Effect of γ Irradiation on the Microflora of Freshwater Fish: II. Generic Identification of Aerobic Bacteria from Yellow Perch Fillets1

Studies on the generic identification of bacteria isolated from nonirradiated and irradiated (0.3 and 0.6 Mrad) yellow perch fillets during the course of microbial spoilage have been conducted. After the enumeration and tabulation of macrocolonies on petri dish cultures obtained from fillets, isolates were examined and keyed out essentially according to modified morphological and biochemical protocols of Shewan. Identification was further confirmed through reference to Bergey''s Manual. Data obtained from each isolate were coded and recorded on IBM cards to facilitate identification. Total aerobic microbial plate counts obtained from nonirradiated perch before storage ranged from 10⁵ to 10⁶ microorganisms per gram of fish. Organisms isolated from these fillets, in order of decreasing number, consisted of Achromobacter, Alcaligenes, Pseudomonas, Brevibacterium, Micrococcus, Flavobacterium, Bacillus, Sarcina, Microbacterium, Corynebacterium, yeasts, Lactobacillus, Vibrio, Aeromonas, and a few Proteus and Escherichia cells. During storage and as spoilage progressed, the flora shifted and the pseudomonads became predominant. Irradiation of fillets to 0.3 and 0.6 Mrad reduced the aforementioned flora to the Achromobacter-Alcaligenes group, which constituted the residual flora throughout fillet storage.     

Effect of gamma Irradiation on the Microflora of Freshwater Fish: II. Generic Identification of Aerobic Bacteria from Yellow Perch Fillets

Studies on the generic identification of bacteria isolated from nonirradiated and irradiated (0.3 and 0.6 Mrad) yellow perch fillets during the course of microbial spoilage have been conducted. After the enumeration and tabulation of macrocolonies on petri dish cultures obtained from fillets, isolates were examined and keyed out essentially according to modified morphological and biochemical protocols of Shewan. Identification was further confirmed through reference to Bergey's Manual. Data obtained from each isolate were coded and recorded on IBM cards to facilitate identification. Total aerobic microbial plate counts obtained from nonirradiated perch before storage ranged from 10⁵ to 10⁶ microorganisms per gram of fish. Organisms isolated from these fillets, in order of decreasing number, consisted of Achromobacter, Alcaligenes, Pseudomonas, Brevibacterium, Micrococcus, Flavobacterium, Bacillus, Sarcina, Microbacterium, Corynebacterium, yeasts, Lactobacillus, Vibrio, Aeromonas, and a few Proteus and Escherichia cells. During storage and as spoilage progressed, the flora shifted and the pseudomonads became predominant. Irradiation of fillets to 0.3 and 0.6 Mrad reduced the aforementioned flora to the Achromobacter-Alcaligenes group, which constituted the residual flora throughout fillet storage.     

Study of Microflora in Malaysian Dried Fishes and Their Decontamination by Gamma-irradiation

The distribution of microorganisms in 10 samples of salted dried fish and the effects of irradiation of them were studied. The total aerobic bacteria in commercial dried fish were determined to be from 2 × 10⁴ to 3 × 10⁶ per gram. Mold counts were 1 × 10² to 7 × 10³ per gram with a lower amount of yeasts. In spoiled dried fish, total aerobic bacteria were determined to be 4× 10⁶ or 1 × 10⁷ per gram with a few yeasts. Coliforms were not isolated on MacConkey agar plates from any of the samples. The predominant bacteria occurring in spoiled dried fish were Pediococcus halophilus, Vibrio costicola and Planococcus sp. More than 50% of the molds consisted of the Aspergillus niger group, whereas lower amounts of the A. flavus, A. fumigatus and A. ochraceus groups, Penicillium chrysogenum series, etc. were also isolated from many samples of dried fish. All kinds of putrefactive microorganisms were radiation sensitive, and a dose of ca. 500 krad appears to be sufficient for extension of the shelf-life of dried fish from 2 to 4 times.     

