Expression of AmpC beta-lactamase in Enterobacter cloacae isolated from retail ground beef, cattle farm and processing facilities.
OBJECTIVE
To better understand antibiotic resistance of Enterobacter cloacae isolates originated from food animals, the phenotypic and genotypic resistance of Ent. cloacae isolates from retail ground beef, cattle farm, processing facilities and clinical settings were investigated.


RESULTS
The ampC, ampD and ampR genes in the isolates were sequenced and analysed. beta-Lactamase activities and beta-lactamase profiles of the isolates were analysed by the enzymatic hydrolysis of nitrocefin and isoelectric focussing, respectively. The ampC gene of the Ent. cloacae isolate was cloned and transformed into Escherichia coli strains. The genomic DNA profiles of Ent. cloacae isolates were analysed by using pulse field gel electrophoresis (PFGE). Mutation at one residue (Val-54-->Ile) in the AmpR amino acid sequence was consistently found in Ent. cloacae isolates that were resistant to a broadspectrum of beta-lactam agents. The enzyme activity in the isolates was induced by cefoxitin. The pI (isoelectric point) of the enzymes produced by the test strains ranged from 8.4 to 8.9. Cloning of ampC gene of the Ent. cloacae isolate conferred the resistance to ampicillin, cephalothin and amoxicillin in recipient E. coli strains. One recipient of E. coli O157:H7 strain additionally acquired resistance to ceftiofur. The genomic analysis of Ent. cloacae isolates by PFGE showed that the isolates from various sources were genetically unrelated.


CONCLUSIONS
The spread of diverse clones of AmpC-producing Ent. cloacae occurred in the ecosystem and retail products.


CONCLUSIONS
Our findings suggested that AmpC-producing Ent. cloacae could be a contributor in spreading beta-lactamase genes in farm environments and food processing environments.
Kim
S-H
SH
Department of Nutrition and Food Science, University of Maryland, College Park, MD 20742, USA. shinkim@umd.edu
Wei
C-I
CI
D000595:Amino Acid Sequence; D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics*; D002417:Cattle; D016972:Enterobacter cloacae / Q000187:drug effects / Q000201:enzymology / Q000235:genetics*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D020869:Gene Expression Profiling / Q000379:methods; D015964:Gene Expression Regulation, Bacterial / Q000235:genetics; D005798:Genes, Bacterial / Q000235:genetics; D005838:Genotype; D008460:Meat / Q000382:microbiology*; D009238:N-Acetylmuramoyl-L-alanine Amidase / Q000235:genetics; D010641:Phenotype; D010802:Phylogeny; D018440:beta-Lactam Resistance / Q000235:genetics; D001618:beta-Lactamases / Q000235:genetics*; D047090:beta-Lactams / Q000494:pharmacology
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D047090:beta-Lactams; C071526:AmpR protein, Bacteria; C062460:AmpD protein, Bacteria; D009238:N-Acetylmuramoyl-L-alanine Amidase; C048795:AmpC beta-lactamases; D001618:beta-Lactamases