DEVELOPMENT AND TESTING OF A LOW-COST INACTIVATION BUFFER THAT ALLOWS DIRECT SARS-COV-2 DETECTION IN SALIVA

Massive testing is a cornerstone in efforts to effectively track infections and stop COVID-19 transmission, including places where good vaccination coverage has been achieved. However, SARS-CoV-2 testing by RT-qPCR requires specialized personnel, protection equipment, commercial kits, and dedicated facilities, which represent significant challenges for massive testing implementation in resource-limited settings. It is therefore important to develop testing protocols that facilitate implementation and are inexpensive, fast, and sufficiently sensitive. In this work, we optimized the composition of a buffer (PKTP) containing a protease, a detergent, and an RNase inhibitor, that is compatible with the RT-qPCR chemistry, allowing for direct testing of SARS-CoV-2 from saliva in an RNA extraction-independent manner. This buffer is compatible with heat-inactivation reducing the biohazard risk of handling the samples. We assessed the PKTP buffer performance in comparison to the RNA-extraction-based protocol of the US Centers for Disease Control and Prevention in saliva samples from 70 COVID-19 patients finding a good sensitivity (82.2% for the N1 and 84.4% for the N2 target, respectively) and correlations (R=0.77, p<0.001 for N1, and R=0.78, p<0.001 for N2). We also propose an auto-collection protocol for saliva samples and a multiplex reaction to reduce the number of PCR reactions per patient and further reduce overall costs while maintaining diagnostic standards in favor of massive testing.

A procedure to detect 6 basic STSs and 11 extended STSs in the AZF region using multiplex PCR

Microdeletions of Y chromosomes frequently occur in 3 subregions of the AZF, namely, AZFa, AZFb, and AZFc, with 6 basic STS marker sequences, which are sY84, sY86 (AZFa), sY127, sY134 (AZFb), and sY254, sY255 (AZFc). According to EAA/EMNQ guidelines, 11 additional AZFabc marker sequences should be used to determine the extent of the microdeletion in the AZF region of infertile men, which is known as 11 extended STSs. By applying mPCR, the authors develop an optimal detection procedure for the 6 basic STS and 11 extended STS using 3 multiplex PCR reactions. The first multiplex PCR reaction includes 6 basic STS plus the 2 control sequences sex-determining region Y (SRY) and zinc finger protein X/Y-linked (ZFX/Y). The second multiplex PCR reaction includes the 6 extended STS sY88, sY1182, sY105, sY121, sY1191, and sY1291 and the 2 control sequences SRY and ZFX/Y. The third multiplex PCR reaction includes the 5 extended STS sY153, sY160, sY82, sY143, and sY83 and the 2 control sequences SRY and ZFX/Y. Six basic primer sequences and eleven extended primer sequences are redesigned to simultaneously pair and amplify STS in the same multiplex reaction: set of 8 primers for 6 basic STS: 6 basic STS + 2 (SRY, ZFX/Y), 8 extension primers set E1: 6 extended STS + 2 (SRY, ZFX/Y), and 7 extension primers set E2: 5 extended STS + 2 (SRY, ZFX/Y). We successfully designed primer pairs with high specificity and stability and successfully amplified 6 basic STS and 11 extended STS, which ensures that the STSs have the correct sequence as recommended by EAA/EMQN and are consistent with the NCBI gene bank. This study has successfully developed a procedure to simultaneously detect 17 STSs, including 6 basic STSs and 11 extended STSs in the AZF region using 3 multiplex PCR reactions.

Combination of quadruplex qPCR and next-generation sequencing for qualitative and quantitative analysis of the HIV-1 latent reservoir

HIV-1 infection requires lifelong therapy with antiretroviral drugs due to the existence of a latent reservoir of transcriptionally inactive integrated proviruses. The goal of HIV-1 cure research is to eliminate or functionally silence this reservoir. To this end, there are numerous ongoing studies to evaluate immunological approaches, including monoclonal antibody therapies. Evaluating the results of these studies requires sensitive and specific measures of the reservoir. Here, we describe a relatively high-throughput combined quantitative PCR (qPCR) and next-generation sequencing method. Four different qPCR probes covering the packaging signal (PS), group-specific antigen (gag), polymerase (pol), and envelope (env) are combined in a single multiplex reaction to detect the HIV-1 genome in limiting dilution samples followed by sequence verification of individual reactions that are positive for combinations of any two of the four probes (Q4PCR). This sensitive and specific approach allows for an unbiased characterization of the HIV-1 latent reservoir.

