TABLE 5.
Observed minimal inhibitory concentrations (MICs) (mg/L) or zone of inhibition diameter (ZD) (mm) of each antibiotic for the eight studied Serratia marcescens strains.
| Antibiotics and | Available | Contemporary collection | Historical collection | ||||||
| Resistance genes | since |
MICs (mg/L) or ZD (mm) |
MICs (mg/L) or ZD (mm) |
||||||
| O1-16 | O7-16 | O10-16 | O11-16 | 4F-69 | 6F-69 | 13F-69 | 15F-69 | ||
| Beta-lactams | |||||||||
| Ampicillin | 1961 | >16 | >16 | >16 | >16 | >16 | >16 | >16 | >16 |
| Amoxicillin–Clavulanate | 1972 | >16/8 | >16/8 | >16/8 | >16/8 | >16/8 | >16/8 | >16/8 | >16/8 |
| Piperacillin–Tazobactam | 1993 | ≤8 | ≤8 | ≤8 | ≤8 | ≤8 | >64 | ≤8 | ≤8 |
| Cefazolin | 1971 | >16 | >16 | >16 | >16 | >16 | >16 | >16 | >16 |
| Cefuroxime | 1978 | >16 | >16 | >16 | >16 | >16 | >16 | >16 | >16 |
| Cefoxitin | 1972 | 16 | >16 | >16 | 16 | 16 | >16 | 16 | 16 |
| Ceftazidime | 1984 | ≤1 | ≤1 | >16 | ≤1 | ≤1 | >16 | ≤1 | ≤1 |
| Cefotaxime | 1980 | ≤1 | ≤1 | >32 | ≤1 | ≤1 | >32 | ≤1 | ≤1 |
| Cefepime | 1994 | ≤1 | ≤1 | >16 | ≤1 | ≤1 | 8 | ≤1 | ≤1 |
| Aztreonam | 1986 | ≤1 | ≤1 | >16 | ≤1 | ≤1 | >16 | ≤1 | ≤1 |
| Imipenem | 1977 | ≤1 | ≤1 | ≤1 | ≤1 | ≤1 | ≤1 | ≤1 | ≤1 |
| Ertapenem | 2001 | ≤0.5 | ≤0.5 | >4 | ≤0.5 | ≤0.5 | ≤0.5 | ≤0.5 | ≤0.5 |
| Aminoglycosides | |||||||||
| Gentamicin | 1963 | ≤2 | ≤2 | >8 | ≤2 | ≤2 | ≤2 | ≤2 | ≤2 |
| Tobramycin | 1997 | ≤2 | ≤2 | >8 | ≤2 | ≤2 | 4 | 4 | ≤2 |
| Amikacin | 1976 | ≤8 | ≤8 | >32 | ≤8 | ≤8 | ≤8 | ≤8 | ≤8 |
| Streptomycin* | 1943 | 15 | 15 | 11 | 16 | 13 | 17 | 0 | 9 |
| Ciprofloxacin | 1987 | ≤0.5 | ≤0.5 | 1 | ≤0.5 | ≤0.5 | ≤0.5 | ≤0.5 | ≤0.5 |
| Nalidixic acid | 1965 | ≤16 | ≤16 | >16 | ≤16 | ≤16 | ≤16 | ≤16 | ≤16 |
| TMP/SMX | 1968-78 | ≤2/38 | ≤2/38 | ≤2/38 | ≤2/38 | ≤2/38 | ≤2/38 | ≤2/38 | ≤2/38 |
| Tetracycline* | 1953 | 14 | 12 | 15 | 13 | 21 | 21 | 0 | 12 |
MIC values or zone diameters over the clinical cutoff (based on EUCAST 2019 criteria) are highlighted in bold, underlined numbers. NA, not available; TMP/SMX, trimethoprim/sulfamethoxazole. Asterisk, antibiotics tested only by disk diffusion test (25 μg for streptomycin and 30 μg for tetracycline).