Daily HIV pre-exposure prophylaxis (PrEP) with tenofovir disoproxil fumarate-emtricitabine reduced Streptococcus and increased Erysipelotrichaceae in rectal microbiota\nDownload PDF\nDownload PDF\nDaily HIV pre-exposure prophylaxis (PrEP) with tenofovir disoproxil fumarate-emtricitabine reduced Streptococcus and increased Erysipelotrichaceae in rectal microbiota\nScientific Reports volume 8, Article number: 15212 (2018) Cite this article\n6179 Accesses\n20 Citations\n10 Altmetric\nMetrics details\nAbstract\nDaily PrEP is highly effective at preventing HIV-1 acquisition, but risks of long-term tenofovir disoproxil fumarate plus emtricitabine (TDF-FTC) include renal decline and bone mineral density decrease in addition to initial gastrointestinal side effects.\n\nWe investigated the impact of TDF-FTC on the enteric microbiome using rectal swabs collected from healthy MSM before PrEP initiation and after 48 to 72 weeks of adherent PrEP use.\n\nThe V4 region of the 16S ribosomal RNA gene sequencing showed that Streptococcus was significantly reduced from 12.0% to 1.2% (p = 0.036) and Erysipelotrichaceae family was significantly increased from 0.79% to 3.3% (p = 0.028) after 48–72 weeks of daily PrEP.\n\nCatenibacterium mitsuokai, Holdemanella biformis and Turicibacter sanguinis were increased within the Erysipelotrichaceae family and Streptococcus agalactiae, Streptococcus oralis, Streptococcus mitis were reduced.\n\nThese changes were not associated with host factors including PrEP duration, age, race, tenofovir diphosphate blood level, any drug use and drug abuse, suggesting that the observed microbiome shifts were likely induced by daily PrEP use.\n\nLong-term PrEP resulted in increases of Catenibacterium mitsuokai and Holdemanella biformis, which have been associated with gut microbiome dysbiosis.\n\nOur observations can aid in characterizing PrEP’s side effects, which is likely to improve PrEP adherence, and thus HIV-1 prevention.\n\nSimilar content being viewed by others\nImpact of long-term antiretroviral therapy on gut and oral microbiotas in HIV-1-infected patients\nArticle Open access 13 January 2021\nExploring the interplay between antiretroviral therapy and the gut-oral microbiome axis in people living with HIV\nArticle Open access 01 August 2024\nAdults on pre-exposure prophylaxis (tenofovir-emtricitabine) have faster clearance of anti-HIV monoclonal antibody VRC01\nArticle Open access 28 November 2023\nIntroduction\nTruvada, a fixed-dose combination of the nucleoside reverse transcriptase inhibitors (NRTI) tenofovir disoproxil fumarate (TDF) plus emtricitabine (FTC), was approved for daily HIV-1 pre exposure prophylaxis (PrEP) in 2012, and by 2015 more than 79,000 people in US are estimated to have started TDF-FTC for PrEP1.\n\nDaily PrEP is highly effective at preventing HIV-1 infection, reducing HIV-1 acquisition by over 90% in MSM2.\n\nAs a key part of the national HIV/AIDS strategy, PrEP use is expected to continue to increase, and thus understanding the side effects of widespread PrEP adoption is an important task.\n\nIn randomized studies in long-term PrEP users, kidney function decline3 and bone mineral density decrease4 have been reported, which are in concordance with the observations among TDF-treated HIV-infected individuals5,6.\n\nRenal tubular toxicity of TDF has been suggested as a mechanism for kidney abnormalities7.\n\nTDF-induced bone mineral density decreases have been explained by osteoblast gene expression changes8 and tubular dysfunction and resulting phosphaturia9.\n\nWe may gain further insights on these long-term PrEP side effects by profiling the gut microbiome as the human gut microbiota is reported to be correlated with both chronic kidney disease and osteoporosis.\n\nIncreases in uremic toxins and inflammation among chronic kidney disease patients were in part due to the gut microbiome’s role in the fermentation of short-chain fatty acids10.\n\nSeveral studies reported a significant association between the intestinal microbiota, calcium absorption, and bone health11,12.