COMPARISON OF DIRECT-PLATING AND ENRICHMENT METHODS FOR ISOLATION OF VIBRIO-CHOLERAE FROM DIARRHEA PATIENTS

A direct-plating method on thiosulfate citrate bile salts sucrose agar (DIR-TCBS) in conjunction with enrichment in alkaline peptone mater ( APW) incubated for both 6 h and 24 h followed by subculture onto TCBS (APW6h-TCBS and APW24h-TCBS, respectively) nas performed on 16,034 rec tal swab samples for isolating Vibrio cholerae. A total of 2,932 (18.3 %) rectal swab samples were positive for V. cholerae O1 biotype El Tor , with the Ogawa serotype constituting 99.2% of the isolates, There we re no significant differences in V. cholerae O1 isolation rates betwee n the three culture systems nor between the combinations of any two sy stems, However, direct plating plus enrichment demonstrated a signific antly higher V. cholerae O1 isolation rate than DIR-TCBS alone (P < 0. 02), Conversely, enrichment procedure, alone or in combination with DI R-TCBS, yielded significantly more (P < 0.0001) V. cholerae non-O1 iso lates than DIR-TCBS alone, The length of incubation time of the enrich ment broth, 6 h, offers no significant advantages over 24 h for thf is olation of V. cholerae ae O1 and non-O1. A 24-h enrichment broth incub ation period has the practical advantage of being easy to integrate in to a normal laboratory workday, whereas 6-h broth enrichment, although more commonly recommended, requires that arrangements be made for aft er-hours subculture.