Microbiological characterization of Streptococcus pneumoniae and non-typeable Haemophilus influenzae isolates as primary causes of acute otitis media in Bulgarian children before the introduction of conjugate vaccines

Table 3 Distribution of ampicillin resistance classes of paediatric middle ear fluids H. influenzae isolates according to their β-lactamase production, susceptibilities to ampicillin and amoxiclav, and amino acid substitutions present in ampicillin nonsusceptible strains with mutations in ftsI gene

Resistance class	No. of strains (%)	β-lac	MIC (mg/L)		Amino acid substitution(s) in *ftsI* gene	Group
			Ampicillin	Amoxiclav
BLNAS	30 (75.0)	-	≤ 1.0	≤ 2.0	ND	-
BLPAR	4 (10.0)	+	≥ 8.0	≤ 2.0	No changes	-
BLNAR	1 (2.5)	-	4.0	4.0	Arg517His	I
BLNAR	1 (2.5)	-	2.0	4.0	Asn526Lys	IIa
BLPACR	1 (2.5)	+	≥ 8.0	4.0	Asp350Asn, Gly490Glu, Asn526Lys, Ala530Ser	IIa
BLNAR	2 (5.0)	-	4.0	8.0	Asp350Asn, Met377Ile, Gly490Glu, Ala502Val, and Asn526Lys	IIb
BLNAR	1 (2.5)	-	4.0	8.0	Asp350Asn, Ala502Thr, Asn526Lys	IIc
Total	40 (100.0)

Abbreviations: β-lac, β-lactamase production; Amoxiclav, amoxicillin-clavulanic acid (2:1 ratio). MIC refers to amoxicillin value. ND, DNA sequencing of ftsI gene was not done; BLNAS, β-lactamase negative, ampicillin-susceptible strains; BLPAR, β-lactamase positive ampicillin-resistant H. influenzae without amino acid substitutions in the PBP 3; BLNAR, β-lactamase negative ampicillin-resistant H. influenzae with amino acid substitutions in the PBP 3; BLPACR, β-lactamase positive strains with amino acid substitutions in the PBP 3; No changes along the section of amino acids 350 to 530. The strains with ftsI gene mutations were classified into groups according to the proposed criteria by Dabernat et al. [22].

ISSN: 1476-0711