Nasal Rejection of Experimentally Inoculated Staphylococcus Aureus: Evidence for an Immune Reaction in Man

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Abstract
Summary: A study of susceptibility to experimental staphylococcal nasal colonization in 39 volunteers was carried out by determining both the minimal number of S. aureus organisms required to establish 5-day intranasal implantation and the total duration of survival of this inoculum in vivo. These two measures of susceptibility were initially related: the longer durations of colonization, 3 to 70 weeks, were observed predominantly in those persons susceptible to the smallest 5-day inoculum, 104 organisms. Once the host spontaneously eliminated the inoculated S. aureus strain, however, its intranasal survival on reinoculation of the same number of organisms was almost always uniformly brief—2 weeks or less—while other susceptible subjects continued to be colonized for 4 weeks or more. Rapid rejection of a fixed inoculum of the S. aureus was found to persist for 4 challenges. Specificity of nasal rejection of inoculated staphylococci was evident. Subjects repeatedly rejecting the reinoculated staphylococcus after 2 weeks or less were experimentally colonized for 3 to 14 weeks with the same inoculum of 2 different staphylococci. The natural development, persistence and specificity of rapid rejection of an intranasally inoculated strain of S. aureus are interpreted as evidence of an immune reaction. There was no evidence of specific bacterial interference to the experimentally inoculated S. aureus strain by S. aureus strains naturally colonizing the volunteers. However, a nonspecific inhibitory effect of the total population of the host's resident microflora is considered likely to have prevented implantation of small numbers of staphylococci, 101 to 103 organisms, not surviving 5 days. The elaboration of substances inhibiting staphylococcal growth was not detected in samples of resident nasal microflora of 18 volunteers. Bacteriostatic activity of serum from 14 subjects in titers of 1/8 to 1/128 was found against one staphylococcal strain but its relation to resistance to nasal colonization is not clear.