Hidemasa Kodaka

Evaluation of a new medium for the enumeration of total coliforms and Escherichia coli in Japanese surface waters

Aim:  A new medium, EC‐Blue‐10, containing chromogenic and fluorogenic substrates, KNO3 and sodium pyruvate has been developed for the rapid simultaneous detection and enumeration of total coliforms and Escherichia coli in water.

Evaluation of the Compact Dry VP method for screening raw seafood for total Vibrio parahaemolyticus.

Compact Dry VP (CDVP) is a ready-to-use method for enumerating Vibrio parahaemolyticus in food. The presterilized plates contain a culture medium comprising peptone, NaCl, bile salts, antibiotics, chromogenic substrates, and polysaccharide gum as a cold water-soluble gelling. After diluting raw seafood samples in a phosphate-buffered saline solution, a 1-ml aliquot was inoculated onto the center of the plate and allowed to diffuse by capillary action. Blue-green colonies forming on the plates were counted after 18 to 20 h of incubation at 35 degrees C. A total of 85 V. parahaemolyticus strains (62 tdh+ strains and 23 tdh- strains) were studied for inclusivity, 81 (95.3 %) of which produced blue-green colonies. When 97 strains (14 strains of Vibrio spp., 33 strains of coliform bacteria, and 50 strains of noncoliform bacteria) were assessed for exclusivity, 10 strains of Vibrio spp. produced non-blue-green colonies, and 87 strains failed to grow. The CDVP and U.S. Food and Drug Administration Bacteriological Analytical Manual (FDA-BAM) methods were compared with the use of four different types of raw seafood that were inoculated with four different V. parahaemolyticus strains. For raw tuna and oysters, the FDA-BAM colony lift method was used, whereas the FDA-BAM most-probable-number method was used for salmon and scallop. The linear correlation coefficients between the CDVP and FDA-BAM methods were 0.99 for fresh raw tuna, 0.95 for fresh raw oysters, 0.95 for frozen raw salmon, and 0.95 for frozen raw scallops. These results suggest that the CDVP method is useful for screening raw seafood for V. parahaemolyticus.

Evaluation of the dry sheet medium (Compact Dry LS) for screening of total Listeria count in food samples

The Compact Dry LS (CD-LS), ready-to-use dry sheet selective medium for Listeria species, was evaluated for inclusivity and exclusivity by using 107 strains including 20 Listeria species strains. All tested Listeria species strains other than Listeria seeligeri that grew as blue colored colony on CD-LS. CD-LS were compared with those on Oxford agar and ALOA agar as conventional methods using Listeria species inoculated from 100 food samples. The correlation coefficients between CD-LS and Oxford agar, and CD-LS and ALOA agar were 0.983 and 0.978, respectively. Our results suggested CDLS was a suitable alternative medium for screening of Listeria species.