Identification of Branhamella catarrhalis in 2.5 min with an indoxyl butyrate strip test

Abstract

Branhamella catarrhalis, an occasional cause of human respiratory infections, unlike most other members of the family Neisseriaceae, produces a butyrate esterase. This is capable of breaking the ester linkage between butyryl groups and carrier molecules. B. caviae and B. ovis, which are rarely encountered in pathological specimens, also produce butyrate esterase. This property can be used as a rapid test in the identification of B. catarrhalis. The recently reported rapid test for butyrate esterase relies on the release of methylumbelliferate, which can be detected only by using UV light after 5 min of incubation. In the rapid test described here, indoxyl is liberated from indoxyl butyrate by butyrate esterase and spontaneously forms indigo in the presence of oxygen. B. catarrhalis can be distinguished from other oxidase-positive, gram-negative cocci after 2.5 min by inoculating the organism onto a filter paper strip containing this compound.