A differential agar for the further detection of presumptive Escherichia coli O157 strains among typical sorbitol negative and cefixime-tellurite resistant strains was investigated. For this purpose, in parallel to colonies of 8 reference strains, 1130 suspect colonies picked from the surface of cefixime-tellurite (CT)-sorbitol MacConkey (SMAC) (CT-SMAC) agar plates of food samples (white cheese, raw milk and ground beef) were transferred to differential agar plates. After a 6-h incubation period at 42 ºC, only 47 (4.15%) of the 1130 colonies appeared as typical E. coli O157 on the differential agar plates (100 x 15 mm) gridded into 25 numbered sections. Salicin (S), rhamnose (R) and cellobiose (C) were tested separately and together in combination with MUG. The best results were obtained from the combined use of the 3 in SMAC medium (SRC-MUG-SMAC). When violet red bile lactose agar (VL) was used in the same manner as SRC-MUG-SMAC, only 16 (1.41%) of the 1130 colonies remained typical. In this procedure, no biochemical test was required for further identification. The use of an SRC-MUG-SMAC plate immediately after the colony selection step appeared to be more discriminative than the addition of these sugars and MUG to the primary isolation media. As a result, the testing of presumptive E. coli O157 colonies using a differential agar plate including MUG and 3 (or more) sugars that are not fermented by this organism is a rapid, easy, precise and relatively inexpensive isolation procedure, and it is particularly ideal for use in routine screening laboratories.
A differential agar for the further detection of presumptive Escherichia coli O157 strains among typical sorbitol negative and cefixime-tellurite resistant strains was investigated. For this purpose, in parallel to colonies of 8 reference strains, 1130 suspect colonies picked from the surface of cefixime-tellurite (CT)-sorbitol MacConkey (SMAC) (CT-SMAC) agar plates of food samples (white cheese, raw milk and ground beef) were transferred to differential agar plates. After a 6-h incubation period at 42 ºC, only 47 (4.15%) of the 1130 colonies appeared as typical E. coli O157 on the differential agar plates (100 x 15 mm) gridded into 25 numbered sections. Salicin (S), rhamnose (R) and cellobiose (C) were tested separately and together in combination with MUG. The best results were obtained from the combined use of the 3 in SMAC medium (SRC-MUG-SMAC). When violet red bile lactose agar (VL) was used in the same manner as SRC-MUG-SMAC, only 16 (1.41%) of the 1130 colonies remained typical. In this procedure, no biochemical test was required for further identification. The use of an SRC-MUG-SMAC plate immediately after the colony selection step appeared to be more discriminative than the addition of these sugars and MUG to the primary isolation media. As a result, the testing of presumptive E. coli O157 colonies using a differential agar plate including MUG and 3 (or more) sugars that are not fermented by this organism is a rapid, easy, precise and relatively inexpensive isolation procedure, and it is particularly ideal for use in routine screening laboratories.
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Thompson, J.S., Hodge, D.S., Smith, D.E., Yong, Y.A.: Use of tri- gas incubator for routine culture of Campylobacter species from fecal specimens. J. Clin. Microbiol., 1990; 28: 2802-2803.
Fujisawa, T., Sata, S., Aikawa, K., Takahashi, T., Yamai, S., Shimada, T.: Modification of sorbitol MacConkey medium containing cefixime and tellurite for isolation of Escherichia coli O157:H7 from radish sprouts. Appl. Environ. Microbiol., 2000; 66: 3117-3118.
Okrend. A.J.G., Rose, B.E., Lattuada, C.P.: Use of 5-bromo-4- chloro-3-indoxyl-b-D- glucuronide in MacConkey sorbitol agar to aid in the isolation of Escherichia coli O157:H7 from ground beef. J. Food Prot., 1990; 53: 941-943.
Reinders, R.D., Barna, A., Lipman, L.J., Bijker, P.G.: Comparison of the sensitivity of manual and automated immunomagnetic separation methods for detection of Shiga toxin-producing Escherichia coli O157:H7 in milk. J. Appl. Microbiol., 2002; 92: 1015-1020.
De Boer, E., Heuvelink, A.E.: Methods for the detection and isolation of Shiga toxin –producing Escherichia coli. J. Appl. Microbiol., 2000; 88: 133-143.
Manafi M.: New developments in chromogenic and fluorogenic culture media. Int. J. Food Microbiol., 2000; 60: 205-218.
Manafi, M., Kremsmaier, B.: Comparative evaluation of different chromogenic/fluorogenic media for detecting Escherichia coli O157:H7 in food. Int. J. Food Microbiol., 2001; 71: 257-262.
Karakulska, J.: Biochemical properties of enterotoxic and enterohemorrhagic E. coli strains. Med. Dosw. Mikrobiol., 2002; 54: 215-223.
Weagant, S.D., Bryant, J.L., Jinneman, K.G.: An improved rapid technique for isolation of Escherichia coli O157:H7 from foods. J. Food Prot., 1995; 58: 7-12.
Hammack, T.S., Feng, P., Amaguana, R.M., June, G.A., Sherrod, P.S., Andrews, W.H.: Comparison of sorbitol MacConkey and hemorrhagic coli agars for recovery of Escherichia coli O157:H7 from brie, ice cream, and whole milk. J. AOAC Int., 1997; 80: 335-340.
Tortorello, M.L., Reineke, K.F., Stewart, D.S., Raybourne, R.B.: Comparison of methods for determining the presence of Escherichia coli O157:H7 in apple juice. J. Food Prot., 1998; 61: 1425-1430.
Gunzer, F., Bohm, H., Russmann, H., Bitzan, M., Aleksic, S., Karch, H.: Molecular detection of sorbitol-fermenting Escherichia coli O157 in patients with hemolytic-uremic syndrome. J. Clin. Microbiol., 1992; 30: 1807-1810.
Hayes, P.S., Blom, K., Feng, P., Lewis, J., Strockbine, N.A., Swaminathan, B.: Isolation and characterization of a beta-D- glucuronidase-producing strain of Escherichia coli serotype O157:H7 in the United States. J. Clin. Microbiol., 1995; 33: 3347-3348.
Colombo, S., Pacciarini, M.L., Fusi, P.: Isolation of a new phenotypic variant of E coli O157:H7 from food. Vet. Rec., 1998; 142: 144-145.
Ikedo, M., Komatsu, O., Hara-Kudo, Y., Yamamoto, S., Kumagai, S.: Development of chromogenic agar medium for isolation of enterohaemorrhagic Escherichia coli O26. Kansen. Zasshi, 2001; 75: 291-299 (Abstr.).
Camguilhem, R., Milon, A.: Biotypes and O serogroups of Escherichia coli involved in intestinal infections of weaned rabbits: clues to diagnosis of pathogenic strains. J. Clin. Microbiol., 1989; 27: 743-747.