ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01519.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Lactic acid bacteria isolated from vacuum‐packaged fresh meat stored at 4°C were shown to produce antagonistic substances active against closely related bacteria. Growth medium, pH and growth temperature all affected the production of the inhibitory substances. Ten strains including aciduricLactobacillus‐type organisms,Carnobacteriumspp. andLeuconostocspp. were selected that produced protein‐aceous substances that caused inhibition of indicator strains. These were considered to be bacteriocins or bacteriocin‐like compounds based on their inactivation with protease, generally narrow spectra of antibacterial activity and bactericidal or bacte‐riostatic modes of action. Activity was not lost from supernatant fluids as a result of heat treatment at 62°C for 30 min, except for theLeuconostocstrains. Inhibitory spectra of some strains includedEnterococcusspp. andListeria monocytogenes. Some strains were of interest because their inhibitory substances were detected in the supernatant fluid early in the growth cycle. The inhibitory substances differed in characteristics between strains and there is evidence that more than one bacteriocin‐like substance may be produced by

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01520.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Obiolor is an acidic non‐alcoholic beverage prepared by fermenting sorghum and millet malts. The traditional process for the production and microbiological characteristics of the beverage were investigated.Bacillusspp.,Lactobacillus plantarumandStreptococcus lactiswere the associated micro‐organisms most actively involved. Yeasts were present in low numbers towards the end of the fermentation. Other micro‐organisms isolated did not appear to play a role in the fermentation process. Variations in the important microbial groups involved and their metabolic products were studied. Titratable acidity increased gradually until the end of the fermentation while the total soluble solids and pH declined.Acetobacterspp. were probably responsible for the unacceptability of the product after

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01522.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A quantitative method was developed for the measurement of micromolar quantities of H2O2produced in Rogosa broth and peptonized milk broth by vaginal strains of lactobacilli isolated from women. The production of substantial amounts reproducibly was dependent on the growth of the organisms in acid media (pH ≤6.0) under anaerobic or micro‐aerophilic conditions with continuous agitation. The addition to the media of the enzyme inhibitor, 3‐amino‐l,2,4‐triazole, with or without catalase sometimes induced the production of H2O2especially in non‐agitated cultures. However, other agents such as concanavalin ando‐dianisidine had no enhancing effect, and catalase or peroxidase alone completely inhibited H2O2production.The H2O2produced in the acid media was stable for more than a month at 5°C but not in media at pH ≥ 7.0. Of five strains of lactobacilli tested by the quantitative method and by a chromogenic qualitative method (Rogosa‐catalase or ‐peroxidase agar), three consistently produced H2O2measurable by the former method, but none did so after growth of the organisms on Rogosa‐catalase/peroxidase agar which suggested that the qualitative method was unreliable. The fact that H2O2was produced in substantial quantities by some strains and not at all by others enabled H2O2‐producers and non‐producers

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01523.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The ability of 60 strains ofAeromonasto produce enterotoxin and haemolysin after cultivation at 5°C for 7–10 d was investigated. The strains were isolated from lamb meat, offal, carcasses and faeces, and had previously been tested for their ability to produce these exotoxins at 37°C. The results showed that some strains ofAeromonas hydrophilaandA. sobriawere capable of producing enterotoxin and haemolysin at 5°C, but none of theA. caviaestrains tested produced these two factors. Of the 30A. hydrophilastrains investigated 25 and 27 were enterotoxigenic and haemolytic respectively. Likewise, of the 24A. sobriastrains investigated 16 and 18 were enterotoxigenic and haemolytic respectively. The results indicate that certain strains ofAeromonasspecies, in particularA. hydrophilaandA. sobria, are of potential public health significance in meats stored at refrigeration tempera

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01524.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

Open fronted Class I and II microbiological safety cabinets (MSCs) are required by the British Standard 5726 to provide similar levels of operator protection (viz. 105). In laboratories that are naturally ventilated large numbers of both types of cabinets have been shown to exceed this requirement consistently over a number of years. The designs of some mechanically ventilated laboratories, however, produce excessive turbulence and draughts that can prejudice containment at the front aperture. On‐site commissioning tests to determine operator protection factor are now well established and are recognized as being essential to the setting up of all open fronted cabinets in both ventilated and unventilated laboratories. This paper shows that where environmental conditions induce unsatisfactory cabinet containment, adjustments to air supply and exhaust systems can be made which will enable both Class I and II cabinets to produce operator protection factors in excess of 105. When compatibility is achieved between the local environment and the cabinets it is demonstrated that disturbances at the front aperture, caused by operator working procedures or by disturbances due to personnel movement within the room, have similar effects on both Class I and II cabinets. Once performance levels have been satisfactorily achieved, regular containment testing has shown that consistent performance can be maintained. These aspects of open fronted safety cabinet performance are discussed in relation to ventilated laboratories suitable for work with the human immunodeficiency virus (HIV). Of paramount importance in the future is the necessity to design laboratory air systems that will be compatible with satisfactory safety cabinet performance—a relatively new requirement in ventilation system specificati

