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Susceptibility of ampicillin-resistant Haemophilus influenzae to seven penicillins
Abstract:
Sixty-seven clinical isolates of Haemophilus influenzae from various sections of the United States, England, and Germany were tested for susceptibility to penicillin, ampicillin, amoxicillin, epicillin, carbenicillin, ticarcillin, and methicillin. Fifty-three of the strains had previously been judged to be ampicillin resistant and 14 had been determined to be ampicillin susceptible. Fifty-two of the 53 resistant strains produced beta-lactamase, but none of the susceptible strains produced it. On the basis of minimal inhibitory concentrations, the most active compounds were ticarcillin and carbenicillin. Whether this greater activity is useful clinically has not been established.
Insights
Most clinical Haemophilus influenzae isolates resistant to ampicillin produce beta-lactamase. Ticarcillin and carbenicillin showed the greatest activity against these bacteria, though clinical utility remains unproven.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Haemophilus influenzae is a significant human pathogen.
- Antibiotic resistance, particularly to ampicillin, is a growing concern.
- Beta-lactamase production is a common mechanism of resistance.
Purpose of the Study:
- To evaluate the susceptibility of clinical Haemophilus influenzae isolates to various penicillins.
- To determine the prevalence of beta-lactamase production in ampicillin-resistant strains.
- To compare the in vitro activity of different beta-lactam antibiotics.
Main Methods:
- Testing 67 clinical isolates of Haemophilus influenzae from the US, UK, and Germany.
- Assessing susceptibility to penicillin, ampicillin, amoxicillin, epicillin, carbenicillin, ticarcillin, and methicillin.
- Detecting beta-lactamase production in ampicillin-resistant and susceptible strains.
- Determining minimal inhibitory concentrations (MICs) for comparative analysis.
Main Results:
- 53 of 67 isolates were ampicillin-resistant; 14 were ampicillin-susceptible.
- Beta-lactamase was produced by 52 of the 53 ampicillin-resistant strains.
- None of the ampicillin-susceptible strains produced beta-lactamase.
- Ticarcillin and carbenicillin demonstrated the highest activity based on MICs.
Conclusions:
- Beta-lactamase production is strongly associated with ampicillin resistance in clinical Haemophilus influenzae isolates.
- Ticarcillin and carbenicillin exhibit potent in vitro activity against these strains.
- Further clinical studies are needed to establish the therapeutic value of ticarcillin and carbenicillin.