Detection and incidence of specific species of spoilage bacteria on fish. II. Relative incidence of Pseudomonas putrefaciens and fluorescent pseudomonads on haddock fillets

Bacterial Communities Changes during Food Waste Spoilage

Food waste is an important component of municipal solid waste worldwide. There are various ways to treat or utilize food waste, such as, biogas fermentation, animal feed, etc. but pathogens and mycotoxins that accumulate in the process of spoilage can present a health hazard. However, spoilage of food waste has not yet been studied, and there are no reports of the bacterial communities present in this waste. In this research, food waste was collected and placed at two different temperatures. We investigated the spoilage microbiota by using culture-independent methods and measured the possible mycotoxins may appear in the spoilage process. The results showed that lactic acid bacteria are the most important bacteria in the food waste community, regardless of the temperature. Few microbial pathogens and aflatoxins were found in the spoilage process. This suggests that if food waste is stored at a relatively low temperature and for a short duration, there will be less risk for utilization.

Pseudomonads and achromobacters in the spoilage of irradiated haddock of different preirradiation quality

The effect of initial quality of fish on postirradiation (100 krad) changes in the bacterial flora of haddock fillets during aerobic storage at 3 C has been investigated, with emphasis on the Pseudomonas and Achromobacter groups. The quality was related to the length of time the eviscerated fish had been stored in ice prior to filleting. Increased numbers of organisms, in particular Pseudomonas putrefaciens, were found initially on fillets cut from older fish. Pseudomonads were reduced by 2 to 3 log orders by irradiation, and achromobacters and gram-positive isolates predominated in the immediate postirradiation flora. Little difference could be detected in either types or relative proportions of organisms occurring during storage of unirradiated fish of different quality. Pseudomonads outgrew achromobacters and dominated the spoilage flora in all cases. After spoilage, however, the growth rate of pseudomonads declined markedly. In irradiated fish, achromobacters predominated throughout storage. In fish of better initial quality, bacterial numbers were 1 to 2 log orders higher at spoilage than in their unirradiated counterparts and in the poorer quality of irradiated samples. The increased number of organisms was accompanied by a radical change in the character of the predominant achromobacters. Pseudomonads were found to increase in numbers during storage of irradiated fish, in particular in poorer quality fish on which they were initially present in higher numbers. Detection of pseudomonads, even when present in high numbers, was found to be limited by the identification techniques normally used.

Bacterial composition and succession during storage of North-Atlantic cod (Gadus morhua) at superchilled temperatures

BACKGROUND

The bacteriology during storage of the North-Atlantic cod has been investigated for the past decades using conventional cultivation strategies which have generated large amount of information. This paper presents a study where both conventional cultivation and cultivation independent approaches were used to investigate the bacterial succession during storage of cod loins at chilled and superchilled temperatures.

RESULTS

Unbrined (0.4% NaCl) and brined (2.5% NaCl) cod loins were stored at chilled (0 degrees C) and superchilled (-2 and -3.6 degrees C) temperatures in air or modified atmosphere (MA, % CO2/O2/N2: 49.0 +/- 0.6/7.4 +/- 0.2/43.7 +/- 0.4). Discrepancy was observed between cultivation enumeration and culture independent methods where the former showed a general dominance of Pseudomonas spp. (up to 59%) while the latter showed a dominance of Photobacterium phosphoreum (up to 100%).Gas chromatography-mass spectrophotometry (GC-MC) showed that trimethylamine was the most abundant volatile in mid- and late storage periods. Terminal restriction polymorphism (t-RFLP) analysis showed that the relative abundance of P. phosphoreum increased with storage time.

CONCLUSION

The present study shows the bacteriological developments on lightly salted or non-salted cod loins during storage at superchilled temperatures. It furthermore confirms the importance of P. phosphoreum as a spoilage organism during storage of cod loins at low temperatures using molecular techniques. The methods used compensate each other, giving more detailed data on bacterial population developments during spoilage.

Shewanella putrefaciens adhesion and biofilm formation on food processing surfaces