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01525.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A blood‐free egg yolk medium (BCP) containing pyruvate, inositol, mannitol and a bromocresol purple indicator in a nutrient agar base has been developed to initiate the growth ofClostridium perfringens. It is comparable to blood agar for the growth of normal, chilled stored vegetative cells and heat‐injured spores ofCl. perfringensandBacillus cereus. It has the advantage over blood agar in exhibiting presumptive evidence ofCl. perfringens(production of lecithinase and inositol fermentation) after an overnight incubation at 43°C‐45°C. Pyruvate, catalase and other hydrogen peroxide degraders were found to remove toxins rapidly formed in media exposed to air and light. Free radical scavengers of superoxide, hydroxyl ions and singlet oxygen were ineffective. Without scavengers the formation of 10–20 μg/ml hydrogen peroxide in the exposed medium was indicated and found lethal to injuredCl. perfringens.The BCP medium has been used successfully for the rapid identification and enumeration ofCl. perfringensin foods and faeces from food poisoning outbreaks and cases of suspected infectious diarrhoea. Greater recovery of severely injured vegetativeCl. perfringenscould be obtained by pre‐incubation at 37°C of inoculated media for 2–4 h followed by overnight incubation at 43°C‐45°C. Tryptose‐sulphite‐cyclo‐serine and Shahidi‐Ferguson‐perfringens agar base were found to inhibit the growth of several strains of injured vegetativeCl. perfringens. This was not completely overcome by the addition of pyruvate. The inclusion of mannitol also allows the medium to be used for the presumptive identification ofB. cereus. Growth and lecithinase activity are profuse on BCP. Heat‐injured spores are recovered equally well on BCP and blood agar. A scheme for the identification of some other

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01526.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The resistance of stationary phaseSalmonella typhimuriumto heating at 55°C was greater in cells grown in nutritionally rich than in minimal media, but in all media tested resistance was enhanced by exposing cells to a primary heat shock at 48°C. Chloramphenicol reduced the acquisition of thermotolerance in all media but did not completely prevent it in any.The onset of thermotolerance was accompanied by increased synthesis of major heat shock proteins of molecular weight about 83, 72, 64 and 25 kDa. When cells were shifted from 48°C to 37°C, however, thermotolerance was rapidly lost with no corresponding decrease in the levels of these proteins. There is thus no direct relationship between thermotolerance and the cellular content of the major heat shock proteins. One minor protein of molecular weight about 34 kDa disappeared rapidly following a temperature down‐shift. Its presence in the cell was thus correlated with the thermotolerant

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01527.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

A total of 152 strains ofCampylobacter jejuni, C. coli, C. laridisandC. fetussubsp.fetuswere tested for haemolysis on blood agar plates. Distinct haemolysis was detected in 92.% (96/104) of strains ofC. jejuniand 21.7% (5/23) of strains ofC. colion sheep blood heart infusion agar after incubation for 4 d microacrobically at 42°C. Haemolysis was also detected on horse blood heart infusion agar. Haemolysis was not detected at 37°C except with one of 50 strains ofC. jejunitested at this temperature, which was weakly positive.Campylobacter laridiswas not haemolytic;C. fetussubsp.fetus, which does not grow at 42°C, showed no haemolysis at 37°C. Blood agar (Oxoid, BA Base No. 2) was not suitable for testing for haemolysis by these organisms. A microaerobic gas mixture containing hydrogen is better than that containing nitrogen because the medium has a brighter colour, making haemolysis casier to detect. There was no synergistic haemolysis withStaphylococcus aureusorStreptococcus agalactiae. The plate haemolysis test as described here may aid differentiation within the thermophilic campylobact

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01528.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY

摘要:

The influence of incubation temperature, and of acetic, lactic and citric acids on the minimum pH for the initiation of growth of six strains ofYersinia enterocoliticawas 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 HC1 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°, 10°, 7° and 4°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/1 acetic acid adjusted to pH values between 5.1 and 5.9 at intervals of approximately 0.2 unit, 24, 48 and 95 mmol/1 citric acid adjusted to pH values between 41 and 4.9 at intervals of approximately 0.2 unit, and 22, 44, and 111 mmol/1 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>lactic>citric and the minimum inhibitory concentrations were greater at higher t

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1990.tb01529.x

出版商:Blackwell Publishing Ltd    

年代:1990

数据来源: WILEY