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Biomedical subjects

B M Lund

Publications and source records attributed to B M Lund.

At least 19 recordsLinked to original sources
PubMed1996

The effect of nisin on Listeria monocytogenes in culture medium and long-life cottage cheese.

The sensitivity to nisin of 27 strains of Listeria monocytogenes, four of L. innocua and one of L. ivanovii was estimated at pH 6.8 and pH 5.5. Strains of L. monocytogenes showed differences in sensitivity which were not correlated with serotype. Strains of L. innocua were as resistant as the most resistant strains of L. monocytogenes, whereas the strain of L. ivanovii was relatively sensitive. Two of the most resistant strains of L. monocytogenes multiplied in aerated liquid medium adjusted to pH 5.0 with HCl, incubated at 20 degrees C; nisin, 500 IU ml-1, prevented multiplication and caused death. Following inoculation of a resistant strain into long-life cottage cheese, pH 4.6-4.7, the number of viable L. monocytogenes decreased approximately 10-fold during storage at 20 degrees C for 7 d; addition of nisin, 2000 IU g-1, to the cottage cheese increased the rate of inactivation to approximately a 1000-fold decrease in 3 d.

Anti-Bacterial Agents↗
PubMed1995

Effect of heat treatment on survival of, and growth from, spores of nonproteolytic Clostridium botulinum at refrigeration temperatures.

Spores of five type B, five type E, and two type F strains of nonproteolytic Clostridium botulinum were inoculated into tubes of an anaerobic meat medium plus lysozyme to give approximately 10(6) spores per tube. Sets of tubes were then subjected to a heat treatment, cooled, and incubated at 6, 8, 10, 12, and 25 degrees C for up to 60 days. Treatments equivalent to heating at 65 degrees C for 364 min, 70 degrees C for 8 min, and 75 degrees C for 27 min had little effect on growth and toxin formation. After a treatment equivalent to heating at 85 degrees C for 23 min, growth occurred at 6 and 8 degrees C within 28 to 40 days. After a treatment equivalent to heating at 80 degrees C for 19 min, growth occurred in some tubes at 6, 8, 10, or 12 degrees C within 28 to 53 days and at 25 degrees C in all tubes within 15 days. Following a treatment equivalent to heating at 95 degrees C for 15 mine, growth was detected in some tubes incubated at 25 degrees C for fewer than 60 days but not in tubes incubated at 6 to 12 degrees C. The results indicate that heat treatment of processed foods equivalent to maintenance at 85 degrees C for 19 min combined with storage below 12 degrees C and a shelf life of not more than 28 days would reduce the risk of growth from spores of nonproteolytic C. botulinum by a factor of 10(6).(ABSTRACT TRUNCATED AT 250 WORDS)

Anaerobiosis↗
PubMed1992

An investigation of the antibacterial effect of carrot on Listeria monocytogenes.

Carrot slices immersed in a potassium phosphate buffer (0.1 mol/l, pH 7.0) or carrot tissue macerated in the buffer had a lethal effect on Listeria monocytogenes. This antilisterial activity was suppressed by anaerobiosis, thiol compounds (1 mmol/l) and bovine serum albumin (0.05%) but was not affected by sodium ascorbate (200 mmol/l), propyl gallate (25 mmol/l), catalase (1100 U/ml), superoxide dismutase (357 U/ml), or chelating agents (10 mmol/l). Free-radical scavengers had no effect at 10 mmol or 50 mmol/l but histidine and diazabenzocyclooctane at 100 mmol/l reduced the antilisterial activity. The addition of Tween 20, 0.05% (v/v), to carrot macerates improved the recovery of the activity in the supernatant liquid after centrifugation at 10,000 g for 2 min. The addition of higher concentrations of the detergent to the macerate reduced the antilisterial activity.

Anaerobiosis↗
PubMed1991

The lethal effect of carrot on Listeria species.

When shredded or sliced carrots were inoculated with Listeria monocytogenes the number of viable listerias decreased rapidly. On carrot slices stored at 8 degrees C there was a decrease after 3d followed by an increase, after 7d, to numbers similar to those present initially. The numbers of spoilage micro-organisms increased throughout storage at 8 degrees C. Carrots macerated in a Stomacher Lab Blender also showed an antilisterial activity which resulted in a decrease in number of viable bacteria and in sublethal damage. The effect was shown by five carrot cultivars and acted on nine strains of L. monocytogenes and single strains of L. innocua, L. ivanovii, L. seeligeri, L. melshimeri. This antilisterial effect was heat-labile, was inactivated after a few hours at 4 degrees C or at 30 degrees C and was active over the pH range 5.8 to 7.0. Maceration of carrots in an Atomix blender for 1 min or in liquid nitrogen destroyed the antilisterial activity.

Colony Count, Microbial↗
PubMed1991

The survival of Listeria monocytogenes in cottage cheese.

