Abstract
We investigated whether production of histamine by bacteria isolated from sputum of patients with infective lung diseases could be attributed to the presence of histidine decarboxylase (HD). Twenty gram-positive and 20 gram-negative organisms were studied for their ability to decarboxylate 14C-histidine in vitro over the pH range 4.5-7.5. Of the bacteria investigated, lysates from the gram-negative species Haemophilus influenzae, H. parainfluenzae, Moraxella (Branhamella) catarrhalis and Pseudomonas aeruginosa liberated 14CO2 and histamine from 14C-histidine in the presence of the cofactor pyridoxal phosphate. In contrast, results obtained in the absence of cofactor were similar to those of negative (lysate-free) controls suggesting that the HD enzymes of these species resembled those previously described in other gram-negative bacteria. No HD activity was detected over this pH range in lysates from gram-positive species. This finding correlated with earlier observations that these gram-positive organisms did not produce histamine in vitro.