Rapid polymerase chain reaction method for detection of Kanagawa positive Vibrio parahaemolyticus in seafoods

Detection of Kanagawa positive strains of Vibrio parahaemolyticus by polymerase chain reaction (PCR) was tested. Primer pairs for specific amplification of tdh gene fragment is described. The assay could detect contamination of seafood homogenate when PCR was performed using lysate prepared directly from fish homogenates. The sensitivity of the assay could be improved to detect less than 10 cells of V. parahaemolyticus by performing PCR after 8 h enrichment in alkaline peptone water.

Incidence of Listeria spp. in tropical fish

The incidence of Listeria spp. in tropical fish and shellfish was studied. The isolation protocol included a pre-enrichment, followed by two selective enrichment steps and plating on three selective agars. Listeria monocytogenes could be detected in 17.2% of finfish and 12.1% of shellfish. L. innocua was the most common species encountered. In 6.9% finfish and 5.6% shellfish, both L. monocytogenes and L. innocua were detected. Polymerase chain reaction (PCR)-based amplification of internal fragments of the iap gene was found to be useful in differentiation of L. monocytogenes from L. innocua.

Rapid detection of Vibrio cholerae contamination of seafood by polymerase chain reaction

The possibility of detecting Vibrio cholerae contamination of seafood using a technique based on polymerase chain reaction (PCR) was studied. Direct PCR on lysate prepared from fish homogenates containing 10(3) V. cholerae/ml gave a positive reaction. When combined with alkaline peptone water (APW) enrichment, homogenates containing 1.4 cells/ml gave amplification signal. The technique could also detect V. cholerae O139, the recent epidemic serotype in the Indian subcontinent. An environmental isolate of non-O1 V. cholerae that produced cholera toxin was also positive in this assay. The results suggest that PCR-based techniques have great potential in quick detection of toxigenic V. cholerae in seafoods.

Ultrastructural study of Listeria monocytogenes entry into cultured human colonic epithelial cells

Evidence that Listeria monocytogenes enters Caco-2 cells through the apical surface is presented. Attachment of bacteria to host cells seems to induce modifications of microvilli which are either in direct contact with the bacterial surface or in close vicinity, resulting in the formation of lamellipodia involved in the cellular uptake of the bacteria. Such modifications are not induced by L. monocytogenes SLCC 53, which carries a deletion in the prfA gene, although attachment of this mutant to Caco-2 cells occurs. Listeria innocua does not attach well to Caco-2 cells and also fails to cause structural alterations of the microvilli. Treatment of confluent monolayers of Caco-2 cells with ethylene glycol-bis(beta-aminoethyl ether)- N,N,N1,N1-tetraacetic acid (EGTA), which disrupts intercellular junctions, greatly reduced the uptake of Listeria cells. Attachment and invasion of L. monocytogenes was not accompanied by accumulation of filamentous actin around the entering bacterial cell.

Listeria ivanovii is capable of cell-to-cell spread involving actin polymerization

Listeria ivanovii has been considered to be pathogenic to animals but has rarely been found associated with human infections. It has been claimed that L. ivanovii lacks the actA gene, which in L. monocytogenes encodes a protein required for interaction with host cell actin. Using fluorescence microscopy and electron microscopy, we demonstrate that L. ivanovii can invade mammalian cells, lyse the phagosomal membrane, polymerize host cell actin, reorganize actin to form tails, and spread from cell to cell. However, no DNA homologous to the actA gene could be detected by polymerase chain reaction. Further, L. ivanovii lacks the 90-kDa surface protein which in L. monocytogenes is encoded by actA. Despite the ability to spread from cell to cell, L. ivanovii differed significantly from L. monocytogenes in being unable to form plaques on monolayers of 3T3 fibroblast cells.

A toxin profile for shellfish involved in an outbreak of paralytic shellfish poisoning in India

Toxin profiles of clams and oysters involved in the outbreak of paralytic shellfish poisoning in India in 1983 were studied by a liquid chromatographic technique. Gonyautoxins 1, 2, 3, 4 and 8, and 11-epigonyautoxin 8 appeared to be the major toxins along with small amounts of saxitoxin, neosaxitoxin, decarbamoylsaxitoxin, decarbamoylgonyautoxins 2 and 3, C3 and C4. Toxin profile suggests the involvement of Alexandrium spp. in this outbreak.