Because of the difficulty of ensuring that cottage cheese is produced in conditions that prevent contamination with Listeria monocytogenes, the ability of this bacterium to survive in cottage cheese from three sources was investigated (a) during shelf-life at chill temperature and (b) in conditions of temperature abuse. Three batches of creamed cottage cheese, from three sources, received within 24 h of production, were inoculated with L. monocytogenes strain F6861 and stored at 4, 8 or 12 degrees C for 14 d. The three batches differed in their initial pH, titratable acidity and content of lactic acid and of lactic acid bacteria. No increase in numbers of L. monocytogenes occurred in the cottage cheeses during storage in these conditions. The numbers of listeria decreased; the rate of decrease differed in products from the three sources and was least in the product with the highest pH and lowest content of lactic acid. Acid formation by lactic acid bacteria during storage of the products probably contributed to the inhibition of listeria.

Cheese↗
PubMed1990

The influence of pH, temperature and organic acids on the initiation of growth of Yersinia enterocolitica.

The influence of incubation temperature, and of acetic, lactic and citric acids on the minimum pH for the initiation of growth of six strains of Yersinia enterocolitica was determined. The strains included two of serotype O : 9, two of serotype O : 3, and one each of serotypes O : 8 and O : 5, 27. In a culture medium acidified with HCl to pH values between 4.0 and 6.0 at intervals of approximately 0.1 unit the minimum pH at which growth was detected after incubation at 20 degrees, 10 degrees, 7 degrees and 4 degrees C for 21 d was in the ranges 4.18-4.36, 4.26-4.50, 4.36-4.83 and 4.42-4.80, respectively. The minimum pH for growth was also determined in media that contained 17, 33 and 50 mmol/l acetic acid adjusted to pH values between 5.1 and 5.9 at intervals of approximately 0.2 unit, 24, 48 and 95 mmol/l citric acid adjusted to pH values between 4.1 and 4.9 at intervals of approximately 0.2 unit, and 22, 44, and 111 mmol/l lactic acid adjusted to pH values between 4.3 and 5.7 at intervals of approximately 0.4 or 0.5 unit. The effect of these concentrations of organic acids was, in most cases, to increase the minimum pH that allowed growth. The order of effectiveness of the organic acids in raising the minimum pH for growth was acetic greater than lactic greater than citric and the minimum inhibitory concentrations were greater at higher temperatures.

Acetates↗
PubMed1990

The combined effect of incubation temperature, pH and sorbic acid on the probability of growth of non-proteolytic, type B Clostridium botulinum.

It has been reported that non-proteolytic strains of Clostridium botulinum will grow at 3.3 degrees C, and they are therefore of concern in relation to certain chilled foods. The effects of combinations of inhibitory factors may be used to reduce the risk of growth of these bacteria in foods. The combined effect of pH values between 4.8 and 7.0, temperatures between 6 degrees and 30 degrees C, and sorbic acid concentrations up to 2270 mg/l on the probability of growth from a single spore of non-proteolytic, type B strains in a culture medium has been determined. A mathematical model has been developed that enables the effect of varying combinations of these factors on the probability of growth of non-proteolytic, type B Cl. botulinum to be predicted.

Clostridium botulinum↗
PubMed1989

Survival and growth of food poisoning bacteria following inoculation into cottage cheese varieties.

Following inoculation into cottage cheese varieties with and without sorbic acid, obtained directly from the manufacturer, strains of enteropathogenic Escherichia coli and other E. coli survived but failed to multiply during storage at 7, 10 or 25 degrees C. In the absence of sorbic acid spoilage due to Pseudomonas fluorescens occurred after storage for 5-13 days at 7 or 10 degrees C and 1-2 days at 25 degrees C. Salmonella enteritidis, S. hadar, S. saint-paul, S. typhimurium and S. virchow survived but failed to multiply at 10 degrees C and, in the case of most strains, at 20 or 25 degrees C. S. typhimurium multiplied 100-fold in one batch of cottage cheese with peppers and onion in the absence of sorbic acid during storage at 25 degrees C for 2 days; spoilage of this batch occurred due to yeasts or yeasts and moulds after storage for 4-8 days at 10 degrees C and 0-2 days at 20 or 25 degrees C. Following inoculation into cottage cheese varieties, prepared in the laboratory and which did not contain sorbic acid, as contaminants of the added protein or vegetable ingredients the numbers of Staphylococcus aureus declined during storage at 10 and 20 degrees C, the numbers of Bacillus cereus and S. typhimurium increased at both temperatures, and the numbers of Yersinia enterocolitica increased at 10 degrees C, but declined at 20 degrees C. Spoilage occurred due to the growth of moulds and P. fluorescens after storage for 5-14 days at 10 degrees C, and due to P. fluorescens after storage for up to 2 days at 20 degrees C. In products inoculated in a similar way but which contained sorbic acid (500-530 mg/kg), the numbers of S. aureus and B. cereus declined and in most products the numbers of S. typhimurium and Y. enterocolitica remained constant. In cottage cheese with chicken, however, the numbers of Y. enterocolitica increased 100-fold during storage of the product for 14 days at 10 degrees and the numbers of S. typhimurium increased 100-fold during storage for 2 days at 20 degrees C. Spoilage of this product due to P. fluorescens occurred after storage for 8-14 days at 10 degrees C, but was not evident at 20 degrees C after 2 days.

