Diarrhea is a common gastrointestinal disorder characterized by frequent passage of loose stools (at least three times daily) and accompanying symptoms such as abdominal cramps, bloating, and nausea. Of particular importance is antibiotic-associated diarrhea (AAD), which occurs in 5-35 % of patients receiving antibiotic therapy. Among the significant causative agents is Klebsiella oxytoca, which produces the toxins tilivaline and tilimicin upon overgrowth. These toxins can cause severe antibiotic-associated hemorrhagic colitis (AAHC) – inflammation of the colon with bloody diarrhea, particularly during treatment with β-lactam antibiotics such as penicillin. K. oxytoca is normally present in the intestine but becomes problematic when the microbiota balance is disrupted by antibiotics. In this study, we employed simultaneous real-time PCR methodology to determine the toxigenicity of K. oxytoca bacteria in pure cultures and clinical specimens. The obtained results demonstrate that the molecular method performed well for rapid and accurate detection of bacteria K. oxytoca and determination of its toxigenicity through simultaneous detection of all three key AAHC virulence genes: pehX, npsA, and npsB. In the scope of our master's thesis, we analyzed 208 samples, in which the bacteria K. oxytoca was detected in 150 cases, representing 72,12% of all tested samples. The analysis showed that toxigenic K. oxytoca, a causative agent of hemorrhagic colitis, was present in 91 cases, which represents 60,67% of all positive samples. The non-toxigenic strain of the bacterium was detected in 59 cases, representing 39,33%.
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