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Characterization of ampicillin-resistant Haemophilus parainfluenzae
Abstract:
Carriage of ampicillin-resistant (Ampr) Haemophilus parainfluenzae has become frequent among children in our community, although carriage of Ampr Haemophilus influenzae remains uncommon. In this study we characterized the mechanism of ampicillin resistance in 27 representative isolates of H. parainfluenzae. As determined by isoelectric focusing, each isolate had a TEM-1 beta-lactamase; substrate profiles assessed for enzymes from 10 strains were also consistent with TEM-1 enzyme. Agarose gel electrophoresis revealed a plasmid of 23 to 34 megadaltons in each isolate and a small plasmid (less than or equal to 4 megadaltons) in 14 isolates. Transfer of ampicillin resistance to H. influenzae Rd was achieved during membrane mating with 14 of 15 donors. The transconjugants exhibited high-level ampicillin resistance (greater than or equal to 50 micrograms/ml), which was stable despite serial passage of isolates on antibiotic-free media. The transconjugants tested retained fertility. Cryptic plasmids were discovered in 7 of 25 antibiotic-susceptible H. parainfluenzae isolates. Our data suggest that H. parainfluenzae may play an important role in the exchange of Ampr genes among throat bacteria.
Insights
Ampicillin resistance in Haemophilus parainfluenzae is common in children, often due to TEM-1 beta-lactamase. This study shows H. parainfluenzae can transfer ampicillin resistance genes via plasmids to other bacteria.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Ampicillin-resistant (Ampr) Haemophilus parainfluenzae carriage is frequent in children.
- Ampicillin-resistant Haemophilus influenzae carriage is uncommon in the same population.
Purpose of the Study:
- Characterize the ampicillin resistance mechanism in H. parainfluenzae isolates.
- Investigate the role of plasmids in ampicillin resistance gene transfer.
Main Methods:
- Isoelectric focusing to identify beta-lactamase.
- Agarose gel electrophoresis to analyze plasmids.
- Conjugation experiments (membrane mating) to assess gene transfer.
Main Results:
- All 27 H. parainfluenzae isolates possessed TEM-1 beta-lactamase.
- Plasmids (23-34 megadaltons) were present in all isolates; smaller plasmids were found in 14.
- Ampicillin resistance successfully transferred to H. influenzae Rd in 14/15 cases, conferring high-level resistance.
Conclusions:
- H. parainfluenzae frequently carries TEM-1 beta-lactamase, conferring ampicillin resistance.
- Plasmids facilitate the transfer of ampicillin resistance genes between H. parainfluenzae and H. influenzae.
- H. parainfluenzae may be a significant reservoir for ampicillin resistance gene exchange in the throat microbiome.