Bacillus cereus↗
PubMed1988

The effect of pH on the initiation of growth of cottage cheese spoilage bacteria.

The influence of pH on strains of Pseudomonas spp. and Enterobacter agglomerans that cause spoilage of cottage cheese varieties during storage at 7 degrees C has been investigated. In a culture medium adjusted to the required pH with HCl, 57 of 64 strains of Pseudomonas spp. grew at pH 4.8 when incubated at 7 degrees C but a very low proportion of strains grew at pH 4.7 or pH 4.6 and none at pH 4.5. At 20 degrees C some of the pseudomonads grew at pH 4.4. Three out of nine strains of E. agglomerans grew at pH 3.8 when incubated at 7 degrees C and at pH 3.6 when incubated at 20 degrees C. In cultures of E. agglomerans at controlled pH and 20 degrees C, after a lag phase the doubling time at pH 4.1 was 2 h, and at pH 7.0 was 1.4 h.

Cheese↗
PubMed1988

Growth and formation of toxin by Clostridium botulinum in peeled, inoculated, vacuum-packed potatoes after a double pasteurization and storage at 25 degrees C.

A process that claims to use a double pasteurization to produce vacuum-packed potatoes for storage at ambient temperature has been evaluated. After the first pasteurization, potatoes are vacuum-packed and stored at 25 degrees-35 degrees C for up to 24 h, which is intended to allow germination of bacterial spores, and are then pasteurized again. When potatoes were inoculated with spores of Clostridium botulinum and subjected to this double-pasteurization process a high proportion of spores remained viable and resulted in growth and formation of toxin within 5-9 d at 25 degrees C. To provide an appropriate reduction in the risk o survival and growth of Cl. botulinum, peeled, vacuum-packed potatoes for storage at ambient temperature should be given a heat treatment equivalent to an F(0)3 process. If they are not given such a heat treatment they should be stored at a temperature below 4 degrees C.

Botulinum Toxins↗
PubMed1987

The combined effect of sub-optimal temperature and sub-optimal pH on growth and toxin formation from spores of Clostridium botulinum.

Low-acid foods (pH greater than or equal to 4.5) are not sufficiently acidic to prevent growth of Clostridium botulinum in otherwise optimal conditions. The combination of sub-optimal pH and sub-optimal temperature may, however, result in a very significant reduction in the risk of growth of this bacterium compared with the risk in optimal conditions. The combined effect of incubation temperatures of 12 degrees and 16 degrees C and pH values between 5.2 and 5.5 on growth and toxin production from spores of Cl. botulinum during incubation for 28 d has been investigated. Growth and formation of toxin (type B) were detected only in medium at pH 5.5 and incubated at 16 degrees C, corresponding to a probability of growth from a single spore within 14 d of 1.6 x 10(-5). The probability of growth in 28 d in the remaining conditions was less than 9 x 10(-6). After transfer of inoculated media from 12 degrees to 30 degrees C growth occurred at pH 5.2-5.5 within 19 d. After transfer of inoculated media from 12 degrees to 20 degrees C growth occurred at pH 5.5 and 5.4 but not at pH 5.3 or 5.2 in 40 d. Growth at pH 5.2-5.5 was accompanied by formation of toxin, in most cases of types A or B. In addition to the effect of sub-optimal temperature and pH, chelation of divalent metal ions by citrate may have contributed to inhibition.

Botulinum Toxins↗
PubMed1987

A note on the microbiology of retail packs of prepared salad vegetables.

Retail packs of mixed, prepared salad vegetables from two different manufacturers were stored at 7 degrees C until the end of storage-life (sell-by date plus 1 d), when the microbial flora was examined. The quality of the salads was acceptable at the end of storage life. The oxygen concentrations in packs were lower, and the carbon dioxide concentrations were higher, than those in air. High numbers of bacteria were present, with Pseudomonas spp. and Enterobacter agglomerans predominating in packs of both salads, together with lactic acid bacteria in one of the salads. Significant numbers of pectolytic bacteria including Pseudomonas spp. and Erwinia carotovora were detected. Despite the presence of high numbers of coliform bacteria, Escherichia coli was not detected in batches of one salad, and was detected in relatively low numbers in batches of the other. Yersinia spp., predominantly environmental strains of Yersinia enterocolitica, were isolated by enrichment from all samples tested; Staphylococcus aureus and enterococci were not detected.

Carbon Dioxide↗