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Quantitative inhibition of Haemophilus influenzae by trimethoprim/sulfamethoxazole
Abstract:
We evaluated the inhibitory effect of trimethoprim (TMP) and sulfamethoxazole (SMZ), alone and in combination, against 34 strains of Haemophilus influenzae. Growth inhibition was determined after incubation for 18 h by comparing viable counts of cultures in drug-containing medium with corresponding counts of control cultures in drug-free medium. In a modified, thymidine-deficient Levinthal broth, the numbers of colony-forming units of all the isolates tested were reduced 100-fold or more by TMP/SMZ (1.25/25 mug/ml) as compared with growth without drug. Inhibition was significantly greater with TMP/SMZ than with either TMP or SMZ alone. Ampicillin-susceptible and ampicillin-resistant strains were equally susceptible to TMP/SMZ. Growth of nontypable strains was inhibited more than growth of type b organisms.
Insights
Trimethoprim (TMP) and sulfamethoxazole (SMZ) combination therapy effectively inhibited Haemophilus influenzae growth. This antibiotic combination showed greater efficacy than individual drugs, impacting both ampicillin-susceptible and resistant strains.
Area of Science:
- Microbiology
- Pharmacology
- Infectious Diseases
Background:
- Haemophilus influenzae is a significant human pathogen.
- Antibiotic resistance in H. influenzae poses a clinical challenge.
- Trimethoprim (TMP) and sulfamethoxazole (SMZ) are commonly used antibiotics.
Purpose of the Study:
- To evaluate the in vitro inhibitory effect of TMP and SMZ, alone and in combination, against H. influenzae.
- To compare the efficacy of the TMP/SMZ combination with individual agents.
- To assess susceptibility differences between ampicillin-susceptible and resistant strains, and between different H. influenzae serotypes.
Main Methods:
- The study involved 34 strains of H. influenzae.
- Growth inhibition was assessed by comparing viable colony counts in drug-containing media versus drug-free controls after 18-hour incubation.
- A modified, thymidine-deficient Levinthal broth was utilized.
Main Results:
- The combination of TMP/SMZ (1.25/25 µg/ml) achieved a ≥100-fold reduction in colony-forming units for all tested H. influenzae isolates compared to controls.
- TMP/SMZ demonstrated significantly greater inhibition than either TMP or SMZ used alone.
- Both ampicillin-susceptible and ampicillin-resistant strains exhibited equal susceptibility to TMP/SMZ.
- Nontypable H. influenzae strains showed greater growth inhibition by TMP/SMZ than type b strains.
Conclusions:
- The combination of trimethoprim and sulfamethoxazole is highly effective in inhibiting the in vitro growth of Haemophilus influenzae.
- TMP/SMZ offers a potent therapeutic option against H. influenzae, including ampicillin-resistant strains.
- Nontypable H. influenzae may be more susceptible to TMP/SMZ than type b strains, suggesting potential strain-specific efficacy.