HIV Status Does Not Affect Rectal Microbiome Composition,Diversity,or Stability over Time: A Chicago Women's Interagency HIV Study

Background

Individuals with controlled HIV have excess morbidity and mortality that appear to be driven, in part, by immune activation related to gut microbial translocation. ^1,2 A shift in the gut microbiome or “dysbiosis” has been reported in HIV as well as other systemic inflammatory disorders such as metabolic syndrome, inflammatory bowel disease, and cardiovascular disease. ³ Several researchers have found correlations between specific “dysbiotic” microbes and gut barrier function in HIV-infected individuals. ^4,5 This difference appeared to persist even when those with suppressed HIV were compared with HIV negative controls. ⁶ These studies, however, included mostly male HIV-infected subjects. Recent publications suggest that differences in microbiota between HIV-infected and uninfected individuals are specific to men who have sex with men (MSM) rather than HIV infection. ⁷ Noguera-Julian et al. demonstrated that the Prevotella-predominant enterotype is associated with MSM rather than HIV status. Kelley et al. also showed a shift toward Prevotellaceae in HIV-uninfected MSMs who reported condomless receptive anal intercourse. ⁸ Currently there is a paucity of published data comparing the gut and/or rectal microbiome of HIV-infected and sociodemographically similar uninfected women, particularly from the same geographic locale. Diet, environmental, behavioral, and mental health factors also appear to be determinants of gut microbiome composition, making it difficult to tease out HIV-driven changes. ⁹

Data from simian immunodeficiency virus (SIV)-infected nonhuman primates in controlled settings with standardized environment and diet have failed to show persistent changes in the gut microbiome associated with SIV infection. ¹⁰ Studies of chimpanzees in their natural habitat, however, have suggested that SIV infection leads to greater instability of the gut microbiome over time. ¹¹ Gut mucosal CD4 cells often do not recover after antiretroviral therapy and this may lead to inability to select beneficial microbes and eliminate harmful ones. ¹² The makeup of the gut microbiome of HIV-infected individuals, particularly those with low CD4 may thus be more strongly influenced by the environment and less stable over time. We sought to determine whether the rectal microbiota composition and stability of HIV-infected women was similar to uninfected women.

Methods

Results

Of 202 women enrolled in the Cook County WIHS site who were approached for inclusion, 95% (191: 136 HIV-infected and 55 HIV uninfected) women agreed to enroll and were included in analyses for visit 41, 70 HIV-infected and 30 HIV-uninfected women provided samples on both visit 41 and 43. Demographics were similar between HIV-infected and uninfected women, although the proportion of HIV-uninfected women who were African American was slightly higher (Table 1). HIV-infected and uninfected women reported similar consumption of all food/nutrient groups except for whole grains, which HIV-uninfected women reported eating more frequently (p = .01) (Table 2). Of the HIV-infected women, 84% were prescribed antiretroviral treatment and 71% had a current undetectable HIV viral load at the time of rectal swab collection.

Shannon diversity index (Mann–Whitney, p = .14) and Bray–Curtis dissimilarity indices (analysis of similarity, R = 0.0027, p = .488) did not differ by HIV status (Fig. 1A). Bray–Curtis analysis of samples from the same individuals collected 1 year apart demonstrated similar rectal microbiome over time in both HIV-infected and HIV-uninfected women (Mann–Whitney, p = .889) (Fig. 1B). There were no statistically significant taxa that differed by HIV status (HIV infected vs HIV uninfected) (Fig. 1C). After correction for false discovery rate (FDR), HIV treatment status did not appear to influence overall microbial community structure but did impact the prevalence of several genera. Staphylococcus (logFC = 6.66, q = 5xE⁻¹⁰) and Corynebacterium (logFC = 3.69, q = 1.67xE⁻⁹) were statistically significantly enriched and Lactobacillus (logFC = −4.75, q = 7.62xE⁻³) were depleted in those (n = 22) with untreated HIV infection compared with HIV-uninfected women. Staphylococcus (logFC = 6.31, q = 8.51E⁻¹⁵) and Corynebacterium (logFC = 4.45, q = 2.48E⁻¹⁹) were also enriched in untreated HIV-infected versus treated HIV-infected. Prevotella were not enriched in untreated women compared with those on treatment (0.95).

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FIG. 1.

(A) NMDS plot of Bray–Curtis indices compared with HIV status. VID: 41 represents Visit 41 (ANOSIM R = 0.0027, p = .49) and VID: 43 is Visit 43 (ANOSIM R = −0.021, p = .67). (B) Bray–Curtis similarity between visits 41 and 43 (Mann–Whitney U test, p = .89). (C) Stacked histogram of 10 most common genera by HIV status. ANOSIM, analysis of similarity; NMDS, non-metric multidimensional scaling.

