Attributes of microbial associations of meat growing as xenic batch cultures in a meat juice at 4 degrees C.

Strains of Gram-positive (Carnobacterium piscicola, Leuconostoc mesenteroides subsp. mesenteroides, Brochothrix thermosphacta) and Gram-negative (Pseudomonas fragi and Hafnia alvei) bacteria isolated from minced lamb packaged under a modified atmosphere were cultivated in a meat (lamb) juice at 4 degrees C. Carbohydrates were catabolised in the order glucose > glucose 6-phosphate during the development of the population. Under an atmosphere enriched with carbon dioxide the Gram-negative portion of the population was suppressed during the exponential phase but H. alvei became the dominant organism towards the end of a protracted stationary phase of growth. With the aerobic atmosphere P. fragi catabolised creatine and became the dominant species in the stationary phase. The inability of C. piscicola to catabolise glucose 6-phosphate was reflected in its population being smaller than those of the other Gram-positive organisms (C. piscicola < L. mesenteroides subsp. mesenteroides < B. thermosphacta). During the stationary phase of growth, indigenous L-lactic acid and the D-isomer produced by leuconostocs were oxidised to acetic acid by the Gram-positive flora under an atmosphere enriched with carbon dioxide. These oxidations, which occurred after depletion of glucose, were supported by the oxygen in the system. D-Lactic and acetic acid appeared to be possible parameters for the estimation of the microbiological quality of packaged meat.

The influence of sodium chloride and pH on the growth of Salmonella enteritidis PT4.

Sodium or potassium chlorides at concentrations of ca 2.0% (w/v) stimulated the growth of Salmonella enteritidis PT4 and PT6 but not PT8 in nutrient broth acidified to < or = 5.5 with acetic but not with citric, propionic or hydrochloric acids. Stimulation was noted also with an acidified defined medium. The most pronounced stimulation occurred with incubation at 37 degrees C. Supplementation of acidified nutrient broth with sucrose or glycerol had no effect on the growth of salmonellas.

Metabolic activities of pseudomonads in batch cultures in extract of minced lamb.

Pseudomonas fragi, Ps. lundensis and Ps. fluorescens were studied in axenic batch cultures growing in a lamb juice (pH 6.0) aerobically or in an atmosphere (Ps. fragi only) enriched with carbon dioxide at 4 degrees C. With all but a glucose dehydrogenase-deficient strain of Ps. fluorescens there was a sequential catabolism of glucose and lactate. Diauxic growth was observed in a nutrient-deficient meat juice supplemented with glucose and lactate. A transient peak in the concentration of gluconate and pyruvate was associated with the catabolism of glucose and lactate respectively. With Ps. fluorescens deficient in glucose dehydrogenase there was simultaneous catabolism of glucose and lactate. The stereoisomers of lactate were catabolized simultaneously in a laboratory medium. Glucose-6-phosphate was oxidized to 6-phosphogluconate by Ps. fragi and Ps. lundensis under aerobic conditions only. Creatine and creatinine were catabolized by Ps. fragi under aerobic conditions only. There was a slight decrease in the concentration of total amino acids (ninhydrin-reactive material) during the exponential phase of growth. The results suggest that the dominance of Ps. fragi in the climax populations in meat is due to catabolism of amino acid related substrates, creatine and creatinine.

Effect of faecal extract on the growth of Salmonella enteritidis in artificially contaminated hens' eggs.

1. Salmonella enteritidis PT 4 grew in eggs stored at 25 degrees C, but not at 10 degrees C. 2. The incidence of generalised infection of the egg contents (greater than 10(6) salmonellas/ml) was greater in eggs inoculated with cells suspended in faecal extract compared to those with cells in Ringer's solution. 3. The removal of most of the iron did not decrease the growth-promoting effect of the faecal extract.

Persistence of contamination of hens' egg albumen in vitro with Salmonella serotypes.

A study was made of the persistence of different Salmonella serotypes in hens' egg albumin in vitro at 4, 20 and 30 degrees C. The majority of serotypes remained viable but did not increase in numbers at 20 and 30 degrees C for 42 days. At 4 degrees C many of the serotypes died out. The addition of ferric ammonium citrate on the 42nd day of incubation induced multiplication of organisms incubated at 20 and 30 degrees C, but not at 4 degrees C. The pH and glucose concentration of the albumen diminished only when heavy growth occurred. Salmonella enteritidis remained viable on the air cell membrane in vitro for 17 days at 4, 20 and 30 degrees C. Thirty percent of the organisms also remained motile in albumen for 42 days at 25 degrees C and up to 5% of the cells remained motile for up to 20 days at 4 degrees C.

