillus have the advantage that, due to their capacity to sporulate, they survive at ambient temperatures as well as during desiccation by methods that involve moderate heating, such as spray dryers, avoiding the use of lyophilization or other expensive technologies (10). This property also makes possible the administration of spores mixed with powdered vehicles instead of gels or liquids used with non sporulated bacteria. Although several strains of different species of Bacillus are being used for this purpose, information concerning their properties was seldom reported.Probiotic CenBiot, prepared with a strain of Bacillus cereus at Centro de Biotecnologia of Universidade Federal de Pelotas, Rio Grande do Sul, Brazil, was tested in commercial farms showing beneficial effects in the control of diarrhoea and feed conversion in pigs (21). The effects of some factors that could affect the survival of Bacillus cereus in the intestinal tract and during manufacturing, such as interaction with enteropathogens, resistance to heat and to variation of pH, are reported in this work.The strain was classified as Bacillus cereus due to its morphology, Gram staining, capacity to form 12 C. Gil-Turnes et al. thin wall spores in aerobic conditions, growth in glucose broth under anaerobic conditions, production of lecithinase and acetyl-methyl-carbinol and absence of urease (20). To obtain spore suspensions, cultures were heated at 80 o C for 15 minutes, centrifuged, and after three successive washings with ultrapure water, resuspended in ultrapure sterile water pH 7.2.To test the effect of heat, aliquots of 300µl of spore suspensions were heated in a water bath at 50 o C for 4 days, 80 o C for 60 min, 85 o C for 60 min and 90 o C for 40 min. Samples were collected every 24 hours, 10 min,...

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