摘要:

An enrichment method was used to monitorErwinia carotovorain soil or the rhizosphere of different crops and weeds in 17 fields with different cropping histories on three farms. The bacteria were detected in all fields not cropped with potatoes, although not consistently, and the mean annual frequency of detection was generally low (<10%). Fields in which potatoes were grown were extensively contaminated after harvest in September but contamination declined over the winter to very low levels by early summer in the following year. Contamination level tended to rise in some fields without potatoes regardless of their cropping history but for only a short time during autumn and winter. The bacteria were no more frequent in rhizosphere soil of any of the weeds or crops examined, with the exception of brassicas, than in bare soil. In fields where more than 16 months had elapsed since cropping with potatoes, 91% of erwinia isolates obtained wereE. carotovorasubsp.carotovora, the remainder beingE. carotovorasubsp.atroseptica.The bacteria were shortlived in soil and in the rhizospheres of inoculated field and pot grown crop and weed plants. Longevity was greater in dry (10% moisture) than in wet (21% moisture) soil and decreased as temperatures rose, particularly above 25°C. Survival was best in association with brassica plants, moderate on grasses and cereals, and least on potatoes and weeds.E.c. carotovorasurvived better thanE.c. atroseptica.Because survival of the bacteria in soil is apparently restricted, their presence in fields could be attributed to recurrent introductions from different sources

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02459.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Suspensions of epiphytic bacteria from submerged stems ofPhragmites australis, collected from a gravel‐pit pond, were prepared by treatment in a stomacher and by brushing. The two procedures were equally successful in dislodging bacteria. These epiphytic bacteria were compared with planktonic bacteria in water samples from within the reed bed. Colony‐forming units (cfu) as a percentage of acridine‐orange direct counts (AODCs), percentage of cells capable of intracellular reduction of 2‐(p‐iodophenyl)‐3‐(p‐nitrophenyl)‐5‐phenyl tetrazolium chloride (INT) to INT‐formazan, percentage of cells able to form microcolonies, and cell length were all greater for epiphytic bacteria. Epiphytic bacteria ofP. australisfrom six further gravel‐pit ponds were also compared with bacterioplankton; cfu as a percentage of AODCs, and percentage of cells capable of INT reduction were again greater for epiphytic bacteria. Because the epiphytic bacteria in these non‐organically‐enriched, gravel‐pit ponds were physiologically different from the planktonic bacteria it is suggested that there was not continual casual exchange, by largely identical bacterial cells, between the epiphytic and planktonic mode. Instead, epiphytic and planktonic populations were independent of each other and/or if there was exchange then bacteria were more successful while in the attached mode, perhaps because of greater organic‐nutrient a

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02460.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Cells ofCampylobacter jejuniexposed to heating or freezing were progressively less able to grow at 43°C, particularly on selective media. This influenced the recovery of damaged cells from naturally and artificially contaminated samples. With broth culture the isolation rate could be increased by pre‐enrichment in basal or selective media at 37°C for 4 h. With membrane filtration or surface plating techniques the inclusion of agents that quench toxic derivatives of oxygen was more import

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02461.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

The applicability of enzyme‐linked immunosorbent assay (ELISA) for the detection of salmonellas in foodstuffs was investigated. Several factors affecting the sensitivity of the ELISA, such as the type of protein used for plate post‐coating, the method of antibody labelling, and accelerators for antigen‐antibody and enzyme‐substrate reactions, were studied. Labelling of the antibody with horseradish peroxidase and the use ofo‐phenylenediamine as substrate in the detection system were demonstrated to be most suitable for the enzyme assay.Based on these findings, an improved ELISA method was developed for the detection ofSalmonella typhimurium.The improved technique was able to detect as few as 5×104‐105cell/ml of salmonellas, and about 24 h were required to enrich the bacteria in food samples and to perform the test. With some modifications, the ELISA assay could reach a very high level of sensitivity and provide excellent repr

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02462.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Lipolytic and proteolytic psychrotrophs were isolated from raw and pasteurized goats’milk, which had been stored at 5°C for 7d. The 241 strains isolated and 20 reference strains were examined by 149 biochemical, physiological, and morphological tests. The results yielded 195 characters suitable for taxonomic analysis. Computer‐assisted complete linkage analysis, using the Jaccard coefficient, produced 22 phenons at 75% S. The results showed thatPseudomonas fluorescenswas the predominant psychrotrophic bacterium, but thatPseudomonas fragiwas dominant in some milk samples. Strains ofSerratia liquefaciensandFlavobacterium balustinumwere also identi

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02463.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A comparison was made of 27 ‘endemic’ strains ofStaphylococcus aureusand 35 strains from freshly slaughtered birds, isolated at five commercial slaughterhouses processing chickens or turkeys. Of 112 biochemical and physiological tests used, 74 gave results which differed among the strains. Cluster analysis revealed several distinct groupings which were influenced by strain type, processing plant and bird origin; these included a single group at the 72% level of similarity containing most of the ‘endemic’ strains. In comparison with strains from freshly slaughtered birds, a higher proportion of ‘endemic’ strains produced fibrinolysin, aP‐glucosidase and urease and were β‐haemolytic on sheep‐blood agar. The ‘endemic’ type also showed a greater tendency to coagulate human but not bovine plasma, and to produce mucoid growth and clumping. The last two properties, relevant to colonization of processing equipment, were less evident in heart infusion broth than in richer media or process water collected during def

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02464.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A laser‐light pulse counting method was developed and investigated for its ability automatically to count acridine orange‐stained bacteria and microcolonies of bacteria on the surface of polycarbonate membrane filters. The system consisted of an Argon laser which delivered a 5 μm diameter spot of coherent 488 nm wavelength light which was raster scanned across a 5×2 mm area of the membrane. Fluorescence pulses of orange light (ca650 nm) were detectedviaa dichroic mirror and barrier filter with a photomultiplier tube. For microcolony preparations a good relationship between the number of light pulses and cell density down to below 102/ml was observed, but at lower cell densities counting was not reliable, probably because of fluorescent debris. The method was also able to count single cells, but background auto‐fluorescence and photo‐bleaching produced a high and variable background signal in som

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02465.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

A cell‐bound pectinolytic enzyme was isolated from cells ofSelenomonas ruminantiumand purified about 360‐fold. The optimum pH and temperature for enzyme activity was 7.0 and 40°. The enzyme degraded polymeric substrates by hydrolysis of digalacturonic acid units from the non‐reducing end; the best substrate was nona‐galacturonic acid. Unsaturated trigalacturonate was also degraded, but 30% slower than the saturated analogue. The enzyme was classified as a poly (1,4‐aP‐D‐galactosiduronate) digalacturono‐hydrolase; EC 3.2.1.82. Another enzyme, hydrolysing digalacturonic acid to monomers, was also produced in a very small amount

ISSN:0021-8847    

DOI:10.1111/j.1365-2672.1989.tb02466.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY