Vergleichende Charakterisierung von ESBL-bildenden Escherichia coli in Diensthunden der Deutschen Bundeswehr

Antimicrobial resistance is a growing concern in clinical microbiology today. Regarding the unsuccessful treatment of bacterial infections in human or animal patients, consequences reach from extended treatment times through complications and may end with a death of an individual patient due to untreatable bacterial infection. The beta-lactam antibiotics, namely penicillins, the cephalosporins (rarely the carbapenems) are highly used in veterinary medicine. Enterobacteriaceae easily develop a broad variety of antimicrobial resistance. Beta-lactamase producing bacteria, or even more powerful „extended-spectrum“ beta-lactamase producing Enterobacteriaceae (ESBL) have been described since 1979. Since the 1990s bacterial resistance against beta-lactam antibiotics was found in dogs. Currently the asymptomatic colonization with extended-spectrum beta-lactamase (ESBL) producing Enterobacteriaceae has been described for humans, various mammal species, and birds. In the present study about the characterization of ESBL-producing Escherichia coli in military working dogs in the German Armed Forces antimicrobial resistant bacteria were recovered from dog feces. During the study time, the dogs lived together in a group of working dogs, but also stayed with companion dogs at the home of their family. Most of the isolates were obtained from the military working dogs within a longitudinal collection over eleven months. The dogs had not been treated with antibiotics during the past year until the beginning of the study period. More study isolates were recovered from stray dogs originating from the theatre of operations of the German Armed Forces. In all 101 bacterial isolates were investigated in the present study originating from Germany, Republic of Kosovo, Afghanistan, Croatia and Ukraine. To characterize the bacterial isolates, the in vitro antimicrobial susceptibility testing was carried out using the extended-spectrum cephalosporins cefoxitin, cefotaxime, ceftazidime, and cefepime, with the last three listed also tested in combination with clavulanic acid. As well, susceptibility testing was done using the carbapenem antibiotics ertapenem and meropenem. The determined minimal inhibitory concentration (MIC) values revealed divers resistance patterns against single or all investigated beta-lactam antibiotics, with none of the 101 isolates resistant against the two tested carbapenem antibiotics. Furthermore, whole genome sequence analysis was carried out to support the in vitro data and revealed an insight into molecular data. Regarding antimicrobial resistance 23 different but species-specific coding DNA sequences (CDS) were identified proving antimicrobial resistance on a molecular basis. A phylogenetic analysis was carried out using canonical single nucleotide polymorphisms (SNPs). The results revealed clonal bacterial isolates originating from different dogs, suggesting transmission between dogs from the same community. These clonal isolates however were not detected over a period longer than seven days. Finally performing multi locus sequence typing (MLST) out of the 85 resistant E. coli isolates identified 31 different sequence types (ST). The most frequent ST were ST744 (n=9), ST10 (n=8), and ST648 (n=6), respectively. Amongst these, the world-wide human hospital-associated CTX-M beta-lactamase producing ST131 was not detected. Further epidemiologic interpretation did not support a correlation among the longitudinal isolates. There was no molecular proof of relationship between dog-isolates of different geographic origin. The data of the present thesis proof a high prevalence of ESBL-producing bacteria in healthy dogs, independent to prior treatment with antibiotics. It could be shown that single isolates were transmitted between individuals of the same community. These isolates however were as well eliminated after a short time. Most of the characterized bacteria revealed few characteristics signing them host-specific for dogs at this point. Within the present study, the whole genome analysis data were publicly published and are available to contribute for future epidemiologic questions regarding the exciting research field of antimicrobial resistant bacteria