Effect of the pH of growth on the survival of Lactobacillus delbrueckii subsp. bulgaricus to stress conditions during spray-drying.

AIMS: The aim of this study was to optimize survival of Lactobacillus delbrueckii subsp. bulgaricus during spray-drying and subsequent storage through optimizing the pH of growth conditions. METHODS AND RESULTS: Cell concentrates previously grown without or with pH controlled were spray-dried and stored at 20 degrees C and heat treated at 57 degrees C. Cells grown under noncontrolled pH were more resistant to both drying and heating than cells grown under controlled pH but no significant differences were observed during storage. The intracellular proteins profile of cells grown under both conditions was studied by two-dimensional SDS-polyacrylamide gel electrophoresis. Eight proteins were identified using automated mass spectrometry (MS) and tandem mass spectrometry (MS/MS) data acquisition. Of the identified proteins, only cochaperonin GroES corresponded to a known heat shock protein (HSP). The other proteins identified are proteins involved in glycolysis. For cells grown under noncontrolled pH the expression of the Hsp70, GroES and GroEL, measured by Western blotting, was enhanced. CONCLUSIONS: The higher resistance of cells grown under noncontrolled pH correlates with the enhanced production of heat shock proteins. SIGNIFICANCE AND IMPACT OF THE STUDY: Growth of L. bulgaricus under controlled pH (commonly used by the starter cultures production industry) results in cells more sensitive to stresses frequently encountered by the cells during starter cultures preparation/storage/utilization.

Bacteriocin production by spray-dried lactic acid bacteria.

AIMS: Cell survival and antagonistic activity against Listeria innocua, Listeria monocytogenes and Staphylococcus aureus were investigated after spray-drying three bacteriocin-producing strains of lactic acid bacteria: Carnobacterium divergens, Lactobacillus salivarius and Lactobacillus sakei. METHODS AND RESULTS: Bacterial cell concentrates were spray-dried and stored at 4 degrees C and 18 degrees C and 0.3% ERH (equilibrium relative humidity). Enumeration and antagonistic activity were evaluated before and after spray-drying and at regular intervals during storage. CONCLUSIONS: A higher survival rate was obtained when survival was performed at 4 degrees C. With the exception of Carnobacterium divergens which lost the inhibitory activity against Staph. aureus after drying, antagonistic production was not affected by the process nor by the storage. Of the three species studied, Lact. salivarius showed the highest resistance to the spray-drying and storage processes. SIGNIFICANCE AND IMPACT OF THE STUDY: Spray-drying is a potentially useful process for large scale production of dried powders containing viable organisms with antagonistic activity against pathogens.

Improved methods for the enumeration of heterotrophic bacteria in bottled mineral waters.

At this time the European Union regulations require that the heterotrophic plate counts (HPC) of mineral waters be assessed at two recovery temperatures: 22 degrees C for 72 h and 37 degrees C for 24 h. This procedure is time consuming and expensive. Development of new rapid methods for microbiological assessment of the microbial flora in the bottled water is an industry-driven need. The objectives of this work were to develop a method for the HPC that utilises only one recovery temperature and one incubation period and evaluate the use of, the LIVE/DEAD(R) BacLight Bacterial Viability Kit, 5-cyano-2,3-ditotyl tetrazolium chloride (CTC) and impedance methods to enumerate viable bacteria in bottled mineral water. Results showed that incubation at 30 degrees C could be used instead of incubation at 22 degrees C and 37 degrees C. Good correlation exists between counts at 30 degrees C and counts at 22 degrees C (r>0.90) and all the pathogens important in mineral water analyses grow similarly at 30 degrees C and 37 degrees C during 24 h. It was demonstrated that impedance methods might be useful to the mineral water industry as a rapid indicator of microbiological quality of the water. Results obtained with BacLight and CTC were similar to those obtained with plate counts.

Growth of filamentous fungi in submerged culture: problems and possible solutions.

Filamentous fungi are important organisms industrially and continue to attract research interest as microbiologists attempt to overcome the problems associated with their behavior in submerged culture. This review critically examines the literature describing these problems and where available suggests possible solutions to them. The influence of the chemical and physical environment on culture morphology, the process engineering challenges presented by different fungal morphologies, and the relationship between fungal morphology and metabolite production are all discussed.