Microcosm method to assess survival of recombinant bacteria associated with plants and herbivorous insects

A microcosm method was developed to investigate survial and fate of genetically engineered bacteria associated with plant surfaces and a plant-feeding insect, the variegated cutworm,Peridroma saucia. Larvae on radish plants in microcosms were sprayed with nonrecombinantPseudomonas cepacia and a recombinant strain ofP. cepacia carrying the transmissible plasmid R388::Tn1721. Leaf, whole insect, foregut, and frass samples were periodically assayed over a 48-h period to enumerate total bacteria andP. cepacia strains. Immediately after spraying,P. cepacia comprised about 20%–30% of the total population on leaves, which was 2×10⁷ cfu/g of leaf. Approximately 4×10⁷ total cfu were recovered from each gram of whole insect, when theP. cepacia strains averaged about 3×10⁵ cfu/g. After 2 days, the total epiphytic population had increased approximately fourfold, while theP. cepacia strains had decreased to 2%–30% of their initial numbers. After 24 and 48 h, eachP. cepacia strain numbered between 10⁴ and 10⁵ cfu/g of insect in foregut samples, whereas none was detectable in frass. Plasmid transfer fromP. cepacia R388::Tn1721 to the nonrecombinant recipientP. cepacia strain was not observed.     

Effect of γ Irradiation on the Microflora of Freshwater Fish: III. Spoilage Patterns and Extension of Refrigerated Storage Life of Yellow Perch Fillets Irradiated to 0.1 and 0.2 Megarad1

Maximal shelf life was determined and microbial flora were compared for irradiated (0.1 and 0.2 Mrad) and nonirradiated yellow perch fillets stored at 1 C. Shelf life was estimated by organoleptic determinations. Microbiological studies included determination of the effects of irradiation on the total aerobic microbial population, lag phase, and rate of growth. Genera of organisms isolated from fillets through the course of microbial spoilage were identified, and the proteolytic activity of the organisms was determined. Plate counts for fish prior to irradiation showed the presence of approximately 10(6) organisms per g of sample. Irradiation to 0.1 and 0.2 Mrad produced 1.4 and 3 logarithm reductions of the initial count, respectively. Irradiation to 0.1 and 0.2 Mrad approximately doubled the product's shelf life. Organisms initially isolated from the nonirradiated fillets, in order of decreasing number, consisted of Flavobacterium, Micrococcus-Sarcina, Achromobacter-Alcaligenes-Mima, Pseudomonas, Microbacterium, Vibrio, Bacillus, Corynebacterium, Lactobacillus, Brevibacterium, and Aeromonas. By the 6th and 9th days of fillet storage, Pseudomonas and the Achromobacter group were the predominant organisms. All members of the genus Flavobacterium, but not all members of the genus Pseudomonas, were proteolytically active on raw fish juice-agar and skim milk-agar media. The Achromobacter group was found to be nonproteolytic on both media. Residual flora of fillets irradiated to 0.1 and 0.2 Mrad consisted of the Achromobacter group, Lactobacillus, Micrococcus-Sarcina, and Bacillus. Their sequence in predominance, however, varied with dose level. Not all proteolytic bacteria in the fillets were eliminated by 0.1 and 0.2 Mrad; proteolytic Micrococcus-Sarcina survived these treatments.     

Effect of γ-Irradiation on the Microflora of Freshwater Fish: I. Microbial Load,Lag Period,and Rate of Growth on Yellow Perch (Perca flavescens) Fillets

Microbial flora were compared in irradiated and nonirradiated yellow perch fillets. These studies included effects of irradiation on the total microbial population, the lag phase, and rate of growth in this freshwater fishery product. The work was conducted concurrently with sensory and chemical evaluation, and constituted part of an investigation designed to evaluate the effect of substerilization doses (0.3 and 0.6 Mrad) of Co⁶⁰ γ rays on the storage life of yellow perch fillets at 1.0 or 6.0 C. In five storage tests, total plate counts prior to irradiation did not exceed 8.7 × 10⁵ per gram of sample; this count was reduced nearly 100% by irradiation with either 0.3 or 0.6 Mrad. Progressively lower maximal bacterial populations and lengthened lag phases were obtained as more radiation was used. The growth rate of the population did not appear to decrease significantly. Microbial data obtained in these studies confirmed the sensory and chemical studies, by indicating that irradiation can significantly extend the refrigerated shelf life of freshwater fish.     

