Virulence of Escherichia coli strains for chick embryos.

Powell, Calvin J., Jr. (Walter Reed Army Institute of Research, Washington, D.C.), and Richard A. Finkelstein. Virulence of Escherichia coli strains for chick embryos. J. Bacteriol. 91:1410-1417. 1966.-Fifty-three strains of Escherichia coli, freshly isolated from patients at Children's Hospital, Washington, D.C., were tested for virulence for 13-day chick embryos by allantoic inoculation of serial dilutions of viable cell suspensions. No clear-cut relationship could be demonstrated between inoculum size and response (death of the embryos) which would permit comparisons of virulence based on ld(50) determinations. However, the strains were classified into three groups according to the proportion of embryos which succumbed, regardless of inoculum size. There was no association between enteropathogenicity and embryo virulence, although there was high correlation between hemagglutinative activity for chicken erythrocytes and virulence of strains for embryos. Differences in virulence were not related to ability to multiply in the allantoic cavity nor did bacteremia appear to be essential for death of the embryos. Serial passage in eggs failed to alter virulence. Both the route of inoculation and the age of the embryos had a marked effect on the outcome of challenge with strains of varying virulence. The embryos were most susceptible to challenge by the intravenous route. The susceptibility of younger embryos decreased with increasing embryonic maturity, although some reversal of this trend was noted with 19-day embryos. The toxicity of culture filtrates and filtrates of allantoic fluid from infected embryos seemed to be related to strain virulence, suggesting that elaboration and availability of toxic factors may have an important bearing on the lethality of E. coli strains for chick embryos.