For example, proteases produced by Staphylococcus aureus and Aerococcus viridans enhance influenza replication and pathogenicity in mice by increasing cleavage of influenza virus HA, which is required for virus release [45], [46], and Serratia marcescens facilitates HA cleavage activation indirectly by generating plasmin from plasminogen [47]. Here, PLG is linked to influenza.