Wiley

TÓM TẮT: Giới thiệu một môi trường nuôi cấy cải tiến cho vi khuẩn lactobacilli. Môi trường này hỗ trợ sự phát triển tốt của lactobacilli nói chung, và đặc biệt hữu ích cho một số chủng nhạy cảm chỉ phát triển kém trong các môi trường chung khác. Ngoài ra, trong môi trường này không cần sử dụng nước ép cà chua, một nguyên liệu có sự biến đổi cao. Khi được điều chỉnh một chút, môi trường này cũng có thể được sử dụng như môi trường cơ bản cho các thử nghiệm lên men.

Spores of Bacillus cereus T germinated and formed vegetative cells in Tryptone Soya broth (TSB), pH 9‐0 and 7‐4 at 30^oC. Spores germinated but did not form vegetative cells when suspended in hen egg white (pH 9‐0) supplemented with L‐alanine and inosine. Using a split image eyepiece, the volumes of germinating spores in egg white were seen to increase as a result of increases in both length and breadth. In TSB at the same pH, the major volume increase resulted from a progressive increase in cell length. Egg white supplemented with L‐alanine and inosine (pH 7‐6 30^oC) allowed limited outgrowth to occur but the vegetative cells differed in morphology to those in TSB. Fe(NH₄)₂(SO₄)2.6H₂O overcame the inhibition of outgrowth in egg white at pH 7–8 but not in egg white at pH 9‐1. Solutions containing trace elements, growth factors and casamino acids could not replace iron in this respect. Sporulation occurred in egg white only when iron was present.

Samples of egg melange taken from an egg packing station contained an average of 7·3 x 10⁴ organisms/ml which survived laboratory pasteurization at 65°C for 3 min. Many of the organisms surviving pasteurization were found to be coryneform bacteria related to Microbacterium lacticum which could be differentiated into several groups. The remainder were a miscellaneous collection of unidentified cocci and coccobacilli and some Bacillus spp. The coryneform bacteria were shown to be the most heat‐resistant isolates with negligible loss of viability after 60 min at 65°C, At least two of the representative strains were very heat‐resistant, 0·01% surviving 20 and 38 min at 80°C in phosphate buffer at pH 7·1. Growth tests showed that none of the isolates grew at 5°C after 10 d incubation but those capable of growing most rapidly at 10° and 15°C were also the most heat‐resistant. Such strains had a doubling time at 15°C of between 6 and 8 h in whole egg. Freezing the coryneform bacteria in liquid whole egg at –18°C had negligible effect on viability or heat‐resistance at 65°C.

The antimicrobial properties of aqueous solutions of peracetic acid and hydrogen peroxide have been compared. Peracetic acid exhibited excellent antimicrobial properties, especially under acidic conditions. Reductions by a factor of 10⁶ in the numbers of vegetative bacteria are obtained within 1 min at 25°C using a solution containing 1.3 mmol/l of peracetic acid. Rapid activity against bacterial spores and yeasts also occurs. Hydrogen peroxide is more effective as a sporicide than as a bactericide, with sporicidal action being obtained using a solution containing 0.88 mol/l. Bactericidal action is poor but hydrogen peroxide was bacteriostatic at concentrations above 0.15 mmol/l.

Autotrophic ammonia‐oxidizing bacteria were detected in some Bangladesh and Sri Lanka tea soils and in three other Bangladesh soils. Numbers ranged from 25 to 5500 organisms/g dry soil. Pure cultures were obtained from all the soils either by picking colonies from silica gel plates used for counts or by enrichment culture procedures. The isolates were identified as species of Nitrosolobus, Nitrosomonas and a new species of Nitrosospira.

Of the meat strains of streptobacteria, leuconostocs, Enterobacteriaceae and Brochothrix thermosphacta tested, only Hafnia alvei and Serratia liquefaciens showed diamine‐producing potential during growth in pure culture on beef stored in vacuum packs at 1°C. Both organisms produced cadaverine at concentrations similar to those reported previously in naturally contaminated beef stored under the same conditions. Putrescine concentrations produced by the two organisms, however, were an order of magnitude lower. During the growth on beef of either H. alvei or S. liquefaciens in mixed culture with arginine‐utilizing strains of streptobacteria, putrescine as well as cadaverine concentrations were similar to those detected in naturally contaminated samples.

Disc‐diffusion, agar‐dilution and microdilution methods were compared for testing the antibiotic sensitivity of anaerobic bacteria. Eight antibiotics and 31 test organisms were used. There was a poor correlation between MIC values obtained by the agar‐dilution and microdilution procedures. The test organisms showed an apparently increased sensitivity to the antibiotics when tested by the agar‐dilution, as compared with the microdilution, procedures. Columbia Blood Agar and Thioglycollate Haemin agar, were evaluated for the disc‐diffusion and agardilution procedures. There was a poor correlation between the MIC values and inhibition zone diameters for the two media, with lower MIC values and larger zones on Thioglycollate Haemin agar.

Incubation of sporulating cultures of Bacillus anthracis, B. cereus, B. subtilis and B. thuringiensis in 1°0 mol/l sodium sulphate markedly increased the release of free spores from sporangia. It is postulated that the release of spores is due to activation of latent autolysins which hydrolyse sporangial cell walls. Sodium sulphate‐induced lysis of sporangia represents a novel and highly effective method for the recovery of spores from cultures of Bacillus species.

Tempeh was prepared from Delmar variety soybeans inoculated with the traditional Indonesian inoculum (usar) and six pure culture strains of Rhizopus oligosporus. The strains BTU3K1 and CT11K2 produced the best quality tempeh. The phytic acid content of soybeans was reduced from 1mD07% in whole dry soybeans to 0mD67–0mD75% in tempeh. Most mould strains did not have a significantly different effect on reducing the phytic acid content in tempeh, although the traditional inoculum was significantly different to strains CTU7K2, BTU3K1, BT1K4 and CT11K2.