Laboratory model systems were developed for studying Shewanella putrefaciens adhesion and biofilm formation under batch and flow conditions. S. putrefaciens plays a major role in food spoilage and may cause microbially induced corrosion on steel surfaces. S. putrefaciens bacteria suspended in buffer adhered readily to stainless steel surfaces. Maximum numbers of adherent bacteria per square centimeter were reached in 8 h at 25 degrees C and reflected the cell density in suspension. Numbers of adhering bacteria from a suspension containing 10(8) CFU/ml were much lower in a laminar flow system (modified Robbins device) (reaching 10(2) CFU/cm(2)) than in a batch system (reaching 10(7) CFU/cm(2)), and maximum numbers were reached after 24 h. When nutrients were supplied, S. putrefaciens grew in biofilms with layers of bacteria. The rate of biofilm formation and the thickness of the film were not dependent on the availability of carbohydrate (lactate or glucose) or on iron starvation. The number of S. putrefaciens bacteria on the surface was partly influenced by the presence of other bacteria (Pseudomonas fluorescens) which reduced the numbers of S. putrefaciens bacteria in the biofilm. Numbers of bacteria on the surface must be quantified to evaluate the influence of environmental factors on adhesion and biofilm formation. We used a combination of fluorescence microscopy (4',6'-diamidino-2-phenylindole staining and in situ hybridization, for mixed-culture studies), ultrasonic removal of bacteria from surfaces, and indirect conductometry and found this combination sufficient to quantify bacteria on surfaces.

Chemical and sensory changes associated with microbial flora of Mediterranean boque (Boops boops) stored aerobically at 0, 3, 7, and 10 degreesC

The development of a microbial population and changes in the physicochemical and sensorial characteristics of Mediterranean boque (Boops boops), called gopa in Greece, stored aerobically at 0, 3, 7, and 10 degreesC were studied. Pseudomonads and Shewanella putrefaciens were the dominant bacteria at the end of the storage period, regardless of the temperature tested. Enterobacteria and Brochothrix thermosphacta also grew, but their population density was always 2 to 3 log10 CFU g-1 less than that of pseudomonads. The concentration of potential indicators of spoilage, glucose and lactic acid, decreased while that of the alpha-amino groups increased during storage. The concentrations of these carbon sources also decreased on sterile fish blocks inoculated with strains isolated from fish microbial flora. The organic acid profile of sterile fish blocks inoculated with the above-mentioned bacteria and that of naturally spoiled fish differed significantly. An excellent correlation (r = -0.96) between log10 counts of S. putrefaciens or Pseudomonas bacteria with freshness was observed in this study.

Relative incidence of Alteromonas putrefaciens and Pseudomonas putrefaciens in ground beef

Of 65 H(2)S-producing isolates from seven samples of ground beef, 64 were found to be Alteromonas putrefaciens. Isolates of Pseudomonas putrefaciens were not encountered. The mean guanine-plus-cytosine content of DNAs from 10 of the representative isolates, obtained from thermal denaturation determinations, was 46.5 +/- 1.0 mol%, which is consistent with the designation A. putrefaciens.

Microflora of Drainage from Ice in Fishing Vessel Fishholds

The microbial load in ice-melt drainage collected from fishholds of fishing vessels stowing lizard fish, black croakers, cuttle fish, or nemipterids was very high, ranging from 2.1 � 10 7 to 2.2 � 10 9 /ml for bacteria and 6.3 � 10 3 to 7.2 � 10 4 /ml for yeasts and molds. Analysis of 100 colonies each randomly isolated from drainage samples of cuttle fish and lizard fish showed that the occurrence of bacterial genera as a percentage of the total was Moraxella-Acinetobacter , 61 to 62%; Pseudomonas , 19 to 21%; Alcaligens , 5 to 10%; Flavobacterium , 1 to 4%; Micrococcus , 1 to 4%; Bacillus, Vibrio 0 to 2%; Corynebacterium , 1 to 2%; and others, 1 to 2%. The organisms demonstrated versatile hydrolytic activities to a wide range of biological substrates including casein, gelatin, starch, DNA, and RNA. The possible connection between these bacteria and the deterioration of fish quality are discussed.

Detection of volatile sulfide-producing bacteria isolated from poultry-processing plants

A technique using filter paper strips impregnated with 5-5'-dithiobis-nitrobenzoic acid was developed to allow the detection of bacteria (isolated from poultry-processing environs) which produced volatile sulfides (H2S, CH3SH, [CH3]2S). The technique is preferred to conventional methods in that it allows the detection of volatile organic sulfides in addition to hydrogen sulfide.

Spoilage association of chicken leg muscle

The ability of pure cultures of bacteria isolated from spoiling chicken leg muscle to produce strong off-odors was tested by using sterile leg muscle sections. Changes in the flora during storage and the incidence and identity of organisms capable of producing strong off-odors were noted.

Characteristics of Heavily Mucoid Bacterial Isolated from Fish Pen Slime

Weakly gram-positive pleomorphic rods isolated from the slime on the storage pen surfaces of fishing trawlers were found to produce extensive capsular material and intensely mucoid colonies. The isolates studied produced highly pleomorphic club-shaped cells indicative of coryneforms. Their DNA base composition ranged from 64.2 to 68.2 mol% guanine plus cytosine on the basis of melting point determinations.

