Microbial translocation is a significant contributor to chronic immune activation and inflammation in HIV–infected humans. In SIV–infected rhesus macaques (RM), translocation has been demonstrated to occur across the gastrointestinal barrier; however, translocating bacterial taxa are not representative of the gut microbiota, with Proteobacteria appearing to preferentially translocate. To fully characterize translocating bacterial populations, we isolated translocated bacteria from chronically SIV-infected macaques and identified them subsequent to live culture.
Liver, mesenteric lymph node, and spleen samples were taken during necropsy from one uninfected and twenty chronically SIV– or SHIV−infected RM, including some Vancomycin−treated animals. Tissue samples were homogenized and plated on: a) Brain Heart Infusion, b) TSA+Tween 80, and c) TSA+5% Sheep’s Blood media under aerobic conditions, and d) Brucella Blood and e) CDC Blood media under anaerobic conditions. Isolates were grown for 1−7 days, colonies re−streaked for purity, and identified using MALDI−TOF and 16S rDNA sequencing. Shannon α−diversity was calculated for a) SIV+, b) SIV+ Vancomycin−treated and c) SIV+ or SHIV+ animals (no Vancomycin).
Thirty-six species have been identified thus far, 5 Proteobacteria (Enterobacteriaceae), 4 Actinobacteria (50% Actinomycetaceae, 25% Corynebacteriaceae, 25% Coriobacteriaceae), 2 Bacteroidetes (50% Odoribacteraceae, 50% Prevotellaceae) and 25 Firmicutes (32% Lactobacillaceae, 16% Streptococcaceae, 12% Enterococcaceae, 8% Aerococcaceae, 8% Eubacteriaceae, 8% Leuconostocaceae, 4% Bacillaceae, 4% Planococcaceae, 4% Staphylococcaceae, 4% Veillonellaceae). Surprisingly, although our cohort exhibited comparable microbial translocation, α-diversity between tissue sites was significantly reduced in the Vancomycin group as compared to the infected but untreated group with higher levels of Proteobacteria having translocated in Vancomycin-treated animals (two-way paired t-test, p=0.0739).
While PCR has been relied upon in previous studies to show the presence of translocated bacteria, this study reveals that several translocated bacteria are replication competent and that dysbiosis could influence the types of bacteria which translocate. It remains to be seen whether reduced diversity in Vancomycin-treated animals is due to a further alteration in taxa crossing the epithelial barrier or a change in selection pressure once they’ve translocated.