Inhibition of bacilli in industrial starches by nisin.

The properties of Bacillus coagulans and of other bacilli that contaminate paper and paperboard manufacturing processes were investigated under simulated industrial conditions. Nisin (0.05 to 0.125 microg ml(-1) blocked growth of indigenous bacilli that contaminate sizing starches. B. coagulans starch isolates, B. licheniformis, B. amyloliquefaciens, and B. stearothermophilus grew at > or = 50 degrees C in industrial starch and produced alpha-glucosidase and cyclodextrins. The industrial isolates and reference strains of B. amyloliquefaciens, B. cereus, B. coagulans, B. flexus, B. licheniformis, B. pumilus, B. sporothermodurans, B. stearothermophilus and Alicyclobacillus acidoterrestris were inhibited by < or = 0.125 microg of nisin on agar. B. coagulans and B. stearothermophilus were similarly inhibited by < or = 0.025 microg of nisin ml(-1) and by 3 microg of the biocide DBNPA ml(-1) in industrial starch. B. licheniformis and B. amyloliquefaciens strains were less sensitive. About 40% of nisin added to starch was retained after cooking. Fifty percent of the nisin remained active after 11 h of storage at 60 degrees C. The results show that nisin has potential as a preservative for modified industrial starches.

Properties of Bacillus cereus and other bacilli contaminating biomaterial-based industrial processes.

This paper is an overview on bacilli in industrial processes, with focus on food grade paper and paperboard production. Paperboards mainly contain sporeforming bacteria belonging to the genera Bacillus, Paenibacillus and Brevibacillus, usually found in quantities from < 50 to 250 cfu g(-1) homogenized paperboard. Of those frequently found, Bacillus cereus group, B. licheniformis, B. subtilis and Brevibacillus brevis are important for food hygiene because of their hydrolytic activities on food components and the ability of some strains to produce food poisoning toxins or to grow at refrigerated temperatures. We found that the phenotypic properties (lecithinase activity, nitrate reduction) used in standard methods (e.g., ISO, FDA, IDF) to recognize B. cereus, were unreliable for industrial isolates. Whole cell fatty acid composition of a group of the industrial isolates deviated so much from those in a widely used commercial database that the strains were not or only poorly recognized as B. cereus. Industrial isolates, including toxigenic ones, often missed one or more of these characters, even in cases where 100% 16S rDNA identity was found with B. cereus or with B. thuringiensis. 11-Methyldodecanoic acid and trans-9-hexadecenoic acid were found without exception in over 200 industrial B. cereus group isolates and in over 30 culture collection strains. The detection of these fatty acids is a secure method for the identification of B. cereus. Negative reaction for starch hydrolysis and for BCET-RPLA test and a specific ribotype were found in all B. cereus strains producing the emetic toxin.

Evaluation of methods for recognising strains of the Bacillus cereus group with food poisoning potential among industrial and environmental contaminants.

Toxin production, biochemical properties and ribotypes of Bacillus cereus group (B. cereus, B. thuringiensis, B. mycoides) strains originating from industrial and environmental sources (n = 64), from food poisoning incidents (n = 22) and from reference sources (n = 7) were analysed. Forty ribotypes were found among the 93 strains. Eleven strains from food poisoning incidents produced emetic (mitochondrio) toxin, as determined by the boar spermatozoa toxicity test. These strains possessed closely similar ribotypes which were rare among strains of other origins. Sperm toxin producing (cereulide positive) strains did not hydrolyse starch and did not produce haemolysin BL, as determined by the reverse passive latex agglutination test. Sixteen different ribotypes were found among B. cereus strains from board machines (n = 16) and from packaging board (n = 16), indicating many different sources of B. cereus contamination in board mills. Strains originating from packaging board had predominantly different ribotypes from those of dairy and dairy product originating strains. Nine (53%) out of 17 strains from a single dairy process shared the same ribotype whereas strains from milk and milk products from different dairies had different ribotypes indicating that B. cereus group populations were dairy specific. Twenty-two percent of strains isolated from the paperboard industry on non-selective medium were lecithinase negative, including enterotoxin producing strains. This stresses the importance of other detection methods not based on a positive lecithinase reaction.

Bacillus cereus in a whey process.

A cheese dairy and its whey manufacturing line were examined for Bacillus cereus. Colonies typical of B. cereus were detected in 120 (17%) samples out of 720 analysed. Only 3% of the sampled raw milk contained B. cereus ( > or = 10 cfu ml(-1)) whereas in evaporated whey concentrate B. cereus was present in 76% of the samples. Nitrate reductase negative and weakly casein hydrolysis isolates were rare in raw milk and the early parts of the process but these defective biotypes became increasingly frequent towards the end of the whey process. The composition of whole cell fatty acids of B. cereus isolates originating from the whey part of the process was different from that of the type strain and of the isolates originating from the raw materials of cheese making. The B. cereus strains in concentrated whey were 100% similar to the type strain in 16S rDNA sequence (500 bp) although they were not or only poorly recognized as B. cereus by a commercial whole cell fatty acid library. All of B. cereus isolates in raw milk were sensitive to one or more of the B. cereus group phages (n = 17) whereas 43% of the isolates from the whey process were sensitive to none. None of the 23 strains originating from the whey processing lines grew at < or = 8 degrees C. although strains with minimum growth temperatures of 5.3 degrees C and 7.0 degrees C were present in the raw materials. Our results indicate that the B. cereus population of the warm ( > 30 degrees C) parts of the cheese dairy process was separate from that of cold (2 degrees C to 4 degrees C) part of the process.

Bacterial contaminants in liquid packaging boards: assessment of potential for food spoilage.

Liquid packaging boards and blanks were examined for microbial contaminants. A total of 218 strains were identified and representatives of the most frequent species were characterized for their potential for food spoilage. Contaminants found were aerobic spore-forming bacteria, mostly Bacillus megaterium, B. licheniformis, B. cereus group, B. pumilus, Paenibacillus macerans, P. polymyxa, P. pabuli and B. flexus. Production of amylolytic, proteolytic, lipolytic and phospholipolytic enzymes was common. Approximately 50% of the B. cereus group strains were positive in the diarrhoeal enterotoxin immunoassay test or in the enterotoxin reversed passive latex agglutination test. Strains capable of growth at 6 degrees C were found among B. cereus group, P. pabuli, P. validus, B. megaterium and P. polymyxa. All b. licheniformis strains grew at 55 degrees C. The spores of B. licheniformis were most resistant to hydrogen peroxide. The B. cereus group strains were recognizable by fatty acid components not present in any of the other paperboard strains, 11-methyldodecanoic acid (13:0 iso) and trans-9-hexadecenoic acid (16:1 omega 7 trans), each contributing 7% or more to the total cellular fatty acids.