Comparative Analysis of Verification Parameters of Event-Specific Methods in GMO Maize

The second most dominant genetically modified (GM) crop is maize. Increasing number of GM maize events puts significant pressure on GMO testing laboratories to achieve the level of competence necessary to fulfill legal requirements. In the European Union, Polymerase Chain Reaction (PCR) is the method of choice for identification and quantification of GMOs. We performed verification of validated methods for identification of four GM maize events. Additionaly we aimed to explore the option of designing a method for simultaneous detection of these events in a multiplex PCR reaction. DNA was extracted from certified reference materials (CRM) using validated CTAB extraction protocol. Concentration of DNA was measured using Qubit dsDNA Broad Range Assay. Amplification of taxon specific marker for maize and all event-specific methods was performed according to the JRC Compendium of Reference Methods for GMO Analysis. Absolute limit of detection (LODabs) was determined for taxon specific and four event specific RealTime PCR based methods. DNA extracted from CRMs showed sufficient concentration for downstream analyses and preparation of dilutions for determination of LODabs. Determined LODabs for all tested methods meet acceptance criteria. As expected, the methods performance with respect to the repeatability and precision decline with the decrease in concentration of the target. Event-specific GA21 and NK603 methods show high Ct values at the determined LODabs. However, by adjusting the concentrations of primers and probes sensitivity of these two methods should be improved. Considering that the amplicons for all five methods are quite short (<120 bp) optimization of multiplex reaction conditions for simultaneous amplification should be feasible

Detection of Nicotiana DNA in Tobacco Products Using a Novel Multiplex Real-Time PCR Assay

Establishing that a product contains tobacco is a requirement for the U.S. Food and Drug Administration's regulation and/or prosecution of tobacco products. Therefore, a multiplex real-time PCR method was designed to determine if Nicotiana (tobacco) DNA is present in tobacco products. The PCR method simultaneously amplifies a 73 bp fragment of the cytochrome P450 monoxygenase CYP82E4 gene and 66 bp fragment in the nia-1 gene for nitrate reductase, which are detected using dual-labeled TaqMan probes. The assay is capable of detecting approximately 7.8 pg purified tobacco DNA, with a similar sensitivity for either gene target while incorporating an internal positive control (IPC). DNA was extracted from prepared tobacco products—including chewing tobacco, pipe tobacco, and snuff—or from the cut fill (no wrapper) of cigarettes and cigars. Of the 13 products analyzed, 12 were positive for both tobacco-specific markers and the IPC. DNA was also extracted from the fill of five varieties of herbal cigarettes, which were negative for both tobacco-specific gene targets and positive for the IPC. Our method expands on current assays by introducing a multiplex reaction, targeting two sequences in two different genes of interest, incorporating an IPC into the reaction, and lowering the LOD and LOQ while increasing the efficiency of the PCR.

Improving genetic monitoring of the northern hairy-nosed wombat (Lasiorhinus krefftii)

The endangered northern hairy-nosed wombat (Lasiorhinus krefftii) has been monitored via remote sampling and genetic techniques since 2000, thus avoiding the detrimental effects on the animals of trapping and increasing the precision of abundance estimates. The currently available dinucleotide microsatellite markers used for this task are prone to stutter and other polymerase chain reaction artefacts, making allele calling difficult, and requiring costly duplication to ensure accuracy. To remedy this we have developed eight new tri- and tetranucleotide microsatellite markers that reduce the problem of stutter in DNA analysis. These new markers, along with three of the existing markers (two microsatellites and the SRY gender marker) were optimised in a single multiplex reaction that will reduce the time and cost of future northern hairy-nosed wombat hair censuses. We tested this new multiplex on 277 non-invasively collected hairs. One locus was rejected due to null-allele issues. The remaining nine microsatellite loci had two or three alleles. Genotype frequencies in the sample of detected individuals did not differ significantly from Hardy–Weinberg equilibrium and there was no evidence of linkage disequilibrium. This new multiplex provides comparable power to distinguish individuals, fewer issues with stutter artefacts and a reduced time and cost of analysis. It will be useful for future population censuses and long-term monitoring of individuals once they have been scored in previously genotyped and assigned samples.