Bacterial Interference Induced in Embryonated Eggs by Staphylococci*

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Abstract
Studies of experimental infections in embryonated eggs demonstrated that prior allantoic infection with avirulent staphylococci afforded significant protection against subsequent challenge with virulent strains. All strains of coagulase-positive and coagulase-negative staphylococci tested that were relatively avirulent for embryonated eggs were capable of producing interference. The interference induced afforded protection not only against challenge with virulent staphylococci, but also against Diplococcus pneumoniae, Salmonella typhimurium, Escherichia coli, Proteus mirabilis, and one strain of influenza virus (A2J 305). Prior allantoic infection with avirulent staphylococci also protected against intravenous as well as allantoic infection with challenge strains. Interference required infection with viable bacteria. The onset of interference appeared within a few minutes after injection of the interfering strain, but was not maximal until 24 hours had elapsed between injection of the interfering and challenge strains. The protection afforded by the production of interference could not be overcome by increased inoculum size of the challenge strain and extended even to challenge with 109 bacteria. Studies of in vitro and in vivo growth of challenge strains in allantoic fluid demonstrated that some interfering strains inhibited growth of the challenge strains. Other strains produced interference without producing prolonged inhibition of the growth of challenge strains. Similarly, interference could not be attributed to attenuated virulence of the challenge organisms. All interfering strains studied produced enhanced bactericidal activity of whole blood from the affected embryos, but whether this affected leukocyte activity, opsonization, or other host defense mechanisms has yet to be determined.