Background: Gram negative bacteria especially members of family Enterobacteriaceae are among the most frequently isolated organisms from the clinical specimens. Rapid diagnosis of the pathogen in a clinical sample is always very important. Conventional methods are time-consuming. Among molecular techniques, PCR is very useful but unless very specific primers are used, non-specific amplifications are a problem. Objectives: PCR-ribotying is a technique that gives very specific multiple bands by use of a single primer set. This study was designed to establish patterns for five common pathogens of Enterobacteriaceae, namely Escherichia coli, Salmonella enterica serovar Typhi (Salmonella Typhi), Proteus vulgaris, Klebsiella aerogenes, and Cirtobacter freundii along with another very common and problematic gram negative pathogen Pseudomonas aeruginosa. Results: Each species gave a specific ribotyping pattern. Escherichia coli gave four amplification products of 1200, 850, 800, and 700 bps. Four amplification products of different sizes were also observed in Citrobacter freundii (3000, 850, 700, and 580 bps), Proteus vulgaris (900, 800, 750 and 700 bps), and Klebisella aerogenes (3000, 870, 700 and 520 bps). More discrimination with five amplification products was seen in Salmonella Typhi (3000, 1200, 900, 850, and 700 bps). On the other side of spectrum was Pseudomonas aeruginosa only a single amplification product of 750 bps was observed. Conclusion: PCR-ribotyping can very efficiently and specifically differentiate between opportunistic gram negative human pathogens.
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