\n\nAs suggested from these findings, study of the microbiome profile, in the absence of HIV infection during PrEP, may provide an important correlate for addressing long-term side effects attributable to TDF-FTC use.\n\nA direct interaction between a drug and the enteric microbiome has been demonstrated for different classes of drugs13,14,15.\n\nOther drugs may also have indirect and unintended antimicrobial activities16.\n\nIndeed, a recent population-level study found medication to have the greatest influence on gut microbiome composition, compare to other covariates such as gender, diet, and health status17.\n\nIn this study, we investigated the impact of PrEP on the enteric microbiome using serial specimens collected from healthy individuals before initiation of PrEP (baseline) and after 48 to 72 weeks of adherent PrEP use in the California Collaborative Treatment Group study 595 (NCT01761643).\n\nCCTG 595 was a randomized controlled trial in high risk MSM and transgender women to compare the impact of daily text messaging to standard care on daily TDF-FTC adherence18.\n\nWe chose study participants with documented adequate adherence to PrEP and these are optimal for investigating the direct impact of daily PrEP on the enteric microbiome profile.\n\nBy performing next-generation sequencing of the bacterial 16S ribosomal RNA (rRNA) gene, we assessed the relative abundance of each family and genus before and after PrEP administration and identified microbiome shifts after long-term PrEP.\n\nIn addition, we conducted long-read next-generation sequencing of bacterial 16S-23S rRNA to identify which species are impacted by long-term daily PrEP.\n\nResults\nWe compared the microbiome composition of 8 study participants’ rectal specimens before PrEP administration and after 48 to 72 weeks of adherent PrEP use.\n\nTable 1 lists each study participant’s age, race, duration of PrEP use, tenofovir diphosphate (TFV-DP) level measured at 48 weeks post PrEP initiation, and any other drug usage and abuse.\n\nThe next-generation sequencing reads of the V4 region of the 16s ribosomal RNA gene were obtained and processed as described in Methods.\n\nThe number of sequencing reads before and after processing are provided in Supplementary Table S1.\n\nPrEP-induced changes in the microbiome composition were assessed with two methods.\n\nFirst, we statistically addressed the impact of PrEP on the microbiome composition using a permutation test.\n\nTo control for the small sample size, we performed a permutation test in which we randomly permuted all specimens’ PrEP status (pre-PrEP or post-PrEP) to identify any meaningful differences in the microbiome composition at the family and genus levels.\n\nAn empirical p-value was obtained for each family or genus through 100,000 PrEP status permutations.\n\nWe also conducted a paired-permutation test by permuting each individual’s PrEP status and evaluating the chance to observe the measured t-statistic, compared to the t-statistic distribution for all possible 28 arrangements.\n\nSecond, we calculated the log fold change of each family or genus, defined as log2 of the ratio between mean abundances after and before PrEP.\n\nFigure 1 plots the abundance of each family and genus from eight subjects before and after PrEP, sorted by the empiric p-value obtained from the permutation test.\n\nAt the family level, the permutation test indicated that the abundances of Erysipelotrichaceae and Streptococcaceae were statistically significantly altered with a minimum of 48 weeks PrEP administration (p = 0.028 and p = 0.039, respectively).\n\nErysipelotrichaceae and Streptococcaceae remained significantly different under the paired-permutation test (p = 0.031 and p = 0.039, respectively).\n\nPre-PrEP specimens had 0.79% of Erysipelotrichaceae on average, however, its relative abundance was increased to 3.3% after PrEP, resulting in a mean log2(fold change) of 2.1.\n\nAs shown in Fig.\n\n2A, six out of eight participants showed Erysipelotrichaceae increase after PrEP.\n\nOn the contrary, relative abundance of Streptococcaceae was decreased after PrEP with log2 (fold change) of −3.3.