John C. Ribble

BACTERIAL INTERFERENCE BETWEEN STRAINS OF S. aureus

The ability of one strain of S. aureus to interfere with the growth of a second strain of S. aureus has been observed in vitro and in vivo, in animals and man. The phenomenon termed bacterial interference can be demonstrated in the test tube,1*2 the yolk sac of fertile hens burned surfaces of rabbits and guinea pigs,g the nasal mucosa of guinea pigs,l0 and most recently on the nasal mucosa and intestinal tract of We have been interested in the phenomenon of bacterial interference in man for the past 10 years, and have particularly emphasized the use of the concept in clinical situations. In 1961, epidemiologic observations during a nursery outbreak of staphylococcal disease suggested to us that colonization of the nasal mucosa or umbilical stump of an infant by S. aureus prevented subsequent colonization at the same site by a second strain of S . aureus.13 In order to test this hypothesis, further observations by direct inoculation of S. aureus were made on a series of infants, medical students, nurses, and prisoner For inoculation, a coagulase-positive S. aureus strain of low virulence was used, susceptible to penicillin and incapable of being induced to produce 6-lactamase. The organism is lysed by group I11 staphylococcal phages and is referred to as strain 502A. TABLE 1 presents the data on a series of 78 babies, deliberately colonized. A striking relationship was noted between the prior presence of S. aureus and the failure to implant strain 502A. Coagulase-negative staphylococci exerted a much weaker effect while under the conditions of the experiment. No interference could be demonstrated by other organisms that colonized the nasal mucosa.l3

Bacterial Interference in Chick Embryos

Chick embryos infected intra-allantoically with nonvirulent staphylococci are protected from death due to infection with virulent staphylococci. The protection is associated with a delay in growth of the challenge strain and a delay in the production of toxic substances in the allantoic fluid. The protection is influenced by the number of bacteria in the protecting and challenge inocula and by the interval between the administration of the protecting and challenge strains. Protection cannot be transferred by administration of sterile filtrates of allantoic fluid in which the protecting strain has grown.

Laboratory Assistance in the Treatment of Bacterial Infections

The microbiology laboratory can assist the clinician in the treatment of bacterial infections by isolating and identifying the responsible organisms and by determining their susceptibility to antibiotic drugs.