Isolation of Shigella sonnei by fluid media

Selenite F broth prepared in the laboratory from single ingredients was found to be significantly more efficient than nutrient broth in the isolation of Shigella sonnei from human faeces. It was more efficient than direct plating on deoxycholate citrate agar for diagnosisng Sonne dysentery in a local outbreak. The difference was significant. There was, however, no significant advantage for enrichment over direct plating when stools posted from Briston to Cardiff were examined. Laboratory prepared selenite F broth was preferable to the same medium purchased commercially from two different firms. The product of one frim was significantly better than that of the other. Two methods of sterilization of laboratory prepared selenite F broth were studied. Seitz filtered selenite was less inhibitory to the growth of samll numbers of Shigella sonnei. Sterilization by heating in free steam for periods of 15 min and over impaired the ability of selenite F broth to allow multiplication of small numbers of Shigella sonnei.