Bacterial Interference among Strains of Staphylococcus aureus in Man

Factors related to artificial colonization by and persistence of Staphylococcus aureus (strain 502A) were characterized. Carriers of S. aureus were treated with antibiotics and antibacterial soaps and challenged with strain 502A. All subjects who lost their original S. aureus after treatment with antibiotics were colonized successfully with either 1.5 × 108 or 2 × 109 colony-forming units of strain 502A; these bacteria persisted in 67%–80% of subjects for 23 weeks. Eighty percent of subjects became colonized by strain 502A with persistence in 17% when the original strain(s) of S. aureus were reduced but not eliminated. Subjects not treated with antibiotics and challenged with strain 502A were temporarily colonized, and the extent of colonization was related to dose. A challenge inoculum of 109S. aureus 502A caused colonization in 100%, while 50% were colonized with 107 and 105 colony-forming units. Of the 12 subjects in this group, persistence at 10 weeks was noted in only a single individual who received an inoculum of 2.1 × 109, Colonization and persistence in subjects who initially resisted colonization by strain 502A and were treated later with antibiotics were similar to those in treated subjects. The data suggest that (1) eradication of the original strain of S. aureus is an important factor for optimal colonization and persistence of strain 502A; (2) it is possible to overwhelm the normal mucosa of persons who carry S. aureus with large numbers of strain 502A; and (3) carriers who initially rejected artificial colonization can become susceptible to colonization by and persistence of S. aureus strain 502A after treatment with antibiotics.