Rj. Callan et al., CLEAVAGE OF INFLUENZA-A VIRUS H1 HEMAGGLUTININ BY SWINE RESPIRATORY BACTERIAL PROTEASES, Journal of virology, 71(10), 1997, pp. 7579-7585
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.