CLEAVAGE OF INFLUENZA-A VIRUS H1 HEMAGGLUTININ BY SWINE RESPIRATORY BACTERIAL PROTEASES

Cleavage of influenza A virus hemagglutinin (HA) is required for expre ssion of fusion activity and virus entry into cells. Extracellular pro teases are responsible for the proteolytic cleavage activation of avir ulent avian and mammalian influenza viruses and contribute to pathogen icity and tissue tropism, The relative contributions of host and micro bial proteases to cleavage activation in natural infection remain to b e established. We examined 23 respiratory bacterial pathogens and 150 aerobic bacterial isolates cultured from the nasal cavities of pigs fo r proteolytic activity. No evidence of secreted proteases was found fo r the bacterial pathogens, including Haemophilus parasuis, Pasteurella multocida, Actinobacillus pleuropneumoniae, Bordetella bronchiseptica , and Streptococcus suis. Proteolytic bacteria were isolated from 7 of 11 swine nasal samples and included Staphylococcus chromogenes, Staph ylococcus hyicus, Aeromonas caviae, Pseudomonas aeruginosa, Stenotroph omonas maltophilia, and Enterococcus sp. Only P. aeruginosa secreted a protease, elastase, that cleaved influenza virus HA. However, compare d to trypsin, the site of cleavage by elastase was shifted one amino a cid in the carboxyterminal direction and resulted in inactivation of t he virus, Under the conditions of this study, we identified several ba cterial isolates from the respiratory tracts of pigs that secrete prot eases in vitro, However, none of these proteolytic isolates demonstrat ed direct cleavage activation of influenza virus HA.