| Summary: | Non-typeable Haemophilus influenzae (NTHi) is an opportunistic pathogen causing a variety of respiratory tract infections in human. Co-trimoxazole (SXT), being one of the drugs for the treatment, loses its importance due to emergence of SXT-resistant strains. This study aims to determine whether conjugal transfer of SXT-resistant genes from an NTHi strain to a typeable strain could occur when both strains co-exist in human upper respiratory tract. Conjugal transfer of the resistance genes from an NTHi (strain H152, donor) to a Haemophilus influenzae type b (Hib strain H582, recipient) were performed by using three different methods (filter, solid and broth mating) in ratios of 1:1 and 1:10. Repeated experiments showed that all attempts failed to produce any transconjugants. Whole genome sequencing of both strains revealed 11 amino acid changes in dihydrofolate reductase (DHFR) and a 15-bp insertion sequence in dihydropteroate synthetase (DHPS) in the donor strain, which attributed to the SXT resistance in strain H152. The tRNALeu sequences for DNA site-specific recombination were detected only in the recipient strain H582 but absent in donor strain H152. Furthermore, it was shown that type IV secretory pathway, the VirB4/VirD4, which is vital for conjugation was only present in H582 strain. One of the possibilities of the inability for SXT-resistance genes in this strain of NTHi to transfer to Hib by conjugation was due to the inadequate presence of the necessary genes components for transfer. © 2019 Malaysian Society for Biochemistry and Molecular Biology. All rights reserved.
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