Purpose: Determine AR, the presence of integrons and replicon types of plasmids in Dublin isolated from cattle and humans submitted to NARMS (1999-2011).
Methods: AR was determined to 15 antimicrobials using a semi-automated broth microdilution system (Sensitire®, Trek Diagnostic Systems, Inc., Cleveland, Ohio) for 272 cattle (C) and 69 human (H) isolates. Resistance was determined using Clinical and Laboratory Standards Institute breakpoints, when available. Isolates were screened for integrons (class 1, 2 and 4) and incompatibility (Inc) replicon types (Carattoli et al. scheme) using standard PCR protocols.
Results: Percent resistance was observed most often to: Ampicillin (63% C; 41% H), Ceftriaxone (19%C; 20%H), Chloramphenicol (60% C; 43% H), Kanamycin (51% C; 39% H), Streptomycin (69% C, 43% H), Sulfa antimicrobials (65% C; 49% H), and Tetracycline (67%C; 46% H). No resistance to Amikacin or Ciprofloxacin was observed. MDR (>5 antimicrobials) was observed in 43% of both cattle and humans isolates. The most common MDR pattern in cattle was Amoxicillin – Clavulanic Acid/Ampicillin/Cefoxitin/Ceftiofur/Ceftriaxone/Chloramphenicol/Kanamycin/Streptomycin/Sulfa/Tetracyline (n = 27) and Ampicillin/Chloramphenicol/Kanamycin/Streptomycin/Sulfa/Tetracycline (n=11) in humans. Only class 1 integrons were identified in 30% (n = 82) and 25% (n = 17) of the cattle and human isolates, respectively. The replicon types identified from both MDR and susceptible isolates were: FIIS (80% C; 91% H), A/C (52% C; 29% H), H1 (17% C;16% H), FIA (17% C; 3% H), I1 (7% C; 1% H), FIB (6% C; 3% H), P (3% C; 1% H) and N (1% C; 0% H ).
Significance: The presence of integrons and the “epidemic resistance plasmids” Inc FIIS, Inc A/C, Inc I1 and Inc N may be useful in addition to phenotypic susceptibility testing when studying the transmission of resistance genes and developing mitigation strategies.