Effect of γ-Irradiation on the Microflora of Freshwater Fish: I. Microbial Load, Lag Period, and Rate of Growth on Yellow Perch (Perca flavescens) Fillets

Microbial flora were compared in irradiated and nonirradiated yellow perch fillets. These studies included effects of irradiation on the total microbial population, the lag phase, and rate of growth in this freshwater fishery product. The work was conducted concurrently with sensory and chemical evaluation, and constituted part of an investigation designed to evaluate the effect of substerilization doses (0.3 and 0.6 Mrad) of Co⁶⁰ γ rays on the storage life of yellow perch fillets at 1.0 or 6.0 C. In five storage tests, total plate counts prior to irradiation did not exceed 8.7 × 10⁵ per gram of sample; this count was reduced nearly 100% by irradiation with either 0.3 or 0.6 Mrad. Progressively lower maximal bacterial populations and lengthened lag phases were obtained as more radiation was used. The growth rate of the population did not appear to decrease significantly. Microbial data obtained in these studies confirmed the sensory and chemical studies, by indicating that irradiation can significantly extend the refrigerated shelf life of freshwater fish.     

Microbial Flora of Irradiated Dungeness Crabmeat and Pacific Oysters

The microorganisms in Dungeness crabmeat (Cancer magister) and Pacific oysters (Crassostrea gigas) were identified by the replica-plating and computer analysis method. The initial flora of the shellfish and the flora change during storage at 7 C were determined. The microbial flora shifts in both shellfish were also determined after irradiation at 0.1 and 0.4 Mrad and during subsequent storage at 7 C. The Achromobacter species predominated in the initial flora of crabmeat (77.0%). The predominant position of this group increased to 99.2% after 0.1 Mrad and 100% after 0.4 Mrad. A large percentage of Lactobacillus was detected in oysters (55.0%). The Lactobacillus species were the predominant survivors after 0.1 Mrad (92.4%) but the predominant survivors after 0.4 Mrad were Achromobacter species (99.3%).     

Methanogenesis and sulfate reduction in timber and drainage water from a gold mine

Biogenesis of methane in the heartwood of diseased trees has been shown, but never in timber in service. Studies were undertaken to establish whether methan‐ogens and sulfate‐reducers were present in wooden pit props and drainage water from underground sites in a gold mine. The predominant methanogen in the mine ecosystem was tentatively identified as Methanobacterium bryantii. The sulfate‐reducers comprised Desulfovibrio desulfuricans and Desulfotomaculum antarcticum. Most probable numbers (MPN) of bacteria indicated that 3.5 × 10⁵ methanogenic and 7.9 × 10³ sulfate‐reducing bacteria were present per milliliter of stagnant drainage water. MPN values per gram of timber were lower for methanogens but comparable for sulfate‐reducers. Laboratory model systems predicted a maximum rate of methan‐ogenesis of 2.3 mL methane/g wood per day; however, rates would never attain this value because of nutrient limitations and environmental restrictions. Analysis of gas samples extracted from sealed areas of the gold mine verified the presence of methane.     

Endophytic bacterial flora in the stem tissue of a tropical maize (<Emphasis Type="Italic">Zea mays</Emphasis> L.) genotype: isolation,identification and enumeration

The genotypic diversity of indigenous bacterial endophytes within stem of tropical maize (Zea mays L.) was determined in field and greenhouse experiments. Strains were isolated from stem tissues of a tropical maize cultivar (PEHM-1) by trituration and surface disinfestation and their population dynamics was determined. Endophytes were found in most of the growing season at populations ranging from 1.36–6.12 × 10⁵ colony-forming units per gram fresh weight (c.f.u./gm fw) of stem. Analysis of these bacterial endophytes using Gas Chromatography—Fatty Acid Methyl Ester (GC-FAME) led to the identification of Bacillus pumilus, B. subtilis, Pseudomonas aeruginosa and P. fluorescens as the relatively more predominant group of bacterial species residing in maize stem. When the maize seedlings grown in a greenhouse were inoculated with these four isolates individually, their population densities decreased (1.6–3.1 × 10⁵ c.f.u./gm fw of stem) as compared to the field-grown maize (1.8–3.8 × 10⁵ c.f.u./gm fw of stem). The highest persistence, however, was recovered in the case of B. subtilis with a population density of 3.1 × 10⁵ c.f.u./gm fw of stem tissue on 28 days after emergence (DAE). This is the first report on population dynamics of bacterial endophytes from tropical maize and the results establish that symptomless populations of bacteria exist in the maize stem.     