\n\nFour participants showed a considerable reduction of Streptococcaceae with an over 10 percent decrease.\n\nAt the genus level, Streptococcus was significantly reduced after PrEP administration (permutation test, p = 0.036 and paired-permutation test, p = 0.035).\n\nThe average relative abundance of Streptococcus across eight study participants was 12.0% before PrEP initiation.\n\nHowever, after 48–72 weeks of daily TDF-FTC, the average abundance was reduced to 1.2%.\n\nFigure 2B compares the Streptococcus abundance before and after PrEP for each of eight study participants.\n\nThe mean log2(fold change) over eight participants was −3.3 and we observed more than a 10 percent reduction in Streptococcus level in four participants (Fig.\n\n2B).\n\nIn particular, participant XNT showed a reduction from 51% to 1.9%.\n\nWithin the Streptococcaceae family, Streptococcus was the dominant genus (>99%) in all eight participants, resulting in significant shifts at both the family and genus levels.\n\nTable 2 lists each family’s p-value and fold change.\n\nWe next examined the associations between host factors and microbiome abundance changes.\n\nFigure 3A plots Erysipelotrichaceae abundance difference before and after PrEP as a function of PrEP duration, age, race, TFV-DP level, any drug use status and drug abuse status.\n\nThe Erysipelotrichaceae change was not dependent on either PrEP duration (Spearman’s correlation ρ = 0.21 and p = 0.62) or age (ρ = 0.071 and p = 0.88).\n\nThe abundance difference was not correlated with TFV-DP levels at 48 weeks after PrEP (ρ = −0.19 and p = 0.66).\n\nThe Erysipelotrichaceae abundance difference was not sensitive to race (Kruskal-Wallis test, p = 0.37) and was not affected by any drug use (Wilcoxon rank sum test, p = 0.51) or drug abuse (Wilcoxon rank sum test, p = 1.0).\n\nLikewise, the Streptococcus change was not correlated with PrEP duration (ρ = 0.33 and p = 0.42).\n\nAs shown in Fig.\n\n3B, age was not associated with abundance change (ρ = 0.33 and p = 0.43).\n\nThe abundance change was not sensitive to race (Kruskal-Wallis test, p = 0.11) and was not correlated with TFV-DP levels at 48 weeks after PrEP (ρ = 0.21 and p = 0.62).\n\nThe Streptococcus abundance difference was not affected by any drug use (p = 0.64) or drug abuse (p = 0.39).\n\nThis lack of significance of the differences might be due to the small sample size, however, Fig.\n\n3 does not indicate any trends in the associations.\n\nFigure 4 compares the family composition of eight individuals before and after PrEP.\n\nConsistent with previous reports on the healthy human gut microbiome profiles19,20, the CCTG 595 cohort was dominated by the phyla Bacteroidetes and Firmicutes.\n\nPrevotellaceae was the most dominant family in all specimens, except three pre-PrEP samples (XNT, 5FX, and 7RJ), with average abundance of 36% across all 16 specimens.\n\nBefore the initiation of PrEP, the most prevalent family in participant XNT and participant 5FX was Streptococcaceae with relative abundances of 51% and 17%, respectively.\n\nThe most prevalent family in participant 7RJ prior to PrEP initiation was Fusobacteriaceae with 40% abundance.\n\nAcross 16 specimens from eight participants, the average abundance of Lachnospiraceae (11%), Fusobacteriaceae (9.1%), Family_XI (8.8%), and Streptococcaceae (6.6%) were observed to be greater than five percent.\n\nEach participant’s overall microbial diversity was comparable before and after PrEP.\n\nMicrobiome diversity within a single specimen was assessed by α diversity, Shannon diversity index.\n\nThe dissimilarity between a pair of specimens was assessed by β diversity which accounts for phylogenetic tree distances of microbial sequences in a pair of specimens.\n\nAs shown in Fig.\n\n5A, the average α diversity was 4.22 before PrEP and 4.95 after PrEP (Wilcoxon signed-rank test, p = 0.15).\n\nWe plotted the β diversity of each participant’s paired specimens in Fig.\n\n5B.\n\nAcross 8 pairs, The average β diversity across 8 pairs was 0.68 and the paired specimens of the participant XRQ showed the lowest level of β diversity.