Nagy E, Pragai Z, Kóczián Z, Hajdú E, Fodor E
Department of Clinical Microbiology, Albert Szent-Györgyi Medical School, Szeged, Hungary.
Acta Microbiol Immunol Hung. 1998;45(3-4):433-46.
Chromosomal or plasmid-encoded beta-lactamases are the most frequent causes of resistance to broad-spectrum beta-lactam antibiotics in clinical isolates of Gram-negative bacteria. Different screening methods can be used for their detection during routine laboratory work, while molecular biological methods may help in the detection of the genetic background of the phenotypic resistance. Clinical isolates of Klebsiella pneumoniae (170) and Enterobacter cloaceae (82) were obtained from different parts of Hungary, whereas those of Serratia marcescens (15) were isolated in our Department from a nosocomial outbreak. Disk diffusion and the Etest were used to screen inducible Class C beta-lactamase and plasmid-mediated extended spectrum beta-lactamases (ESBLs) among clinical isolates of Enterobacteriaceae. Single-strand conformation polymorphism (SSCP) analysis of the PCR products obtained after using SHV-specific primers revealed the presence of SHV-2 and SHV-5 ESBL among 170 K. pneumoniae strains in 12 and 3 cases, respectively. The results of the screening methods and the PCR-SSCP analysis suggested that 14 of the 15 S. marcescens strains not only produced the Class C, inducible chromosomal beta-lactamase, but also acquired a plasmid-mediated SHV-2-type ESBL. One strain isolated from the environment during the outbreak was genetically related to the other isolates, as demonstrated by the different typing methods, but it did not produce ESBL. The in vivo transfer of SHV-2 gene was assumed from an SHV-2 positive K. pneumoniae strain present in the same ward, in the same patient and at the same time. A very high prevalence of the stable derepressed mutants of E. cloaceae was confirmed among the Hungarian isolates. Seventy seven per cent of the strains produced high amounts of beta-lactamase without induction being responsible for their resistance to third-generation cephalosporins. Nineteen per cent of the strains were inducible when cefoxitin or imipenem was used, as confirmed by direct measurement of the MICs with the Etest.
染色体或质粒编码的β-内酰胺酶是革兰氏阴性菌临床分离株对广谱β-内酰胺抗生素耐药的最常见原因。在常规实验室工作中可使用不同的筛选方法来检测它们，而分子生物学方法可能有助于检测表型耐药的遗传背景。肺炎克雷伯菌（170株）和阴沟肠杆菌（82株）的临床分离株来自匈牙利不同地区，而粘质沙雷氏菌（15株）是在我们科室从一次医院感染暴发中分离得到的。采用纸片扩散法和Etest法筛选肠杆菌科临床分离株中的可诱导C类β-内酰胺酶和质粒介导的超广谱β-内酰胺酶（ESBLs）。使用SHV特异性引物后获得的PCR产物的单链构象多态性（SSCP）分析显示，在170株肺炎克雷伯菌菌株中，分别有12株和3株存在SHV-2和SHV-5 ESBL。筛选方法和PCR-SSCP分析结果表明，15株粘质沙雷氏菌中的14株不仅产生C类可诱导染色体β-内酰胺酶，还获得了质粒介导的SHV-2型ESBL。暴发期间从环境中分离出的一株菌株与其他分离株存在遗传相关性，不同的分型方法证明了这一点，但它不产生ESBL。同一病房、同一患者、同一时间存在的一株SHV-2阳性肺炎克雷伯菌菌株推测发生了SHV-2基因的体内转移。匈牙利分离株中阴沟肠杆菌稳定去阻遏突变体的患病率非常高。77%的菌株在未诱导的情况下产生大量β-内酰胺酶，这是它们对第三代头孢菌素耐药的原因。用Etest直接测量MIC证实，19%的菌株在用头孢西丁或亚胺培南时是可诱导的。
