Szmolka Ama, Lestár Barbara, Pászti Judit, Fekete Péter, Nagy Béla
Institute for Veterinary Medical Research, Centre for Agricultural Research, Hungarian Academy of Sciences , Hungária krt. 21, H-1143 Budapest , Hungary.
National Center for Epidemiology , Budapest , Hungary.
Acta Vet Hung. 2015 Dec;63(4):425-43. doi: 10.1556/004.2015.040.
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.
产肠毒素大肠杆菌（ETEC）常导致新生仔猪和断奶仔猪出现水样腹泻。携带不同肠毒素和菌毛黏附素基因的质粒，以及赋予抗菌药物耐药性的质粒，在ETEC的流行病学和发病机制中至关重要。最近的研究揭示了携带四环素抗性基因tet(B)和肠毒素基因的猪ETEC质粒pTC的重要性。相比之下，tet(A)质粒在猪ETEC耐药性转移中的作用尚不太清楚。本研究的目的是对代表中欧和美国猪肉产区的断奶后猪ETEC菌株的抗菌药物耐药性和毒力基因谱进行比较分析，特别关注携带tet(A)基因的质粒。通过纸片扩散法和PCR测定了从奥地利、捷克共和国、匈牙利和美国中西部断奶后腹泻病例中分离出的87株猪ETEC菌株的抗菌药物耐药表型和基因型。对携带tet(A)或tet(B)的中欧菌株进一步进行其tet质粒的分子特征分析。结果表明，超过90%的ETEC菌株具有磺胺甲恶唑（91%）、四环素（84%）和链霉素（80%）耐药的共同多重耐药（MDR）模式。四环素耐药最常见由tet(B)基因决定（38%），而tet(A)在所有分离株的26%中被鉴定到，两种tet基因类型在一些国家之间范围广泛，且1类整合子和耐药基因通过接合共同转移。毒力基因谱包括肠毒素基因（lt、sta和/或stb）以及黏附素基因（k88/f4、f18）。对来自中欧的猪F18(+) ETEC的两个代表性tet(A)质粒进行特征分析表明，捷克菌株的IncF质粒（pES11732，约120 kb）携带tet(A)并与catA1相关联，赋予氯霉素耐药性。匈牙利菌株的IncI1质粒（pES2172，约138 kb）携带tet(A)基因和一个1类整合子，其可变区异常，长度为2735 bp，由两个基因盒组成：estX-aadA1，编码链丝菌素-壮观霉素/链霉素耐药性，这例证了猪ETEC的tet(A)质粒同时募集、组装和转移多重耐药基因的情况。由此，我们首次描述了负责tet(A)基因与多重耐药性共同转移的F18(+)猪产肠毒素大肠杆菌的IncF和IncI1型质粒。此外，编码链丝菌素耐药性的异常决定簇estX首次在猪产肠毒素大肠杆菌中报道。