Growth and survival of Pseudomonas cepacia DBO1(pRO101) in soil amended with 2,4-dichlorophenoxyacetic acid

The 2,4-dichlorophenoxyacetic acid (2,4-D) degrading pseudomonad, Pseudomonas cepacia DBO1(pRO101), was inoculated at approximately 10⁷ CFU/g into sterile and non-sterile soil amended with 0, 5 or 500 ppm 2,4-D and the survival of the strain was studied for a period of 44 days. In general, the strain survived best in sterile soil. When the sterile soil was amended with 2,4-D, the strain survived at a significantly higher level than in non-amended sterile soil. In non-sterile soil either non-amended or amended with 5 ppm 2,4-D the strain died out, whereas with 500 ppm 2,4-D the strain only declined one order of magnitude through the 44 days.The influence of 0,0.06, 12 and 600 ppm 2,4-D on short-term (48 h) survival of P. cepacia DBO1(pRO101) inoculated to a level of 6×10⁴, 6×10⁶ or 1×10⁸ CFU/g soil was studied in non-sterile soil. Both inoculum level and 2,4-D concentration were found to have a positive influence on numbers of P. cepacia DBO1(pRO101). At 600 ppm 2,4-D growth was significant irrespective of the inoculation level, and at 12 ppm growth was stimulated at the two lowest inocula levels. P. cepacia DBO1(pRO101) was able to survive for 15 months in sterile buffers kept at room temperature. During this starvation, cells shrunk to about one third the volume of exponentially growing cells.Abbreviations AODC acridine orange direct count - CFU colony forming units - PTYG-Agar peptone, tryptone, yeast & glucose agar - TET tetracycline - LB Luria Bertani medium     

Quantitative and qualitative study of the bacterial flora of farmed freshwater prawn (Macrobrachium rosenbergii) larvae

Quantitative and qualitative studies of the bacterial flora of farmed freshwater prawn (Macrobrachium rosenbergii) larvae in Saudi Arabia were performed, and isolates identified where possible. Physico‐chemical characteristics, bacterial counts, and the nature of the bacterial flora of larvae rearing tank water, sediment, tank wall surfaces, larval surface, supplied water, and feed were investigated. Bacterial counts ranged from 2.1 ± 1.3 × 10⁵ to 2.2 ± 0.8 × 10⁷ colony forming units (CFU) ml^?1 in tank water; 4.4 ± 0.9 × 10⁷ to 8.3 ± 1.7 ×10⁹ CFU g^?1 in tank sediment; 8.6 ± 1.0 × 10² to 9.8 ±0.7 × 10⁴ CFU cm^?2 on the tank wall surface; 1.3 ± 1.1 × 10⁴ to 7.7 ± 1.6 × 10⁶ CFU per larva surface, 7.9 ± 1.2 × 10⁵ to 5.0 ± 1.5 × 10⁷ CFU g^?1 in washed larval tissue slurries, 9.1 ± 0.7 × 10³ CFU ml^?1 in supplied water, and 2.4 ± 1.9 ×10¹⁰ CFU g^?1 in mixed feed. Fourteen bacterial genera were identified, including Chryseomonas sp., Vibrio spp., Cellulomonas sp., Aeromonas hydrophila, and Pasteurella sp. The tank water and sediment had similar bacteria to those on the prawn larvae. Chryseomonas sp., Cellulomonas sp. and Vibrio sp. were the most dominant species (prevalence >10%) in tank water; Chryseomonas sp., Pseudomonas alcaligenes and Shewanella putrefaciens in the sediment; Ps. alcaligenes and Cellulomonas sp. on the tank wall surface; Chryseomonas sp., and Cellulomonas sp. on the larval surface; and Chryseomonas sp., Vibrio vulnificus, Sh. putrefaciens and V. alginolyticus in the washed larval tissue slurries (prevalence 10%). Pseudomonas alcaligenes, Moraxella sp., Serratia liquefaciens, Gordona sp. and Burkholderia glumae were absent in larvae but identified in the culture water, tank sediment, and tank wall surface. Pseudomonas sp., Chryseomonas sp., Pasteurella sp. and V. alginolyticus were the prevalent bacteria (>12%) in supplied water. The feed contained V. alginolyticus, A. hydrophila and Cellulomonas sp. as the dominant bacteria (>13%). In the culture water and larvae samples, 83% of the feed and supplied water bacteria were identified.     