The previously noted significant genera-specific differences were not seen when HIV-infected women on treatment were compared with HIV-uninfected women for Staphylococcus (q = 0.09) and for Corynebacterium (q = 0.95). Prevotella abundance was not different between HIV-infected women on treatment and HIV-uninfected women (p = .95). However, Actinomyces (logFC = −1.81, q = 4.43E⁻⁶) and Clostridium (logFC = −1.03, q = 5.44E⁻⁴) were depleted in HIV-infected women on treatment compared with HIV-uninfected women. Clostridium was also depleted in HIV-infected women on versus off therapy (logFC = −2.54, q = 9.32E⁻¹¹). The family Streptococcaceae and the genus Streptococcus were slightly more enriched, although with borderline significance, in HIV-infected women with undetectable versus detectable viral load (Kruskal–Wallis, p = .001, FDR = 0.05 for both). Diversity measured by Shannon and Bray–Curtis indices were not associated with HIV viremia status. HIV-infected women were categorized by current CD4 into three groups: <200, 201–350, and >350 cells/mm³. CD4 group did not correlate with Shannon index, Bray–Curtis index, or any individual taxa.

Discussion

This study of sociodemographically similar HIV-infected and uninfected Chicago women suggests that HIV status is not associated with significant community shifts in rectal microbiota. There were no differences in the diversity, complexity, or stability of rectal microbiota by HIV status. These findings are similar to those of Noguera-Julian et al. who found that HIV status was not associated with differences in microbiota but rather that the MSM enterotype was likely driving the difference between HIV-infected and uninfected individuals. ⁷ Our data demonstrate that change in gut microbiome as measured by rectal swabs in HIV-infected women for a 1-year period is low and similarly stable to that of matched HIV-uninfected women. The stability of the gut microbiome seen in HIV-infected women, including those with low CD4, suggests that the gut mucosal immune system may play a smaller role than previously believed in managing gut ecology, specifically at the rectum.

Gut immune function may focus on excluding organisms with high pathogenic potential or only affect mucosa-associated microbes. ²⁰ The HIV-associated Prevotella-enriched “dysbiosis” reported by others but not found in our relatively large sample may reflect differences in sampling site (stool/biopsy) as opposed to rectal swabs. The majority of prior publications have used stool or colonic samples, making direct comparisons difficult. ³ McHardy et al. did, however, use rectal samples and found changes in microbiota composition associated with HIV in men. ²¹ Several studies suggest that rectal swab microbiota may closely resemble samples from upstream sites. ^22,23 Kelley et al., using rectal biopsies, also found a similar Prevotellaceae-enriched enterotype associated with condomless receptive anal intercourse in HIV-uninfected MSM, suggesting that rectal sampling is sufficient to identify this Prevotella-enriched enterotype. ⁸ Mounting evidence, including study by Noguera-Julian et al. and Kelley et al., suggests differences between HIV-infected and uninfected are due to behavioral or environmental confounders rather than HIV infection.

We cannot, however, rule out involvement by the gut immune system in selecting organisms associated with the mucosa or more proximal bowel. The enrichment of the family Streptococcaceae and genus Streptococcus in HIV-infected aviremic versus viremic participants has not previously been reported. If it were related to immunosuppression we would expect to see depletion associated with lower CD4 as well, which we did not, suggesting that viral replication and its direct effects on the gut may be responsible.

Among HIV-infected women, untreated status was strongly associated with the abundance of the genera Staphylococcus and Corynebacterium, which does not seem to be explained by persistent HIV viral replication since we did not see these same genera-specific correlations in comparisons between HIV viremic versus aviremic women. The relatively low abundance of Clostridium in HIV-infected women on antiretroviral treatment may suggest that antiretrovirals directly impact the gut microbiome.

This study has several strengths. Our large sample size affords adequate power to find HIV-associated microbial shifts should they exist. The use of the Chicago WIHS cohort, which includes HIV-infected and uninfected women with similar demographic and behavioral characteristics living in the same urban neighborhoods, allowed us to minimize several known environmental, social, dietary, and behavioral confounders. Lastly, examining two samples collected 1-year apart allowed us to address microbiome stability overall and by HIV status. A systems-based approach to integrate measurements of gut microbial metabolites, metagenomics, gut permeability, gut mucosal immune recovery, systemic immune activation, and behavior will be necessary to begin uncovering the effects that gut microbes have on clinical outcomes in HIV. Further data from this cohort will be presented in future articles, including further dietary analysis and serum markers of immune activation. Hopefully, this study will better inform design of those studies by demonstrating the limited role that HIV infection plays in modulating the gut microbiome.