Ridley A, Threlfall E J
Laboratory of Enteric Pathogens, PHLS Central Public Health Laboratory, London.
Microb Drug Resist. 1998 Summer;4(2):113-8. doi: 10.1089/mdr.1998.4.113.
The epidemiology of antibiotic resistance genes in epidemic multiresistant S. typhimurium DT 104 of human and animal origin was investigated. DNA prepared from 45 human and 21 animal strains isolated between 1984 and 1997, including eight isolated in other European countries, the USA, Trinidad, and South Africa and resistant to ampicillin, chloramphenicol, streptomycin, sulphonamides, spectinomycin, tetracyclines (R-type ACSSuSpT) were examined for the presence of integrons by PCR. Integron hot spots were observed in all strains conferring resistance to ACSSuSpT in two copies, determined by two discrete bands of approximately 1.0 and 1.2 kb. Direct nucleotide sequencing of the individual amplicons of selected strains indicated that the 1.0 kb gene product was ant (3")-Ia, responsible for resistance to streptomycin and spectinomycin; the 1.2 kb amplicon contained the gene blaPSE-1, encoding the beta-lactamase PSE-1 (CARB-2). Both integrons were encoded on a single XbaI macrorestriction fragment of approximately 10 kb. All isolates of DT 104 of this resistance phenotype contained the same inserted gene cassettes, irrespective of source and country of origin, supporting the suggestion of the spread of an epidemic clone. Sequence analysis of the quinolone resistance determining region (QRDR) of gyrA of 15 multiresistant strains conferring additional resistance to nalidixic acid and ciprofloxacin (R-type ACSSuSpTNxCp) identified two discrete base substitutions at codon Asp-87. Conversion of Asp-87 --> Asn was most commonly observed, in 7/10 human and 4/5 animal isolates, suggesting that this codon plays a major role in the development of ciprofloxacin resistance in multiresistant S. typhimurium DT 104.
对源自人类和动物的流行多重耐药鼠伤寒沙门氏菌DT104中的抗生素抗性基因流行病学进行了调查。从1984年至1997年间分离出的45株人类菌株和21株动物菌株中提取DNA，这些菌株包括在其他欧洲国家、美国、特立尼达和南非分离出的8株，对氨苄青霉素、氯霉素、链霉素、磺胺类药物、壮观霉素、四环素具有抗性（R型ACSSuSpT），通过聚合酶链反应（PCR）检测整合子的存在。在所有对ACSSuSpT具有抗性的菌株中均观察到整合子热点，通过两条约1.0和1.2 kb的离散条带确定为两个拷贝。对选定菌株的单个扩增子进行直接核苷酸测序表明，1.0 kb基因产物是ant(3")-Ia，负责对链霉素和壮观霉素的抗性；1.2 kb扩增子包含blaPSE-1基因，编码β-内酰胺酶PSE-1（CARB-2）。两个整合子均编码在一个约10 kb的单一XbaI宏观限制性片段上。这种抗性表型的所有DT104分离株都含有相同的插入基因盒，无论其来源和原产国如何，这支持了流行克隆传播的观点。对15株对萘啶酸和环丙沙星具有额外抗性的多重耐药菌株（R型ACSSuSpTNxCp）的gyrA喹诺酮抗性决定区（QRDR）进行序列分析，在第87位密码子Asp处鉴定出两个离散的碱基替换。在10株人类分离株中的7株和5株动物分离株中的4株中最常观察到Asp-87向Asn的转换，表明该密码子在多重耐药鼠伤寒沙门氏菌DT104中环丙沙星抗性的发展中起主要作用。