Recovery of Pseudomonas spp. from chronically fuel oil-polluted soils in Jordan and the study of their capability to degrade short chain alkanes

Enumeration of bacteria and recovery of the dominant species have been conducted for soils contaminated with fuel spills for more than 10 years at seven gas stations in Jordan. Bacterial counts of these polluted soils ranged between 0.68 × 10⁸ and 32.8 × 10⁸ c.f.u./g soil with two different bacterial colony types recovered on agar plates. Phenotypic examination of the recovered bacteria revealed that they belonged mainly to the genus Pseudomonas and was represented by the following species: P. acidovorans, P. putrefaciens, P. cepacia, P. vesicularis and P. fluorescens. The ability of these bacteria to grow on hexane or heptane was revealed by a colorimetric test. Action of five Pseudomonas spp.: Pseudomonas putrefaciens, P. cepacia, P. acidovorans, P. vesicularis and P. fluorescens and Rhodococcus erythropolis on 0.1% (v/v) hexane or heptane was followed at 1, 2, 6 and 12 h. Pseudomonas putrefaciens, P. cepacia and P. acidovorans were capable of degrading both hydrocarbons as indicated by the yellow colour formation (positive reaction); however, P. vesicularis and P. fluorescens showed no such capability.     

Changes in the Microflora of Irradiated Petrale Sole (Eopsetta jordani) Fillets Stored Aerobically at 0.5 C

The microfloral changes on irradiated petrale sole fillets during aerobic (packaged with oxygen-permeable film), refrigerated storage were determined by the identification of bacterial and yeast isolates to the generic level. The samples were irradiated at 0.0, 0.1, 0.15, 0.2, 0.3, and 0.4 Mrad by use of a cobalt-60 gamma source, were stored at 0.5 C, and were examined periodically for spoilage, total microbial population, and composition. The preirradiation flora of the fresh fillets consisted of coryneforms, Achromobacter, Micrococcus, Flavobacterium, Pseudomonas, and Lactobacillus. Immediately after irradiation, Micrococcus, Achromobacter, coryneforms, and Bacillus were predominant. The flora of the nonirradiated fillets at the time of spoilage consisted of Pseudomonas and Achromobacter. The flora of the irradiated fillets at the time of spoilage consisted of Achromobacter and Trichosporon.     

Abundance and Diversity of Sulfur-Oxidizing Bacteria along a Salinity Gradient in Four Qinghai-Tibetan Lakes,China

