Comparison of Four Agar Media for Detection of Histamine-Producing Bacteria in Tuna 1.

In a comparative study to determine their effectiveness for early detection of prolific histamine-producing bacteria from tuna samples, Niven's medium proved to be superior to three modifications of the medium. Presumptive colonies could be detected in 24 h on Niven's agar surface-plated and incubated at 35°C. Following confirmatory histamine determination with high performance liquid chromatography of the tuna fish infusion broth inoculated with presumptive histamine-producers and non-producers, detection rates of 95.8 and 93.9% were obtained from temperature-abused and bacteria-spiked tuna samples, respectively, using Niven's agar. The other three modifications provided much lower detection rates and higher false-positive and false-negative results than did Niven's agar.

Evaluation of Dichloran-Rose Bengal Agar for Enumeration of Fungi in Foods 1.

Samples of flour, corn meal, ground meat and carrots were analyzed by standard procedures for presence of fungi using both Dichloran-Rose Bengal (DRBC) and Plate Count agar with antibiotics. Bacterial contamination was so extensive with ground meat and carrot samples on DRBC that meaningful fungal counts could not be obtained. Therefore, DRBC is not recommended for routine enumeration of fungi in foods.

Incidence of Salmonellae in Clams, Oysters, Crabs and Mullet 1.

Sixty samples each of oysters ( Crassostrea virginica ), clams ( Mercenaria mercenaria ), striped mullet ( Mugil cephalus ), and blue crab ( Callinectes sapidus ) were analyzed for the presence of salmonellae within 4 h of harvesting from an east and west coast location in Florida. Mullet was the only seafood from which salmonellae were not recovered. Clams from the west coast location had the highest incidence (43%) of salmonellae. Eleven serotypes of Salmonella were recovered and identified from the samples. In quantitative MPN studies, the number of salmonellae present in west coast oysters was 2.2 organisms per 100 g of oyster meats. The variety of serotypes isolated, coupled with consistent recoveries throughout the year, suggests that salmonellae may represent a portion of the natural background flora in these seafoods rather than recent single source contamination.

Isolation of Vibrio cholerae from the American Eel, Anguilla rostrata.

Nineteen eels ( Anguilla rostrata ), collected from the Suwannee River estuary in Florida, were examined for Vibrio cholerae . Nonagglutinable V. cholerae were isolated from 11 of the eels for an isolation rate of 58%. Isolates from 6 of the eels were confirmed by the Smith serotyping system and found to be types 17, 68 and 175.

Isolation of Chromobacterium spp. from foods, soil, and water.

Chromobacterium violaceum, a soil and water inhabitant, has been implicated in human disease with a high mortality rate, particularly in the southeastern United States. The psychrotrophic Chromobacterium lividum has been isolated from foods, water, and soil, but is not considered pathogenic. To determine the distribution of Chromobacterium spp. in soil, water, and foods in the Gainesville area, we evaluated Bennett, Ryalls and Moss, and Aeromonas membrane agars for their ability to recover these organisms from various samples when incubated at 25 or 35 degrees C. Bennett agar was best for the isolation of both species when incubated at 25 degrees C; however, at 35 degrees C, Aeromonas membrane agar gave the highest recoveries of C. violaceum. C. violaceum was recovered only from soil and water, whereas C. lividum was frequently recovered from foods as well as soil and water.

Nutritional and Microbial Changes During Production of Tostones (Fried Plantains).

Tostones (fried plantains) are consumed by a large segment of the Latin population in Florida. In addition, their use in specialty restaurants is on the increase. However, little is known about the microbial and nutritional quality of this product, particularly as affected by processing. Tostones are prepared by peeling and cutting the plantains into slices; soaking slices in a salt brine; frying, drying and flattening the slices; and refrying them until golden brown. Protein, ash, crude fiber and carbohydrate content increased during preparation as a result of moisture loss during processing. Fat content increased due to uptake during frying. Phosphorus, Na, Hg, Se and Zn content also increased, whereas that of K and Fe decreased. Changes in water activity and pH were not significantly pronounced. Bacillus and Penicillium species were the only organisms isolated from laboratory-prepared samples. The finished product contained 48.0% carbohydrate, 26.5% moisture, 21.5% fat, 2.5% protein, 1.0% ash, 0.5% crude fiber and 395 Kcal/100 g.

Effect of Planococcus citreus on Selected Quality Indices of Penaeus Shrimp.

Selected biochemical and microbial changes in Penaeus shrimp inoculated with Planococcus citreus were examined to determine the potential of this organism to contribute to spoilage of shrimp. Biochemical and microbial studies were conducted following storage of Penaeus shrimp at 5 C for 0, 4, 8, 12 and 16 days. Three samples, a control (raw shrimp), an irradiated (600 Krad) control and an irradiated (600 Krad) sample inoculated with P. citreus , were analyzed for changes in aerobic plate count, pH, total volatile nitrogen/amino acid nitrogen (TVN/AA-N) ratio, trimethyl amine-nitrogen (TMN) and total extractable protein (TEP). P. citreus counts increased in the inoculated shrimp from 3.0 × 103 bacteria/gram at 0 day to 1.5 × 108 bacteria/gram at the 16th day. By the 16th day of storage, the pH of the inoculated shrimp was significantly higher than the pH of the other samples. P. citreus inoculated onto irradiated shrimp was able to produce a TVN/AA-N ratio of 1.3 by the 10th day of storage, about the same time as that developed by the natural flora on raw shrimp. The increase in TMN content of the control (raw shrimp) and the inoculated sample were not significantly different. P. citreus was also able to bring about a significant decrease in the percent TEP of shrimp during storage. These changes indicate the capabilities of P. citreus in lowering the overall quality of Penaeus shrimp.