\n\nThe β diversity between each participant’s pre and post-PrEP specimens was smaller than the β diversity of pre-PrEP specimen pairs of different individuals (Wilcoxon rank sum test, p = 0.015).\n\nPrincipal coordinate analysis (PCoA) demonstrated that the pre-PrEP and post-PrEP specimens did not form distinct clusters (Fig.\n\n5C).\n\nThe principal coordinate analysis indicates that there is no global shift in the microbiota between the pre and post PrEP specimens.\n\nIndividual family and genus abundance changes were inquired through permutation tests in this study, observing that Erysipelotrichaceae and Streptococcus levels were significantly shifted by PrEP.\n\nNext we performed full-length 16S-23S rRNA long read sequencing to identify which species in Erysipelotrichaceae family and Streptococcus genus were affected by long-term PrEP.\n\nFigure 2 showed that participants XNT, WD5, WT9, XRQ, 7RJ, 5FX had changes in the abundance of either Erysipelotrichaceae or Streptococcus and from these participants, we obtained a total of 3363 reads of the 16S-23S rRNA region for species identification (Supplementary Table S2).\n\nFigure 6A compares the family composition of pre-PrEP and post-PrEP specimens for both v4–16S short read sequencing and 16S-23S long read sequencing.\n\nThe overall family profiles were similar; the family composition root-mean-square-error between v4-16S and 16S-23S sequencings ranged from 0.016 to 0.051 across each of 12 specimens from participants XNT, WD5, WT9, XRQ, 7RJ, 5FX.\n\nObservable differences in the microbiome profiles for the two sequencing methods were also present (Fig.\n\n6A).\n\nWe compared abundance changes in Erysipelotrichaceae and Streptococcus measured by v4-16S sequencing and 16S-23S long read sequencings (Fig.\n\n6B).\n\nPost-PrEP Erysipelotrichaceae increase measured by 16S-23S sequencing was more prominent than that by v4-16S sequencing.\n\nStreptococcus decrease measured by 16S-23S sequencing was consistent with that measured by v4-16S sequencing.\n\nErysipelotrichaceae increase after PrEP was mainly driven by the species Catenibacterium mitsuokai.\n\nHoldemanella biformis and Turicibacter sanguinis were also detected within this family (Fig.\n\n6C).\n\nBefore PrEP initiation, Streptococcus agalactiae, Streptococcus oralis, and Streptococcus mitis were the dominant species in the Streptococcus genus (Fig.\n\n6D).\n\nDiscussion\nPrEP use has increased substantially since 2012 and characterizing its long-term side effects is the first step to improve PrEP regimen and adherence1.\n\nTwo well-known side effects of TDF are kidney function decline and bone mineral density decrease5,6.\n\nRecent studies reported that long-term PrEP users showed impaired kidney function3 and a decrease in bone mineral density4.\n\nThe human gut microbiota is known to be correlated with both chronic kidney disease and osteoporosis.\n\nIncreases in uremic toxins and inflammation among chronic kidney disease patients were in part due to the gut microbiome’s role in the fermentation of short-chain fatty acids, which have an anti-inflammatory impact21.\n\nIntestinal bacterial overgrowth was associated with changes in essential metabolites for bone processes such as calcium, vitamin K, and vitamin B12.\n\nDuring a state of gut microbiome dysbiosis, gut microbiota can affect the absorption of calcium and vitamin D, which can lead to osteoporosis22.\n\nOur study profiled microbiome structures before and after long-term PrEP to identify microbiota signatures altered by TDF-FTC daily use, which have the potential to affect the kidney and bone health.\n\nWe observed that Streptococcus was significantly reduced from 12.0% to 1.2% and the Erysipelotrichaceae was significantly increased from 0.79% to 3.3% after a minimum of 48 weeks of daily PrEP among CCTG-595 study participants.\n\nThis cohort is at high risk of HIV-1 infection and has extensive demographic and clinical details including PrEP adherence data.\n\nBoth Streptococcus and Erysipelotrichaceae abundance changes were not associated with host factors including PrEP duration, age, race, TFV-DP level, any drug use status and drug abuse status, suggesting that the observed microbiome shifts were potentially induced by daily TDF-FTC use.