Haemolysins of Vibrio parahaemolyticus strains passaged in mice

Some phenotypically non-haemolytic strains of V. parahaemolyticus were observed to produce haemolysins after two passages in mices. Depending on the strain, both heat stable and heat labile haemolysins were induced. The heat stable haemolysin so induced, was immunologically different from the thermostable direct haemolysin produced by Kanagawa positive strains of V. parahaemolyticus.

Virulence of Vibrio vulnificus strains isolated from seafoods

A study was carried out on the relation between virulence of V. vulnificus assessed by LD50 in mice and other markers. V. vulnificus strains isolated from seafoods had LD50 ranging from 10(3)-10(7) for mice. Strains showing LD50 10(6) or less were generally haemolytic and settled after boiling. Resistance to bactericidal action of serum and ability to take up congo red was shown by all the strains.

Role of chitin in the survival of Vibrio parahaemolyticus at different temperatures

Washed cells of Vibrio parahaemolyticus declined in numbers when incubated in phosphate-buffered saline for 6 h at different temperatures. Addition of chitin flakes to phosphate-buffered saline not only helped the organism to survive, but also resulted in an increase in cell numbers, particularly at 10 degrees C. The effect of chitin could not be simulated by N-acetylglucosamine, yeast extract, starch, or casein.

Evaluation of methods for enumeration of Vibrio parahaemolyticus from seafood

The efficiency of several enrichment broths in recovering Vibrio parahaemolyticus inoculated into fish homogenates was studied. Recovery by the most probable number technique was very low in all the broths, while direct plating on thiosulfate citrate bile salt sucrose agar yielded better recovery. A decrease in the enrichment time to 8 from 18 h did not improve recovery. At concentrations exceeding 2.5 micrograms/ml, polymyxin was inhibitory to V. parahaemolyticus.

Survival of Vibrio parahaemolyticus in cold smoked fish

Fresh samples of mullet (Mugil cephalus) and oil sardines (Sardinella longiceps) obtained from a fish market were subjected to cold smoking. Some of the samples harboured low levels of Vibrio parahaemolyticus. After cold smoking, however, many samples showed relatively high levels of V. parahaemolyticus suggesting that a small population of naturally occurring organisms could multiply to significant levels during the process of cold smoking or during subsequent storage at room temperature. Nevertheless, smoke components were observed to exert an inhibitory effect on V. parahaemolyticus in broth. Salt concentration 1% appeared to increase the sensitivity of V. parahaemolyticus to smoke components.

Enhancement of Vibrio parahaemolyticus virulence by lysed erythrocyte factor and iron

The effect of lysed blood on the virulence of Vibrio parahaemolyticus for mice was investigated. A factor present in lysed erythrocytes was found to greatly reduce the 50% lethal dose of V. parahaemolyticus for mice. Similar effects were observed with ferric ammonium citrate and manganous sulfate. V. parahaemolyticus grown in brain heart infusion containing lysed erythrocyte factor appeared to produce a lethal toxin which was either inapparent or absent when the organism was grown in brain heart infusion alone.

Levels of Vibrio parahaemolyticus in Indian shrimp undergoing processing for export

A study of 56 samples of raw prawns, 50 samples of processed prawns, and 57 samples of frozen prawns from five prawn-processing factories around Mangalore for the levels of Vibrio parahaemolyticus revealed that most of these samples carry a load of less than 10/g. None of the samples had counts greater than 10(2)/g, indicating that the prawn-processing factories are able to meet the International Commission on Microbiological Specifications for Foods (ICMSF) suggested limit of 10(2) V. parahaemolyticus per gram for frozen prawns.

Production of hemolysin by Vibrio parahaemolyticus in a chemically defined medium

A chemically defined medium capable of supporting the production of heat-stable and heat-labile hemolysins by Vibrio parahaemolyticus is described. The indispensability of serine and glutamic acid for hemolysin production is also demonstrated.