The rise and fall of Escherichia coli O15 in a London teaching hospital.

A marked increase in the prevalence of bacteraemia due to Escherichia coli of serogroup O15 was noted during November and December 1986 at Charing Cross Hospital. This multiresistant strain had been reported by several hospitals in south London. All isolates of E. coli from patients with bacteraemia between October 1986 and the end of September 1988 were assessed for the presence of the O15 antigen and for the unusual pattern of resistance to six antimicrobial agents. As a guide to faecal carriage, isolates from urine were similarly assessed during seven 4-week periods between January 1987 and June 1988. Of the 123 E. coli isolates from blood, 25 (20%) were serogroup O15 and 20 of these expressed the same pattern of multiresistance; 17 of these multiresistant isolates occurred in the 4-month period 1 Nov. 1986-28 Feb. 1987. During the remaining 19 months of the study only eight isolates were serogroup O15 of which only three were multiresistant. In the first 4-week period that urine isolates were studied 21 Jan. 1987-17 Feb. 1987, 26 (13.2%) of the 195 isolates were serogroup O15 of which 20 were multiresistant. The proportion of serogroup O15 isolates fell gradually until, in June 1988, the last period studied, only 8 (4.2%) of the 189 isolates were serogroup O15, of which only one was multiresistant. In a preliminary study of plasmids in six serogroup O15 isolates from blood, three multiresistant isolates and one that was sensitive to chloramphenicol appeared to carry a similar plasmid of c. 100 Mda.(ABSTRACT TRUNCATED AT 250 WORDS)