Table 1. The effect of PAβN on the susceptibility to cephalosporins of clinical isolates of ESβL-positive P. aeruginosa.
| P. aeruginosa a (No. of strains) | β-lactams | No. (%) of strains with the decreased antibiotic MICs in the presence of PAβN | |||
|---|---|---|---|---|---|
| ≥4-fold decrease of antibiotic MICs | restoration of susceptibility to antibiotics b | ||||
| MH c | MH+Mg c | MH | MH+Mg | ||
| group A (n = 18) | cefepime or ceftazidime | 18 (100) d | 18 (100) | 16 (89) e | 15 (83) |
| cefepime | 16 (89) | 14 (78) | 15 (94) | 14 (100) | |
| ceftazidime | 18 (100) | 17 (94) | 15 (83) | 14 (82) | |
| cefepime and ceftazidime | 16 (89) | 13 (72) | 14 (88) | 13 (100) | |
| group B (n = 13) | cefepime or ceftazidime | 13 (100) | 13 (100) | 11 (85) | 7 (54) |
| cefepime | 13 (100) | 12 (92) | 11 (85) | 4 (33) | |
| ceftazidime | 13 (100) | 13 (100) | 7 (54) | 7 (54) | |
| cefepime and ceftazidime | 13 (100) | 12 (92) | 7 (54) | 4 (33) | |
| group C (n = 42) | cefepime or ceftazidime | 7 (17) | 6 (14) | 2 (29) | 2 (33) |
| cefepime | 6 (14) | 5 (12) | 2 (33) | 1 (20) | |
| ceftazidime | 6 (14) | 6 (14) | 2 (33) | 2 (33) | |
| cefepime and ceftazidime | 5 (12) | 5 (12) | 2 (40) | 1 (20) | |
PAβN-efflux pump inhibitor Phe-Arg-β-naphthylamide at a concentration of 80 mg/L; MH-Mueller-Hinton II agar; MH+Mg-Mueller-Hinton II agar with 1mM MgSO4.
a P. aeruginosa isolates were divided into three groups: group A contained strains with cefepime MICs 16–32 mg/L; group B contained strains with cefepime MIC 64 mg/L; group C contained strains with cefepime MICs ≥128 mg/L.
bIn the presence of PAβN, the MIC values of cephalosporins were ≤8 mg/L.
cAntibiotic susceptibility assays were performed on Mueller-Hinton II agar with and without 1 mM MgSO4.
dAs 100% was the number of strains in each group.
eAs 100% was the number of strains with an observed ≥4-fold decrease of antibiotic MICs in the presence of PAβN.