Table 1.

Summary of preclinical studies detailing HIV and opioid-induced microbial alterations.

Author Name, Year	Methods	Main Findings	Supplementary Findings
Meng et al. (79)	n = 48, with 12 controls, 12 morphine treated animals, 12 humanized BLT mice injected with HIV, and 12 humanized BLT mice injected with HIV and subsequently administered morphine, aged 17-19 weeks Treatment: I.V. injection of HIV particles (10 ng of calculated p24 antigen/mice) for 4 weeks; HIV + morphine group: 75 mg slow-release morphine pellet implantation 21 days after HIV infection Region analyzed: Intestinal contents from cecal-colonic region	HIV/morphine group: ↑ Firmicutes, Proteobacteria ↓ Bacteroides, Actinobacteria, Tenericutes, alpha diversity ↓ Lachnospiraceae, Ruminococcaceae, and Muribaculaceae	↓ gut epithelial barrier integrity in HIV/morphine group
Johnson et al. (77)	N = 10 out-bred, Indian-origin rhesus macaques randomly subdivided into saline (n = 5) or morphine (n = 5) treatment groups. Treatment: 7 weeks pre-treatment with 6 mg/kg saline/morphine, followed by I.V. inoculation with 200 TCID50 of SIVmac251 Region analyzed: fecal samples at necropsy	HIV/morphine group: ↓ Firmicutes, Ruminococcacea, butyrate-producing bacteria, alpha diversity. ↑ Bacteroidetes such as Prevotellaceae Positive correlation between Lachnospiraceae and butyrate-producing bacteria	Morphine group: ↓ butyrate-producing bacteria, which is not associated with ↓ in Ruminococcacea
Sindberg et al. (78)	N = 14 out-bred, male, Indian-origin rhesus macaques aged 3-4 years of age divided into morphine alone (n=4), SIV alone (n=4), SIV + morphine (n=4), or saline (n=2) groups Treatment: intramuscular injections t.i.d with 2 mg/kg (week 1), 3 mg/kg (week 2), and 4 mg/kg (week 3) of saline/morphine 70 days before SIV inoculation (104 plaque forming units of virus SIVmacR71/17E) Region analyzed: longitudinal analysis of fecal samples	Microbial diversity unaltered by SIV and morphine. No significant difference in microbial composition in SIV infected group alone. Morphine and Morphine/SIV groups: ↓ Methanobacteriaceae, Streptococcaceae, and Ruminococcaceae family microbes at very early time points of infection (3 weeks after infection)	Select primary bile acids ↓ in morphine animals. Secondary bile acids ↑ in morphine + SIV animals.