Peterson, B. R. | Search bioRxiv

bioRxiv2018

Growth substrate may influence biofilm susceptibility to antibiotics

The CDC biofilm reactor is a robust culture system with high reproducibility in which biofilms can be grown for a wide variety of analyses. Multiple material types are available as growth substrates, yet data from biofilms grown on biologically relevant materials is scarce, particularly for antibiotic efficacy against differentially supported biofilms. In this study, CDC reactor holders were modified to allow growth of biofilms on collagen, a biologically relevant substrate. Susceptibility to multiple antibiotics was compared between biofilms of varying species grown on collagen versus standard polycarbonate coupons. Data indicated that in 13/18 instances, biofilms on polycarbonate were more susceptible to antibiotics than those on collagen, suggesting that when grown on a complex substrate, biofilms may be more tolerant to antibiotics. These outcomes may influence the translatability of antibiotic susceptibility profiles that have been collected for biofilms on hard plastic materials. Data may also help to advance information on antibiotic susceptibility testing of biofilms grown on biologically relevant materials for future in vitro and in vivo applications.

microbiology↗

bioRxiv2018

The C. elegans CHP1 homolog, pbo-1, functions in innate immunity by regulating the pH of the intestinal lumen

Caenorhabditis elegans are soil-dwelling nematodes and models for understanding innate immunity and infection. Previous work has described a regularly-timed pH change in the intestine of Caenorhabditis elegans called the pH wave. To characterize this wave and its function in the worm, we developed a novel fluorescent dye (KR35) that accumulates in the intestine and sensitively responds to dynamic changes in pH. Here, we use KR35 to show that mutations in the Ca2+-binding protein, PBO-1 abrogate the pH wave, causing the anterior intestine to be constantly acidic. Surprisingly, pbo-1 mutants were also more susceptible to infection by several bacterial pathogens. We could suppress pathogen susceptibility in pbo-1 mutants by treating the animals with pH-buffering bicarbonate, suggesting the pathogen susceptibility is a function of the acidity of the intestinal pH. Furthermore, we use KR35 to show that pathogens completely neutralize the pH in the intestine of wild type, but not pbo-1 mutants. C. elegans is known to increase production of reactive oxygen species (ROS), such as H2O2, in response to pathogens, which is an important component of pathogen defense. We show that pbo-1 mutants exhibited decreased H2O2 in response to pathogens, which could also be partially restored in pbo-1 animals treated with bicarbonate. Ultimately, our results support a model whereby pbo-1 functions during infection to permit pH changes in the intestine that are important for fighting pathogens.\n\nAuthor SummaryInnate immunity is critical for host defense against pathogens. However, questions remain about how the host senses and responds to pathogen invasion. Using a pH-sensitive fluorescent dye and a Caenorhabditis elegans pathogen infection model we show that pathogens induce changes in pH of the worm intestine. We also show that intestinal pH directly affects production of reactive oxygen species (e.g. H2O2) important for pathogen defense. Our results show that pH regulation is an important component of the innate immune response to pathogens.

microbiology↗