The aim of the study was to characterize multidrug-resistant (MDR) Escherichia coli isolates collected in Serbia from bovine clinical mastitis cases and diseased pigs, mainly with molecular methods. A total of 48 E. coli isolates was collected during the years 2013-2014, of which 22 were MDR and were included in further analysis. Phylogenetic typing showed that 17 isolates belonged to group A, while two isolates were classified in group B1 and a single one in group D. All isolates showed unique macrorestriction patterns. Phenotypic susceptibility testing revealed resistances of the isolates against up to 13 antimicrobial agents, including resistance to fluoroquinolones. A wide variety of resistance genes was detected by PCR amplification and sequencing of amplicons. Sequence analysis of the quinolone resistance determining regions of topoisomerase genes revealed mutations in gyrA, parC, and/or parE. Plasmid-mediated quinolone resistance genes were detected in two porcine (aac-6'-Ib-cr and qnrS, respectively) isolates and a single bovine (aac-6'-Ib-cr) isolate. Resistance genes were found to be located on conjugative plasmids in 16 cases, many of which conferred a multidrug resistance phenotype. In conclusion, the plentitude of resistance genes located on conjugative plasmids and integrons in E. coli from cows and pigs in Vojvodina, Serbia, pose a high risk for horizontal gene transfer in bacteria from livestock husbandry.

The antimicrobial susceptibility testing was conducted on 174 single isolates from poultry farms in Serbia and it was determined that seven Salmonella spp. were multidrug resistant. Sixteen serotypes were detected, but only serotype Infantis confirmed reduced susceptibility to colistin. Seven colistin resistant Salmonella Infantis were studied in detail using the WGS approach. Three sequence types were identified corresponding to different epizootiology region. The isolate from the Province of Vojvodina 3842 and isolates from Jagodina (92 and 821) are represented by the sequence type ST413 and ST11, respectively. Four isolates from Kraljevo are ST32, a common S. Infantis sequence type in humans, poultry and food. The fosfomycin resistance gene fosA7 in isolate 3842 and the vgaA gene in isolate 8418/2948 encoding resistance to pleuromutilins were reported for the first time in serovar Infantis. The changes in relative expression of the phoP/Q, mgrB and pmrA/B genes were detected. Single nucleotide polymorphisms of the pmrB gene, including transitions Val164Gly or Val164Met, and Arg92Pro are described. Analyses of quinolone resistance determining region revealed substitutions Ser83Tyr in GyrA protein and Thr57Ser and Ser80Arg in ParC protein. Based on WGS data, there are two major clusters among analyzed Salmonella Infantis isolates from central Serbia.

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The objectives of the present paper are the analysis and comparison of the results from available literature regarding the prevalence of tetracyclineresistance in Escherichia coli strains isolated from poultry in different countries. Tetracycline is still one of the most commonly used antibiotic in many developing countries both in human and in veterinary medicine. The main reasons are its relatively low cost and availability. Besides that, this class of antibiotics is still used in developed countries for prophylactic and therapeutic purposes. Th e widespread use of tetracycline in poultry farming could result in horizontal transfer of resistance determinates from poultry to humans as well as to the environment. Escherichia coli, is a commensal bacteria from human and poultry digestive systems, and present one of the most important reservoirs of antibiotic resistance and has a signifi cant role in the transfer of various resistance determinants. Some strains of Escherichia coli are highly pathogenic and can cause several diseases in poultry which require antibiotic therapy. Positive correlation between the usage of antibiotics both in human and in veterinary medicine and the corresponding antibiotic resistance were reported by many authours. Furthermore, there is also some evidence that the positive correlations were also found between the usage of antibiotics in veterinary medicine and the appereance of antibiotic resistance in bacteria isolated from humans. Th e prudent use of tetracycline antibiotic in poultry production is essential as well as permanet monitoring of the presence of the tetracycline resistance.

Clostridium perfringens is a Gram-positive, endospore-forming, anaerobic rod, ubiquitous in nature. C. perfringens strains can produce about 17 toxins. Many of them can lead to miscellaneous diseases, among which the enteric ailment may be the most common and is of utmost importance. In the present work 34 strains of C. perfringens isolated from feed and one from a cow suspected to have died of clostridial infection were subjected to molecular analysis. In order to detect the genotypes, the following genes coding for toxins were targetted: cpa, cpb, cpb2, cpe, etx and iap. The multiplex PCR assay revealed that all C. perfringens isolates from animal feed were of type A and 2-toxinogenic type A strains, possessing only the cpa (n=21), or both the cpa and the cpb2 genes (n=13). The importance of C. perfringens toxins  and -2 in the pathogenesis of enterotoxemia is discussed and the regulation on the detection of this bacteria in animal feed questioned. The use of PCR in practise could enable the toxin-genotyping of C. perfringens isolates and, thus, provide a real basis for the establishment of maximum acceptable limits of this bacteria in feed.