Molecular characterization of Escherichia coli isolates recovered from broilers with cellulitis

Area of Science:

• Veterinary Microbiology
• Antimicrobial Resistance
• Poultry Health

Background:

• Avian cellulitis in broilers, caused by avian pathogenic Escherichia coli (APEC), leads to significant economic losses due to carcass rejections.
• Understanding the genetic relatedness and antimicrobial resistance profiles of APEC isolates is crucial for effective disease management and control in poultry.

Purpose of the Study:

• To analyze the genetic relatedness and antimicrobial resistance of E. coli isolates from broiler chickens with cellulitis.
• To determine if there is clonal spread of APEC or if clinical isolates exhibit genetic diversity.

Main Methods:

• Isolation and characterization of 107 E. coli strains from diseased broilers across 77 German poultry farms.
• Typing methods included serotyping, PCR-based phylotyping, and macrorestriction analysis with pulsed-field gel electrophoresis (PFGE).
• Investigation of virulence genes and antimicrobial susceptibility (disk diffusion), followed by PCR for resistance genes.

Main Results:

• A significant proportion of isolates belonged to the major APEC serotype O78:K80; phylogenetic group D was most common.
• Macrorestriction analysis revealed heterogeneous results with some clustering, indicating both diversity and potential relatedness among isolates.
• High antimicrobial resistance was observed: 83.8% resistant to at least one agent, 40% to at least three classes. Ampicillin resistance (blaTEM) was most frequent.
• Low resistance rates were found for ciprofloxacin (8%), and no resistance to 3rd generation cephalosporins or carbapenems.

Conclusions:

• Genetically diverse APEC strains associated with avian cellulitis are present within and among German poultry farms.
• Widespread antimicrobial resistance is a concern, but resistance to critically important antimicrobials remains low in these clinical isolates.