Béla Nagy

Harley William Moon,DVM, Ph.D., an outstanding American person and researcher of comparative microbiology and pathology of intestinal diseases, the former director of the USDA, ARS, National Animal Disease Center (Iowa), of Plum Island Animal Disease Center (New York) and of Veterinary Research Institute of Iowa State University, member of the National Academy of Sciences (USA) passed away after some difficult and lonely last years of his life, on October 7, 2018 at the age of 82.

Four strains of Salmonella enterica subsp. enterica serovar Infantis isolated from humans (1980 to 1982) and broiler chickens (2016) have been sequenced. They represent the early and recent peak incidences of this serovar in Hungary. Genome sequences of these isolates provide comparative data on the evolution and rise of an endemic S . Infantis clone in Hungary.

Three strains of Salmonella enterica serovar Infantis isolated from healthy broiler chickens from 2012 to 2013 have been sequenced. Comparison of these and previously published S . Infantis genome sequences of broiler origin in 1996 and 2004 will provide new insight into the genome evolution and recent spread of S . Infantis in poultry.

Enterotoxigenic E. coli (ETEC) bacteria frequently cause watery diarrhoea in newborn and weaned pigs. Plasmids carrying genes of different enterotoxins and fimbrial adhesins, as well as plasmids conferring antimicrobial resistance are of prime importance in the epidemiology and pathogenesis of ETEC. Recent studies have revealed the significance of the porcine ETEC plasmid pTC, carrying tetracycline resistance gene tet(B) with enterotoxin genes. In contrast, the role of tet(A) plasmids in transferring resistance of porcine ETEC is less understood. The objective of the present study was to provide a comparative analysis of antimicrobial resistance and virulence gene profiles of porcine post-weaning ETEC strains representing pork-producing areas in Central Europe and in the USA, with special attention to plasmids carrying the tet(A) gene. Antimicrobial resistance phenotypes and genotypes of 87 porcine ETEC strains isolated from cases of post-weaning diarrhoea in Austria, the Czech Republic, Hungary and the Midwest USA was determined by disk diffusion and by PCR. Central European strains carrying tet(A) or tet(B) were further subjected to molecular characterisation of their tet plasmids. Results indicated that > 90% of the ETEC strains shared a common multidrug resistant (MDR) pattern of sulphamethoxazole (91%), tetracycline (84%) and streptomycin (80%) resistance. Tetracycline resistance was most frequently determined by the tet(B) gene (38%), while tet(A) was identified in 26% of all isolates with wide ranges for both tet gene types between some countries and with class 1 integrons and resistance genes co-transferred by conjugation. The virulence gene profiles included enterotoxin genes (lt, sta and/or stb), as well as adhesin genes (k88/f4, f18). Characterisation of two representative tet(A) plasmids of porcine F18⁺ ETEC from Central Europe revealed that the IncF plasmid (pES11732) of the Czech strain (~120 kb) carried tet(A) in association with catA1 for chloramphenicol resistance. The IncI1 plasmid (pES2172) of the Hungarian strain (~138 kb) carried tet(A) gene and a class 1 integron with an unusual variable region of 2,735 bp composed by two gene cassettes: estX-aadA1 encoding for streptothricin-spectinomycin/streptomycin resistance exemplifying simultaneous recruitment, assembly and transfer of multidrug resistance genes by the tet(A) plasmid of porcine ETEC. By this we provide the first description of IncF and IncI1 type plasmids of F18⁺ porcine enterotoxigenic E. coli responsible for cotransfer of the tet(A) gene with multidrug resistance. Additionally, the unusual determinant estX, encoding for streptothricin resistance, is first reported here in porcine enterotoxigenic E. coli.

