Rapid ampicillin susceptibility testing for Haemophilus influenzae

Area of Science:

• Clinical microbiology
• Infectious diseases
• Antimicrobial resistance

Background:

• Emerging ampicillin resistance in Haemophilus influenzae necessitates rapid susceptibility testing.
• Current methods may not provide timely results for effective treatment.

Purpose of the Study:

• To develop and validate a fast, reliable agar-dilution method for determining ampicillin susceptibility in Haemophilus influenzae.
• To enable prompt antibiotic selection for patient treatment.

Main Methods:

• Developed a chocolate agar biplate method with and without ampicillin (2 µg/ml).
• Inoculated 70 clinical specimens directly onto biplates.
• Incubated at 35-37°C in 10% CO2 and assessed results within 6-18 hours.

Main Results:

• The rapid biplate method provided results within 6-18 hours, correlating perfectly with standard MIC determinations.
• False resistance was occasionally observed with standard disk susceptibilities.
• Susceptible strains (MIC < 2 µg/ml) grew only on the antibiotic-free side.

Conclusions:

• The developed agar-dilution biplate method is a rapid, dependable, and reproducible tool for assessing ampicillin susceptibility in Haemophilus influenzae.
• This method facilitates timely and appropriate antibiotic therapy, potentially reducing the use of toxic drugs.