Pasteurized whole milk confers reduced susceptibilities to the antimicrobial agents trimethoprim, gatifloxacin, cefotaxime and tetracycline via the marRAB locus in Escherichia coli

• Published in: Journal of dairy research 2008-11, Vol.75 (4), p.491-496
• Main Authors: Peng, Yang, Hernandez, Ricardo L, Crow, Robert R, Jones, Suzanna E, Mathews, Sara A, Arnold, Ayanna M, Castillo, Eliseo F, Moseley, Jennifer M, Varela, Manuel F
• Format: Article
• Language: English
• Subjects: Animal productions; Animals; Anti-Bacterial Agents - pharmacology; antibiotic resistance; Antimicrobial agent; Antimicrobial agents; Bacteria; bacterial contamination; Biological and medical sciences; Cattle; cefotaxime; Cefotaxime - pharmacology; Dairy farms; Disease; dosage; E coli; Escherichia coli; Escherichia coli - drug effects; Escherichia coli - genetics; Escherichia coli Proteins - drug effects; Escherichia coli Proteins - genetics; Female; Fluoroquinolones - pharmacology; food contamination; Food contamination & poisoning; Food industries; food microbiology; food pathogens; Food Preservation - methods; Fundamental and applied biological sciences. Psychology; gatifloxacin; Infectious diseases; loci; marRAB locus; microbial genetics; Microbial Sensitivity Tests; Microbiology; Milk; Milk - drug effects; Milk - microbiology; Milk and cheese industries. Ice creams; minimum inhibitory concentration; Molecular biology; multiple drug resistance; Pasteurization; pasteurized milk; Repressor Proteins - drug effects; Repressor Proteins - genetics; susceptibility; Terrestrial animal productions; tetracycline; Tetracycline - pharmacology; trimethoprim; Trimethoprim - pharmacology; Vertebrates; whole milk
• ISSN: 0022-0299; 1469-7629
• DOI: 10.1017/S0022029908003567

We inoculated pasteurized whole milk with Escherichia coli strains GC4468 (intact marRAB locus), JHC1096 (Δ marRAB), or AG112 (Δ marR), and incubated each overnight at 37°C. All strains were then recovered from the milk cultures, and susceptibilities to antimicrobial agents were determined by the E-test strip method (CLSI). Cells of strain GC4468, prior to culturing in milk, were susceptible to trimethoprim, gatifloxacin, cefotaxime and tetracycline. After culturing GC4468 in pasteurized milk, however, the minimal inhibitory concentrations (MICs) increased 1·4-fold for trimethoprim (P⩽0·05), 1·5-fold for gatifloxacin (P⩽0·05), 2·0-fold for cefotaxime (P=0·008), and 1·4-fold for tetracycline (P⩾0·05). After culturing GC4468 on milk count agar the MICs were enhanced 3·4-fold for trimethoprim (P⩽0·05), 10-fold for gatifloxacin (P=0·001), 7·1-fold for cefotaxime (P=0·011), and 40·5-fold for tetracycline (P=0·074), but exhibiting tetracycline resistance with a mean MIC of 74·7±18·47 μg/ml (CLSI). The MICs of the antimicrobial agents for JHC1096 cells after culturing in pasteurized whole milk were indistinguishable (P⩾0·05) from baseline MICs measured before culturing in the same type of milk. Thus, Esch. coli cells harbouring the marRAB locus exhibit reduced susceptibilities to multiple antimicrobial agents after culturing in pasteurized whole milk.