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BackgroundTo investigate the presence of metallo-β-lactamase (MBL) genes and the genetic environment of the New Delhi metallo-β-lactamase gene bla NDM-1 in bacteria of food animal origin.Methodology/Principal FindingsGram-negative bacteria with low susceptibility to imipenem (MIC>8 µg/mL) were isolated from swab samples collected from 15 animal farms and one slaughterhouse in eastern China. These bacteria were selected for phenotypic and molecular detection of known MBL genes and antimicrobial susceptibility testing. For the bla NDM-1 positive isolate, conjugation and transformation experiments were carried out to assess plasmid transfer. Southern blotting was conducted to localize the bla NDM-1 genes, and DNA sequencing was performed to determine the sequences of bla NDM-1 and the flanking genes. In total, nine Gram-negative bacteria of four different species presented a MBL phenotype. bla NDM-1 was identified on a mobile plasmid named pAL-01 in an Acinetobacter lwoffii isolate of chicken origin. Transfer of pAL-01 from this isolate to E. coli J53 and JM109 resulted in resistance to multiple β-lactams. Sequence analysis revealed that the bla NDM-1 gene is attached to an intact insertion element ISAba125, whose right inverted repeat (IR-R) overlaps with the promoter sequence of bla NDM-1. Thus, insertion of ISAba125 likely enhances the expression of bla NDM-1.ConclusionThe identification of a bla NDM-1- carrying strain of A. lwoffii in chickens suggests the potential for zoonotic transmission of bla NDM-1 and has important implications for food safety.

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Aims: To evaluate the prevalence and antimicrobial resistance of Enterococcus species from chickens and pigs in Beijing and Shandong Province, China. Methods and Results: Swab samples were collected from four farms in Beijing and two in Shandong Province in 2009 and tested for Enterococcus. Minimum inhibitory concentrations of antimicrobial agents were determined using broth microdilution or agar screening methods. A total of 453 Enterococcus isolates were recovered, belonging to six different Enterococcus species. All isolates were sensitive to vancomycin. Resistance to tetracycline (92Á5%), amikacin (89Á4%), erythromycin (72Á8%) and rifampin (58Á1%), and high-level streptomycin resistance (HLSR, 50Á3%) were prevalent, while resistance to penicillins (7Á9% to penicillin and 4Á2% to ampicillin) was rare. The resistance rates to phenicols (chloramphenicol and florfenicol) and enrofloxacin, and high-level gentamicin resistance (HLGR) were approximately 30%. The vast majority of the Enterococcus isolates were classified as multidrug-resistant organisms. Conclusions: Resistance of Enterococcus sp. to most antimicrobials was more prevalent in China than in European or other Asian countries. Significance and Impact of the study: Our findings reveal a high level of antimicrobial resistance in Enterococcus isolates from food animals in China and underline the need for prudent use of antibiotics in chicken and pig production to minimize the spread of antibiotic-resistant enterococci.

The objective of this study was to clarify the molecular antimicrobial resistance mechanisms of Salmonella enterica serovar Indiana isolated from chickens in China. A total of 327 chicken intestinal content and feces were collected in Shandong, China in 2009. Isolates were serotyped and antimicrobial susceptibility testing was performed. Thirty-five (10.7%) Salmonella isolates were recovered, and 16 (45.7%) were Salmonella enterica serovar Indiana, which were resistant to at least 14 of 15 antimicrobial agents. The 16 Salmonella enterica serovar Indiana detected and other 13 Salmonella enterica serovar Indiana that were selected from 133 Salmonella enterica serovar Indiana isolated in 2008 were subjected to pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Then class 1 integron and drug resistance genes were detected by polymerase chain reaction. Linkage between plasmids and resistance components was determined by conjugation, electrotransformation, S1 nuclease-PFGE, polymerase chain reaction-based replicon typing and Southern blot assays. Regions flanking integrons were sequenced by modified random primer walking strategy. PFGE and MLST suggested that all the 29 Salmonella enterica serovar Indiana isolates that shared >78% similarity in PFGE patterns were of the same MLST type, ST17. Two kinds of class 1 integrons had different integrase genes and the same variable region (dfrA7/aadA4/IS26/aac(6')-Ib/blaOXA-1/catB3/arr-3), and additional antimicrobial resistance genes such as blaCTX-M-24, floR, and so on were detected on IncHI2 plasmids in 29 Salmonella enterica serovar Indiana, and seven plasmids were conjugative. Analysis of the genetic environment of the integrons suggested that these integrons might have been formed by the help of IS26. To our knowledge, the variable region in class 1 integrons is the longest reported in Salmonella to date. The unique integrons and multiple resistance genes co-located on the IncHI2 plasmid contributed to the dissemination of multidrug resistance.