Epithelial coculture and L-lactate promote growth of Helicobacter cinaedi under H2-free aerobic conditions

Abstract

Helicobacter cinaedi is an emerging opportunistic pathogen associated with infections of diverse anatomic sites. Nevertheless, the species demonstrates fastidious axenic growth; it has been described as requiring a microaerobic atmosphere, along with a strong preference for supplemental H2 gas. In this context, we examined the hypothesis that in vitro growth of H. cinaedi could be enhanced by coculture with human epithelial cells. When inoculated (in Ham's F12 medium) over Caco-2 monolayers, the type strain (ATCC BAA-847) gained the ability to proliferate under H2-free aerobic conditions. Identical results were observed during coculture with several other monolayer types (LS-174T, AGS, and HeLa). Under chemically defined conditions, 40 amino acids and carboxylates were screened for their effect on the organism's atmospheric requirements. Several molecules promoted H2-free aerobic proliferation, although it occurred most prominently with millimolar concentrations of L-lactate. The growth response of H. cinaedi to Caco-2 cells and L-lactate was confirmed with a collection of 12 human-derived clinical strains. mRNA sequencing was next performed on the type strain under various growth conditions. In addition to providing a whole-transcriptome profile of H. cinaedi, this analysis demonstrated strong constitutive expression of the L-lactate utilization locus, as well as differential transcription of terminal respiratory proteins as a function of Caco-2 coculture and L-lactate supplementation. Overall, these findings challenge traditional views of H. cinaedi as an obligate microaerophile.