\n\nBoth commensal and pathogenic species of Streptococcus have been found to coexist in the healthy human gut microbiome23.\n\nMembers of the Streptococcus genus have gut-protective influences.\n\nStreptococcus lactis, Streptococcus cremoris, and Streptococcus thermophilus are commonly found in both natural and commensal probiotics24,25.\n\nOur 16S–23S long read sequencing revealed that Streptococcus agalactiae, Streptococcus oralis, and Streptococcus mitis were the closest species significantly greater in pre-PrEP specimens compared to post-PrEP specimens.\n\nStreptococcus agalactiae has been reported to be a harmless commensal bacterium, colonized in the intestine26.\n\nStreptococcus oralis and Streptococcus mitis are both commensal bacterial which predominately reside in the oral cavity27 but these species were also found in fecal samples28.\n\nA common enteric side effect associated with TDF-FTC PrEP is a frequently cited reason for poor adherence to PrEP schedules29.\n\nHowever, this adverse effect, termed “PrEP start up syndrome”, is usually observed within the first month of TDF-FTC PrEP and resolves spontaneously by 3 months of treatment30,31.\n\nHowever, our post-PrEP specimens were collected 48–72 weeks after PrEP initiation.\n\nTherefore, a direct association between the enteric side effects and Streptococcus reduction should be further investigated at the time of PrEP start up syndrome.\n\nAdditionally, the observed microbiota differences found using rectal swab specimens may not be comparable to those from other specimen types, collected from different gastrointestinal sites using mucosal biopsies32,33.\n\nTDF-FTC also appeared to significantly increase the level of Erysipelotrichaceae, a family of bacteria that many species are considered opportunistic pathogens.\n\nErysipelotrichaceae has been studied in conjunction with colorectal cancer and metabolic disorders34.\n\nErysipelotrichaceae was significantly enriched in patients with colorectal cancer, compared to healthy controls35.\n\nSimilarly, an increase in Erysipelotrichaceae abundance was reported in colorectal tumor-bearing mice36.\n\nAdditionally, Erysipelotrichaceae was increased in obese individuals37.\n\nOur long read sequencing showed that Catenibacterium mitsuokai, Holdemanella biformis and Turicibacter sanguinis were bacterial species increased after long-term PrEP within Erysipelotrichaceae family.\n\nBoth Catenibacterium mitsuokai and Holdemanella biformis were associated with gut microbiome dysbiosis caused by high fat and high sugar diet38 and an unhealthy fasting lipid profile39.\n\nCollectively, we speculate that the observed increase in Erysipelotrichaceae in the long-term PrEP treated cohort has a potential to contribute to an increased the risk of colorectal cancer and metabolic disorders, while this increase was due to other factors including dietary factors.\n\nThis speculation is worth further investigation with long-term follow-up of PrEP treated individuals.\n\nIn conclusion we observed that Streptococcus were decreased and Erysipelotrichaceae were increased following daily TDF-FTC for PrEP.\n\nBecause this study is limited by the small population size, these microbiome shifts should be further examined in a large cohort in conjunction with long-term outcomes.\n\nIdentifying PrEP microbiota signatures is an important step toward treating and preventing side effects, which is likely to improve PrEP adherence, and thus HIV-1 prevention.\n\nMethods\nStudy participants\nSelf-collected rectal swab specimens from eight individuals at baseline (pre-PreP) and after taking TDF-FTC daily for 48 to 72 weeks in the California Collaborative Treatment Group (CCTG) study 595 (NCT01761643) were examined18.\n\nParticipants were given a tube with a sterile Dacron rectal swab, along with safety precautions and instructions for rectal swab self-collection.\n\nThe rectal swab was immediately placed in a sterile 15 ml plain conical tube without media, and the screw cap was secured.