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Biomedical subjects

M A Hood

Publications and source records attributed to M A Hood.

24 records · Page 2Linked to original sources
PubMed1982

Isolation and characterization of ultramicrobacteria from a gulf coast estuary.

Viable bacteria were recovered from estuarine waters passed through a 0.2-mum polycarbonate membrane filter. The recovery method included the use of a dilute nutrient broth for primary enrichment followed by conditioning of the organism to a dilute nutrient solid medium. These bacteria were gram-negative rods and coccobacilli having an NaCl requirement and, upon initial culturing, low nutritional requirements. In response to increased nutrient preparations, these microorganisms underwent an increase in size and growth rate, giving rise to visible colonies. Phenotypic characterization suggests that species of Vibrio, Aeromonas, Pseudomonas, and Alcaligenes were among the isolates. The abundance and the nutritional requirements of these ultramicrobacteria imply that they represent a class of microorganisms which have successfully adjusted to poor nutrient conditions.

Journal Article↗
PubMed1982

Survival of Vibrio cholerae and Escherichia coli in estuarine waters and sediments.

In in vitro estuarine water and sediment chambers, the survival of Vibrio cholerae and Escherichia coli was determined by plate counting and direct counting techniques. V. cholerae strains included environmental, clinical, and serotype O1 and non-O1 isolates, whereas E. coli strains included ATCC 25922 and a freshly cultured human isolate. Recovery of V. cholerae varied significantly with incubation temperature. Growth and extended periods of survival occurred in sterile sediments, sterile waters, and nonsterile waters, but not in nonsterile sediments. In contrast to V. cholerae, viable cells of E. coli decreased rapidly in both sterile and nonsterile estuarine waters. Direct counts revealed that E. coli cells were intact in the estuarine water, but attempts to resuscitate them were unsuccessful. The data suggest that V. cholerae survives better in estuarine waters than E. coli. The results may explain the recent observations that V. cholerae levels do not correlate well with fecal coliform concentrations in estuarine waters. Furthermore, the results add increasing evidence to support the theory that V. cholerae is an autochthonous bacterium in estuaries.

Escherichia coli↗
PubMed1982

Diluent composition for use of API 20E in characterizing marine and estuarine bacteria.

Nine chemically defined inoculation diluents, with compositions ranging from 0.85% NaCl to 35% marine salts, were used to evaluate the influence of diluent composition on the biochemical profiles of 30 marine and estuarine bacterial strains, including species of Vibrio, Aeromonas, Allomonas, and Photobacterium. Results demonstrated that a 20% marine salts diluent enabled the characterization of halophilic strains normally nonreactive by the API 20E system. Furthermore, the use of 20% marine salts showed that certain environmental isolates, identifiable as Vibrio parahaemolyticus by the recommended clinical inoculation procedure, were Vibrio vulnificus. An analysis of the profiles provided by the nine diluents indicates that the API 20E system, modified by the use of a diluent composed of 20% marine salts and incubated at 22 degrees C, can provide a reliable tool for the rapid characterization of marine and estuarine bacterial isolates.

Aeromonas↗
PubMed1980

The effects of organophosphorus pesticides on estuarine ammonium oxidizers.

The effects of seven thiophosphorus pesticides and their degradation products on estuarine ammonium oxidizers were examined. Using an axenic, closed-culture, high cell density assay, the pesticides caused little inhibition of ammonium oxidation. However, the degradation product of methyl parathion, p-aminophenol, significantly inhibited ammonium oxidation levels as low as 0.01 mg/L. Estuarine sediments containing indigenous ammonium oxidizers were exposed to the pesticides over a 14-day period and activity of the ammonium oxidizers were inhibited after 14 days. Three pesticides were aged in estuarine sediments under aerobic, anaerobic, and microaerophilic conditions, and axenic cultures of ammonium oxidizers were exposed to the resulting metabolites. Ammonium oxidation was inhibited by 10% in the systems containing pesticides aged under aerobic and anaerobic conditions, whereas under microaerophilic conditions, 20% reduction in activity was observed. The data suggest that the parent compounds of the thiophosphorus pesticides have little effect on ammonium oxidation in estuarine sediments, but that certain metabolites which accumulate from the decomposition of these pesticides, especially in sediments under low O2 levels, may significantly reduce ammonium oxidation.

Ammonia↗
PubMed1975

Microbial indicators of oil-rich salt marsh sediments.

Selected microbial parameters were monitored in sediments from a pristine and an oil-field salt marsh. Although numbers of hydrocarbonoclastic bacteria and fungi were significantly greater in the oil field, the values did not show a strong correlation with levels of hydrocarbons (r = 0.43 and r = 0.49, respectively). However, a high correlation was noted between ratios of hydrocarbonoclastic and total aerobic heterotrophic bacteria and levels of hydrocarbons as well as the relative concentration of hydrocarbons (ratio of hydrocarbons to chloroform extractables) (r = 0.87 and r = 0.77, respectively). Data suggest that this first ratio is a more valid microbial indicator of hydrocarbon abundance than other factors examined. Significant differences in the ratio of pigmented to total colony-forming units, the ratio of different to total colony-forming units, and the diversity index were noted between the natural and oil-field marsh. It is suggested that the presence of hydrocarbons alters the relative abundance of the most predominant aerobic heterotrophic bacteria.

Journal Article↗