Johnson J R, Moseley S L, Roberts P L, Stamm W E
Department of Medicine, University of Washington School of Medicine, Seattle 98195.
Infect Immun. 1988 Feb;56(2):405-12. doi: 10.1128/iai.56.2.405-412.1988.
To assess the role of aerobactin as a virulence factor among uropathogenic Escherichia coli, we determined the prevalence, location, and phenotypic expression of aerobactin determinants among 58 E. coli strains causing bacteremic urinary tract infections. We correlated the presence of the aerobactin system with antimicrobial-agent resistance, the presence and phenotypic expression of other uropathogenic virulence factor determinants (P fimbriae, hemolysin, and type 1 fimbriae), and characteristics of patients. Colony and Southern hybridization of total and plasmid DNA with DNA probes for each virulence factor showed that aerobactin determinants were present in 78% of the strains and were plasmid associated in 21%, whereas P fimbria, hemolysin, and type 1 fimbria determinants were present in 74, 43, and 98% of the strains, respectively, and were always chromosomal. Chromosomal aerobactin, P fimbria, and hemolysin determinants occurred together on the chromosome more often in strains from patients without predisposing urological or medical conditions (P = 0.04). Strains with plasmid-encoded aerobactin lacked determinants for P fimbriae (P = 0.004) and hemolysin (P = 0.0004), were resistant to multiple antimicrobial agents (P = 0.0001), and were found only in compromised patients. Mating experiments demonstrated that some aerobactin plasmids also encoded antimicrobial-agent resistance. These findings suggest that the determinants for aerobactin, P fimbriae, and hemolysin are conserved on the chromosome of the antimicrobial-agent-susceptible uropathogenic strains of E. coli which invade noncompromised patients. In contrast, these chromosomal virulence factors are often absent from E. coli strains causing urosepsis in compromised hosts; these strains may acquire plasmid aerobactin in conjunction with antimicrobial-agent resistance genes.
为评估气杆菌素作为尿路致病性大肠杆菌毒力因子的作用，我们测定了58株引起菌血症性尿路感染的大肠杆菌中气杆菌素决定簇的流行情况、位置及表型表达。我们将气杆菌素系统的存在与抗菌药物耐药性、其他尿路致病性毒力因子决定簇（P菌毛、溶血素和1型菌毛）的存在及表型表达以及患者特征进行了关联分析。用针对每种毒力因子的DNA探针与总DNA和质粒DNA进行菌落杂交及Southern杂交，结果显示78%的菌株存在气杆菌素决定簇，其中21%与质粒相关，而P菌毛、溶血素和1型菌毛决定簇分别存在于74%、43%和98%的菌株中，且均位于染色体上。在没有泌尿系统或其他基础疾病的患者来源的菌株中，染色体上的气杆菌素、P菌毛和溶血素决定簇同时出现的频率更高（P = 0.04）。携带质粒编码气杆菌素的菌株缺乏P菌毛（P = 0.004）和溶血素（P = 0.0004）的决定簇，对多种抗菌药物耐药（P = 0.0001），且仅在有基础疾病的患者中发现。接合实验表明，一些气杆菌素质粒还编码抗菌药物耐药性。这些发现提示，在侵袭无基础疾病患者的对抗菌药物敏感的尿路致病性大肠杆菌菌株的染色体上，气杆菌素、P菌毛和溶血素的决定簇是保守的。相比之下，在有基础疾病的宿主中引起尿脓毒症的大肠杆菌菌株通常缺乏这些染色体毒力因子；这些菌株可能会获得携带抗菌药物耐药基因的质粒气杆菌素。