The aim of these studies was to assess residual virulence and early protective capacity of a negatively markered live attenuated vaccine candidate Salmonella Enteritidis mutant against a highly virulent S. Enteritidis strain using a dayold chicken model. Nonflagellated FliD negative mutants of Salmonella Enteritidis 11 (SE11) with and without the virulence plasmid proved to be sufficiently attenuated (limited invasiveness in vitro/in vivo) without reduced ability to colonise chicken gut. The early protective activity of a nonflagellated, virulence-plasmidcured (fliD–, pSEVΔ) mutant against organ invasion, caecal colonisation and faecal shedding by the highly virulent challenge strain S. Enteritidis 147 Nal^R proved to be effective and safe. The innate and adaptive immunity was demonstrable during the first four weeks of life, and the serological response was clearly distinguishable from the response induced by the wild parental strain. In conclusion, we provided data for the first time about a virulence-plasmid-cured, nonflagellated mutant of S. Enteritidis to serve as a basis for development of a negatively markered potential live oral vaccine against virulent S. Enteritidis in chicken.

After the era of plentiful antibiotics we are alarmed by the increasing number of antibiotic resistant strains. The genetic flexibility and adaptability of E. coli to constantly changing environments allows to acquire a great number of antimicrobial resistance mechanisms. Commensal strains of E. coli as versatile residents of the lower intestine are also repeatedly challenged by antimicrobial pressures during the lifetime of their host. As a consequence, commensal strains acquire the respective resistance genes, and/or develop resistant mutants in order to survive and maintain microbial homeostasis in the lower intestinal tract. Thus, commensal E. coli strains are regarded as indicators of antimicrobial load on their hosts. This chapter provides a short historic background of the appearance and presumed origin and transfer of antimicrobial resistance genes in commensal intestinal E. coli of animals with comparative information on their pathogenic counterparts. The dynamics, development and ways of evolution of resistance in the E. coli populations differ according to hosts, resistance mechanisms and antimicrobial classes used. The most frequent tools of E. coli against a variety of antimicrobials are the efflux pumps and mobile resistance mechanisms carried by plasmids and/or other transferable elements. The emergence of hybrid plasmids (both resistance and virulence) among E. coli is of further concern. Co-existence and co-transfer of these “bad genes” in this huge and most versatile in vivo compartment may represent an increased public health risk in the future. Significance of multidrug resistant (MDR) commensal E. coli seem to be highest in the food animal industry, acting as reservoir for intra- and interspecific exchange and a source for spread of MDR determinants through contaminated food to humans. Thus, public health potential of MDR commensal E. coli of food animals can be a concern and needs monitoring and more molecular analysis in the future.

Extraintestinal pathogenic Escherichia coli (ExPEC) isolates of animals and man are known to carry specific virulence associated genes. The intestinal tract, it is primarily colonized by various strains of commensal E. coli but it may include ExPEC as well. Here we aimed to assess possible genetic and evolutionary linkages between extraintestinal pathogenic and intestinal (commensal) E. coli of poultry. For that purpose we analysed 71 ExPEC isolates, and 40 intestinal isolates assumed to be commensal E. coli (IntEC), from dead chickens and turkey poults for 26 virulence related genes. Although the two groups shared several virulence determinants the genes pic, papC, and cdtIV were exclusively present in ExPEC and further five genes (colV, iss, kpsM, tsh and iutA), were significantly more frequent among ExPEC. Phylogenetic backgrounds of ExPEC and of IntEC isolates indicated significant differences. A 40% of ExPEC belonged to phylogroup A primarily containing strains of serogroup O78. Phylogroup D contained ExPEC strains of serogroups O53 (2 strains) and O115 (5 strains) characterized by the cdt-IV genes, suggesting the existence of new clones of avian ExPEC in phylogenetic group D. On the other hand, a 42.5% of IntEC belonged to phylogroup B1 with diverse serogroups. Our data provide insight into the clonal evolution of avian ExPEC especially in phylogenetic groups A and D, resulting avian ExPEC with similarities to human ExPEC.

Genomic analyses on versatility of the ubiquitous opportunistic pathogen Pseudomonas aeruginosa have been focusing on clinical strains from humans but