Some Hypotheses on the Aetiology of Fatal Infections in Partially Resistant Hosts and their Application to Mice Challenged with Salmonella paratyphi-B or Salmonella typhimurium by Intraperitoneal Injection

Open Access
Publisher Website
Google Scholar
Abstract
SUMMARY: Some hypotheses are considered which describe the aetiology of a fatal infection in a partially resistant host; i.e. a host which does not invariably die after inoculation with one bacterium. The hypothesis of independent action postulates that the mean probability per inoculated bacterium of multiplying to cause (or help to cause) a fatal infection is independent of the number of bacteria inoculated and, for a partially resistant host, is less than unity (1>p>0). It predicts: (1) that the slope, b, of the probit-mortality/log-dose curve will be 2·0 or less at the LD 50 point; (2) that, while hosts dying after inoculation with many LD50 die as a result of the multiplication of many of the inoculated bacteria, most of those dying from 1 LD50 or less do so following the multiplication of only one of the inoculated bacteria, regardless of the total number of bacteria inoculated. When a mixture of several equally virulent, distinguishable variants of a given pathogen are inoculated, fatal infections caused by the growth of one bacterium should result in the predominance of only one variant at post mortem. The hypotheses of maximum and of partial synergism postulate that inoculated bacteria co-operate so that the value of p increases as the size of the dose increases. They predict: (1) that the slope of the dose-response curve may be more than 2·0 at the LD50 point; (2) that all observed fatal infections will be initiated by more than one bacterium and that consequently the inoculation of a mixed inoculum will lead to the predominance of several variants at post mortem.