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首页> 外文期刊>Infection and immunity >Organization of aerobactin, hemolysin, and antibacterial resistance genes in lactose-negative Escherichia coli strains of serotype O4 isolated from children with diarrhea.
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Organization of aerobactin, hemolysin, and antibacterial resistance genes in lactose-negative Escherichia coli strains of serotype O4 isolated from children with diarrhea.

机译：从腹泻患儿分离出的O4型乳糖阴性大肠杆菌菌株中的气杆菌素，溶血素和抗菌素耐药基因的组织。

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摘要

Epidemiologically related, non-lactose-fermenting (NLF) Escherichia coli strains of serotype O4 have been isolated at a high frequency from children with diarrhea in Somalia (M. Nicoletti, F. Superti, C. Conti, A. Calconi, and C. Zagaglia, J. Clin. Microbiol. 26:524-529, 1988). In order to define the virulence potential of these strains, we characterized the replication properties of their high-molecular-weight plasmids and studied the genetic locations and organization of the aerobactin (aer) and hemolysin (hly) determinants encoded by 23 NLF O4 E. coli strains. Southern blot hybridizations, mobilization assays of nonconjugative plasmids, and incompatibility-exclusion experiments conducted with a conjugative incompatibility group FI (IncFI) plasmid showed that (i) 20 out of the 23 strains examined harbor a 160- to 180-kb IncFI plasmid that shares homology with the basic replicons RepFIA, RepFIB, and (except for the plasmid of one strain) RepFIC, and 22 strains also contain a 40- to 140-kb IncFII plasmid sharing homology with the RepFIIA replicon; (ii) the IncFI plasmid is nonconjugative and carries antibiotic resistance genes; (iii) the aer system is located on the IncFI plasmids and/or the chromosomes in the three strains not harboring IncFI, and it is found in an inverted orientation; (iv) the hly determinants are located on the chromosome, and their genetic organization is well conserved and closely resembles that of the reference hemolytic plasmid pHly152; and (v) Hly- mutants obtained by transposon insertion mutagenesis are not cytotoxic to HeLa cell monolayers, indicating that hemolysin is responsible for the high cytotoxic activity we have previously reported for these strains. The structural organization of the plasmid-encoded aer operon, together with the finding that those plasmids also carry antibiotic resistance genes, indicates that the IncFI plasmid of the NLF O4 E. coli strains studied more closely resembles aer-encoding virulence IncFI Salmonella R plasmids than E. coli ColV plasmids. The data presented here cannot rule out whether the strains examined are potentially intestinal or extraintestinal pathogens. Nevertheless, the genetic organization of the virulence genes, together with the epidemiological behavior and the wide spectrum of antibiotic resistance of the NLF O4 E. coli strains, indicates that these strains are structured as typical E. coli pathogenic isolates of human origin.
机译：已从索马里腹泻儿童中高频率分离出O4型血清型的流行病学相关，非乳糖发酵（NLF）大肠杆菌菌株（M. Nicoletti，F.Superti，C.Conti，A.Calconi和C. Zagaglia，J.Clin.Microbiol.26：524-529，1988）。为了确定这些菌株的潜在毒力，我们表征了它们的高分子量质粒的复制特性，并研究了由23种NLF O4 E编码的气杆菌素（aer）和溶血素（hly）决定簇的遗传位置和组织。大肠杆菌菌株。 Southern杂交，非结合型质粒的动员实验以及结合型不相容基团FI（IncFI）质粒进行的不相容性排斥实验表明（i）在所检测的23株菌株中，有20株含有160-180 kb的IncFI质粒与基本复制子RepFIA，RepFIB和（除了一个菌株的质粒）RepFIC的同源性，另外22个菌株还包含40至140kb的IncFII质粒，与RepFIIA复制子具有同源性; （ii）IncFI质粒是非结合性的，并带有抗生素抗性基因; （iii）aer系统位于三个不带有IncFI的菌株的IncFI质粒和/或染色体上，并且方向相反; （iv）hly决定簇位于染色体上，并且它们的遗传组织是高度保守的，并且与参照溶血质粒pHly152的遗传组织非常相似; （v）通过转座子插入诱变获得的Hly-突变体对HeLa细胞单层无细胞毒性，表明溶血素对我们先前报道的这些菌株的高细胞毒活性负责。质粒编码的aer操纵子的结构组织，以及发现这些质粒还带有抗生素抗性基因的发现，表明所研究的NLF O4大肠杆菌菌株的IncFI质粒比aer编码的毒力IncFI Salmonella R质粒更相似。大肠杆菌ColV质粒。这里提供的数据不能排除所检查的菌株是潜在的肠道病原体还是肠道外病原体。然而，毒力基因的遗传组织，连同NLF O4大肠杆菌菌株的流行病学行为和广泛的抗生素抗药性，表明这些菌株被构造为人类起源的典型大肠杆菌病原体。

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