Data collection
The present study, based on a cross-sectional, analytical approach, lasted from February to December 2019. The study involved female students (n = 686) attending different campus from a public university in the Brazilian state of Pará, including 482 students from the state capital, Belém and 204 from campi in three other urban centers in the interior of the state (Altamira [interior 1], Bragança [interior 2], and Castanhal [interior 3]). All the individuals were invited to participate in the study. Prior contact with the students was supported by collaborators on each university campus, and local radio stations announced the dates and places of sample collection. The exclusion criteria were pregnancy, menstruation, and either not wishing to participate in the study or not signing the informed consent form. The participants were required to fill in a questionnaire and were informed about the importance of providing reliable answers, in order to minimize possible biases in the study. The specific variables investigated in the present study were: age, conjugal status, household income (in multiples of the Brazilian minimum wage), use of tobacco, consumption of alcoholic beverages, age at fist sexual intercourse, lifetime number of sexual partners, current relationship, use of condoms, history of miscarriage, and gynecological disorders. Cervical secretions were collected during routine pelvic examinations using an endocervical brush, and the samples were stored in cryogenic tubes containing 1 ml Tris-EDTA buffer [10 mM Tris-HCl pH 8.5; 1 mM EDTA] at a temperature of -20ºC prior to testing.
Extraction Of The Dna
The DNA was extracted using a pureLink Genomic DNA Purification kit (Invitrogen, Carlsbad, CA, USA) according to the manufacturer's instructions and stored at -20°C until analysis. A Polymerase Chain Reaction (PCR) of the human β-globin gene was conducted prior to the detection of C. trachomatis, in order to confirm the suitability of the samples.
Detection of the ompA gene of C. trachomatis
The C. trachomatis DNA sequence was amplified using a nested PCR protocol modified by Jalal et al. (2007) [47], which produced a sequence of 394 base pairs (bps) of the ompA gene of C. trachomatis. The first reaction used 6.0 µL of GoTaq Green Master mix (Promega, Madison, WI, USA), 0.5 µL (20 pmol/µL of each primer) of the primers P1 (A) (5'GACTTTGTTTTCGACCGTGTT-3 ') and P2 (5'AGCRTATTGGAAAGAAGCBCCTAA-3 '), 2 µL of the genomic DNA, and 3 µL of sterile water for a final volume of 12 µL. The second reaction used 0.5 µL of the solution of the first reaction, 6.0 µL of Go Taq Green Master mix (Promega, Madison, WI, USA), 4.5 µL of sterile water, and 0.5 µL (20 pmol/µL) of the primers P3 (5'-AAACWGATGTGAATAAAGARTT-3̕) and P4 (5'-TCCCASARAGCTGCDCGAGC-3̕). In both steps of the nested PCR, negative and positive controls were used to optimize the results. Initial activation was conducted at 95°C in both stages of the PCR, but whereas this temperature was maintained for 5 minutes in the first stage, it was maintained for only 1 minute in the second stage. This activation was followed by 35 cycles of denaturation at 94°C for 40 s, annealing at 54°C for 30s, and extension at 72°C for 90 s, with a final extension step at 72°C for 7 min. The amplified products were visualized by electrophoresis in 1% agarose gel with 0.5 mg/mL of ethidium bromide.
Dna Sequencing
The Sanger method of nucleotide sequencing was used. An approximately 990bp fragment of the ompA gene was amplified by nested PCR using primers P1(B) (5′-ATGAAAAAACTCTTGAAATCGG-3′) and OMP2 (5′-ACTGTAACTGCGTATTTGTCTG-3′), and whenever re-amplification was necessary, the inner primers MOMP87 (5′-TGA ACC AAG CCT TAT GAT CGA CGG A-3′) and RVS1059 (5′-GCA ATA CCG CAA GAT TTT CTA GAT TTC ATC-3′) were used [48]. The first step of the nested PCR was run in a 0.5 µL volume containing 20 pmol/ µL of each primer P1(B) and OMP2 and 5.0 µL of the DNA extracted from the endocervical secretion, 14 µL of sterile water, 1.0 µL of MgCl2, 1.0 µL deoxynucleoside triphosphate (10mM), 2.5 µL of 10x buffer, and 0.5 µL of Hotstar Taq DNA Polymerase 1.5U (Qiagen). Amplification was run in a final reaction volume of 25 µl [48]. In the two steps of nested PCR a negative and a positive control was used to optimize the result, but these controls were not used in the sequencing.
In the initial step of the nested PCR, amplification conditions were 95°C for 5 min, followed by 40 cycles of 94°C for 30 s, 55°C for 30 s, and 72°C for 90 s, and a final extension at 72°C for 7 min. In the nested PCR, the MOMP87-RVS 1059 primer pair was used with 1.5 µl of the product of the first stage of the nested PCR, which was added to a final volume of 25 µl. The conditions of the second step of the nested PCR were the same as those described above, except for the annealing temperature which was 60°C, and the addition of 17.5 µl of sterile water [48].
The amplified products were visualized by ethidium bromide (0.5 mg/mL) staining after electrophoresis in 1% agarose gel. The products obtained by the nested PCR were purified using a BigDye Xterminator Purification kit (Applied Biosystems, Foster City, CA, USA) to sequence both strands. A BigDyeTerminator Cycle kit (Foster City, CA, USA) was used for the sequencing reaction, according to the manufacturer's instructions. The reaction mixtures were sequenced in an ABI 3130 (Applied Biosystems, Foster City, CA, USA).
Genotyping
The sequence obtained of ompA gene from the C. trachomatis was assembled using the CAP3 software, aligned with MAFFT v.7.221 and edited with the Geneious Bioinformatics suite v.8.1.7 and compared with sequences from other studies and available in the GenBank, from the BLAST program of the NCBI (National Center for Biotechnology Information Database) (https://www.ncbi.nlm.nih.gov/) which was also used to the deposit of the sequences obtained in this study. Phylogenetic analysis was performed using maximum likelihood (ML) analysis. Afterwards the phylogenetic reconstruction, also using the software. FastTree was performed using the 1000-replica non-parametric reliability test using the bootstraps method. Finally, the Evolview web server was used to edit the generated phylogenetic tree.
Ethics Statement
This study is part of the project “Detection and genotyping of C. trachomatis in university students attended at the cytopathology laboratory / UFPA: cytological and molecular analysis”. All methods were performed in accordance with the relevant guidelines and regulations. Our research was authorized by the Research Ethics Committee of the Center of Tropical Medicine, at the Federal University of Pará (process number: 103,571). All the participants were legally adult (older than 18 years of age) and provided their free and informed consent for their participation in the study in writing prior to the collection of the samples and the epidemiological data. All the data were analyzed with complete anonymity. The participants that tested positive for sexual infection by C. trachomatis were provided counseling and were referred for medical evaluation.
Statistical analysis
The data were analyzed using the Statistical Package for Social Sciences (SPSS) version 21.0 (SPSS, Chicago, Illinois). The Odds Ratio was used to verify the difference in the prevalence of this infection between the campi of the state capital and the other three urban centers. We pooled the individuals from these localities for the complementary analyses. The degree of association between the prevalence of sexual infection by C. trachomatis and the study variables were evaluated using Chi-square and Binominal Logistic regressions. The 95% confidence interval (CI) was calculated for these comparisons, and a p ≤ 0.05 significance level was considered for all analyses.