TABLE 3.

MIC50, MIC90, range, percentage of resistant and nonsusceptible E. coli strains (n = 119) producing enzymes, from the CTX-M-1 and CTX-M-9 groups, collected in nine Portuguese hospitals

Antimicrobial agentMIC (μg/ml) for strains producing:CLSI breakpointsb (μg/ml)
CTX-M group 1a (n = 110)CTX-M group 9 (n = 9)
MIC50cMIC90dRangeSusceptibilityeMIC50MIC90RangeSusceptibilitySR
R (%)IR (%)R (%)IR (%)
Ampicillin>16>164->16110 (100)110 (100)>16>164->169 (100)9 (100)≤8≥32
Ampicillin-sulbactam>16/8>16/88/4->16/8108 (98)109 (99)>16/8>16/88/4->16/89 (100)9 (100)≤8/4≥32/16
Amoxicillin-clavulanic acid8/416/84/2-16/83 (3)28 (26)≤4/28/4≤4/2-16/80 (0)0 (0)≤8/4≥32/16
Piperacillin>64>6416->64110 (100)110 (100)>64>6416->649 (100)9 (100)≤16≥128
Piperacillin-tazobactam≤1632≤16-647 (6)13 (12)≤16≤16≤16-640 (0)0 (0)≤16/4≥128/4
Ticarcillin>64>648->64110 (100)110 (100)>64>648->649 (100)9 (100)≤16≥128
Cephalothin>16>168->16110 (100)110 (100)>16>168->169 (100)9 (100)≤8≥32
Cefazolin>16>161->16110 (100)110 (100)>16>161->169 (100)9 (100)≤8≥32
Cefuroxime>16>162->16110 (100)110 (100)>16>162->169 (100)9 (100)≤8≥32
Cefotaxime>32>320.5->32109 (99)110 (100)>32>320.5->329 (100)9 (100)≤8≥64
Ceftriaxone>32>322->32110 (100)110 (100)>32>322->329 (100)9 (100)≤8≥64
Aztreonam>16>161->16110 (100)110 (100)8>161->161 (11)2 (22)≤8≥32
Ceftazidime>16>160.5->16108 (98)109 (99)2>160.5->161 (11)1 (11)≤8≥32
Cefepime>16>160.5->16109 (99)109 (99)>16>160.5->167 (78)9 (100)≤8≥32
Cefoxitin≤48≤4-161 (1)5 (5)≤416≤4-160 (0)1 (11)≤8≥32
Imipenem≤0.5≤0.5≤0.5-80 (0)0 (0)≤0.5≤0.5≤0.5-80 (0)0 (0)≤4≥16
Meropenem≤1≤1≤1-80 (0)0 (0)≤1≤1≤1-80 (0)0 (0)≤4≥16
Amikacin≤816≤8-324 (4)8 (7)≤816≤8-320 (0)0 (0)≤16≥64
Gentamicin>8>82->887 (79)87 (79)≤2>8≤2->82 (22)2 (22)≤4≥16
Tobramycin>8>82->8103 (94)104 (95)≤2>8≤2->82 (22)2 (22)≤4≥16
Ciprofloxacin>2>20.5->2108 (98)108 (98)≤0.5>2≤0.5->23 (33)3 (33)≤1≥4
Norfloxacin>8>82->8108 (98)108 (98)≤2>8≤2->83 (33)3 (33)≤4≥16
Ofloxacin>4>40.5->4108 (98)108 (98)≤0.5>4≤0.5->43 (33)3 (33)≤2≥8
Trimethoprim-sulfamethoxazole≤1/19>2/38≤1/19->2/3828 (26)28 (26)≤1/19>2/38≤1/19->2/383 (33)3 (33)≤2/38≥4/76
  • a There were a total of 99 CTX-M-15 producers and 1 CTX-M-32 producer, according to the phylogenetic group 1 defined by Bonnet (3).

  • b As scored according to CLSI guidelines: S, sensitive; R, resistant.

  • c MIC50, MIC at which 50% of the isolates are inhibited.

  • d MIC90, MIC at which 90% of the isolates tested are inhibited.

  • e R, number of resistant isolates; IR, number of nonsusceptible isolates.