[Study of susceptibility of Haemophilus influenzae to beta-lactams by using HTM gelose (Haemophilus test medium)]

HTM agar was used for in vitro study of bêta-lactam antibiotics activity on H. influenzae. Tested strains belong to the three ampicillin phenotypes: sensitive, betalactamase production and ampicillin resistance without production of betalactamase. Using 2 micrograms ampicillin disk, diameters > or = 20 mm and < 20 mm separate ampicillin sensitive and resistant strains. The following zone-size breakpoints could be suggested: ampicillin (10 micrograms) > or = 25 and < 22 mm; amoxicillin (25 micrograms) > or = 26 mm and < 23 mm; ampicillin/sulbactam (10/10 micrograms) > or = 25 mm and < 22 mm; amoxicillin/clavulanic acid (20/10 micrograms) > or = 26 mm and < 23 mm; cefaclor (30 micrograms) > or = 25 mm and < 20 mm; cefuroxime (10 micrograms) > or = 22 mm and < 19 mm; cefixime (10 micrograms) and cefpodoxime (10 micrograms) > or = 26 mm; cefotaxime (30 micrograms) et ceftriaxone (30 micrograms) > or = 30 mm. The zone-size breakpoints concentrations, distribution of bacterial populations, mechanisms of resistance. In vitro study may screen for ampicillin resistance mechanisms.