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Table 6 Beta-lactam susceptibility according to PBP3 resistance genotypes

From: Multilocus sequence typing and ftsI sequencing: a powerful tool for surveillance of penicillin-binding protein 3-mediated beta-lactam resistance in nontypeable Haemophilus influenzae

Study groupsa Resistance genotypesb n MIC50/MIC90(mg/L) and susceptibility categorization (%)c
AMPc AMCc PIPc CXM CTX MEM
Resistant group High-rPBP3 Group III 1 8/- 16/- 0.06/- >16/- 0.25/- 1/-
(0/100) (0/100)   (0/0/100) (0/100) (0/100/0)
   Group III-like 2 2/4 8/16 0.06/0.12 >16/>16 0.06/0.12 0.03/0.03
(0/100) (0/100)   (0/0/100) (100/0) (100/0/0)
  Low-rPBP3 Group II 111 2/4 4/8 0.03/0.06 8/8 0.03/0.12 0.12/0.5
(40/60) (45/55)   (33/11/56) (94/6) (80/20/0)
   Group I 2 0.5/1 0.25/1 0.03/0.06 0.5/16 0.06/0.25 0.016/0.06
(100/0) (100/0)   (50/0/50) (50/50) (100/0/0)
  sPBP3   60 0.25/0.5 0.5/2 0.004/0.03 1/8 0.008/0.06 0.03/0.12
(98/2) (98/2)   (74/13/13) (98/2) (100/0/0)
Susceptible group sPBP3   19 0.12/0.5 0.5/2 0.004/0.06 0.5/8 0.004/0.03 0.03/0.12
(100/0) (95/5)   (79/11/11) (100/0) (100/0/0)
  1. aSee Figure 1.
  2. bSee Table 1.
  3. cMICs (microbroth dilution) and susceptibility categorization (S/R or S/I/R) according to EUCAST clinical breakpoints [37]. The following breakpoints were used (S≤/R>): Ampicillin (AMP), 1/1; amoxicillin (AMC), 2/2; cefuroxime (CXM), 1/2; cefotaxime (CTX), 0.12/0.12; meropenem (MEM), 0.25/1. Clinical breakpoints for piperacillin and piperacillin-tazobactam are not set by EUCAST. Meningitis breakpoints were used for categorization of meropenem.
  4. dFor beta-lactamase positive isolates, ampicillin, amoxicillin and piperacillin MICs were determined in combination with sulbactam (4 mg/L), clavulanate (2 mg/L) and tazobactam (4 mg/L), respectively.