Table 4

Antimicrobial resistance phenotypes of 200 selected extended-spectrum-β-lactamase-producing Escherichia coli isolates (collected in 2000 to 2009) in relation to ST131 and blaCTX-M-15 status

Antimicrobial classSpecific agentaNo. (%) of isolates showing resistance to the indicated agentP valueb
ST131 M15 (group 1; n = 50)ST131 M15+ (group 2; n = 50)ST131+ M15 (group 3; n = 50)ST131+ M15+ (group 4; n = 50)Group 1 vs 2Group 3 vs 4Group 1 vs 3Group 2 vs 4
β-LactamsATM33 (66)47 (94)29 (58)41 (82)0.0010.002
CAZ35 (70)47 (94)34 (68)39 (78)0.0030.04
CRO44 (88)50 (100)39 (78)48 (96)0.030.02
FEP11 (22)27 (54)11 (22)30 (60)0.002<0.001
QuinolonesNA36 (72)49 (98)43 (86)50 (100)<0.0010.02
CIP30 (60)49 (98)43 (86)50 (100)<0.0010.010.006
AminoglycosidesCN23 (46)31 (62)25 (50)17 (34)0.009
SF38 (76)20 (40)36 (72)26 (52)0.001
PhenicolsC23 (46)14 (28)8 (16)2 (4)0.0020.002
TetracyclinesTE45 (90)44 (88)30 (60)38 (76)0.001
Folate antagonistsSF44 (88)39 (78)39 (78)28 (56)0.030.03
W36 (72)39 (78)32 (64)23 (46)0.002
SXT37 (74)37 (74)31 (62)22 (44)0.004
  • a Agents shown are those that yielded P < 0.05 in an initial four-way comparison (not shown), plus at least one pairwise comparison (as shown). These included ATM (aztreonam), C (chloramphenicol), CAZ (ceftazidime), CIP (ciprofloxacin), CN (gentamicin), CRO (ceftriaxone), FEP (cefepime), NA (nalidixic acid), S (streptomycin), SF (sulfonamide), SXT (trimethoprim-sulfamethoxazole), TE (tetracycline), and W (trimethoprim). Agents to which resistance was detected in ≥1 isolate but without significant by-group prevalence differences (definition: overall prevalence) included AMK (amikacin: 10%), AML (amoxicillin-clavulanate: 69%), AMP (ampicillin: 100%), FOX (cefoxitin: 19%), F (nitrofurantoin: 8%), KF (cefazolin: 97%), PIP (piperacillin: 96%), and TZP (piperacillin-tazobactam: 5%). No resistance was detected to IMP (imipenem).

  • b P values (by Fisher's exact test, two-tailed) are shown where P < 0.05.