Epithelial Coculture and l -Lactate Promote Growth of Helicobacter cinaedi under H 2 -Free Aerobic Conditions

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 thatin vitro growth ofH. 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 ofl -lactate. The growth response ofH. cinaedi to Caco-2 cells andl -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 ofH. cinaedi , this analysis demonstrated strong constitutive expression of thel -lactate utilization locus, as well as differential transcription of terminal respiratory proteins as a function of Caco-2 coculture andl -lactate supplementation. Overall, these findings challenge traditional views ofH. cinaedi as an obligate microaerophile.IMPORTANCE H. cinaedi is an increasingly recognized pathogen in people with compromised immune systems. Atypical among other members of its bacterial class,H. cinaedi has been associated with infections of diverse anatomic sites. GrowingH. cineadi in the laboratory is quite difficult, due in large part to the need for a specialized atmosphere. The suboptimal growth ofH. cinaedi is an obstacle to clinical diagnosis, and it also limits investigation into the organism's biology. The current work shows thatH. cinaedi has more flexible atmospheric requirements in the presence of host cells and a common host-derived molecule. This nutritional interplay raises new questions about how the organism behaves during human infections and provides insights for how to optimize its laboratory cultivation.