HIV-induced immunosuppression is associated with colonization of the proximal gut by environmental bacteria.

OBJECTIVES: To evaluate the impact of HIV infection on colonization resistance in the proximal gut.
DESIGN: It was a case-control study.
METHODS: We contrasted microbiota composition between eight HIV-1-infected patients and eight HIV-negative controls to characterize community alteration and detect exogenous bacteria in the esophagus, stomach, and duodenum, as well as the mouth using a universal 16s ribosomal RNA gene survey and correlated the findings with HIV serostatus and peripheral blood T-cell counts.
RESULTS: HIV infection was associated with an enrichment of Proteobacteria (P=0.020) and depletion of Firmicutes (P = 0.005) in the proximal gut. In particular, environmental species Burkholderia fungorum and Bradyrhizobium pachyrhizi colonized the duodenum of HIV patients who had abnormal blood CD4 T-cell counts but were absent in HIV-negative controls or HIV patients whose CD4 cell counts were normal. The two species coexisted and exhibited a decreasing trend proximally toward the stomach and esophagus and were virtually absent in the mouth. B. fungorum always outnumbered B. pachyrhizi in a ratio of approximately 15 to 1 regardless of the body sites (P < 0.0001, r = 0.965). Their abundance was inversely correlated with CD4 cell counts (P = 0.004) but not viral load. Overgrowth of potential opportunistic pathogens for example, Prevotella, Fusobacterium, and Ralstonia and depletion of beneficial bacteria, for example, Lactobacillus was also observed in HIV patients.
CONCLUSIONS: The colonization of the duodenum by environmental bacteria reflects loss of colonization resistance in HIV infection. Their correlation with CD4 cell counts suggests that compromised immunity could be responsible for the observed invasion by exogenous microbes.