Comparison of extracellular DNase- and protease-producing spoilage bacteria isolated from Delaware pond-sourced and retail channel catfish (Ictalurus punctatus).

BACKGROUND: Spoilage of fishery products begins immediately following filleting due to microbial growth that degrades fish tissue quality prior to consumption. Extensive research has been conducted to identify such bacterial populations. A better understanding of the mechanisms involved in fish spoilage is necessary as a novel remedy for microbial spoilage inhibition has yet to be established for fish tissue. The present study identified, for the first time, bacterial populations that produce extracellular DNase and protease from Delaware and local retail distributed channel catfish (Ictalurus punctatus) fillets. RESULTS: A clear trend was identified between bacteria derived from catfish filleted under aseptic conditions where Pseudomonas was the dominant genus. Bacteria isolated from retail catfish contained high quantities of DNase-producing isolates, in contrast to aseptic-filleted catfish tissue which had none. Both types of catfish sample maintained high populations of protease-producing bacterial colonies throughout the duration of the study. Most bacteria isolated from catfish intestines exhibited DNase production with no protease production. CONCLUSION: Specific spoilage organism populations were significantly higher on retail-derived catfish in comparison to lab-filleted Delaware cultured catfish tissue. It is suggested that DNase production and protease production contribute to the spoilage of fish tissue as a result of mishandling and septic filleting being the major cause of rapid catfish tissue spoilage.

Usefulness of Chromogenic CromoCen® AGN agar medium for the identification of the genus Aeromonas: Assessment of faecal samples.

Selective screening media for the detection and identification of Aeromonas strains are needed to guide primary isolation procedures in the clinical laboratory. This study compared the selective CromoCen® AGN chromogenic agar medium for the detection and identification of Aeromonas strains that were isolated from various samples against the conventional selective agar media that are commonly used for the isolation of this organism in food, environmental and clinical samples. The Miles and Misra and ecometric methods were used to evaluate the microbiological performance of CromoCen® AGN chromogenic agar medium, which was shown to be satisfactory. A total of 14 reference Aeromonas strains, 44 wild strains and 106 clinical stool specimens were examined using both non-chromogenic selective agars that are commonly used for Aeromonas isolation and CromoCen® AGN agar. The latter exhibited 94.73% sensitivity and 100% specificity for the various samples. On CromoCen® AGN agar medium, Aeromonas formed colonies with light green, greenish and salmon pigments with or without a surrounding wide transparent zone (halo) of 2-3mm in diameter around the entire border. This medium is recommended for the isolation and potential identification of the Aeromonas genus.

Assessment of toxicity of a glyphosate-based formulation using bacterial systems in lake water.

A new Aeromonas bioassay is described to assess the potential harmful effects of the glyphosate-based herbicide, Roundup, in the Albufera lake, a protected area near Valencia. Viability markers as membrane integrity, culturability and beta-galactosidase production of Aeromonas caviae were studied to determine the influence of the herbicide in the bacterial cells. Data from the multifactor analysis of variance test showed no significant differences (P>0.05) between A. caviae counts of viability markers at the studied concentrations (0, 50 and 100 mg l-1 of glyphosate). The effects of Roundup on microbial biota present in the lake were assessed by measuring the number of indigenous mesophilic Aeromonas in presence of different amounts of the herbicide at 0, 50 and 100 mg l-1 of glyphosate. In samples containing 50 and 100 mg l-1 of glyphosate a significant (P<0.05) increase in Aeromonas spp. counts and accompanying flora was observed. The acute toxicity of Roundup and of Roundup diluted with Albufera lake water to Microtox luminescent bacterium (Vibrio fischeri) also was determined. The EC50 values obtained were 36.4 mg l-1 and 64.0 mgl-1 of glyphosate respectively. The acidity (pH 4.5) of the herbicide formulation was the responsible of the observed toxicity.

[A comparison of BRILA-MUG and lauryl sulfate-MUG bouillon as detection media for total and fecal coliform bacteria in bathing waters in conformity with the Economic Community Guideline 76/160 EWG]. / Ein Vergleich von BRILA-MUG- und Laurylsulfat-MUG-Bouillon als Nachweismedien für gesamt- und fäkalcoliforme Bakterien in Badegewässern gemäss EG-Richtlinie 76/160 EWG.

The spectrum of gram-negative rods occurring in surface waters is wide and depending on the season, i.e. the water temperature. The concentration of bacteria is higher in summer than in winter. However, the seasonal difference of the concentration of Enterobacteriaceae is less than that of the Aeromonas spec. and of the non-fermenters. The comparison of yields of total and faecal coliforms determined in samples of surface water by using the brilliant green bile lactose 4-methylumbelliferyl-beta-D-glucuronide (BRI-LA-MUG) broth and the lauryl sulfate-MUG broth, respectively, shows that the BRILA-MUG broth is more sensitive and gives higher yields than the lauryl sulfate-MUG broth. On the other hand, the lauryl sulfate-MUG broth inhibits more the growth of gram-negative rods, especially that of Aeromonas spec. and non-fermenters, whereas the Enterobacteriaceae are less inhibited.