LAUSR

Gallibacterium anatis (G. anatis) is able to cause lesions such as oophoritis, follicle degeneration, salpingitis, peritonitis in chickens, rendering loss in egg production, and increased mortality in egg-laying chickens [7]. Currently, aminoglycosides and beta-lactam antibiotics have been widely used to treat G. anatis infection. However, irrational use of antibiotics can lead to the development of antibiotic resistance. The increasing multi-drug resistance is complicating the treatment of the infections related to G. anatis [1]. However, the mechanism of multi-drug resistant in G. anatis remains poorly understood. Integrons are known to be one of the mobilizable elements that capture external antibiotic resistance gene cassettes and result in the rapid spread of resistance in Gram-negative bacteria [4]. To date, whether integrons and associated resistance genes exist in G. anatis has not been explored in depth. In the present study, the detection of integrons among 61 G. anatis strains isolated from diseased hens in central China was carried out by PCR as previously reported [8]. The DNA sequences of gene cassettes were compared with the sequences deposited in the NCBI database using the BLAST program (http://www.ncbi.nlm.nih.gov/BLAST /). Antibiotic susceptibility to 13 antibiotics of G. anatis isolates was assessed as previously reported [5]. The results showed that 31.2% (19/61) of the isolates were positive for intI1, 94.7%(18/19) of which were positive for the variable region. No intI2 or intI3 were detected in any of the isolates examined. We then identified five different class 1 integron gene cassette arrays in the intI1-positive G. anatis isolates: aadB-aadA1-blaOXA-10-aadA1 (Accession No. KU728263), aadB-PSE-1 (Accession No. KU145265), aadB-aadA1 (Accession No. KU145267), aadA2 (Accession No. KU145268), and aadB (Accession No. KU145266) and found that their overall detection rates were 68.4% (13/19), 10.5% (2/19), 84.2% (16/19), 26.3% (5/19), and 26.3% (5/19), respectively. In this study, class 1 integrons were firstly identified in clinical G. anatis isolates and the incidence of class 1 integrons occurred in G. anatis (31.1%, 19/61) was less than that in klebsiella pneumonia (60.1%) [9] and in E. coli (62.2%) [2]. Most importantly, extended-spectrum β-lactamases (ESBLs) genes blaOXA-10 with high incidence (68.4%, 13/19) and beta-lactamase gene PSE-1 (10.5%, 2/19) were also firstly discovered from class 1 integrons in G. anatis isolates. BlaOXA-10 has been found within integrons mainly in Pseudomonas aeruginosa and Salmonell, resulting in ESBLs producing bacteria spread widely among humans and animals [3]. Class 1 integrons are often present in plasmids, transposons, and insertion sequences, and their horizontal movement depends on both transduction and conjugational processes [4]. Furthermore, natural transformation, a common feature of G. anatis [6], may facilitate interspecies transfer of integrons and gene cassettes, especially blaOXA-10. In brief, our study demonstrated the presence of blaOXA-10 and PSE-1 within class 1 integrons in G. anatis isolates, which may accelerate the dissemination of ESBLs among different Gram-negative bacteria. Therefore, it is necessary to focus on the detection and surveillance of ESBLs genes in G. anatis isolates, and to trace the source of the resistance genes to lessen the occurrence of multi-resistant strains (Figures 1, 2).