ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04433.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

A number of pseudomonad bacteria were investigated for theirin vitroantagonism on agar againstPseudomonas tolaasii, the causative agent of bacterial blotch of the cultivated mushroom. Addition of FeCl3to the culture medium suppressed the antagonism in 14 of the 20 bacteria tested and the production of a substance with an absorption peak at 400 nm by all antagonists was eliminated by the presence of Fe3+. Both observations indicated that siderophores could be involved in the mode of action of some antagonists. The addition of the iron chelators EDTA and bipyridyl to the medium used for culture of antagonists and pathogens did not generally prevent growth. Siderophore production is not essential for thein vivoactivity of antagonists.

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04434.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Extracts of black tea exhibited bactericidal activity againstVibrio choleraeO1. The tea extract inhibited the haemolysin activity ofV. choleraeO1, El Tor and the morphological changes of Chinese hamster ovary cells induced by cholera toxin. Tea extract also reduced fluid accumulation induced by cholera toxin in sealed adult mice and byV. choleraeO1 in ligated intestinal loops of rabbits. These findings suggest that tea has protective activity againstV. choleraeO1.

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04435.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Promoter elements fromLactobacillus caseiwere isolated with anEscherichia colipromoter probe vehicle and inserted 5′ to theluxA/Bgenes fromVibrio fischerilocated within a pCK1‐based shuttle vector. Three independent promoter‐luxconstructs were each used to transformLactobacillus casei, Lactococcus lactisandLactococcus lactissubsp.diacetylactisby electroporation. Transformants of all three bacteria which expressed a bioluminescent phenotype in the presence of exogenous dodecanal were obtained. By virtue of monitoring changes in light production, these recombinant micro‐organisms could form the basis of a rapid monitoring system for antimicrobial substances in milk active against starter culture bacteria. In addition, the research potential ofin vivobioluminescence for monitoring gene expression in lactic acid bacteriain situwithin fermentation systems can now be ad

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04436.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The polymerase chain reaction (PCR) amplification technique was investigated as a tool for direct detection ofListeria monocytogenesin soft cheeses. Different sets of oligonucleotide primers were used, and parts of theL. monocytogenesDth18‐gene could be amplified specifically when either a plasmid vector carrying the cloned gene or chromosomal DNA was used as a template. The detection limit forL. monocytogenesin dilutions of pure cultures was between 1 and 10 colony‐forming units. In extracts from soft cheeses containingL. monocytogenesDNA, the amplification was strongly inhibited. This inhibition could be reduced by an additional purification step. Despite this the detection limit showed a large variation, depending on the brand of cheese used. In some cheeses 103cfu/0.5 g could be visualized whereas in others the presence of 108cfu/0.5 g did not yield a detectable quantity of amplified prod

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04437.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

A heterofermentative lactic acid bacterium isolated from meat packaged under elevated CO2levels was identified asLeuconostoc gelidum, based on the description of this new species by Shaw&Harding (1989). It grows well at refrigeration temperatures but not at 35°C. The organism produces an inhibitory substance that is inactivated by protease and trypsin, but not by catalase or by heating at 62°C for 30 min. The bacteriocin‐like inhibitory substance is produced early in the growth cycle, at 1, 5 and 25°C. The inhibitory substance is active against a large number of closely related lactic acid bacteria, as well as a strain ofEnterococcus faecalisandListeria monocytogenes. There is initial evidence that the genetic information determining production of, and resistance to, the bacteriocin‐like substance is plasmid mediated. Of the three plasmids found in this organism, loss of the 7.6 MDa plasmid resulted in loss of inhibitor production and resistance to the inhibitory substance. Loss of the 5.0 MDa plasmid did not result in a detectable phenotypic change in the or

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04438.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The suitability of a variety of media and procedures for the enumeration of sulphite‐reducing clostridia in food was investigated. The most suitable procedure was pasteurization of the 1/10 macerate for at least 1 min at 80°C; followed by culture at 30°C for up to 3 d in a sulphite‐based, differential reinforced clostridium medium, without bicarbonate or lactate but with an increased iron concentration, and sulphite and iron added after sterilization. Black sulphite‐reducing colonies were finally tested for sensitivity to metronidazole and confirmation of their failure to grow on agar slopes under aerobic con

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04439.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

The effect of ciliate protozoa on the activity of polysaccharide‐degrading enzymes in microbial populations from the digesta solids and liquor fractions of rumen contents was examined after the refaunation of ciliate‐free sheep with an A‐type rumen protozoal population. Although the culturable rumen bacterial population was reduced after refaunation the number of fibrolytic micro‐organisms detected was higher; the xylanolytic bacterial population and numbers of fungal zoospores were increased after refaunation. The proportion of propionic acid was lower in the refaunated animals, whereas the concentration of ammonia and the acidic metabolites acetate, butyrate and valerate were all increased. The range of enzyme activities present in the digesta subpopulations were the same in defaunated and refaunated animals. The activities of the polysaccharide‐degrading enzymes, however, were increased in the microbial populations associated with the digesta solids after refaunation, and at 16 h after feeding the activities were 4–8 times (β‐d‐xylosidase 20 times) higher than the levels detected in the adherent population from defaunated sheep. The protozoa, either directly through their own enzymes or indirectly as a consequence of their effects on the population size and activity of the other fibrolytic micro‐organisms present, have an important role in determining the level of activity of polysaccharide‐degrading enzymes in the rumen ecosystem. Although the extent of ryegrass (Lolium perenne) hay digestion was similar after 24 h in the absence or presence of protozoa, the initial ruminal degradation was higher

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04440.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

Sublethal concentrations of formic acid (10 mmol/l) and propionic acid (5 mmol/l) at pH 5.0 preferentially inhibit DNA synthesis and stop cell multiplication in the absence of a corresponding cessation in the increase of culture turbidity. The possibility that the acids induce the SOS response by starving cells of thymine or by causing physical damage to the DNA molecule has now been investigated. Accumulation of thymine into the cytoplasm of whole cells was not inhibited by either acid. Mutants defective in excision repair (uvrA6), recombination repair (recA56) and polymerase activity (polA1) were not more sensitive to the acids than their isogenic parent. No significant increase in cell length was observed from measurements of transmission electron microscope images of acid‐treated cells. It is concluded, therefore, that sublethal concentrations of formic and propionic acid inhibit DNA synthesis without physically damaging DNA molecule, or starving the cell of essential thymine or otherwise inducing an SOS respons

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04441.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY

摘要:

When strains ofEscherichia coliK12 andSalmonellaspp. were incubated with 0.5–0.7 mol/l formic or propionic acid at pH 5.0, propionic acid was more active than formic acid. It killed 90% of the cell population within 60 min compared with over 3 h for formic acid. Cell death was not associated with a reduction in culture turbidity or a loss of membrane integrity since morphologically normal membranes were observed by electron microscopy and only a small proportion of the cytoplasmic enzyme β‐galactosidase leaked into the supernatant fluid of acid‐treatedE. coliK12 cu

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1991.tb04442.x

出版商:Blackwell Publishing Ltd    

年代:1991

数据来源: WILEY