\n\nThe tube containing the sample was transported to the laboratory at room temperature and frozen at −80 °C within two hours of collection.\n\nCCTG 595 was a randomized controlled trial in high risk MSM and transgender women to compare the impact of daily text messaging to standard care on adherence to daily TDF-FTC18.\n\nRegimen adherence was assessed at 48 weeks by testing dried blood spots for tenofovir diphosphate (TFV-DP).\n\nThis study included only participants with intracellular TFV-DP levels greater than 719 fmol/punch at week 48 weeks, a level associated with taking four or more doses of TDF a week40.\n\nAlcohol and substance use were assessed using the SCID substance use screening questionnaire, DAST-10, and AUDIT questionnaires.\n\nNone of the participants reported diarrhea.\n\nThe participants’ dietary intake information is not available, which can be an important factor for microbial composition.\n\nSix of eight participants reported rectal douching at baseline, one participant reported no use of rectal douching, and one participant declined to answer.\n\nAll participants signed an informed consent document subject to approval at each site’s IRB (University of Southern California, University of California, San Diego, and Harbor-University of California, Los Angeles).\n\nAll the procedures and experiments were conducted in accordance with relevant guidelines and regulations.\n\nMicrobiome DNA extraction\nThe previously frozen swabs were placed in a sterile 1.5 ml Eppendorf tube and the excess swab handle was removed using sterile razor blades or scissors.\n\nMicrobiome DNA was extracted using the Omega Mag-Bind Universal Pathogen DNA Kit (OMEGA bio-tek).\n\nGlass beads, 700 µL of SLX-Mlus Buffer were added to the thawed swab specimen.\n\nAfter 1 minute of vortexing, the tube was centrifuged at 1500 g for 5 minutes.\n\n250 µL of the supernatant was collected, 275 µL SLX-Mlus Buffer was added, and heated to 65 °C for 10 minutes and 95 °C for 10 minutes.\n\nSpecimens were vortexed at maximum speed using a horizontal adapter (Qiagen) for 8 minutes.\n\nAfter the elution, specimens were purified and concentrated using a Clean & Concentrator-5 kit (Zymo Research).\n\nThe sample concentration was measured using PicoGreen (Invitrogen).\n\n16S ribosomal RNA sequencing\nThe next-generation sequencing library of the V4 region of the 16S rRNA gene was constructed by the following procedures.\n\nThe extracted microbiome DNA was amplified using primers 515F-over (5′-TCGTCGGCAGCGTCAGATGTGTATAAGAGACAGGTGCCAGCMGCCGCGGTAA-3′) and 805R-over (5′- GTCTCGTGGGCTCGGAGATGTGTATAAGAGACAGGACTACHVGGGTATCTAATCC-3′) in a reaction volume of 20 µL (5 µL of 0.2 ng/ µL extracted DNA, 13 µL AccuStart II PCR ToughMix, 0.25 µL of 20 µM 515F-over, 0.25 µL of 20 µM 805R-over and 1.5 µL nuclease-free water).\n\nThe PCR condition was at 94 °C for 3 minutes, followed by 35 cycles of 94 °C for 30 seconds, 60 °C for 30 seconds, then 70 °C for 90 seconds with a final extension at 70 °C for 10 minutes.\n\nThe PCR product was purified using Agencourt AMPure XP (Beckman Coulter).\n\nThe index PCR was then performed using primers S5xx (5′-AATGATACGGCGACCACCGAGATCTACACxxxxxxxxTCGTCGGCAGCGTC-3′) and N7xx (5′-CAAGCAGAAGACGGCATACGAGATxxxxxxxxGTCTCGTGGGCTCGG-3′) in a reaction volume of 50 µL (4 µL of purified PCR product, 25 µL AccuStart II PCR ToughMix, 16 µL nuclease-free water, 2.5 µL of 4 µM S5xx and 2.5 µL of 4 µM N7xx).\n\nThe PCR condition was at 94 °C for 3 minutes, followed by 8 cycles of 94 °C for 30 seconds, 45 °C for 30 seconds, 70 °C for 120 seconds and 10 cycles of 94 °C for 30 seconds, 60 °C for 30 seconds, 70 °C for 120 seconds with a final extension at 70 °C for 10 minutes.\n\nThe PCR product was purified using Agencourt AMPure Xp (Beckman Coulter).\n\nEach sample concentration was determined using PicoGreen (Invitrogen), normalized and pooled and sent to the University of California, Los Angeles Technology Center for Genomics and Bioinformatics for Illumina MiSeq sequencing.\n\n16S–23S ribosomal RNA sequencing\nWe performed 16S-23S rRNA long read sequencing on pre-PrEP and post-PrEP specimens from participants XNT, WD5, WT9, XRQ, 7RJ, 5FX.