PENICILLIN TOLERANCE IN ARCANOBACTERIUM-HAEMOLYTICUM

It waspreviously found that Arcanobacterium haemolyticum, which can cause tonsillitis with exanthema, is not eradicated from the pharynx by administration of phenoxymethylpenicillin, despite minimum inhibitory concentration values of 0.015-1.0 μml. Therefore, recent clinical isolates were studied for penicillin tolerance by using a disk diffusion screening test and a pour plate assay. Macrobroth dilution minimum inhibitory and bactericidal concentrations and antibiotic kill kinetics were determined for 4 isolates. Tolerance was present in 38 of 40 clinical isolates with the disk diffusion assay. With the pour plate assay all 40 isolates were tolerant, 34 of them highly tolerant. The presence ofthe tolerant phenotype was confirmed by macrobroth dilution assays. It is concluded that A. haemolyticumis often penicillin-tolerant, suggesting that phenoxymethylpenicillin administration would beineffective in eradicating A. haemolyticum from the pharynx. © 1990 by The University of Chicago. All rights reserved.