Sulfur-oxidizing bacteria (SOB) play important roles in the sulfur cycle and are widespread in a number of environments, but their occurrence and relationship to geochemical conditions in (hyper)saline lakes are still poorly understood. In this study, the abundance and diversity of SOB populations were investigated in four Qinghai-Tibetan lakes (Erhai Lake, Gahai Lake 1, Gahai Lake 2 and Xiaochaidan Lake) by using quantitative polymerase chain reaction (qPCR) and soxB gene- (encoding sulfate thiohydrolase) based phylogenectic analyses. qPCR analyses showed that in the studied lakes, the total bacterial 16S rRNA and soxB gene abundances in the sediments were distinctly higher than in the overlying waters. The 16S rRNA gene abundance in the waters ranged 5.27 × 10⁶–6.09 × 10⁸ copies per mL and 7.39 × 10¹⁰–2.9 × 10¹¹ copies per gram sediment. The soxB gene abundance in the waters ranged from 1.88 × 10⁴ to 5.21 × 10⁵ per mL and 4.73 × 10⁶–2.65 × 10⁷ copies per gram sediment. The soxB gene in the waters of the two hypersaline lakes (Gahai Lake 2 and Xiaochaidan Lake) was more abundant (2.97 × 10⁵ and 5.21 × 10⁵ copies per mL) than that in the two low-salinity lakes (1.88 × 10⁴ and 3.36 × 10⁴ copies per mL). Phylogenetic analysis showed that Alpha- and Betaproteobacteria were dominant SOB in the investigated lakes, and the composition of proteobacterial subgroups varied with salinity: in freshwater Erhai Lake and low-salinity Gahai Lake 1, the SOB populations were dominated by the Betaproteobacteria, whereas in hypersaline Lake Gahai 2 and Xiaochaidan Lake, the SOB populations were dominated by Alphaproteobacteria. Overall, salinity played a key role in controlling the diversity and distribution of SOB populations in the investigated Qinghai-Tibetan lakes.     

Yeast colonizing the intestine of rainbow trout (Salmo gairdneri) and turbot (Scophtalmus maximus)

Yeast were isolated from the intestine of farmed rainbow trout (Salmo gairdneri), turbot (Scophtalmus maximus), and free-living flat-fish (Pleuronectes platessa and P. flesus). The average number of viable yeasts recovered from farmed rainbow trout was 3.0 × 10³ and 0.5 × 10² cells per gram homogenized intestine for white and red-pigmented yeasts, respectively. The dominant species were Debaryomyces hansenii, Saccharomyces cerevisiae, Rhodotorula rubra, and R. glutinis. In 5 of 10 free-lving marine fish, > 100 viable yeast cells per gram intestinal mucus were recovered. Red-pigmented yeasts dominated and composed >90% of the isolates. Colonization experiments were performed by inoculating rainbow trout and turbot with fish-specific, isolated yeast strains and by examining the microbial intestinal colonization at intervals. Inoculation of experimental fish with pure cultures of R. glutinis and D. hansenii HF1 yielded colonization at a level several orders of magnitude higher than before the inoculation. Up to 3.8 × 10⁴, 3.1 × 10⁶, and 2.3 × 10⁹ viable yeast cells per gram intestine or feces were recovered in three separate colonization experiments. The high level of colonizing yeasts persisted for several weeks. The concentrations of yeasts in the tank water never exceeded 10³ viable cells per milliliter. No traces of fish sickness as a result of high yeast colonization were recorded during any of the colonization experiments. For periods of the experiments, the concentration of aerobic bacteria in the fish intestine was lower than the intestinal yeast concentration. Scanning electron microscopy studies demonstrated a close association of the yeasts with the intestinal mucosa. The mucosal colonization was further demonstrated by separating intestinal content, mucus, and tissue. All compartments were colonized by >10³ viable yeast cells per gram. No bacteria were detected on the micrographs, indicating that their affinity for the intestinal mucosa was less than that of the yeasts. Correspondence to: Thomas Andtid     

Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) in soil inoculated with Pseudomonas cepacia DBO1(pRO101), Alcaligenes eutrophus AEO106(pRO101) and Alcaligenes eutrophus JMP134(pJP4): effects of inoculation level and substrate concentration

