title: Spurious ampicillin resistance by testing Haemophilus influenzae with agar containing supplement C.
abstract: Ampicillin resistance (minimal inhibitory concentration >/=10 mug/ml) in the absence of beta-lactamase activity by Haemophilus influenzae was noted in tests performed with Mueller-Hinton agar containing one lot of supplement C. All strains, except five with known resistance due to beta-lactamase activity, were inhibited by 0.6 mug or less of ampicillin per ml of chocolatized blood agar.
mesh_terms: D000667:Ampicillin / Q000494:pharmacology*; D003470:Culture Media; D006193:Haemophilus influenzae / Q000187:drug effects*; D010403:Penicillin Resistance
chemical_list: D003470:Culture Media; D000667:Ampicillin