TABLE 4.

Resistance phenotypes of the distinguished fractions of CTX-M-3-producing isolates and their transconjugants

Isolate (no. of isolates)MIC (μg/ml)a
PIPTZPCTXCTX + CLACAZCAZ + CLAATMATM + CLAFOX
K. pneumoniaeb (21)256–>5121–2562–512≤0.03–40.25–160.06–20.5–128≤0.03–42–16
K. oxytocab (3)512–>5121–416–640.06–0.1252–40.125–0.54–80.06–0.1254–64
E. colib (18)256–>512≤0.5–328–128≤0.03–0.250.5–80.06–0.52–16≤0.03–0.52–32
E. cloacaeb (5)>5122–16128–2560.5–480.5–216–320.125–1128–512
C. freundiib (8)512–>5121–3264–5120.125–12–160.25–18–640.06–0.564–512
S. marcescensb (4)256–>5122–864–2561–41–20.25–0.58–320.25–232–64
M. morganiib (1)>512≤0.516≤0.030.250.251≤0.038
K. pneumoniae CTX-M-3 + SHVc (8)>51216–25616–640.125–0.564–1281–4128–2560.125–0.52–64
K. pneumoniae CTX-M-3 + TEMd (3)>5124–64128–2560.125–232–640.5–232–640.125–0.54–128
K. pneumoniae SZ 3733 and SZ 3734e (2)>512>512>5121283241283232
K. pneumoniae WAII 8933, WA IV 9172e (2)>512512–>512512–>512256–51232–6416–32128–25664–25664–128
E. cloacae CTX-M-3 + AmpC derepressedf (3)>51232–512256–51264–25664–1286432–12816–64256–512
C. freundii CTX-M-3 + AmpC derepressedg (3)512–>51232–64256–51232–6464–12832–12832–6416–32128–512
S. marcescens CTX-M-3 + AmpC derepressedh (3)512–>51232–51251264–256164–832–648–32128–256
R+ strainsi (65)128–256≤0.5–24–32≤0.03–0.060.25–2≤0.03–0.251–8≤0.03–0.061–4
R+ (K. pneumoniae WAV 7888) CTX-M-3 + SHV (1)256≤0.516≤0.0380.125160.062
R+ (K. pneumoniae CZ 9455 and CZ 9459) TEM (2)64–1281–24–8≤0.0340.062–4≤0.032
R+ (K. pneumoniae SZ 3733 and SZ 3734)j (2)>5121–21280.12580.5320.1254
R+ (K. pneumoniae WA II 8933)k (1)256216≤0.0310.254≤0.032
E. coli A15≤0.51–2≤0.03≤0.030.06–0.125≤0.03≤0.03≤0.031–2
  • a Abbreviations: PIP, piperacillin; TZP, piperacillin with tazobactam; CTX, cefotaxime; CLA, clavulanate; CAZ, ceftazidime; ATM, aztreonam; FOX, cefoxitin.

  • b Isolates of different species, in which CTX-M-3 was considered to be the major mechanism affecting the resistance phenotype.

  • c K. pneumoniae isolates SU 8406, SU 8815, SU 8912, SU 9148, SU 9161, SU 972, SZ 2941, and WA V 7888.

  • d K. pneumoniae isolates CZ 9455, CZ 9459, and KR 3443.

  • e The resistance phenotypes of these isolates are postulated to be strongly influenced by the decreased permeability and, in the case of K. pneumoniae SZ 3733 and SZ 3734, by the higher level of CTX-M-3 expression.

  • f E. cloacae isolates CZ 8320, KA 3663 and WA IV 838.

  • g C. freundii isolates SU 9050, WA V 3324, and WA V 3570.

  • h S. marcescens isolates CZ 9424, WA I 4172, and WA V 3033.

  • i R+, transconjugant. The major fraction of transconjugant strains expressed only CTX-M-3 and the pI 5.4 β-lactamases.

  • j Transconjugants of the isolates, in which a significantly higher level of CTX-M-3 is postulated.

  • k The MICs for the transconjugant of K. pneumoniae WA II 8933 are shown separately only for comparison with those for the clinical isolate.