Naturally-occurring fusidic acid resistance in staphylococci and its linkage to other resistances.

Although Staph. aureus resistant to fusidic acid can be selected in vitro and has been found in vivo following treatment, naturally occurring strains without previous exposure to the drug have not, so far, been reported. Four such strains were isolated in the area of the North West Surrey Group Laboratory between August and September 1965, and six at Hammersmith Hospital during the first four months of 1966. In two of these resistance to fusidic acid was very unstable and its loss was accompanied by loss of resistance to penicillin in the first and to tetracycline and kanamycin in the second, although this strain remained resistant to penicillin.