Detection of common mobile genetic elements and genotyping of multidrug-resistant Gram-negative bacilli in blood specimens from septicemia patients in southern China Yongyu Rui,* Wengting Lu,* Si Li, Cancan Cheng, Jingjing Sun, Qiu Yang Laboratory Medicine Center, Nanfang Hospital, Southern Medical University, Guangzhou, People’s Republic of China *These authors contributed equally to this work Background: Integron, ISCR1 and complex class 1 integrons lead bacteria to become resistant to antibiotic regimens. The aim of this study was to detect common mobile genetic elements of multidrug-resistant Gram-negative bacilli and evaluate the genotyping of these bacilli in blood specimens from septicemia patients in southern China. Methods: A total of 837 Gram-negative bacilli including 578 strains containing Enterobacteriaceae and 259 strains containing non-fermentative bacilli were investigated in blood samples collected from septicemia patients between 2011 and 2014 in southern China. Mobile genetic elements, such as class 1 integrons, the insertion sequence common region 1 (ISCR1), and complex class 1 integrons, were detected from the 837 strains. Results: Twenty-seven types of gene cassette arrays were found among 837 strains in which 492 (58.8%) class 1 integron-positive isolates and 254 (51.6%) gene cassette-positive isolates were found, including the first description of two types, aacA4-blaIMP-1-blaOXA-30-catB3 and aac(6′)-II-aadA13-cmlA8-blaOXA-10, in the corresponding species and two gene cassettes, putative helicase and aadA-like, originally detected in integrons. Twelve types of ISCR1-linked resistance gene regions in 196 ISCR1-positive bacilli and seven different types of complex class 1 integron-positive strains were obtained including four distinct complex class 1 integrons that have never been described in any species. Enterobacterial repetitive intergenic consensus (ERIC)-PCR fngerprinting showed that isolates with identical gene profles were clonally unrelated. Conclusion: Our results indicated that we should pay more attention to enhance the quality of infection control measures and prevent hospital infection, so as to avoid the outbreak of multidrug-resistant Gram-negative bacilli. Keywords: septicemia, multidrug-resistant, integron, ISCR1, complex class 1 integrons