Ampicillin-Resistant β-lactamase-negative Haemophilus Influenzae Strains Isolated in the Czech Republic in 2010-2018

According to the results of regular surveillance of resistance of bacterial pathogens of respiratory tract infections, the number of Haemophilus influenzae strains with non-enzymatic resistance to -lactam antibiotics is increasing in the Czech Republic. Non-enzymatic resistance is caused by mutations in the ftsI gene encoding penicillin-binding protein (PBP3), which result in a reduced ability to bind -lactam antibiotics. Demonstration of this type of resistance is more difficult than detection of -lactamase, which is still the most common cause of aminopenicillin resistance in H. influenzae. Analysis of a set of 228 H. influenzae strains revealed that the highest possible detection (99.5%) of isolates with non-enzymatic resistance due to mutations in the ftsI gene could be achieved in routine practice by simultaneous examination of penicillin, ampicillin, amoxicillin and cefuroxime disc diffusion method according to the EUCAST methodology. The currently recommended EUCAST method using only penicillin had a lower mutation detection rate of 95.7%. Sequence analysis showed considerable variability in ftsI gene mutations. In the set of 228 strains, a total of 37 different combinations of amino acid substitutions were found to occur at 23 positions in the PBP3 protein (V329I, D350N, S357N, A368T, M377I, S385T,..