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Armenta-Leyva B, Munguía-Ramírez B, Cheng TY, Ye F, Henao-Díaz A, Giménez-Lirola LG, Zimmerman J. Normalizing real-time PCR results in routine testing. J Vet Diagn Invest 2024; 36:78-85. [PMID: 37919959 PMCID: PMC10734596 DOI: 10.1177/10406387231206080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2023] Open
Abstract
Normalization, the process of controlling for normal variation in sampling and testing, can be achieved in real-time PCR assays by converting sample quantification cycles (Cqs) to "efficiency standardized Cqs" (ECqs). We calculated ECqs as E-ΔCq, where E is amplification efficiency and ΔCq is the difference between sample and reference standard Cqs. To apply this approach to a commercial porcine reproductive and respiratory syndrome virus (PRRSV) RT-qPCR assay, we created reference standards by rehydrating and then diluting (1 × 10-4) a PRRSV modified-live vaccine (PRRS MLV; Ingelvac) with serum or oral fluid (OF) to match the sample matrix to be tested. Sample ECqs were calculated using the mean E and reference standard Cq calculated from the 4 reference standards on each plate. Serum (n = 132) and OF (n = 130) samples were collected from each of 12 pigs vaccinated with a PRRSV MLV from -7 to 42 d post-vaccination, tested, and sample Cqs converted to ECqs. Mean plate Es were 1.75-2.6 for serum and 1.7-2.3 for OF. Mean plate reference standard Cqs were 29.1-31.3 for serum and 29.2-31.5 for OFs. Receiver operating characteristic analysis calculated the area under the curve for serum and OF sample ECqs as 0.999 (95% CI: 0.997, 1.000) and 0.947 (0.890, 1.000), respectively. For serum, diagnostic sensitivity and specificity of the commercial PRRSV RT-qPCR assay were estimated as 97.9% and 100% at an ECq cutoff ≥ 0.20, and for OF, 82.6% and 100%, respectively, at an ECq cutoff ≥ 0.45.
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Affiliation(s)
- Betsy Armenta-Leyva
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Lloyd Veterinary Medical Center, Iowa State University, Ames, IA, USA
| | - Berenice Munguía-Ramírez
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Lloyd Veterinary Medical Center, Iowa State University, Ames, IA, USA
| | - Ting-Yu Cheng
- Department of Veterinary Preventive Medicine, College of Veterinary Medicine, the Ohio State University, Columbus, OH, USA
| | - Fangshu Ye
- Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA, USA
| | | | - Luis G. Giménez-Lirola
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Lloyd Veterinary Medical Center, Iowa State University, Ames, IA, USA
| | - Jeffrey Zimmerman
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Lloyd Veterinary Medical Center, Iowa State University, Ames, IA, USA
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Armenta-Leyva B, Munguía-Ramírez B, Giménez-Lirola LG, Lin X, Ye F, Zimmerman J. Critical evaluation of strategies to achieve direct real-time PCR detection of swine pathogens in oral fluids. J Vet Diagn Invest 2023; 35:521-527. [PMID: 37337714 PMCID: PMC10467463 DOI: 10.1177/10406387231182102] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/21/2023] Open
Abstract
Based on publications reporting improvements in real-time PCR (rtPCR) performance, we compared protocols based on heat treatment or dilution followed by direct rtPCR to standard extraction and amplification methods for the detection of porcine reproductive and respiratory syndrome virus (PRRSV), influenza A virus (IAV), porcine epidemic diarrhea virus (PEDV), or Mycoplasma hyopneumoniae (MHP) in swine oral fluids (OFs). In part A, we subjected aliquots of positive OF samples to 1 of 4 protocols: protocol 1: heat (95°C × 30 min) followed by direct rtPCR; protocol 2: heat and cool (25°C × 20 min) followed by direct rtPCR; protocol 3: heat, cool, extraction, and rtPCR; protocol 4 (control): extraction and then rtPCR. In part B, positive OF samples were split into 3, diluted (D1 = 1:2 with Tris-borate-EDTA (TBE); D2 = 1:2 with negative OF; D3 = not diluted), and then tested by rtPCR using the best-performing protocol from part A (protocol 4). In part A, with occasional exceptions, heat treatment resulted in marked reduction in the detection of target and internal sample control (ISC) nucleic acids. In part B, sample dilution with TBE or OF produced no improvement in the detection of targets and ISCs. Thus, standard extraction and amplification methods provided superior detection of PRRSV, IAV, PEDV, and MHP nucleic acids in OFs.