Identification of Enterobacteriaceae Isolated from Seafoods 1.

Fifty-three retail samples of seafood were examined for members of the family Enterobacteriaceae , using violet red bile agar with 1% glucose. Isolation and identification of 99 typical colonies showed them all to be members of the family Enterobacteriaceae . Enterobacter species were most frequently isolated with Erwinia , Klebsiella , Hafnia , Proteus , Serratia , Escherichia and Yersinia recovered with decreasing frequency.

Effect of Delayed Heading on Some Quality Attributes of Penaeus Shrimp 1.

To determine the effect of delayed heading on shrimp quality, shrimp were stored on ice with and without heads for 10 days. Some shrimp were delay-headed after 5 days and returned to ice for the remainder of the storage period. Microbiological studies were conducted at 0, 5 and 10 days of storage. Total aerobic plate counts were done using Standard Plate Count agar with an added 0.5% NaCl. Incubation was at 20 C for 5 days. Analyses indicated similar counts on shrimp tails stored with or without heads and those delayed-headed. Counts ranged from 2.4 × 106 bacteria/gram at 0 day to 1.6 × 109 bacteria/gram on the 10th day. Identification of the flora present revealed that the same major groups of organisms predominated on shrimp tails subjected to the different storage treatments and the head did not alter development of the usual flora. Flavobacterium , Pseudomonas , Planococcus , Moraxella and the Vibrio/Aeromonas group were the major genera encountered. A shift in bacterial populations was observed during storage. Flavobacterium species predominated during the first 5 days of storage; however, after the fifth day Pseudomonas species predominated. Sensory panel data revealed no differences in acceptability between shrimp tails stored with or without heads and those delay-headed.

Single or Multiple Antibiotic-Amended Media to Enumerate Yeasts and Molds 1.

Gentamicin, chloramphenicol and chlortetracycline were evaluated singly and in combination for their ability to control bacteria in media to enumerate yeast and molds. No single antibiotic tested at 50 or 100 ppm was totally effective in controlling bacteria. Chlortetracycline in combination with either chloramphenicol or gentamicin inhibited the contaminating bacteria as long as the antibiotics were added after autoclaving. It is recommended that for routine use, reliance not be placed upon a single antibiotic to control bacteria when enumerating fungi.

Residual Bisulfite in Iced Penaeus Shrimp 1.

Shrimp dipped in sodium bisulfite solutions of 1.25 and 5.0% were analyzed for residual bisulfite during iced storage for up to 15 days. Most of the bisulfite was located on the shell and was readily leached away by the melting ice. A further reduction in bisulfite occurred when shrimp were rinsed in either water or hypochlorite solutions after storage, with the greatest reductions occurring during the hypochlorite rinses.

Organisms From Positive MPN Tubes Inoculated With Samples That Yielded No Growth on Pour Plates.

Twenty samples of cold ready-to-eat cereal were analyzed for total organisms using the pour plate and Most Probable Number technique (MPN). Nine samples enhibited growth in MPN tubes but not on pour plates. Of the 28 isolates obtained from the MPN tubes, 16 were members of the genus Bacillus and the remainder were predominately other gram-positive organisms. The data support the working hypothesis that aside from the mathematical bias associated with the MPN procedure, microbial recovery is more favorable in a liquid environment than in an agar medium.

Identification of yeasts from the suwannee river Florida estuary.

The yeast flora of the Suwannee River estuary in Florida has been studied. The predominant genera were Candida and Rhodotorula; however, the yeast most frequently isolated was Cryptococcus laurentii. Nine ascosporogenous species were isolated, with Hansenula saturnus predominating. The salinity range of the sediments was 0.4 to 20.6%; in the estuary water, 0.07 to 0.25%; and in the open Gulf of Mexico, 18 to 20%.

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.

Isolation of Vibrio parahaemolyticus from Salt Springs in Florida.

Vibrio parahaemolyticus was isolated from various locations in two salt springs of Florida and appears to be a normal inhabitant of these artesian waters.

Response of the Mimeae to some physical and chemical agents.

Isolates of Mima polymorpha and Herellea vaginicola obtained from retail food products were investigated for their ability to hydrolyze proteins, starch, and lipids as well as for their ability to initiate growth under varying conditions of pH, sodium chloride concentration, and temperature. None of the isolates hydrolyzed starch and a few hydrolyzed proteins, whereas most were actively lipolytic. Members of each genus grew over the range 6 to 42 C; in general, H. vaginicola was more tolerant to high concentrations of sodium chloride and to acid conditions than was M. polymorpha.