Unique class 1 integron and multiple resistance genes co-located on IncHI2 plasmid is associated with the emerging multidrug resistance of Salmonella Indiana isolated from chicken in China.

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.

Lai J ，Wang Y ，Shen J ，Li R ，Han J ，Foley SL ，Wu C ... -  《-》

Emergence of Salmonella enterica serovar Indiana and California isolates with concurrent resistance to cefotaxime, amikacin and ciprofloxacin from chickens in China.

The aim of this study was to investigate the prevalence and characterization of Salmonella concerning the poultry industry in China. A total of 170 non-duplicate Salmonella isolates were recovered from the 1540 chicken samples. Among the Salmonella isolates from chickens, the predominant serovars were S. enterica serovar Enteritidis (S. Enteritidis) (49/170, 28.8%), S. enterica serovar Indiana (S. Indiana) (37/170, 21.8%) and S. enterica serovar California (S. California) (34/170, 20.0%). High antimicrobial resistance was observed for ciprofloxacin (68.2%), amikacin (48.2%) and cefotaxime (44.7%). Of particular concerns were the 18 S. Indiana and 17 S. California isolates, which were concurrently resistant to cefotaxime, amikacin and ciprofloxacin. The bla genes, 16S rRNA methylase genes (armA, rmtD or rmtC) and five plasmid-mediated quinolone resistance (PMQR) determinants (aac(6')-Ib-cr, oqxAB, qnrB, qepA and qnrD) were identified in 18 S. Indiana and 17 S. California isolates. To clarify their genetic correlation, pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were further conducted. PFGE profiles showed that the majority of S. Indiana and S. California isolates were clonally unrelated with a standard cut-off of 85%. The results of MLST demonstrated that ST17 and ST40 were the most common ST types in S. Indiana and S. California isolates, respectively. Our findings indicated that the multiple antibiotic resistant S. Indiana and S. California isolates were widespread in chicken in China and might pose a potential threat to public health.

Wang Y ，Zhang A ，Yang Y ，Lei C ，Jiang W ，Liu B ，Shi H ，Kong L ，Cheng G ，Zhang X ，Yang X ，Wang H ... -  《-》

Characterization of multidrug-resistant Salmonella enterica serovars Indiana and Enteritidis from chickens in Eastern China.

A total of 310 Salmonella isolates were isolated from 6 broiler farms in Eastern China, serotyped according to the Kauffmann-White classification. All isolates were examined for susceptibility to 17 commonly used antimicrobial agents, representative isolates were examined for resistance genes and class I integrons using PCR technology. Clonality was determined by pulsed-field gel electrophoresis (PFGE). There were two serotypes detected in the 310 Salmonella strains, which included 133 Salmonella enterica serovar Indiana isolates and 177 Salmonella enterica serovar Enteritidis isolates. Antimicrobial sensitivity results showed that the isolates were generally resistant to sulfamethoxazole, ampicillin, tetracycline, doxycycline and trimethoprim, and 95% of the isolates sensitive to amikacin and polymyxin. Among all Salmonella enterica serovar Indiana isolates, 108 (81.2%) possessed the blaTEM, floR, tetA, strA and aac (6')-Ib-cr resistance genes. The detected carriage rate of class 1 integrons was 66.5% (206/310), with 6 strains carrying gene integron cassette dfr17-aadA5. The increasing frequency of multidrug resistance rate in Salmonella was associated with increasing prevalence of int1 genes (rs = 0.938, P = 0.00039). The int1, blaTEM, floR, tetA, strA and aac (6')-Ib-cr positive Salmonella enterica serovar Indiana isolates showed five major patterns as determined by PFGE. Most isolates exhibited the common PFGE patterns found from the chicken farms, suggesting that many multidrug-resistant isolates of Salmonella enterica serovar Indiana prevailed in these sources. Some isolates with similar antimicrobial resistance patterns represented a variety of Salmonella enterica serovar Indiana genotypes, and were derived from a different clone.

Lu Y ，Zhao H ，Sun J ，Liu Y ，Zhou X ，Beier RC ，Wu G ，Hou X ... -  《PLoS One》

Highly Drug-Resistant Salmonella enterica Serovar Indiana Clinical Isolates Recovered from Broilers and Poultry Workers with Diarrhea in China.

Highly drug-resistant Salmonella enterica serovar Indiana became the most common serovar in broilers with diarrhea in China over the course of this study (15% in 2010 to 70% in 2014). While most S. Indiana isolates (87%, 384/440) were resistant to 13 to 16 of the 16 antibiotics tested, 89% of non-S. Indiana isolates (528/595) were resistant to 0 to 6 antibiotics. Class 1 integrons and IncHI2-type plasmids were detected in all S. Indiana isolates, but only in 39% and 1% of non-S. Indiana isolates.

Gong J ，Wang C ，Shi S ，Bao H ，Zhu C ，Kelly P ，Zhuang L ，Lu G ，Dou X ，Wang R ，Xu B ，Zou J ... -  《-》

Detailed structure of integrons and transposons carried by large conjugative plasmids responsible for multidrug resistance in diverse genomic types of Salmonella enterica serovar Brandenburg.

To evaluate the incidence, molecular basis and distribution among genomic types of antimicrobial drug resistance in Salmonella enterica (S.) serovar Brandenburg isolates recorded in the Principality of Asturias, Spain. Thirty-seven S. Brandenburg isolates were tested for susceptibility to antimicrobial agents and typed by random amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE). PCR amplifications, together with DNA cloning and sequencing, were used to identify resistance genes, integrons and transposons and to establish the structure and physical associations between them. Conjugation experiments were applied to establish the location of the identified elements. Twenty-one isolates were resistant to one or more unrelated drugs. Resistances to streptomycin, tetracycline, kanamycin, chloramphenicol, ampicillin and trimethoprim-sulfamethoxazole, encoded by aadA1, tet(A) or tet(B), aphA1, catA1, bla(TEM) and dfrA1-sul1-sul3, respectively, were most frequently observed. Multidrug resistance (32.4%) was mainly mediated by mobile genetic elements. These included: (i) class 1 integrons (with dfrA1-aadA1 gene cassettes in their variable region), which were part of Tn21-related transposons associated with Tn9; (ii) a Tn1721-derivative containing tet(A); (iii) a defective Tn10 that carried tet(B), and was linked to an integron; and (iv) large conjugative plasmids carrying a class 1 integron-Tn21-Tn9-like structure, together with the Tn1721- or the Tn10-related element. Two-way-RAPD and XbaI-PFGE discriminated the isolates into 15 and 12 profiles, respectively. Complex genetic elements have apparently been responsible for the recruitment, assembly and dispersion of resistance genes among the highly diverse genomic types of S. Brandenburg, identified as causal agents of human salmonellosis in the Principality of Asturias, over recent years.

Martínez N ，Mendoza MC ，Rodríguez I ，Soto S ，Bances M ，Rodicio MR ... -  《JOURNAL OF ANTIMICROBIAL CHEMOTHERAPY》