Early in 1963 neomycin-resistant Staph. aureus appeared in the burns of patients in a burns unit; after a period of 7 weeks three-quarters of the strains of Staph. aureus isolated from patients in the unit were resistant to neomycin, and after 22 weeks almost half of the patients in the burns wards were carrying the organism on their burns. When treatment with neomycin and kanamycin was stopped in the Burns Unit, neomycin-resistant strains gradually diminished in numbers and were no longer found in the ward after 6 months.
The neomycin-resistant staphylococci appeared during controlled trials of local neomycin and systemic kanamycin, and were much more frequently isolated from the burns of patients treated with these antibiotics than from patients in the control series.
During the previous 9 years local neomycin application had been used on many patients; though all staphylococci were tested for sensitivity to neomycin for a considerable part of this time, no resistant staphylococci were found.
All the neomycin-resistant staphylococci showed a pattern of inhibition by phages 6, 47, 54 and 77, and many also by phages 7, 53, 75 and 75B at 1000 R.T.D. No neomycin-sensitive staphylococci with this phage pattern were found at the time when resistant strains first appeared (though two such strains were found later); it seemed likely, therefore, that the resistant strain was introduced from outside the hospital. Preliminary tests of habituation to neomycin of sensitive strains with the phage inhibition pattern are described.
Back mutation to sensitivity was not found in tests on neomycin-resistant staphylococci.