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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.