Mineralization of 2,4-dichlorophenoxyacetic acid (2,4-D) by two Alcaligenes eutrophus strains and one Pseudomonas cepacia strain containing the 2,4-D degrading plasmids pJP4 or pRO101 (=pJP4::Tn1721) was tested in 50 g (wet wt) samples of non-sterile soil. Mineralization was measured as ¹⁴C-CO₂evolved during degradation of uniformly-ring-labelled ¹⁴C-2,4-D. When the strains were inoculated to a level of approximately 10⁸ CFU/g soil, between 20 and 45% of the added 2,4-D (0.05 ppm, 10 ppm or 500 ppm) was mineralized within 72 h. Mineralization of 0.05 ppm and 10 ppm, 2,4-D by the two A. eutrophus strains was identical and rapid whereas mineralization by P. cepacia DBO1(pRO101) occurred more slowly. In contrast, mineralization of 500 ppm 2,4-D by the two A. eutrophus strains was very slow whereas mineralization by P. cepacia DBO1 was more rapid. Comparison of 2,4-D mineralization at different levels of inoculation with P. cepacia DBO1(pRO101) (6×10⁴, 6×10⁶ and 1×10⁸ CFU/g soil) revealed that the maximum mineralization rate was reached earlier with the high inoculation levels than with the low level. The kinetics of mineralization were evaluated by nonlinear regression analysis using five different models. The linear or the logarithmic form of a three-half-order model were found to be the most appropriate models for describing 2,4-D mineralization in soil. In the cases in which the logarithmic form of the three-half-order model was the most appropriate model we found, in accordance with the assumptions of the model, a significant growth of the inoculated strains.Abbreviations 2,4-D 2,4-dichlorophenoxyacetic acid - CFU colony forming units - PTYG peptone, tryptone, yeast & glucose - DPM disintegrations per minute     

Application of Replica Plating and Computer Analysis for Rapid Identification of Bacteria in Some Foods: II. Analysis of Microbial Flora in Irradiated Dover Sole (Microstomus pacificus)

This investigation was carried out to determine the nature of the microbial flora shifts in dover sole as a result of irradiation and storage at 6 C. The relationship was determined between the microorganisms which initially survive irradiation and those making up the final spoilage flora. A total of 2,723 isolates were examined by use of the replica-plating and computer analysis method. The spoilage of the unirradiated control samples during storage at 6 C was almost entirely due to the growth of Pseudomonas. This group, which occupied 25% of the fresh flora, grew to nearly 100% in 2 days of storage. In contrast, irradiation doses of 0.1, 0.2, 0.3, and 0.4 Mrad favored the growth of Achromobacter and yeasts. The Micrococcus, which survived radiation, did not grow at 6 C. At 0.5 Mrad, spoilage of fish samples was due entirely to the growth of yeasts.     

A Field and Storage Rot of Onion (Allium cepa L. var. cepa) Caused by Pseudomonas cepacia in Lowland Papua New Guinea

A bacterium consistently isolated from rotting onions in the field and in storage was shown by biochemical and pathogenicity tests to be Pseudomonas cepacia. In experiments to determine the mode of entry of the pathogen only injured bulbs developed a soft rot after a 10 min soak in a suspension of P. cepacia (approx. 10⁸ cfu/ml).     

Distinct signal transduction processes by IL-4 and IL-13 and influences from the Q551R variant of the human IL-4 receptor alpha chain

Background

Pseudomonas aeruginosa and Burkholderia cepacia infections of cystic fibrosis patients' lungs are often resistant to conventional antibiotic therapy. Protegrins are antimicrobial peptides with potent activity against many bacteria, including P. aeruginosa. The present study evaluates the correlation between protegrin-1 (PG-1) sensitivity/resistance and protegrin binding in P. aeruginosa and B. cepacia.

Methods

The PG-1 sensitivity/resistance and PG-1 binding properties of P. aeruginosa and B. cepacia were assessed using radial diffusion assays, radioiodinated PG-1, and surface plasmon resonance (BiaCore).

Results

The six P. aeruginosa strains examined were very sensitive to PG-1, exhibiting minimal active concentrations from 0.0625–0.5 μg/ml in radial diffusion assays. In contrast, all five B. cepacia strains examined were greater than 10-fold to 100-fold more resistant, with minimal active concentrations ranging from 6–10 μg/ml. When incubated with a radioiodinated variant of PG-1, a sensitive P. aeruginosa strain bound considerably more protegrin molecules per cell than a resistant B. cepacia strain. Binding/diffusion and surface plasmon resonance assays revealed that isolated lipopolysaccharide (LPS) and lipid A from the sensitive P. aeruginosa strains bound PG-1 more effectively than LPS and lipid A from resistant B. cepacia strains.

Conclusion

These findings support the hypothesis that the relative resistance of B. cepacia to protegrin is due to a reduced number of PG-1 binding sites on the lipid A moiety of its LPS.