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].