Lower respiratory tract isolates of non-typeable Haemophilus influenzae in Western Sichuan, China: Antimicrobial susceptibility, mechanisms of β-lactam resistance and decade changes

Abstract

ObjectivesThe aims of this study were to analyse the serotypes of epidemic Haemophilus influenzae and changes in mechanisms of β-lactam resistance over the past decade. ResultsHaemophilus influenzae isolates in Western Sichuan from 2013–2014 were non-typeable H. influenzae (NTHi). β-Lactam MICs for NTHi isolated during 2013–2014 were significantly higher than those from 2003–2004 (P < 0.05). Of 274 NTHi, 141 (51.5%) were β-lactamase-positive (TEM-1 type). There were 35 amino acid (AA) substitutions in ftsI among NTHi isolated from 2013–2014. However, NTHi isolates from 2003–2004 had only nine AA substitutions. Ordered multiple classification logistic regression analysis showed that different AA substitution patterns in ftsI had different effects on β-lactam MICs. The main factors affecting the ampicillin MIC were the mutations R517H (OR = 6.999), L389F (OR = 7.128), N526K (OR = 4.660) and D350N (OR = 0.450). The main factor influencing the amoxicillin/clavulanic acid MIC was an N526K mutation (OR = 9.349). The main factors affecting the cefuroxime MIC were the mutations S357N (OR = 37.453) and N526K (OR = 14.816). Compared with 2003–2004, gBLNAR and gBLPAR isolated from 2013–2014 increased significantly from 13.0% (7/54) and 9.3% (5/54) to 38.2% (84/220) and 45.5% (100/220), respectively (P < 0.001). In the ‘others’ group of ftsI gene mutations, 13 NTHi had the same ftsI gene mutation pattern and 24 AA substitutions. ConclusionThese results confirm that β-lactam-resistant NTHi isolates increased rapidly. AA substitutions in ftsI were more complex and diversified in 2013–2014.