COMPARISON OF 2 MOLECULAR METHODS FOR TRACING NOSOCOMIAL TRANSMISSIONOF ESCHERICHIA-COLI K1 IN A NEONATAL UNIT

Escherichia coli K1, a normal inhabitant of the human flora, is also a n important cause of serious infections in newborns. We compared two m olecular methods, ribotyping and arbitrarily primed polymerase chain r eaction (AP-PCR), to study the apparent nosocomial transmission of an E. coli K1 clone in a nursery for premature neonates. Sixty-two E. col i K1 strains isolated from 41 premature neonates from December 1991 to June 1992 and six strains isolated from ambient sources were studied. Eight E. coli K1 strains isolated from infants in the nursery between 1989 and September 1991 were included as controls. The properties of the strains isolated between December 1991 and June 1992 were as follo ws: 43 belonged to ribotype I, 12 belonged to ribotype III, and the re maining 13 isolates were distributed among 10 ribotypes. The eight con trol strains belonged to seven different ribotypes, but none was ribot ype I. Between December 1991 and February 1992, the majority of strain s from premature infants colonized with E. coli K1 were of ribotype I. Isolates from the ventilation system and from a storage shelf were al so of ribotype I. When DNA from 56 selected strains was tested by AP-P CR by using the 5'-TTGTAAAACGACGGCCAG-3' oligonucleotide, 15 different profiles were obtained. Twenty-five of 56 strains were of ribotype I and had identical profiles by AP-PCR. Strains with ribotypes VI, VII, and X to XV had different profiles by AP-PCR. We conclude that ribotyp ing and AP-PCR correlate well and permit demonstration of the nosocomi al dissemination of E. coli K1 in a unit for premature neonates.