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Toxigenic Vibrio cholerae O1 Inaba, resembling the epidemic Latin American strains (C6706, C6707), was recovered from oysters taken from Mobile Bay, Alabama, on five separate occasions between July 1991 and September 1992. Levels of toxigenic V. cholerae in the oysters, estimated by the most probable number procedure, ranged from 101 to 107 per 100 g. Isolates characterized by pulsed field gel electrophoresis resembled isolates previously recovered from five cargo ships docked at Gulf of Mexico ports. This study details the first reported isolation of toxigenic V. cholerae O1 from oysters in U.S. coastal waters. As with the Gulf Coast strain, the occurrence of the epidemic strain seems to be sporadic and essentially limited to the warmer months.

Oysters and seawater collected from the southeastern United States were examined for fecal coliforms and Escherichia coli , using the current procedure of the American Public Health Association (APHA) and the fluorogenic 4-methylumbelliferyl-β-D-glucuronide (MUG) modified APHA procedure. After the presence of E. coli in both methods was confirmed by conventional IMViC procedures, there was no significant difference between method means at the α = 0.05 level. In oysters, low confirmation rates of 67 and 77% were observed by the APHA and the MUG methods, respectively. Seawater had the greatest confirmation rates (95%) by the MUG method. The MUG method may be a suitable alternative to the current APHA method for the microbiological evaluation of oysters and seawater.

A total of 227 samples, including oysters, shrimp, and water, was collected along the U.S. Gulf Coast and examined to determine the presence of Listeria spp. Listeria spp. were recovered more frequently from shrimp than from water but were not recovered from oysters. Recovery of Listeria spp. from shrimp and waters was improved at temperatures ≤20°C; however, recovery was not affected by salinity or related to the fecal coliform standard for shellfish-growing waters. Although only 5% of the test samples were positive for L. monocytogenes , all Listeria positive shrimp contained L. monocytogenes . The incidence of Listeria spp. in shrimp was low; nevertheless, shrimp represent a potential source of Listeria contamination to processing plants and their products.

Vibrio cholerae non-O1 was found throughout the Apalachicola, FL, estuary. V. cholerae O1 was isolated primarily at the City of Apalachicola sewage treatment plant, Scipio Creek and the north shore of St. George Island. Highest concentrations of both serogroups occurred in August and November. Concentrations were lowest in February and increased substantially in May. A cholera toxin-like toxin was not detected in any of the V. cholerae cultures by the Y-1 mouse adrenal cell assay or the enzyme-linked immunosorbent assay (ELISA). However, 35% of the V. cholerae O1 and 22% of the V. cholerae non-O1 cultures selected for testing caused diarrhea in infant rabbits. The proportion of V. cholerae O1 and non-O1 isolates pathogenic to infant rabbits increased as water temperature decreased. Fecal coliforms appeared to be more useful than total coliforms as indicators of the numbers of V. cholerae in water, but neither of those National Shellfish Sanitation Program indicator groups ensured against the presence of pathogenic V. cholerae in shellfish-growing areas.

Three international methods were evaluated for enumerating Escherichia coli in estuarine waters, oysters ( Crassostrea virginica ), mussels ( Mytilus edilus ) and clams ( Mercenaria mercenaria ). Results of the French most probable number (MPN) method, a modification of the MacKenzie, Taylor and Gilbert (1948) method, were obtained within 48 h and compared favorably with those obtained by the standard American Public Health Association (APHA) MPN procedure in all sample types. Results of the Australian Anderson and Baird-Parker plate count method, obtained within 24 h, were significantly lower than those obtained with the standard APHA procedure for all sample types. Results of the British roll tube method, a 24-h direct count method, compared favorably with the standard APHA procedure only for mussels and waters.

A method was developed to enhance recovery of thermally stressed Listeria monocytogenes from internally contaminated shrimp. Shrimp tail meat was inoculated with 105 L. monocytogenes cells/g and boiled for 1-5 min. Thermally stressed L. monocytogenes cells were recovered following cold enrichment for 3 d without broth. Methods of the Food and Drug Administration and the U.S. Department of Agriculture for isolating L. monocytogenes permitted recovery of the organism from shrimp boiled for 1 min: however, with the new method, L. monocytogenes cells were recovered from shrimp boiled up to 5 min. No Listeria spp. were recovered from naturally contaminated, frozen, imported shrimp after 1 min of boiling.

Numerous hepatitis A outbreaks were linked to the consumption of raw molluscan shellfish in the United States between 1960 and 1989. However, there had been no major molluscan shellfish‐associated hepatitis A outbreaks reported in the United States for more than a decade (1989 to 2004). Beginning in late August 2005, at least 10 clusters of hepatitis A illnesses, totaling 39 persons, occurred in four states among restaurant patrons who ate oysters. Epidemiologic data indicated that oysters were the source of the outbreak. Traceback information showed that the implicated oysters were harvested from specific Gulf Coast areas. A voluntary recall of oysters was initiated in September. Hepatitis A virus (HAV) was detected in multiple 25-g portions in one of two recalled samples, indicating that as many as 1 of every 15 oysters from this source was contaminated. Comparing 315 nucleotides within the HAV VP1-2B region, 100% homology was found among four amplicons recovered from a total of six independent experiments of the implicated oysters, and an identical HAV sequence was detected in sera from all 28 patient serum specimens tested. Ten percent heterogeneity over 315 nucleotides (31 variants) was observed between the outbreak strain (subgenotype 1A) and an HM-175 strain (subgenotype 1B) used in the laboratory where the oysters were processed. To our knowledge, this investigation is the first in the United States to identify an HAV-identical strain in persons with hepatitis A as well as in the food that was implicated as the source of their infections.

Oysters (Crassostrea virginica) harvested from the Gulf Coast, containing 10(2) to 10(4) most probable number (MPN) per gram of Vibrio vulnificus, were subjected to a commercial heat-shock process. After 1 to 4 min at internal oyster meat temperatures exceeding 50 degrees C, shellstock oysters were shucked, chilled, washed, and packed. V. vulnificus and total bacterial levels in Gulf Coast oysters were significantly reduced from 1 to 4 logs in the finished product. Similar reductions were not observed in shellstock oysters that were subject to conventional processing. Under the National Shellfish Sanitation Program, heat shocking is an acceptable process to use to assist in the shucking of shellstock. This research revealed that the heat-shock process may also serve to significantly reduce V. vulnificus in summer Gulf Coast oysters.

In a study conducted throughout U.S. Gulf Coastal waters, Vibrio cholerae non-O1 was isolated more frequently from water samples than from shellfish or sediment samples. Frequency of V. cholerae recovery was directly related to water temperature and inversely related to salinity. The presence of V. cholerae was not adequately indicated by the fecal coliform standards for shellfish-growing waters and market shellfish as established by the National Shellfish Sanitation Program. Although all cultures tested by the Y-1 mouse adrenal cell assay or by radioimmunoassay for production of a cholera toxin-like toxin were negative, 4 of 13 isolates caused diarrhea in the infant rabbit.