Defining how Antibiotic Treatments shape Host Immunity

Abstract

Abstract Although antibiotics are clinically crucial, little is known about how they impact a patient’s immune response to infection. We address that gap by investigating how macrophages respond to bacteria treated with different classes of antibiotics. We treated a broadly susceptible E. coli strain with 8 separate antibiotics, infected macrophages, and compared how much TNF the various antibiotic-treated bacteria elicited from macrophages. We found that bacteria treated with cidal antibiotics (that kill bacteria) elicited ~2–3 fold more TNF than macrophages infected with equivalent amounts of bacteria treated with bacteriostatic (growth limiting) antibiotics. A panel of 12 clinical isolates from patients (4 each of E.coli, Enterobacter and Klebsiella) showed a similar pattern of antibiotic class-dependent inflammatory cytokine output. We then evaluated an in vivo IP injection model with antibiotic pre-treated bacteria, heat-killed bacteria, or vehicle alone. At two hr post infection, we saw ~35–200% increases in serum levels of pro-inflammatory cytokines induced by cidal-treated bacteria compared to static-treated bacteria. Consistent with prior data, both the vehicle and the killed bacteria elicited no inflammatory cytokines. Preliminary imaging data suggest that treatment with the cidal drugs causes most of the dead bacteria to form large aggregates, while treatment with the static drugs does not. We now aim to clarify the role of these aggregates in driving this inflammatory outcome. This may identify additional patterns of immune responses to antibiotic treated bacteria that could guide the development of improved antimicrobial treatment strategies. This work is supported by the Intramural Research Program of NIAID, NIH. Supported by Intramural Research Program of NIAID, NIH.