Relationships of temperature and sodium chloride concentration to the survival of Vibrio parahaemolyticus in broth and fish homogenate

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.

Recovery of chill-stressed Vibrio parahaemolyticus from oysters with enrichment broths supplemented with magnesium and iron salts

The effects of magnesium and iron salts on the recovery and growth of chill-stressed cells of Vibrio parahaemolyticus were studied. Supplementation of glucose salt Teepol (GST) broth with 20 to 100 mM of Mg2+ significantly (P less than or equal to 0.05) increased the number of cells recovered from oyster homogenate stored at 3 degrees C. Populations detected with supplemented GST were comparable to those obtained with Horie arabinose ethyl violet (HAE) broth, with or without Mg2+. Recovery of V. parahaemolyticus from homogenates stored at -18 degrees C was also improved when enrichment broths supplemented with Mg2+ were used. Ferric iron (added as FeCl3) at 240 microM in GST and 240 or 960 microM in HAE significantly enhanced the extent of recovery of chilled cells. Ferrous iron was generally less effective. Teepol did not influence the growth of nonchilled cells, but significantly reduced the viable population in suspensions of chilled cells when used at a level of 0.4% in GST. The relatively high pH (9.0) of HAE caused a significant reduction in the number of viable, chill-stressed cells of V. parahaemolyticus. The overall results indicated that HAE broth is superior to GST for recovering V. parahaemolyticus from refrigerated and frozen oyster homogenates.

Growth of heat-injured Vibrio parahaemolyticus in media supplemented with various cations

Mid- to late logarithmic growth phase cells of Vibrio parahaemolyticus grown in tryptic soy broth (TSB) containing 0.5, 3.0, and 7.5% NaCl were heated for 8 min at 45 degrees C in 0.1 M phosphate buffer (pH 7.2) containing 3% NaCl. Colony formation on thiosulfate-citrate-bile salts-sucrose agar (TCBS) containing 2% NaCl was greatest for unheated cells that had been grown in 7.5% NaCl-TSB; cells grown in 0.5% NaCl-TSB formed a greater number of colonies on 1.0% NaCl-TCBS. Thermal injury was evident in heated cells, regardless of the NaCl concentration in TSB growth medium. The effects of Mg2+, K+, and Li+ added as chlorides to 0.5% NaCl-TSB on the growth of nonheated and heated V. parahaemolyticus were studied. Lower levels of Mg2+ and slightly higher levels of K+ were required to replace Na+ in TSB inoculated with thermally injured cells that had been originally grown in 3.0 and 7.5% NaCl-TSB. LiCl had an inhibitory effect on both nonheated and heated cells when present in the recovery medium (0.5% NaCl-TSB) at concentrations as low as 0.5%. Increased numbers of colonies were formed by heated cells plated in MgCl2-supplemented TCBS, regardless of the NaCl concentration in the original growth medium. Potassium had little, if any, effect on colony formation by nonheated V. parahaemolyticus recovered on TCBS and may have had a detrimental effect on heat-injured cells.

Relationships between heat resistance and phospholipid fatty acid composition of Vibrio parahaemolyticus

Vibrio parahaemolyticus was grown in tryptic soy broth (TSB) containing NaCl levels of 0.5, 3.0, and 7.5% (wt/vol). Cultures incubated at 21, 29, and 37 C were harvested in late exponential phases and thermal death times at 47 C (D47 c; time at 47 C required to reduce the viable population by 90%) were determined in phosphate buffer containing 0.5, 3.0, and 7.5% NaCl. At a given NaCl concentration in the growth medium, D47 c values increased with elevated incubation temperatures and with elevated levels of NaCl in the heating menstrua. Differences in thermal resistance of cells cultured at a particular temperature were greater between those grown in TSB containing 0.5 and 3.0% NaCl than between those grown in TSB containing 3.0 and 7.5% NaCl. D47c values ranged from 0.8 min (grown at 21 C in TSB with 0.5% NaCl) to 6.5 min (grown at 37 C in TSB with 7.5%, heated in 7.5% NaCl buffer). Methyl esters of major phospholipid fatty acids extracted from cells were quantitated. The ratio of saturated to unsaturated fatty acids in cells grown at a given NaCl concentration increased with elevated incubation temperature. At a particular growth temperature, however, saturated to unsaturated fatty acids ratios were lowest for cells grown in TSB containing 3.0% NaCl.

Interacting effects of pH, temperature, and salt concentration on growth and survival of Bibrio parahaemolyticus

Thermal resistance and minimal pH and temperature conditions for growth of Vibrio parahaemolyticus in artificial media containing 3 and 7% sodium chloride were studied. Growth was observed at pH 4.8 and at 5 C.