Diagnostic Evaluation of Streptococcus gallolyticus Infection in Patients with Colon Diseases by Polymerase Chain Reaction (PCR) and Culturing Methods

Abstract

Background: Different types of Streptococcus gallolyticus are associated with malignant bowel cancer. Objectives: The aim of this study was to compare two culture and molecular methods in identifying Streptococcus gallolyticus in patients with colon diseases. Methods: A descriptive study was conducted to detect Streptococcus gallolyticus in 55 patients with colon diseases referring to hospitals in Babol and Chalus, Iran. A polymerase chain reaction and culture technique were performed. Detection of Streptococcus gallolyticus after deoxyribonucleic acid (DNA) extraction from designed primers (PCO3, PCO4) was used for SODA gene. From the general culture medium, brain heart infusion (BHI) broth and specific medium for bacterial growth and detection were used. Then, the characteristics of the two methods were evaluated. Results: Of 55 biopsy samples of patients with colon diseases, 3 samples (5.5%) with 95% confidence interval were positive and 52 (94.5%) were reported negative in terms of DNA of Streptococcus gallolyticus. According to the culture test, 9 (16.4%) were positive and 46 (83.6%) were negative for diagnosis of Streptococcus gallolyticus bacteria. Based on the diagnostic agreement between the two methods, the ratio of 9 positive cases of culture method to 3 positive cases by polymerase chain reaction (PCR) method (3.6%) were reported positive both in terms of molecular and positive culture, and 7 (12.7%) out of 9 (16.4%) were negative. To investigate the agreement between the culture and PCR methods, the Kappa test was used, which was statistically significant (P < 0.015). Other studies which have been conducted using the culture method, reported a significant relationship between the family history of colorectal cancer, diabetes, and the presence of Streptococcus gallolyticus bacteria. Conclusions: Considering the advantages, disadvantages, and the characteristics of both methods, none of them can be considered as a comprehensive, standard test at present. The simultaneous use of the two methods is recommended in cases where achieving fast results prevails, or when there is a likelihood of sample infection or late-growing microorganisms.