The decisive period in the primary infection of muscle by Escherichia coli

Abstract

Escherichia coli superinfected with a non-replicating phage was used to study the course of infection in the adductor muscle of mice in terms of the content of viable bacilli and the in vivo multiplication rate. The infection was characterized by a steady decrease of bacterial numbers to 5% of the inoculum within 4 hours without any compensating multiplication. Within the next 3 hours there was slight multiplication (2 generation or less) followed by a slow decrease of numbers to nil in 72 hours. In terms of the viable count, the infection was temporarily enhanced between three- and eight-fold when the following modifiers were given at the time of inoculation: local adrenaline, liquoid and ferric iron, systemic malonate and ferric iron, and hypovolaemic shock. Within 1-2 hours the inoculum was preserved from the bactericidal action of the muscle and multiplied to a limited extent (up to 3 generations). Given 2 hours after the inoculation, all the modifiers enhanced infection, but not when given 4 hours afterwards.

The results confirm the hypothesis, based on studies of local intracutaneous infections in the guinea-pig, that during the first few hours of infection, there is an extensive kill of the primary lodgement of bacteria by local defences that cease to operate after this period; and that the subsequent course of the local infection is determined by the number of bacteria surviving after this early decisive period.