The influence of temperature on the behaviour of mixed bacterial contamination of the shell membrane of the hen's egg.

The inner membrane of the air cell of hens' eggs was inoculated with Pseudomonas putida, Staphylococcus xylosus, Enterococcus faecalis, Escherichia coli and Salmonella enteritidis. The first mentioned eventually dominated the contamination of the albumen of eggs stored at 4, 15, and 20 degrees C. The last mentioned did so in eggs stored at 37 degrees C. The interval between inoculation of the membrane and gross contamination of the albumen was markedly influenced by site of contamination relative to yolk movement.

Role of magnesium in egg shell formation in the domestic hen.

1. The effects of feeding diets containing various amounts of magnesium on plasma concentration of calcium and magnesium in the domestic hen were investigated. 2. Plasma concentrations of calcium and magnesium decreased during shell formation in all birds. 3. Plasma magnesium content and egg shell thickness were severely reduced in birds given diets containing either 207 or 132 mg Mg++/kg. 4. Using electron microscopy, a precise correlation was observed between the normal distributions of magnesium and organic material across the egg shell of the domestic hen.

Effect of phenolic compounds and oleuropein on the germination of Bacillus cereus T spores.

The phenolic compounds extracted from olives with ethyl acetate inhibited germination and outgrowth of Bacillus cereus T spores. Purified oleuropein, a well-characterized component of olive extract, inhibited these processes also. The addition of oleuropein and olive extracts 3 or 5 min after germination began, immediately decreased the rate of change of phase bright to phase dark spores and delayed significantly outgrowth.

Growth of Salmonella enteritidis in artificially contaminated hens' shell eggs.

The effect of some factors on the growth of Salmonella enteritidis phage type 4 in artificially contaminated shell eggs was investigated. Salmonella enteritidis was found to be resistant to the antimicrobial properties of the albumen. Growth occurred on storage at 25 degrees C but not at 4 or 10 degrees C. The rate and extent of infection was influenced by the size of inoculum, the site of contamination relative to yolk movement, and the presence of iron in the inoculum.

Staphylococcus aureus S-6: factors affecting its growth, enterotoxin B production and exoprotein formation.

The growth of Staphylococcus aureus S-6, enterotoxin production and exoprotein formation were always higher in NZ-amine A medium compared with brain heart infusion medium. The formation of exoproteins, including enterotoxin B, per bacterial cell in static culture was influenced by the addition of glucose. Lactate and amino acids were used by Staph. aureus S-6 in media without additional glucose. When both media were supplemented with glucose, lactic and acetic acids were produced. Different electrophoretic patterns for exoprotein formation were obtained when the organism was grown in shaken or static culture.

A study of sulfite-tolerant yeasts from comminuted lamb products.

The sulfite tolerance of meat yeasts was shown to be determined by pH, sulfite concentration, substrate availability, and the composition of the preincubation medium. Acetaldehyde production by Candida norvegica was sulfite-induced and occurred during the exponential growth phase in sulfited (500 micrograms SO2 ml-1) lab lemco glucose broth cultures buffered at pH 5, 6, or 7. Growth at pH 4, however, was inhibited by sulfite. Acetaldehyde production occurred in sulfited medium containing fructose or ethanol but not lactate nor a range of other assimilable substrates. A non-acetaldehyde-producing yeast, Candida vini, grew in sulfited (500 micrograms SO2 ml-1) lab lemco broth containing glucose or lactate buffered at pH 6 or 7 but not at pH 4 or 5.

Glucose, the key substrate in the microbiological changes occurring in meat and certain meat products.

The literature dealing with the role of glucose in the microbiological changes of meat and certain meat products is reviewed. Discussion is centered on two aspects. First, glucose plays a part in the selection of the dominant spoilage organisms, Pseudomonas fragi, Ps. lundensis, and Ps. fluorescens, on red meat stored aerobically under chill (2-7 degrees C) conditions. It is concluded that the pseudomonads flourish because they convert glucose to the less commonly used substrate, gluconate. The latter serves as an extracellular energy store. With its depletion, the pseudomonads utilize amino acids, thereby producing the characteristic off-odors of spoiled meat. Storage of meat in a modified atmosphere (viz., 20% CO2:80% O2) selects Gram-positive flora (lactobacilli and Brochothrix thermosphacta) which impart a "cheesy odor" through acid production from glucose and volatile fatty acids from amino acids. The first mentioned organisms produce the same off-odors in "acid" meat (pH 5.5) from which oxygen is excluded. So too does the less acid-tolerant Br. thermosphacta in less acid meat (pH greater than 5.8), especially if trace amounts of O2 are present. Such meat may be colonized by Shewanella putrefaciens also, with green discoloration resulting from the release of H2S from amino acids. The addition of glucose and NO2- to, and the exclusion of oxygen from, comminuted meat selects a flora dominated by Lactobacillus spp. and staphylococci such as Staphylococcus carnosus. Second, sulfite, the preservative of British-style sausages, has a sparing action on glucose. As a consequence of its curtailed breakdown there is only a meager acid drift with storage even though a fermentative flora of lactobacilli and Br. thermosphacta is selected. Yeasts also contribute to the microbial association in sausages; members of four of the six commonly occurring genera bind sulfite through acetaldehyde production. Glucose appears to be essential for acetaldehyde synthesis. The role of glucose in spoilage and the conditions which select particular groups of spoilage organisms are considered in the context of chemical probes and/or instrumental methods for routine assessment of the "freshness" of meat and meat products.

