O47 – The gut during prolonged critical illness harbors low membership pathogen communities that are less virulent as a group than individually
Author(s):
Background: Loss of intestinal microflora is emerging during critical illness under constant pressure from antibiotic use.
Hypothesis: Here we hypothesized that as low membership communities adapt to the gut during critical illness, their virulence is repressed by each other as a mechanism of survival. Therefore the aim of this study was to examine the interdependence of individual pathogen community members on overall virulence among low membership communities.
Methods: Using 16S rRNA and culture analyses, we examined the composition of 30 stool samples from 14 patients treated in the ICU at the University of Chicago for extended periods. We selected 2-member pathogen communities and determined their virulence, together and individually, using Caenorhabditis elegans killing assays as a model of intestinal infection.
Results: Among 30 stool samples analyzed by 16S rRNA, 17 were determined to harbor low membership pathogen communities (1-4) consisting at the genera level of Enterococcus or Staphylococcus, or at the family level of Enterobacteriaceae only. Culture analysis revealed Candida spp. in >75% of samples (15/17). Surprisingly a subset of 4 samples contained only 2 members: Sample 1 had C. albicans+ multi-drug resistant (MDR) Enterococcus faecium; sample 2- C. grabrata + MDR CoA- Staphylococcus; sample 3- C. glabrata + MDR Klebsiella pneumoniae, and sample 4- C. albicans + MDR K. pneumoniae. C. albicans and C. glabrata alone were highly lethal against C. elegans, however in each case their lethality was markedly attenuated in the presence of their bacterial community member (n=40/group, p<0.01). For example, C. albicans from the sample 1 killed 100% of C. elegans at 72 hrs while the same amount of C. albicans incubated with E. faecium, resulted in only 30% mortality. Phenotype analysis demonstrated that E. faecium completely suppressed hyphae formation of C. albicans.
Conclusions: The survival, evolution, and virulence phenotype of intestinal microbes exposed to prolonged critical illness and their effect on outcome remains ill- defined. As they adapt and survive, loss of one community member can affect the virulence of the other. Metagenomic interrogation of intestinal community structure, function, and virulence capacity is now possible and may offer surprising insight into the untoward effect of prolonged antibiotic use during critical illness.