title: Innate immune response to Streptococcus iniae infection in zebrafish larvae.
abstract: Streptococcus iniae causes systemic infection characterized by meningitis and sepsis. Here, we report a larval zebrafish model of S. iniae infection. Injection of wild-type S. iniae into the otic vesicle induced a lethal infection by 24 h postinfection. In contrast, an S. iniae mutant deficient in polysaccharide capsule (cpsA mutant) was not lethal, with greater than 90% survival at 24 h postinfection. Live imaging demonstrated that both neutrophils and macrophages were recruited to localized otic infection with mutant and wild-type S. iniae and were able to phagocytose bacteria. Depletion of neutrophils and macrophages impaired host survival following infection with wild-type S. iniae and the cpsA mutant, suggesting that leukocytes are critical for host survival in the presence of both the wild-type and mutant bacteria. However, zebrafish larvae with impaired neutrophil function but normal macrophage function had increased susceptibility to wild-type bacteria but not the cpsA mutant. Taking these findings together, we have developed a larval zebrafish model of S. iniae infection and have found that although neutrophils are important for controlling infection with wild-type S. iniae, neutrophils are not necessary for host defense against the cpsA mutant.
authors.affiliation: Microbiology Doctoral Training Program, Department of Medical Microbiology and Immunology, University of Wisconsin-Madison, Madison, Wisconsin, USA.
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Harvie
authors.forename: Julie M
authors.initials: JM
authors.lastname: Green
authors.forename: Melody N
authors.initials: MN
authors.lastname: Neely
authors.forename: Anna
authors.initials: A
authors.lastname: Huttenlocher
mesh_terms: D000818:Animals; D016667:Bacterial Capsules / Q000276:immunology; D001426:Bacterial Proteins / Q000276:immunology; D007113:Immunity, Innate / Q000276:immunology; D007814:Larva; D008264:Macrophages / Q000276:immunology / Q000382:microbiology; D022423:Myeloid Cells / Q000276:immunology / Q000382:microbiology; D009504:Neutrophils / Q000276:immunology / Q000382:microbiology; D010587:Phagocytosis / Q000276:immunology; D013290:Streptococcal Infections / Q000276:immunology* / Q000382:microbiology; D013291:Streptococcus / Q000276:immunology*; D015027:Zebrafish / Q000276:immunology* / Q000382:microbiology*
chemical_list: D001426:Bacterial Proteins