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Affiliation(s)
- Betsy Armenta-Leyva
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Berenice Munguía-Ramírez
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Luis G. Giménez-Lirola
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Xue Lin
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Fangshu Ye
- Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA, USA
| | - Jeffrey Zimmerman
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
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Munguía-Ramírez B, Armenta-Leyva B, Henao-Díaz A, Ye F, Baum DH, Giménez-Lirola LG, Zimmerman JJ. Evaluation of a Porcine Endogenous Reference Gene (Internal Sample Control) in a Porcine Reproductive and Respiratory Syndrome Virus RT-qPCR. Vet Sci 2023; 10:381. [PMID: 37368767 DOI: 10.3390/vetsci10060381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2023] [Revised: 05/29/2023] [Accepted: 05/30/2023] [Indexed: 06/29/2023] Open
Abstract
Endogenous reference genes are used in gene-expression studies to "normalize" the results and, increasingly, as internal sample controls (ISC) in diagnostic quantitative polymerase chain reaction (qPCR). Three studies were conducted to evaluate the performance of a porcine-specific ISC in a commercial porcine reproductive and respiratory syndrome virus (PRRSV) reverse transcription-qPCR. Study 1 evaluated the species specificity of the ISC by testing serum from seven non-porcine domestic species (n = 34). In Study 2, the constancy of ISC detection over time (≥42 days) was assessed in oral fluid (n = 130), serum (n = 215), and feces (n = 132) collected from individual pigs of known PRRSV status. In Study 3, serum (n = 150), oral fluid (n = 150), and fecal samples (n = 75 feces, 75 fecal swabs) from commercial herds were used to establish ISC reference limits. Study 1 showed that the ISC was porcine-specific, i.e., all samples from non-porcine species were ISC negative (n = 34). In Study 2, the ISC was detected in all oral fluid, serum, and fecal samples, but differed in concentration between specimens (p < 0.05; mixed-effects regression model). The results of Study 3 were used to establish ISC reference limits for the 5th, 2.5th and 1.25th percentiles. Overall, the ISC response was consistent to the point that failure in detection is sufficient justification for re-testing and/or re-sampling.
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Affiliation(s)
- Berenice Munguía-Ramírez
- Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Betsy Armenta-Leyva
- Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Alexandra Henao-Díaz
- Pig Improvement Company (PIC) México, Santiago de Querétaro 76040, Querétaro, Mexico
| | - Fangshu Ye
- Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA 50011, USA
| | - David H Baum
- Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Luis G Giménez-Lirola
- Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
| | - Jeffrey J Zimmerman
- Veterinary Diagnostic and Production Animal Medicine Department, College of Veterinary Medicine, Iowa State University, Ames, IA 50011, USA
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Munguía-Ramírez B, Armenta-Leyva B, Henao-Díaz A, Cheng TY, Zhang J, Rawal G, Ye F, Giménez-Lirola L, Zimmerman JJ. Effect of extrinsic factors on the detection of PRRSV and a porcine-specific internal sample control in serum, oral fluid, and fecal specimens tested by RT-rtPCR. J Vet Diagn Invest 2023:10406387231174556. [PMID: 37166086 DOI: 10.1177/10406387231174556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/12/2023] Open
Abstract
We characterized the effect of 1) temperature × time, 2) freeze-thaw cycles, and 3) high porcine reproductive and respiratory syndrome virus (PRRSV) RNA concentrations on the detection of PRRSV and a porcine-specific internal sample control (ISC) in serum, oral fluid, and fecal samples using a commercial PRRSV RT-rtPCR assay (Idexx). In study 1, the effect of temperature × time on PRRSV and ISC detection was shown to be specimen dependent. In serum stored at 4, 10, or 20°C, PRRSV detection was consistent for up to 168 h, but storage at 30°C reduced detectable PRRSV RNA. ISC RNA was stable in serum held at 4 and 10°C, but not at 20 and 30°C. In contrast, PRRSV and ISC RNAs in oral fluid and fecal samples continuously decreased at all temperature × time treatments. Based on these data, serum samples should be stored at ≤ 20°C to optimize PRRSV RNA detection. Oral fluid and fecal samples should be frozen in a non-self-defrosting freezer until tested. In study 2, freeze-thaw cycles had little impact on PRRSV and ISC detection, but more so in oral fluids than serum or fecal samples. Thus, freeze-thaw cycles in oral fluids should be minimized before RT-rtPCR testing. In study 3, the ISC was not affected by high concentrations of PRRSV RNA in serum, oral fluid, or fecal samples. It should not be assumed that data from our PRRSV study are applicable to other pathogens; additional pathogen-specific studies are required.
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Affiliation(s)
- Berenice Munguía-Ramírez
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Betsy Armenta-Leyva
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | | | - Ting-Yu Cheng
- Department of Veterinary Preventive Medicine, The Ohio State University, Columbus, OH, USA
| | - Jianqiang Zhang
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Gaurav Rawal
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Fangshu Ye
- Department of Statistics, College of Liberal Arts and Sciences, Iowa State University, Ames, IA, USA
| | - Luis Giménez-Lirola
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
| | - Jeffrey J Zimmerman
- Department of Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University, Ames, IA, USA
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