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R-factor involvement in a local outbreak of ampicillin-resistant Haemophilus influenzae infections
Insights
Ampicillin resistance in Haemophilus influenzae was investigated in a Swedish nursery. A single strain, potentially carrying an R-factor, was responsible for most resistant infections, highlighting plasmid involvement in resistance spread.
Area of Science:
- Microbiology
- Infectious Diseases
- Molecular Biology
Background:
- Non-encapsulated Haemophilus influenzae (H. influenzae) is a common nasopharyngeal colonizer in children.
- Ampicillin resistance, often mediated by beta-lactamase production, is a growing concern in H. influenzae infections.
- Understanding the transmission dynamics of resistant strains is crucial for effective treatment strategies.
Purpose of the Study:
- To investigate the origin and spread of ampicillin-resistant, beta-lactamase-producing H. influenzae isolates in a nursery setting.
- To determine if resistance was associated with specific O-antigen types, suggesting a common strain.
- To explore the potential role of plasmids (R-factors) in the dissemination of ampicillin resistance.
Main Methods:
- Isolation and characterization of H. influenzae from the nasopharynx of 15 children.
- Antimicrobial susceptibility testing, specifically for ampicillin resistance.
- Detection of beta-lactamase production.
- Immunodiffusion technique using 18 rabbit antisera to determine O-antigen patterns for strain identification.
- Monitoring resistance changes during antibiotic treatment.
Main Results:
- 11 of 15 children harbored non-encapsulated H. influenzae.
- Six children had ampicillin-resistant, beta-lactamase-producing isolates; five with otitis and one healthy.
- Five of the six resistant isolates shared the same O-antigen pattern, indicating a common strain origin.
- The sixth resistant isolate belonged to a different strain.
- Isolates from the same strain exhibited variable ampicillin sensitivity.
- One child's H. influenzae lost ampicillin resistance during trimethoprim-sulfamethoxazole treatment.
Conclusions:
- A single strain of H. influenzae was likely responsible for the majority of ampicillin-resistant infections observed.
- The presence of both sensitive and resistant isolates from the same strain suggests the involvement of a transferable genetic element, such as an R-factor (plasmid).
- The findings support the hypothesis that R-factors play a role in the distribution and transmission of ampicillin resistance among H. influenzae strains.
Abstract:
In a Swedish nursery 11 of 15 children harboured non-encapsulated Haemophilus influenzae in their nasopharynx. Six children had ampicillin-resistant and beta-lactamase-producing isolates. Five of these children had otitis whereas one was healthy. In order to identify the origin of the H. influenzae isolates their O-antigen determinants were studied by an immunodiffusion technique. 18 different rabbit antisera were used. For each isolate an O-antigen pattern was recorded. Five of the 6 resistant isolates had the same O-antigen pattern, indicating that their origin was one strain. The 6th isolate was from another strain. Different isolates from the same strain were found to be either sensitive or resistant to ampicillin. In one child the H. influenzae lost its resistance during trimethoprim-sulphamethoxazole treatment. It is concluded that an R-factor may have been involved in the distribution of ampicillin resistance in the H. influenzae studied. Previous in-vitro studies have shown that beta-lactamase production can be transmitted by a plasmid among H. influenzae strains.