|Year : 2020 | Volume
| Issue : 2 | Page : 235-236
Utility of polymerase chain reaction assays for confirmation of liquid culture test results for Ureaplasma spp.
Swati Khullar1, Jyoti Rawre1, Neena Khanna2, Vishnubhatla Sreenivas3, Benu Dhawan1
1 Department of Microbiology, All India Institute of Medical Sciences, New Delhi, India
2 Department of Dermatology and Venereology, All India Institute of Medical Sciences, New Delhi, India
3 Department of Biostatistics, All India Institute of Medical Sciences, New Delhi, India
|Date of Submission||24-May-2020|
|Date of Acceptance||04-Jul-2020|
|Date of Web Publication||29-Aug-2020|
Dr. Benu Dhawan
Department of Microbiology, All India Institute of Medical Sciences, New Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Khullar S, Rawre J, Khanna N, Sreenivas V, Dhawan B. Utility of polymerase chain reaction assays for confirmation of liquid culture test results for Ureaplasma spp. Indian J Med Microbiol 2020;38:235-6
|How to cite this URL:|
Khullar S, Rawre J, Khanna N, Sreenivas V, Dhawan B. Utility of polymerase chain reaction assays for confirmation of liquid culture test results for Ureaplasma spp. Indian J Med Microbiol [serial online] 2020 [cited 2020 Oct 24];38:235-6. Available from: https://www.ijmm.org/text.asp?2020/38/2/235/293902
Polymerase chain reaction (PCR) assays should be used to confirm liquid culture test results for Ureaplasma spp. as also suggested by Zhao et al. in their study where they performed real-time PCR for verifying the results of liquid culture for Ureaplasma spp. As rightly highlighted by the authors, most laboratories have replaced use of solid media for culture of Ureaplasma by the use of liquid culture techniques. Although culture on solid media remains the gold standard for diagnosing Ureaplasma infections, it can be time-consuming resulting in longer turnaround time. Furthermore, the lack of sensitivity adds to its demerits.
Ureaplasma can be present as a commensal in healthy asymptomatic individuals. Ureaplasma parvum has been reported as the predominant biovar in genital infections, while Ureaplasma urealyticum has been less commonly isolated. Development of molecular assays such as nucleic acid amplification tests has not only significantly improved the sensitivity and specificity of diagnosis of Ureaplasma infections but also allows for biovar detection.
We performed a laboratory-based retrospective analysis for a period of 1 year (January 2019–December 2019), in which sexually active men and women with genital discharge presenting consecutively to the STD Outpatient Clinic of a tertiary care hospital in New Delhi were included. A total of 530 samples were collected from 382 patients including 181 (47.4%) males and 201 (52.6%) females with a with a mean age of 32.97 years ± standard deviation 11.1 (range: 18–75). Samples included endocervical swabs; first void urine (FVU) from 126 heterosexual males and FVU, rectal swabs and oropharyngeal swabs from 55 men who have sex with men.
Samples were tested for Ureaplasma spp. by liquid culture in pleuropneumonia-like organism broth containing urea and PCR targeting Urease gene as previously described.
Ureaplasma spp. was detected in 6.6% (35/530) of samples by liquid culture and 7.5% (40/530) of samples by PCR. Thirteen samples (2.4%) tested positive by both culture and PCR. Twenty-seven (5.1%) samples were PCR positive but culture negative. Twenty-two (4.1%) samples were culture positive but PCR negative. DNA was extracted from these culture-positive broths and retested by PCR. However, none of these samples tested positive.
All the PCR-positive samples were further biotyped by performing another PCR amplifying the multiple banded antigen gene. U. parvum (Biovar 1) was the most prevalent biovar (67.5%; 27/40) followed by U. urealyticum (Biovar 2).
In our study, approximately two-thirds of the PCR-positive samples were negative by liquid culture. The interpretation of liquid culture is subjective. Low organism load in the liquid culture may result in slight colour change of the broth which could be missed by the naked eye. Molecular assays are known to be more sensitive as they can amplify even small amounts of DNA. Since all the PCR-positive samples including those which were culture negative for Ureaplasma spp. were biotyped by another PCR assay, hence, these PCR-positive samples are true positives.
In our study, we observed that 4.5% of the PCR-negative samples were culture positive. Our results are in concordance with the findings of Zhao et al., who also observed 7% false-positive rate by liquid culture. Our findings further add to the growing body of evidence that the results of liquid culture alone cannot be relied upon and should be reconfirmed by PCR. To conclude, the importance of combing molecular-based methods like PCR along with liquid culture for appropriate diagnosis of Ureaplasma spp. cannot be underscored.
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Conflicts of interest
There are no conflicts of interest.
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