The study identified a dominant variant of the bla TEM-1 gene with a promoter deletion (bla TEM-1 -PΔ) among β-lactamase-positive H. influenzae isolates, which contributes to ampicillin resistance. Additionally, β-lactamase-negative β-lactam-resistant (BLNBR) isolates were found to have amino acid substitutions in PBP-3, which are associated with ampicillin resistance.