Burkholderia cenocepaciaCreates an Intramacrophage Replication Niche in Zebrafish Embryos, Followed by Bacterial Dissemination and Establishment of Systemic Infection

Abstract

Bacteria belonging to the "Burkholderia cepacia complex" (Bcc) often cause fatal pulmonary infections in cystic fibrosis patients, yet little is know about the underlying molecular mechanisms. These Gram-negative bacteria can adopt an intracellular lifestyle, although their ability to replicate intracellularly has been difficult to demonstrate. Here we show that Bcc bacteria survive and multiply in macrophages of zebrafish embryos. Local dissemination by nonlytic release from infected cells was followed by bacteremia and extracellular replication. Burkholderia cenocepacia isolates belonging to the epidemic electrophoretic type 12 (ET12) lineage were highly virulent for the embryos; intravenous injection of <10 bacteria of strain K56-2 killed embryos within 3 days. However, small but significant differences between the clonal ET12 isolates K56-2, J2315, and BC7 were evident. In addition, the innate immune response in young embryos was sufficiently developed to control infection with other less virulent Bcc strains, such as Burkholderia vietnamiensis FC441 and Burkholderia stabilis LMG14294. A K56-2 cepR quorum-sensing regulator mutant was highly attenuated, and its ability to replicate and spread to neighboring cells was greatly reduced. Our data indicate that the zebrafish embryo is an excellent vertebrate model to dissect the molecular basis of intracellular replication and the early innate immune responses in this intricate host-pathogen interaction.

mpeg1 promoter transgenes direct macrophage-lineage expression in zebrafish

“…Detailed examination of inflammation and host-pathogen interactions at the cellular level has been enabled by several transgenic strains marking embryonic and adult neutrophils, such as Tg(mpx:EGFP) 3,4 and lyz-driven transgenes. 5,6 Such lines have been used to study neutrophil responses and fluxes during infection 7,8 and during acute and chronic inflammation. 3,4,9 Combinations of these approaches have provided some important new insights (eg, regarding the role of leukocytes in mycobacterial infection).…”

Quantification of type VI secretion system activity in macrophages infected with Burkholderia cenocepacia

“…Also, B. cenocepacia can be transmitted from patient to patient (Drevinek & Mahenthiralingam, 2010). B. cenocepacia is pathogenic in several plant and non-mammalian animal infection models (Khodai-Kalaki et al, 2015;Thomson & Dennis, 2013;Uehlinger et al, 2009;Vergunst et al, 2010) and can survive intracellularly within epithelial cells (Burns et al, 1996;Sajjan et al, 2006), macrophages (Lamothe et al, 2007;Martin & Mohr, 2000;Saini et al, 1999) and amoebae (Lamothe et al, 2004;Marolda et al, 1999).…”

Deciphering and Imaging Pathogenesis and Cording of <em>Mycobacterium abscessus</em> in Zebrafish Embryos

“…The increasing success of this alternative vertebrate model relies on major and unique opportunities that motivated and validated its use for a better understanding of numerous viral and bacterial infections 19,22,23,24,25,26,27,28,29 . As opposed to most other animal models, zebrafish embryos are optically transparent, allowing non-invasive fluorescence imaging 30 .…”