Adaptation of Francisella tularensis to the mammalian environment is governed by cues which can be mimicked in vitro.
The intracellular bacterium Francisella tularensis survives in mammals, arthropods, and freshwater amoeba. It was previously established that the conventional media used for in vitro propagation of this microbe do not yield bacteria that mimic those harvested from infected mammals; whether these in vitro-cultivated bacteria resemble arthropod- or amoeba-adapted Francisella is unknown. As a foundation for our goal of identifying F. tularensis outer membrane proteins which are expressed during mammalian infection, we first sought to identify in vitro cultivation conditions that induce the bacterium's infection-derived phenotype. We compared Francisella LVS grown in brain heart infusion broth (BHI; a standard microbiological medium rarely used in Francisella research) to that grown in Mueller-Hinton broth (MHB; the most widely used F. tularensis medium, used here as a negative control) and macrophages (a natural host cell, used here as a positive control). BHI- and macrophage-grown F. tularensis cells showed similar expression of MglA-dependent and MglA-independent proteins; expression of the MglA-dependent proteins was repressed by the supraphysiological levels of free amino acids present in MHB. We observed that during macrophage infection, protein expression by intracellular bacteria differed from that by extracellular bacteria; BHI-grown bacteria mirrored the latter, while MHB-grown bacteria resembled neither. Naïve macrophages responding to BHI- and macrophage-grown bacteria produced markedly lower levels of proinflammatory mediators than those in cells exposed to MHB-grown bacteria. In contrast to MHB-grown bacteria, BHI-grown bacteria showed minimal delay during intracellular replication. Cumulatively, our findings provide compelling evidence that growth in BHI yields bacteria which recapitulate the phenotype of Francisella organisms that have emerged from macrophages.
Hazlett
Karsten R O
KR
Center for Immunology and Microbial Disease, Center for Cardiovascular Sciences, Albany Medical College, 47 New Scotland Avenue, Albany, New York 12208, USA. Hazlett@mail.amc.edu
Caldon
Seth D
SD
McArthur
Debbie G
DG
Cirillo
Kerry A
KA
Kirimanjeswara
Girish S
GS
Magguilli
Micheal L
ML
Malik
Meenakshi
M
Shah
Aaloki
A
Broderick
Scott
S
Golovliov
Igor
I
Metzger
Dennis W
DW
Rajan
Krishna
K
Sellati
Timothy J
TJ
Loegering
Daniel J
DJ
D000222:Adaptation, Physiological; D000818:Animals; D001426:Bacterial Proteins / Q000032:analysis; D015153:Blotting, Western; D015169:Colony Count, Microbial; D003470:Culture Media / Q000737:chemistry*; D016207:Cytokines / Q000096:biosynthesis; D005604:Francisella tularensis / Q000737:chemistry / Q000502:physiology*; D008264:Macrophages / Q000276:immunology / Q000382:microbiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D050296:Microbial Viability; D020543:Proteome / Q000032:analysis; D016019:Survival Analysis; D014406:Tularemia / Q000382:microbiology
D001426:Bacterial Proteins; D003470:Culture Media; D016207:Cytokines; D020543:Proteome