Oligonucleotide Microchip for the Identification of Infectious Agents of Reproductive System with Simultaneous Analysis of Determinants of Resistance to Antimicrobial Substances

Hydrogel Droplet Microarray for Genotyping Antimicrobial Resistance Determinants in Neisseria gonorrhoeae Isolates

A multiplex assay based on a low-density hydrogel microarray was developed to identify genomic substitutions in N. gonorrhoeae that determine resistance to the currently recommended treatment agents ceftriaxone and azithromycin and the previously used drugs penicillin, tetracycline, and ciprofloxacin. The microarray identifies 74 drug resistance determinants in the N. gonorrhoeae penA, ponA, porB, gyrA, parC, rpsJ, mtrR, bla_TEM, tetM, and 23S rRNA genes. The hydrogel elements were formed by automated dispensing of nanoliter-volume droplets followed by UV-induced copolymerization of NH₂-containing oligonucleotides with gel-forming monomers. Polybutylene terephthalate plates without special modifications were used as microarray substrates. Sequences and concentrations of immobilized oligonucleotides, gel composition, and hybridization conditions were carefully selected, and the median discrimination ratio ranged from 2.8 to 29.4, allowing unambiguous identification of single-nucleotide substitutions. The mutation identification results in a control sample of 180 N. gonorrhoeae isolates were completely consistent with the Sanger sequencing results. In total, 648 clinical N. gonorrhoeae isolates obtained in Russia during the last 5 years were analyzed and genotyped using these microarrays. The results allowed us to draw conclusions about the present situation with antimicrobial susceptibility of N. gonorrhoeae in Russia and demonstrated the possibility of using hydrogel microarrays to control the spread of antibiotic resistance.

Prediction of ceftriaxone MIC in Neisseria gonorrhoeae using DNA microarray technology and regression analysis

BACKGROUND

Decreased susceptibility of Neisseria gonorrhoeae to extended-spectrum cephalosporins is a major concern. Elucidation of the phenotypic and genetic characteristics of such isolates is a priority task.

METHODS

We developed a method for predicting the N. gonorrhoeae ceftriaxone susceptibility level (MICcro) by identifying genetic determinants of resistance using low-density hydrogel microarrays and a regression equation. A training dataset, containing 5631 isolates from the Pathogenwatch database and 181 isolates obtained in the Russian Federation during 2018-19, was used to build a regression model. The regression equation was tested on 14 WHO reference strains. Ceftriaxone resistance determinants for the 448 evaluated clinical isolates collected in Russia were identified using microarray analysis, and MICcro values were calculated using the regression equation and compared with those measured by the serial dilution method.

RESULTS

The regression equation for calculating MICcro values included 20 chromosomal resistance determinants. The greatest contributions to the increase in MICcro were shown to be PBP2: Ala-501→Pro, Ala-311→Val, Gly-545→Ser substitutions, Asp(345-346) insertion; and PorB: Gly-120→Arg substitution. The substitutions PBP2: Ala-501→Thr/Val, PorB: Gly-120→Asn/Asp/Lys and PBP1: Leu-421→Pro had weaker effects. For 94.4% of the isolates in the evaluation set, the predicted MICcro was within one doubling dilution of the experimentally determined MICcro. No ceftriaxone-resistant isolates were identified in the analysed samples from Russia, and no interpretative errors were detected in the MICcro calculations.

CONCLUSIONS

The developed strategy for predicting ceftriaxone MIC can be used for the continuous surveillance of known and emerging resistant N. gonorrhoeae isolates.

Molecular Typing of Neisseria gonorrhoeae Clinical Isolates in Russia, 2018-2019: A Link Between penA Alleles and NG-MAST Types

This work aimed to study penA gene polymorphisms in clinical isolates of Neisseria gonorrhoeae collected in Russia in 2018-2019 and the contribution of the penA allele type to susceptibility to β-lactam antibiotics. A total of 182 isolates were analyzed. penA allele types were determined by sequencing, and the minimum inhibitory concentrations (MICs) of benzylpenicillin and ceftriaxone were measured. The influence of genetic factors on MICs was evaluated by regression analysis. All isolates were susceptible to ceftriaxone, and 40.1% of isolates were susceptible to penicillin. Eleven penA allele types were identified. The mosaic type XXXIV penA allele and the Gly120Lys substitution in PorB made the greatest contributions to increasing the ceftriaxone MIC; the presence of the bla_TEM plasmid, Gly120Asp, Ala121Gly/Asn substitutions in PorB, and the adenine deletion in the promoter region of the mtrR gene caused an increase in the penicillin MIC. Among 61 NG-MAST types identified, the most frequent were types 228, 807, 9486, 1993, and 6226. A link between penA alleles and Neisseria gonorrhoeae multi-antigen sequence typing (NG-MAST) types was established. Resistance to two groups of β-lactam antibiotics was associated with non-identical changes in penA alleles. To prevent the emergence of ceftriaxone resistance in Russia, NG-MAST genotyping must be supplemented with penA allele analysis.