Sensorial and microbial effects of gaseous ozone on fresh scad (Trachurus trachurus).

The bactericidal activity of gaseous ozone was investigated using a commercial ozone generator. Five species of fish bacteria, Pseudomonas putida, Shewanella putrefaciens, Brochothrix thermosphacta, Enterobacter sp. and Lactobacillus plantarum, were inoculated on agar surfaces and exposed to different ozonation times in a gas chamber. Results showed ozone in relatively low concentrations (< 0.27 x 10(-3) g l-1) was an effective bactericide of vegetative cells of the five fish bacteria. The age of the cell culture was shown to influence the cell response following exposure. Survival rate was not linearly related to ozonation time, but exhibited biphasic death over an extended period. Similar bactericidal effects were observed on fish skin treated with ozone daily in the laboratory, with decreases of 1.0 log cfu cm-2 for the micro-organisms studied. Whole fish treated daily in the laboratory using a commercial ozone generator showed improved scores for sensory analyses compared with the controls. The results were statistically significant. Fish treated on board ships were also analysed for microbiological and sensory changes. Controls were obtained from a similar vessel without the ozone facility in the hold. Similar trends to those recorded in the laboratory for the microbiological and sensory results on ozonated fish were observed.

ICMSF methods study. XVII. An international comparative study of the direct plate and hydrophobic grid-membrane filter methods for enumeration of Escherichia coli in foods. International Commission on Microbiological Specifications for Foods.

Eight laboratories compared counts of Escherichia coli from naturally or artificially contaminated ground beef, other meats and poultry, vegetables, fish and shellfish, cheese, and diverse sources such as swabs, by the Anderson-Baird-Parker direct plate (DP) and a hydrophobic grid-membrane filter (HGMF) method. For five of the eight laboratories overall counts by HGMF were significantly low (51-83%) compared with those by DP. Counts by HGMF tended to be lower for naturally contaminated samples; several possible causes were investigated. In a subsidiary study, analyst variation in counting HGMF ranged from 0.8-7.3%, with little evidence of effects from counting positive versus negative grid cells or from the fullness of growth or staining intensity.

Rapid microbiology: applications of bioluminescence in the food industry--a review.

The bioluminescent assay of ATP is rapid and simple and may be used as an estimate of microbial numbers. It therefore shows great potential as a technique to provide information on the microbiological quality of a food within a few minutes, in comparison with conventional techniques, which provide results retrospectively. However, despite the advantages of speed and sensitivity, no food microbiologists are using the technique for routine quality control and hygiene monitoring. This review seeks to highlight the reasons for this, and to offer some ideas for future research to increase the acceptance of ATP assays within the food industry.

the involvement of Nitric Oxide in the inhibition of the phosphoroclastic system in Clostridium sporogenes by sodium nitrite.

The phosphoroclastic system was demonstrated in cell-free extracts of clostridium sporogenes by the production of carbon dioxide, acetyl phosphate, ATP and reduced NAD in the presence of pyruvate. The kinetics of acetyl phosphate production and NAD reduction were investigated. The addition of sodium nitrite to a suspension of C. sporogenes in glucose medium resulted in a rapid decrease in intracellular ATP concentration which was accompanied by an accumulation of pyruvate in the medium. This accumulation of pyruvate was caused by inhibition of phosphoroclastic system by nitrate. Nitrite inhibits this system by reaction of nitric oxide, formed from nitrate, with the non-haem iron of pyruvate:ferredoxin oxidoreductase.

Staphylococcus aureus in commercial laying flocks: incidence and characteristics of strains isolated from chicks, pullets and hens in an integrated commercial enterprise.

1. Staphylococcus aureus was able to colonise the surface of chicks as young as 1 d old. 2. The organism was detected in a hatchery particularly in the debris from the hatchers and on the working surfaces at the sexing and vaccination areas. 3. The degree of surface colonisation of chicks and pullets was low during rearing but rose to a maximum at mid-lay (50 weeks) when the organism was readily detectable on almost all hens. 4. Strains of Staphylococcus aureus were characterised by phage-typing and cultural characteristics and found to belong predominantly to poultry phage group B2 of Gibbs et al. (1978a). 5. A detailed description of poultry phage group B2 strains is presented; strains of this type can be considered as a second "live-bird" ecovar when compared with Staph. aureus var. gallinae of Witte et al. (1977).

