Virulence factors of Escherichia coli. IV. Association in Escherichia coli of LD50 with haemolysin production, haemagglutinating capacity, antigens K1, K5 colicinogenicity and pathogenicity

Abstract

Haemolysin production (HLY), mannose resistant haemagglutinating activity (MRA), presence of antigens K1 and K5 and colicinogenicity (Col) were compared with LD50 for mice in 663 Escherichia coli strains, including 281 faecal, 129 urinary and 253 other extraintestinal isolates. Those isolates that LD50 value fell into less than or equal to 10(6) LD50 category were arbitrarily termed highly virulent (HV) and those which belonged to greater than or equal to 10(7) LD50 category were considered avirulent (AV). HV isolates occurred significantly more frequently (58%) among strains from different extraintestinal samples than from faeces (14%) or urine (16%). The incidence of HV strains was significantly higher in patients with sepsis (43%) or meningitis (100%) than in patients with enteritis (20%), urinary tract infections (UTI, 16%) or in healthy subjects (28%). The incidence of HV strains in the most frequent (O1, O2, O4, O6, O7, O18, O75) serogroups was significantly higher (60%) than in others (10%). Strains with different virulence markers (HLY, MRA, K1, K5, Col) belonged significantly more frequently to the HV group than those which failed to have these markers (44 vs 27%, 51 vs 25%, 83 vs 17%, 78 vs 27%, 52 vs 16%, respectively). Important role of antigen K1 playing in pathomechanism of meningitis was confirmed by data of analysis according to which significant difference was revealed in the incidence of HV strains between groups of isolates with MRA+K1+ (71%) and MRA+K1- (44%, p less than 0.02), or between groups of isolates with MRA+K1- and MRA-K1+ (91%, p less than 0.001). Moreover there were significant differences in the incidences of HV strains in K1+Col- (73%) and K1-Col+ (29%, p less than 0.001), and in K1+Col+ (86%) and K1-Col+ (29%, p less than 0.001) groups. Further evidence was given by those data that there were no significant differences between groups of HV strains with MRA+K1+ and MRA-K1+ (p greater than 0.05) or with K1+Col+ and K1+Col- (p greater than 0.1) properties. Isolates that possessed simultaneously two of MRA, HLY, Col markers were more pathogenic in LD50 assay than those that had one or the other of these markers alone. Strains in serogroup O18 killed mice significantly more frequently than those of other serogroups independently of having any virulence factor, suggesting that bacteria in serogroups O18 must have some special virulence other than K1, Col, MRA or K5. MRA+HLY+ HV strains occurred frequently in extraintestinal diseases (42%) supporting the preconception that these properties play an important role also in the pathomechanism of extraintestinal infections other than UTI.(ABSTRACT TRUNCATED AT 400 WORDS)