A novel PBP3 substitution in Haemophilus influenzae confers reduced aminopenicillin susceptibility

BMC Microbiology

Table 3 Results of screening for β-lactam resistance and susceptibility testing to various β-lactam antibiotics by BMD

Strain ID	Geno-type	Zone diameter PCG 1 U (mm)	Screening phenotype^a	Susceptible to amino-penicillins^b	MIC^c amoxicillin	MIC ampicillin	MIC amoxicillin clavulanic acid	MIC cefotaxime	MIC ceftriaxone	MIC cefuroxime	MIC imipenem	MIC mero-penem	β-lactamase
NTHi3655	Wild-type	16	Susceptible	Susceptible	0.5	≤0.25	≤0.25	≤0.015	≤0.015	1	0.5	0.06	Negative
NTHi3655-PBP3^Y528H	Y528H	11	Resistant	Susceptible	1	0.5	1	≤0.015	≤0.015	1	1	0.06	Negative
NTHi93–57485	Y528H	6	Resistant	Susceptible	1	1	1	0.06	≤0.015	4	0.5	0.06	Negative

^a As interpreted by EUCAST clinical breakpoints for benzylpenicillin 1 U screening with a zone diameter < 12 mm categorized as resistant
^b Interpreted by EUCAST clinical breakpoints where ampicillin MIC > 1 mg/ L and Amoxicillin MIC > 2 mg/ L are categorized as resistant (assuming i.v. treatment)
^c MIC in mg/ L determined by BMD

ISSN: 1471-2180