Detection of Shigellae from stools of dysentery patients by culture and polymerase chain reaction techniques

In Bangladesh, the isolation rates of Shigella spp, range from 11% to 12% b y the conventional culture technique, Since the sensitivity of this techniq ue is low, the polymerase chain reaction (PCR) technique was used for detec ting small number of Shigellae from patients' stools. Sensitivity and speci ficity of the two techniques were also compared. Stool samples were collect ed from 41 patients with dysentery who attended the Clinical Research and S ervice Centre of the ICDDR,B: Centre for Health and Population Research, Al l stool specimens were directly plated onto MacConkey, Salmonella-Shigella, Xylose lysin deoxycholate and Hectoen enteric agar media, and Shigellae we re detected following standard procedures, DNA was extracted from the stool samples, and the target sequence of invasive plasmid antigen (ipa)H locus was amplified by PCR with 130 ng each of two primers (primer H8 [5'-GTTCCTT GACCGCCTTTCCGATAC-3'] and primer H15 [5'-GCCGGTCAGCCACCCTA-3']) following s tandard procedures. The amplified product was hybridized using an ipaH prob e, The isolation rates of Shigella dysenteriae type 1, S. flexneri, S. sonn ei, and S. boydii were, respectively, 17.1%, 19.5%, 4.9% and 2.4% by the co nventional method. The results of the PCR technique showed that 700 bp frag ment was generated in 18 of the 18 culture-positive and in 7 of the 23 cult ure-negative stools. One hundred twenty-three strains of Escherichia coli w ere also tested by PCR for identifying the enteroinvasive E. coli, but none of them yielded any positive result. This study showed that the sensitivit y of the culture technique is 72% and specificity is 100%, when the PCR tec hnique was considered as gold standard. Therefore, the PCR may be considere d a more sensitive and specific technique than the conventional culture tec hnique and has the potential to be employed in routine diagnosis of dysente ry in clinical centres as well as in epidemiologic studies.