Influence of Spoilage Flora and Temperature on Growth of Staphylococcus aureus in Turkey Meat.

Staphylococcus aureus isolated from a turkey processing plant grew in ground turkey muscle, either leg or breast, contaminated with spoilage bacteria with incubation at 15,20 or 23°C. No growth occurred with incubation at 7 or 10°C. The rate and extent of growth of S. aureus at 15 and 20°C were increased by cooking the muscle before inoculation. Toxin production during growth of S. aureus on turkey muscle was demonstrated on one occasion only.

Natural antimicrobial systems and their potential in food preservation of the future.

The extensive literature on natural antimicrobial systems in animals, plants, and microorganisms is surveyed and particular systems are discussed, viz., the peroxidase systems in saliva and milk, singlet oxygen in the phagosome, cecropins and attacins in insects, complement, lysozyme and, to a limited extent, phytoalexins. The review draws attention to the cardinal role of targets on the cell envelopes of alien cells, especially bacteria, and emphasizes a possible approach to preservation based on the selection of specific agents for particular targets. The available evidence suggests that the perturbation of the homeostasis of all the organisms in the mixed flora of a food is unlikely to be achieved by one antimicrobial substance in isolation. Future studies need to consider therefore a tandem approach with two or more agents chosen because of their complementary action. Alternatively, natural system(s) and an established preservative method, either chemical or physical, warrant investigation. The extensive literature on the mechanisms whereby specialist pathogens overcome the defenses of plants and animals emphasizes the inherent dangers of selection leading to the persistent contamination of food processing areas with organisms tolerant of a particular antimicrobial system.

Sulfite, an elective agent in the microbiological and chemical changes occurring in uncooked comminuted meat products.

The literature dealing with sulfite preservation of meat products is reviewed. Discussion is centered on three aspects: (i) the elective action of sulfite, whereby its presence in meat products encourages the development of an association of Gram-positive bacteria (Brochothrix thermosphacta and homofermentative lactobacilli) and yeasts. Unsulfited products tend to be dominated by Pseudomonas fragi at chill, and Enterobacteriaceae at ambient temperatures; (ii) the diminution of the preservative potential of a meat product, which is associated with the binding of sulfite by acetaldehyde-producing yeasts; and (iii) the sparing action that sulfite has on the carbohydrates contained in the meat or included as an ingredient.

The cytotoxic and photodynamic inactivation of micro-organisms by Rose Bengal.

Rose Bengal was cytotoxic to the following bacteria at the concentrations given in parentheses (highest concentrations of dye in mol/l at which growth occurred on nutrient medium): Brochothrix thermosphacta and Deinococcus radiodurans (1 X 10(-6) or less); Streptococcus, Micrococcus, Staphylococcus, Bacillus, Arthrobacter and Kurthia spp. (1 X 10(-5)-1 X 10(-4], and Pseudomonas spp. and Enterobacteriaceae (5 X 10(-3)-1 X 10(-2) or greater). These organisms were killed rapidly when suspended in illuminated (170 microE/m2/s) solutions of Rose Bengal (1 X 10(-4) mol/l) providing oxygen was present. Singlet oxygen was identified as the lethal agent, because the rate of killing was increased by dissolving the dye in deuterium oxide while the organism were protected against photoinactivation by L-histidine or crocetin. Yeasts from chilled foods were killed in illuminated solutions of Rose Bengal but a light intensity of 315 microE/m2/s was needed for a death rate comparable with that of bacteria. The yeasts present in a range of chilled meat and dairy products failed to form colonies on Rose Bengal (5 X 10(-5) mol/l) media exposed continuously to modest illumination (55-80 microE/m2/s).