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Microbiological characteristics of Dungeness crab (Cancer magister)

Aerobic, heterotropic microorganisms of Dungeness crab (Cancer magister) were isolated from raw crab, cooked crab, crab meats obtained during commercial processing, and from retail crab meat samples. Each microbial isolate was then identified to the genus level employing the revised replica plating procedure. Microbial groups most commonly isolated from crab meat were, in the order of predominance, Moraxella, Pseudomonas, Acinetobacter, Arthrobacter, Micrococcus, Flavobacterium-Cytophaga, and Bacillus sp. Proteus, Staphylococcus, yeasts, Vibrio, and Lactobacillus sp. were found less frequetly in some samples. Distribution patterns of microbial flora in crab meat revealed the presence of three classes of microorganisms. Microorganisms that originated from the raw crab and gained predominance by growth during refrigerated storage were Moraxella, Pseudomonas, Acinetobacter, and Flavobacterium-Cytophaga sp. Those that originated from the crab but did not grow in meat were Arthrobacter and Bacillus sp. Micrococcus, Staphylococcus, and Proteus sp. were introduced during processing, but they did not grow in the refrigerated crab meat.

Characterization of hydrogen sulfide-producing bacteria isolated from meat and poultry plants

A survey of the types of aerobic organisms able to produce H2S on peptone iron agar (Levin, 1968), and commonly occurring in meat and poultry plants, revealed that these could be divided into four distinct groups. The ability of representative strains of each type to grow at low temperatures and cause off-odors on chicken muscle was examined. The results are discussed in relation to the role of these organisms in the psychrophilic spoilage of meat and meat products.

Strains of Pseudomonas putrefaciens from clinical material

Eight strains of Pseudomonas putrefaciens have been received from among 466 strains of Pseudomonas submitted to the Computer Trials Laboratory for identification over the last eight years. Two of the strains of P. putrefaciens from patients with otitis media and otitis externa respectively appear to have played a pathogenic role. The biochemical characteristics of these eight strains were compared with those of seven culture collection strains.

Taxonomic significance of phenethyl alcohol production by Achromobacter isolates from fishery sources

The formation of phenethyl alcohol from L-phenylalanine and ethanol by achromobacter isolates of fishery origin was found to be taxonomically significant for such organisms. Phenylpyruvate, the direct oxidative deamination product of L-phenylalanine, was found to serve as an intermediate precursor to phenethyl alcohol formation. Among ten Acinetobacter isolates examined, none produced phenethyl alcohol. Among nine Moraxella isolates examined, one produced phenethyl alcohol.

Hydrogen sulfide production by Pseudomonas putrefaciens in shrimp experimentally packed in nitrogen

Shrimp refrigerated in a nitrogen atmosphere develop off-odors not typical of normal spoilage. Investigations of this phenomenon showed that hydrogen sulfide developed in the headspace gas, and a large percentage of the microbial population present on the shrimp stored in nitrogen was capable of hydrogen sulfide production, in contrast to the flora on shrimp stored in air. The predominant hydrogen sulfide-producing organism, Pseudomonas putrefaciens, was present in low numbers on fresh shrimp but usually reached high numbers by day 8 of nitrogen storage. Further studies revealed that cysteine and cystine were the probable substrates in shrimp utilized by this organism for hydrogen sulfide production. When shrimp sterilized by irradiation were inoculated with P. putrefaciens and incubated in an atmosphere of nitrogen, hydrogen sulfide and the characteristic off-odors developed.

Volatile compounds produced in sterile fish muscle (Sebastes melanops) by Pseudomonas putrefaciens, Pseudomonas fluorescens, and an Achromobacter species

Volatile compounds produced by Pseudomonas putrefaciens, P. fluorescens, and an Achromobacter species in sterile fish muscle (Sebastes melanops) were identified by combined gas-liquid chromatography and mass spectrometry. Compounds produced by P. putrefaciens included methyl mercaptan, dimethyl disulfide, dimethyl trisulfide, 3-methyl-1-butanol, and trimethylamine. With the exception of dimethyl trisulfide, the same compounds were produced by an Achromobacter species. Methyl mercaptan and dimethyl disulfide were the major sulfur-containing compounds produced by P. fluorescens.

Hydrogen sulfide production by bacteria and sulfmyoglobin formation in prepacked chilled beef

Meat stored at 1 to 2 C under low oxygen tensions, either in gas-impermeable packs or in controlled atmospheres, occasionally exhibited an undesirable green exudate. The green pigment was identified spectrophotometrically as sulfmyoglobin. The conversion of myoglobin to sulfmyoglobin resulted from the production of H(2)S by bacteria tentatively identified as Pseudomonas mephitica. This organism produced H(2)S only when the oxygen tension was about 1% and the pH of the meat was 6.0 and above.