The use of a new phage set for typing poultry strains of Staphylococcus aureus obtained from seven countries.

1. Eighty per cent of poultry strains of Staphylococcus aureus tested from French, Belgian, English, West German, Japanese and Argentinian sources were typable using a set of typing phages isolated in this laboratory. Strains from Bulgaria, however, with few exceptions were not typable with this phage set. 2. Strains isolated from lesions generally resembled those from apparently healthy poultry. 3. The existence of two distinct Staph. aureus biotypes on poultry was confirmed by isolates from six of the countries; one of these biotypes closely resembled Staph. aureus variety gallinae as described by Witte et al. (1977).

Identification of isobutyronitrile and isobutyraldoxime O-methyl ether as volatile microbial catabolites of valine.

G.l.c.--mass-spectral analysis of headspace above cultures of Aeromonas and Moraxella spp. indicates the presence of isobutyronitrile, isobutyraldoxime O-methyl ether, methacrylonitrile and possibly methacrylaldoxime O-methyl ether. Accumulation of these catabolites is maximal under low oxygen concentrations and is enhanced by enrichment of the medium with valine. Isobutyraldoxime O-methyl ether is established as the compound observed but not identified in previous studies with other bacterial species involved in spoilage of meat and chicken.

Vacuum-packaging of bovine edible offal.

Edible offals are relatively perishable and may be frozen before leaving the abattoir, commanding a lower price on the wholesale market than fresh offals. Investigations are described in which a range of offals was vacuum-packaged in an effort to extend the shelf-life of the fresh material. Several visits to two abattoirs revealed that their offals after chilling were generally of rather poor microbiological quality, partly due to handling practices and, in one abattoir, to inadequate chilling. Reductions in the initial microbial load on hearts and tongues were achieved by immersion in water at 90°C, or with 100 ppm free chlorine or 1 % (v/v) lactic acid. However, these treatments offered no advantage over good production methods in extending the safe storage period in the vacuum-package. When offals produced under normal conditions were vacuum-packaged a storage period of 2-3 weeks at 1°C ± 1° was achieved which allowed a subsequent shelf-life of 3-4 days in air at 4°C. Offals produced with low initial numbers of contaminants gave the possibility of 1-2 weeks longer in the vacuum-package. A detailed investigation of the organisms growing on vacuum-packaged liver showed that a lactic flora developed during storage, but this did not inhibit potential spoilage organisms such as Pseudomonas or Alteromonas.

Detection of volatile sulfide-producing bacteria isolated from poultry-processing plants.

A technique using filter paper strips impregnated with 5-5'-dithiobis-nitrobenzoic acid was developed to allow the detection of bacteria (isolated from poultry-processing environs) which produced volatile sulfides (H2S, CH3SH, [CH3]2S). The technique is preferred to conventional methods in that it allows the detection of volatile organic sulfides in addition to hydrogen sulfide.

Sources and properties of some organisms isolated in two abattoirs.

A wide range of organisms was isolated and identified from a number of sites in two abattoirs. Heavily contaminated sites were the water supply to the lairage in one abattoir and animal hair, blood, rumen contents and soil and faecal material from hooves in both abattoirs. Few catalase negative organisms were isolated but other Gram positive organisms included Bacillus spp., coryneforms, M. thermosphactum and coagulase negative cocci. Gram negative organisms were widely distributed in the abattoirs, Pseudomonas spp. being present at most sites, while members of the family Enterobacteriaceae were isolated from all sites except carcass wash water and air samples in the lairages and a boning room. In pure culture 17 of 54 isolates spoiled meat in air at 4°C and 47 at 15°C but under simulated vacuum-package conditions only 7 of 28 at 4°C and 14 of 28 at 15°C gave some indication of spoilage abilities. None of the 10 isolates tested showed marked resistance to chlorine at 20 ppm.