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. 2021 Sep 7;118(37):e2114027118. doi: 10.1073/pnas.2114027118

Fig. 1.

Fig. 1.

Antimicrobial breadths and potencies of hospital gentamicin and its components. (A) Gentamicin C-subtypes are three-ringed structures, containing a central 2-deoxystreptamine with an ammonium group on either side of the deoxy carbon and added at position 4 to ring I, and at position 6 to ring III. (B) The main components of gentamicin differ at the 5′ and 6′ position on ring I. These are termed gentamicin C2 (cyan), C2a (green), C1 (orange), C1a (blue), and C2b (purple); colors used throughout. (C) The antimicrobial breadths of the C-subtypes relative to hospital gentamicin (Hos.), where breadth is defined as the number of strains inhibited by the drug at MIC value ≤ 4 μg/mL. The colors represent different species, the numbers in the columns refer to the number of individual strains inhibited, where black = S. aureus (Sa), gray = E. coli (Ec), blue = K. pneumoniae (Kp), green = P. aeruginosa (Pa); colors used throughout. Hospital gentamicin inhibits 35 of 40 strains tested, with the C-components inhibiting 31–35 strains. (D) The MIC values for all strains (diamond symbols) split by species (10 each). The box indicates the 25–75 percentiles, asterisks indicate geometric means, dashed line indicates the 4 μg/mL cutoff for susceptibility (*P < 0.05, **P < 0.01 Mann–Whitney u test). Gentamicin C1 is less potent than hospital gentamicin against S. aureus strains only (P < 0.05, Mann–Whitney u test, n = 10). There are also some differences between the C-subtypes against S. aureus and P. aeruginosa strains. (E) The antimicrobial breadths of the impurities relative to hospital gentamicin. Hospital gentamicin inhibits 35 of 40 strains tested, with the impurities gentamicin X, A, B, and G418 inhibiting 15–22 strains. The impurity sisomicin inhibited 35 of 40 strains. (F) The MIC values for all strains split by species. The impurities gentamicin X, A, B, and G418 are all significantly less potent than hospital gentamicin (P < 0.05, Mann–Whitney u test). The impurity sisomicin was the same as the hospital gentamicin against E. coli and K. pneumoniae (P > 0.05, Mann–Whitney u test), and was more potent than hospital gentamicin against S. aureus and P. aeruginosa (P < 0.05, Mann–Whitney u test). SI Appendix, Figs. S3 and S4 show individual strains for each drug. ***P < 0.001.]