Katsuhiro Aikawa

Modification of Sorbitol MacConkey Medium Containing Cefixime and Tellurite for Isolation of Escherichia coli O157:H7 from Radish Sprouts

ABSTRACT A modified version of sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC medium) was produced by adding salicin and 4-methylumbelliferyl-β-d-galactopyranoside to CT-SMAC medium; this medium was designated CT-SSMAC medium and was used to isolate Escherichia coli O157:H7 from radish sprouts. Of 101 non-E. coli bacteria isolated from radish sprouts that produced colorless colonies similar to colonies of E. coliO157:H7 grown on CT-SMAC medium, 92 (91%) formed colonies that were red to pink or were β-galactosidase negative and colorless on CT-SSMAC medium. On the other hand, colonies of E. coliO157:H7 strains were colorless and β-galactosidase positive on CT-SSMAC medium. Our results suggest that CT-SSMAC medium is more selective than CT-SMAC medium for isolating E. coliO157:H7.

Evaluation of sorbitol-salicin MacConkey medium containing cefixime and tellurite (CT-SSMAC medium) for isolation of Escherichia coli O157:H7 from raw vegetables.

The utility of CT-SSMAC medium (sorbitol-salicin MacConkey medium containing cefixime and tellurite) for the isolation of Escherichia coli O157:H7 from raw vegetables was investigated. The colonies of all E. coli O157:H7 and O157:NM strains tested were colorless and beta-galactosidase-positive on CT-SSMAC medium. Furthermore, the number of colorless colonies on the CT-SSMAC medium was less than that on the sorbitol MacConkey medium containing cefixime and tellurite (CT-SMAC medium) from several raw vegetable samples. All colorless colonies grown on CT-SSMAC medium from raw vegetable samples were beta-galactosidase-negative. These findings suggest that the CT-SSMAC medium is useful for the isolation of E. coli O157:H7 from raw vegetable samples.

Occurrence of clostridia in glass bottled foods

Forty-one marketed samples of imported and domestic glass bottled foods were tested for clostridia contamination. It was detected in nine (22%) samples. Clostridia were isolated from fish sauce (Nam pla, Nuoc-mam), dressing, mustard, hot and sour soup mix (Tom Yum), mysids boiled down in soy, and salmon flakes. The origin of all clostridia positive samples was Asia. Clostridium botulinum and C. perfringens were not detected. The frequency of occurrence was higher by enrichment broth culture detection methods than by agar plate or pouch methods. These findings suggest that the number of bacteria in most of these clostridia positive food samples is very low, and the use of enrichment methods for detection of clostridia is essential.

Influence of butyric and lactic acids on the β-glucuronidase activity of Clostridium perfringens

T. FUJISAWA, K. AIKAWA, T. TAKAHASHI, S. YAMAI, K. WATANABE, Y. KUBOTA AND M. MIYAOKA. 2001. The β‐glucuronidase activity of intact cells of Clostridium perfringens was not influenced by the presence of either 0·09 or 0·19% lactic or butyric acids. In contrast, the enhanced enzyme activity of intact cells due to sodium deoxycholate was significantly decreased by the presence of these acids. These results suggest the possibility that the development of cancer due to the intake of a high fat diet may be inhibited by the presence of organic acids produced by intestinal bacteria.

Influence of sodium chloride on the β‐glucuronidase activity of Clostridium perfringens and Escherichia coli

While the β‐glucuronidase activity of intact cells of Clostridium perfringens was higher in 0·95% sodium chloride (NaCl) than that in 0, 0·1 or 0·5%, that of Escherichia coli was higher in 0·1% NaCl than that in 0, 0·5 or 0·95% NaCl in 0·1 mol l−1 KH2PO4. However, the enzyme activity of both species of intact cells was higher in buffer containing 16 mEq sodium, 134 mEq potassium and 16 mEq chloride per litre than in that containing 146 mEq sodium, 13 mEq potassium and 146 mEq chloride. These findings suggest that bacterial cells are affected by the presence of NaCl and that the effect of NaCl on the activity of bacterial β‐glucuronidase may differ by location in the large intestine.