\n\nAdditionally, a microbiome standard (ATCC, MSA-1001) consisting of 10 control strains was sequenced.\n\nEach participant’s extracted microbiome DNA (as described above) was amplified using primers 27F (5′-AGAGTTTGATCMTGGCTCAG-3′) and 2409R23 (5′-GACATCGAGGTGCCAAAC-3′), targeting around 4500 base long 16S-23S rRNA region.\n\nPCR was performed in a reaction volume of 20 µL (5 µL of 0.2 ng/ µL extracted DNA, 13 µL of 2x AccuStart II PCR ToughMix, 1.5 µL nuclease-free water, 0.25 µL of 20 µM 27 F and 0.25 µL of 20 µM 2409R23).\n\nThe PCR condition was 94 °C for 3 minutes, 35 cycles of 94 °C for 30 seconds, 60 °C for 30 seconds, 70 °C for 5 minutes, and a final extension at 70 °C for 10 minutes.\n\nThe PCR product was purified with 1.8x Ampure XP Beads, washed twice with 70% ethanol, and eluted in 20 µL of nuclease free water.\n\nThe purified samples were then set up for an index PCR to barcode each sample using primers, 27Fxx (5′-xxxxxxxxxxxxAGAGTTTGATCMTGGCTCAG-3′) and 2409R23xx (5′-xxxxxxxxxxxxGACATCGAGGTGCCAAAC-3′).\n\nThe index PCR was performed in a 50 µL reaction volume with 5 µL of purified PCR product, 25 µL AccuStart II PCR ToughMix, 17.6 µL nuclease-free water, 1.2 µL of 4 µM 27Fxx and 1.2 µL of 4 µM 2409R23xx.\n\nThe PCR condition was at 94 °C for 3 minutes, followed by 10 cycles of 94 °C for 30 seconds, 63 °C for 20 seconds, 70 °C for 5 minutes, and a final extension at 70 C for 10 minutes.\n\nThe index PCR condition for specimen pre-PrEP 5FX was modified by increasing primer volumes (2.5 µL), increasing the purified PCR product volume (7 µL), lowering the annealing temperature (60 °C), and increasing annealing time (60 °C for 30 seconds).\n\nA PicoGreen assay was performed to determine the concentration of each sample.\n\nEquimolar amounts of each of 13 samples were pooled and shipped overnight on dry ice to RTL genomics for PacBio sequencing.\n\nAfter arrival, the samples were checked for concentration using the dsDNA Broad Range DNA kit on the Qubit Fluorometer 3.0 and quality checked with a Fragment Analyzer by Advanced Analytical Technologies using the High Sensitivity Large Fragment 50KB Analysis kit, which were subject to SMRTbell library preparation for PacBio Sequencing.\n\nThis process began with a 0.5x Ampure PB Purification A total of 600 ng of DNA was used for creating circularized double stranded DNA templates by ligating hairpin adaptors to each side of templates.\n\nFollowing the overnight ligation, the circular templates were purified with AMPure PB Beads and SMRTbell sequencing primers were annealed to the adaptors.\n\nThe dsDNA templates were then prepared for loading with a final concentration of 6 pM to initiate SMRTbell template sequencing.\n\nSequence data analysis\nThe forward and reverse reads obtained from the MiSeq sequencing run were assembled using the command, make.contigs in MOTHUR41.\n\nThe obtained fasta file was screened for the presence of ambiguous bases and any reads with such bases were discarded.\n\nThe reads were then subjected to taxonomy annotation after putative chimeric sequences were removed using chimera.uchime.\n\nThe Silva full length sequences and taxonomy references, consisting of 190,661 sequences (release 128), were used for taxonomy annotation42.\n\nTo expedite taxonomy annotation, clustering was performed using pre.cluster by grouping reads that are within one mismatch of each other.\n\nSupplementary Table S1 shows the number of total reads and unique reads, prior to processing and post processing for each of the 16 specimens sequenced in this study.\n\nEach read obtained from a 16S-23S rRNA sequencing run was subjected to taxonomy annotation after removing putative chimeric sequences and clustering.\n\nBLAST with NCBI nucleotide collection database was used to find the bacterial species with the best match for each read.\n\nWhen the best matched strain showed less than 90% identity or the length of the best matched strain was less than 25% of each read length, the read was labeled as unclassified.