Pasteurized whole milk confers reduced susceptibilities to the antimicrobial agents trimethoprim, gatifloxacin, cefotaxime and tetracycline via the marRAB locus in Escherichia coli.
We inoculated pasteurized whole milk with Escherichia coli strains GC4468 (intact marRAB locus), JHC1096 (Delta marRAB), or AG112 (Delta marR), and incubated each overnight at 37 degrees 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 (P0.05), 1.5-fold for gatifloxacin (P0.05), 2.0-fold for cefotaxime (P=0.008), and 1.4-fold for tetracycline (P0.05). After culturing GC4468 on milk count agar the MICs were enhanced 3.4-fold for trimethoprim (P0.05), 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 microg/ml (CLSI). The MICs of the antimicrobial agents for JHC1096 cells after culturing in pasteurized whole milk were indistinguishable (P0.05) 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.
Peng
Yang
Y
Department of Biology, Eastern New Mexico University, Portales, New Mexico 88130, USA.
Hernandez
Ricardo L
RL
Crow
Robert R
RR
Jones
Suzanna E
SE
Mathews
Sara A
SA
Arnold
Ayanna M
AM
Castillo
Eliseo F
EF
Moseley
Jennifer M
JM
Varela
Manuel F
MF
D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002417:Cattle; D002439:Cefotaxime / Q000494:pharmacology*; D004926:Escherichia coli / Q000187:drug effects* / Q000235:genetics; D029968:Escherichia coli Proteins / Q000187:drug effects / Q000235:genetics; D005260:Female; D024841:Fluoroquinolones / Q000494:pharmacology*; D005519:Food Preservation / Q000379:methods; D000077734:Gatifloxacin; D008826:Microbial Sensitivity Tests; D008892:Milk / Q000187:drug effects* / Q000382:microbiology*; D012097:Repressor Proteins / Q000187:drug effects / Q000235:genetics; D013752:Tetracycline / Q000494:pharmacology*; D014295:Trimethoprim / Q000494:pharmacology*
D000900:Anti-Bacterial Agents; D029968:Escherichia coli Proteins; D024841:Fluoroquinolones; C080004:MarR protein, E coli; D012097:Repressor Proteins; D014295:Trimethoprim; D013752:Tetracycline; D000077734:Gatifloxacin; D002439:Cefotaxime