A novel peptide nucleic acid- and loop-mediated isothermal amplification assay for the detection of mutations in the 23S rRNA gene of Treponema pallidum

Introduction. Macrolides could be a potential alternative treatment for Treponema pallidum infections in patients; however, macrolide-resistant T. pallidum is spreading rapidly worldwide.Hypothesis/Gap Statement. There are presently no alternatives to serological tests for syphilis that can be used to evaluate therapeutic effects due to the fact that T. pallidum cannot be cultured in vitro.Aim. In this study, we constructed a method for rapidly identifying T. pallidum and confirming macrolide resistance by using loop-mediated isothermal amplification (LAMP) with peptide nucleic acids (PNAs).Methodology. A set of LAMP primers was designed to span nucleotide positions 2058 and 2059 in 23S rRNA. A PNA clamping probe was also designed to be complementary to the wild-type sequence (A2058/A2059) and positioned to interfere with both the annealing of the 3' end of the backward inner primer and the concomitant extension. Prior to the LAMP assay, swab samples from suspected syphilitic lesions were boiled for DNA extraction.Results. The assay had an equivalent detection limit of 1.0×10¹ copies/reaction and showed specificity against 38 pathogens. In the presence of a 4 µM PNA probe, LAMP amplified up to 1.0×101 copies/reaction using plasmids harbouring the complementary mutant sequences (A2058G or A2059G), whereas amplification was completely blocked for the wild-type sequence up to a concentration of 1.0×10³ copies/reaction. For the 66 PCR-positive clinical specimens, the overall detection rate via LAMP was 93.9 % (62/66). Amplification was successful for all 53 mutant samples and was incomplete for all nine WT samples by the PNA-mediated LAMP assays.Conclusion. We developed a PNA-mediated LAMP method that enabled us to rapidly identify T. pallidum and determine its macrolide susceptibility via a culture-independent protocol.

Resistance of Neisseria gonorrhoeae isolates to beta-lactam antibiotics (benzylpenicillin and ceftriaxone) in Russia, 2015-2017

The goal of this work was to study the phenotypic susceptibility and resistance determinants of N. gonorrhoeae isolates to beta-lactam antimicrobials (benzylpenicillin and ceftriaxone). A total of 522 clinical isolates collected in Russia in 2015–2017 were analysed for susceptibility using the agar dilution method. DNA loci involved in antimicrobial resistance were identified using DNA microarray analysis and sequencing. Resistance to benzylpenicillin remained high, with 7.7% of isolates resistant (MIC_pen > 1 mg/L) and 47.5% of isolates showing intermediate susceptibility (MIC_pen = 0.12–1 mg/L). The most frequent resistance determinant (72.4% isolates) was the Asp345 insertion in penA, both as a single mutation and in combination with other mutations, particularly with the substitution Leu421Pro in ponA (39.0%). Mutations affecting the influx and efflux of drugs were also found, including amino acid substitutions in PorB (26.8% isolates) and delA in the promoter region of mtrR (22.8%). The accumulation of mutations in chromosomal genes (penA, pon, porA, and mtrR) led to a stepwise increase in MIC_pen to values characteristic of intermediate resistance. The presence of bla_TEM plasmids was found in 25 isolates (4.8%), resulting in a strong increase in resistance to penicillin (MIC_pen > 16 mg/L) compared with the chromosomal mutations; 23 plasmids were of the African type with TEM-1 beta-lactamase, and two plasmids were of the Toronto/Rio type with TEM-135 beta-lactamase. Only three isolates were found with reduced susceptibility to ceftriaxone, with MIC_cef = 0.12–0.25 mg/L. Sequencing of penA did not reveal mutations associated with resistance to third-generation cephalosporins, and the gene structure was non-mosaic. The majority of isolates (21 of 25) carrying the bla_TEM plasmid also contained the conjugative plasmid with tetM (resistance to tetracyclines), consistent with previously reported data that the presence of the conjugative plasmid facilitates the transfer of other plasmids associated with antimicrobial resistance.

Tetracycline resistance of Neisseria gonorrhoeae in Russia, 2015-2017

The objective of this study was to estimate the tetracycline resistance level in the modern population of Neisseria gonorrhoeae in the Russian Federation, where this drug was removed from the treatment regimen for gonococcal infections in 2003. A total of 401 isolates collected between 2015 and 2017 were analyzed for genetic markers (chromosomal porB, rpsJ and mtrR gene mutations and the plasmid-located tetM gene) involved in tetracycline resistance. Antibiotic susceptibility testing revealed that 19% of the strains were tetracycline resistant (MIC > 1 mg/L) and that 10% of the strains had intermediate susceptibility (0.5 < MIC ≤ 1 mg/L). Various combinations of mutations identified in the rpsJ (Val57Met/Leu), porB (Gly120Lys/Asp/Asn/Thr and Ala121/Asp/Asn/Gly), and mtrR (-35 del A) genes resulted in MIC increases of up to 1.47 mg/L (geometric mean value). The presence of the tetM gene was detected in 29 strains, including 18 tetM genes of the American type and 11 of the Dutch type. The tetM gene was associated with a strong increase in resistance (MIC > 8 mg/L). One N. gonorrhoeae isolate was found to carry a defective tetM gene with an AG deletion at position 1239-1240, а new stop codon was introduced that caused a defect in TetM protein synthesis and decrease in the tetracycline resistance. Phylogenetic trees constructed using N. gonorrhoeae NG-MAST and tetM loci were compared. Complex relationship was observed between the N. gonorrhoeae sequence type and the tetM plasmid type. Partial recovery of N. gonorrhoeae tetracycline susceptibility was observed relative to the proportion of isolates with resistance detected ten years ago (75%). However, the current levels of tetracycline resistance still preclude the renewed use of these drugs for gonococcal infection therapy.