\n\nEach specimen’s α diversity with the Shannon diversity index was measured using alpha_diversity.py in QIIME43.\n\nTo calculate β diversity, all 16 specimens’ fasta files were combined as a single file.\n\nClosely related sequences with similarities greater than 97% were grouped as an operational taxonomic unit (OTU) using pick_otus.py in QIIME and each OTU’s representative sequence was picked using pick_rep_set.py.\n\nThe selected representative sequences were aligned using align_seqs.py with the MUSCLE algorithm.\n\nThen the OTU table and phylogenetic tree were obtained using make_otu_table.py and make_phylogeny.py, respectively.\n\nUsing QIIME jackknifed_beta_diversity.py, jackknife resampling was performed by sampling 1% of the total sequences and repeated 10 times to obtain specimen pair’s β diversity matrices and principal coordinate analysis (PCoA) plots.\n\nPermutation t test\nWe statistically examined differences in family or genus abundance between pre-PrEP and post-PrEP specimens.\n\nThe standard t-tests for paired measurements assume independence, normality, and constant variance.\n\nWith abundance proportions, it is likely that normality and constant variance are not held and the sample size is not large enough to use approximate normality of the mean.\n\nInstead, we conducted a permutation test in order to empirically assess the asymptotic p-values.\n\nThe permutation test has been widely recommended in multiple statistical testing44,45,46.\n\nFor each family or genus, a t-statistic was computed on the observed diversity data as follows:\n$$t=\frac{POS{T}_{av}-PR{E}_{av}}{\sqrt{(POS{T}_{var}+Pr{e}_{var})/n}},$$\n(1)\nwhere n is the number of participants, POSTav (PREav) is the average abundance of a given family or genus among post-PrEP (pre-PrEP) specimens, and POSTvar (PREvar) is the abundance variance of a given family or genus among post-PrEP (pre-PrEP) specimens.\n\nThe PrEP status was then randomly permuted, holding the numbers of pre-PrEP and post-PrEP specimens constant over permutations; a total of 100,000 such permutations were completed.\n\nA t-statistic in Eq.\n\n(1) was computed for each permutation and the empirical p-value of each family or genus was calculated as the proportion of permutations with a t-test statistic greater than or equal to the t-test statistic derived from the actual data when the original t value was greater than zero.\n\nOtherwise, the empiric p-value was determined as the proportion of permutations with a t-test statistic less than or equal to the negative original t value.\n\nBased on this empirical p-value, the families or genera with significant differences in abundance between pre-PrEP and post-PrEP were determined.\n\nWe also performed paired permutation tests for a given family or genus where we permuted each participant’s pre-PrEP and post-PrEP abundance values, yielding a total of 2n permutations.\n\nFor each permutation, a t-statistic was measured and the empirical p-value was obtained from the proportion of permuted t-statistics that were more extreme than the observed data t-statistic.\n\nData Availability\nAll microbiome sequence data from this study are available at EBI with accession numbers PRJEB29018 and PRJEB29019.\n\n----------\nAs a professional microbiologist, create a concise and comprehensive Chinese scientific report on Erysipelothrix Spp. research based on the provided text, whether it's an article, post, conversation, or passage. Follow these guidelines:\n\n 1. Produce a detailed and in-depth report that remains clear and concise.\n 2. Focus on main ideas and essential information, removing any extraneous language.\n 3. Strictly rely on the provided text without adding external information.\n 4. Format the report in paragraphs for easy understanding.\n 5. Conclude with “[End of Notes, Message #X],” where “X” represents the total number of messages I’ve sent. Increment the message counter with each new message.\n 6. Use English for technical terms, industry terminology, proper nouns, and species names. After you finish, add the following words: {{{ I_finished_papa!!! }}} to the end of you answer