Epsilon Open Archive

Abstract

Plesiomonas shigelloides is an aquatic microorganism recognised recently as potential human and animal pathogen. Plesiomonads are Gram-negative, motile, non-sporeforming bacilli, facultative anaerobic and oxidase positive. Since 2001, P. shigelloides belongs to the family Enterobacteriaceae. The primary reservoirs for this bacterium are fresh- and estuarine water, mainly in temperate climates. Although there were reports on the isolation of P. shigelloides from human patients in Sweden, the occurrence of this bacterium in Swedish freshwaters had not been studied yet. The presence of plesiomonads in lakes and rivers in Sweden is reported for the first time. Interestingly, some serovars seem to be geographically correlated. Some bacterial pathogens have been previously found in extreme climates such as the Polar Circle area. Surprisingly, the investigation of fresh water from lakes north of the Polar Circle in Sweden revealed the presence of P. shigelloides. Non-agglutinating isolates were found which suggest the finding of new serovars. Molecular techniques showed that they were genotypically different. Antimicrobial susceptibility tests showed that P. shigelloides presents a natural resistance to b-lactams despite the geographical region from where they were isolated. Furthermore, some strains may carry genes for resistance to tetracyclines. A correct identification of bacteria is crucial to determine the adequate treatment and for epidemiological studies. P. shigelloides is not specified in many clinical laboratories; therefore, a PCR for specific detection of this bacterium was developed. Detection was successful for all the isolates tested despite their serovar, source of isolation or geographical origin. The primers did not amplify genetic material from close related bacteria. Various molecular techniques were evaluated for genotyping P. shigelloides of the same serovar. PFGE and RAPD showed the highest discriminatory skills detecting 22 and 21 genotypes, respectively, among 24 strains. Animal-human pairs from the same geographical area presented an equal genotype. This finding is the first molecular evidence of the possible role of P. shigelloides as a zoonotic agent. In conclusion, this thesis research has contributed significantly to our knowledge of P. shigelloides by providing new information on its distribution, its specific detection by PCR, intra-species relationship and its possible relation with zoonotic cases.