TABLE 2.
β-Lactam resistance of L. monocytogenes LO28 wild-type, ΔcesR, ΔcesK, and Δorf2420 strains
| β-Lactam | Avg zone of inhibition (mm) ± SDa
|
|||
|---|---|---|---|---|
| Wild type | ΔcesR | ΔcesK | Δorf2420 | |
| Ampicillin | 35.4 ± 0.2 | 40.0 ± 0.1b | 39.6 ± 0.3b | 35.5 ± 0.2 |
| Penicillin G | 33.4 ± 0.2 | 37.7 ± 0.6b | 37.7 ± 0.3b | 33.8 ± 0.5 |
| Cephalothin (I)e | 28.8 ± 0.3 | 32.0 ± 0.1c | 32.1 ± 0.2c | NDd |
| Cefaclor (I) | 21.2 ± 0.5 | 25.3 ± 0.3c | 25.0 ± 0.1c | ND |
| Cefoperazone (III) | 20.2 ± 0.1 | 22.8 ± 0.3c | 23.2 ± 0.2c | ND |
| Cephalexin (I) | 15.9 ± 0.1 | 20.9 ± 0.1b | 20.9 ± 0.1b | ND |
| Ceftriaxone (III) | 15.7 ± 0.2 | 22.4 ± 0.2b | 22.2 ± 0.7b | ND |
| Cefoxitin (II) | 15.6 ± 0.8 | 21.8 ± 0.1b | 21.6 ± 0.1b | ND |
| Cefuroxime (II) | 14.9 ± 0.4 | 29.7 ± 0.2b | 29.5 ± 0.2b | 15.5 ± 0.5 |
| Cefotetan (III) | 12.7 ± 0.2 | 15.6 ± 0.1c | 15.4 ± 0.1c | ND |
| Ceftazidime (III) | 6.2 ± 0.1 | 7.8 ± 0.1c | 7.5 ± 0.1c | ND |
a
The results presented are averages of triplicate experiments.
b
Significant difference (P < 0.01) between the mutant strain and the wild type.
c
Significant difference (P < 0.05) between the mutant strain and the wild type.
d
ND, not determined.
e
The classification of the cephalosporins is indicated in parentheses (I, narrow spectrum; II, expanded spectrum; III, broad spectrum).