TABLE 4.

Laboratory diagnosis of clinical strains producing ESBLs

Strains (n)PCR for blaCTX-M genesaNo. (%) of strains
ScreeningbDisk confirmationc
CPDCAZCTXCAZ/CLACTX/CLACTX/CLA and CAZ/CLA
E. coli (51)Negative51 (100)51 (100)48 (94)34 (67)49 (96)51 (100)
K. pneumoniae (5)Negative5 (100)5 (100)4 (80)3 (60)5 (100)5 (100)
E. coli (24)Positive for CTX-M-I group24 (100)24 (100)24 (100)21 (88)24 (100)24 (100)
E. coli (93)Positive for CTX-M-IV group93 (100)71 (76)93 (100)3 (3)93 (100)93 (100)
K. pneumoniae (2)Positive for CTX-M-IV group2 (100)0 (0)2 (100)0 (0)2 (100)2 (100)
Total (175)175 (100)151 (86)171 (98)61 (35)173 (99)175 (100)
  • a PCR primers for CTX-M subgroups (see Materials and Methods for details). Group I includes CTX-M-1, -3, -10 to -12, -15 (UOE-1), -22, -23, -28, -29, and -30. Group II includes CTX-M-2, -4 to -7, and -20 and Toho-1. Group III includes CTX-M-8. Group IV includes CTX-M-9, -13, -14, -16 to -19, -21, and -27 and Toho-2. Finally, group V includes CTX-M-25 and -26.

  • b NCCLS guidelines for screening ESBL-producing bacteria. CPD, CAZ, and CTX were each used at 1 μg/ml.

  • c NCCLS guidelines for ESBL disk confirmation tests.