Farm disinfectants select for cyclohexane resistance, a marker of multiple antibiotic resistance, in Escherichia coli.
OBJECTIVE
The aim of this study was to determine if three classes of farm disinfectants were able to select for ciprofloxacin or cyclohexane tolerant [indicative of a multiple antibiotic resistance (MAR) phenotype] Escherichia coli and if cyclohexane-tolerant E. coli could be isolated from farms.


RESULTS
Chicken slurry containing ca 1 : 99 ratio ciprofloxacin resistant : susceptible E. coli (10 different resistant strains examined) was treated for 24 h with each of the disinfectants and examined for survival of resistant : susceptible strains. Ciprofloxacin-sensitive (n=5) and -resistant (n=5) E. coli were grown with sublethal concentrations of the disinfectants and then plated to agar containing ciprofloxacin or overlaid with cyclohexane. Escherichia coli (n=389) isolated from farms were tested for cyclohexane tolerance. Minimum inhibitory concentrations (MIC) were determined against representative isolates and mutants. The disinfectants did not select for the ciprofloxacin-resistant E. coli in poultry slurry but following growth with each of the three disinfectants, higher numbers (P < or = 0.023) of cyclohexane-tolerant E. coli were isolated and these had a MAR phenotype. Of the 389 farm E. coli tested, only one was cyclohexane tolerant.


CONCLUSIONS
It is possible that in a farm environment, E. coli could be exposed to similar concentrations of the disinfectants that are selected for MAR type organisms under these laboratory conditions.


CONCLUSIONS
Data from this study suggest that cyclohexane-resistant E. coli are not common on farms, but in view of the ease of isolating them in the laboratory with farm disinfectants, further investigations on farms are warranted.
Randall
L P
LP
Department of Food and Environmental Safety, Veterinary Laboratories Agency (Weybridge), New Haw, Addlestone, Surrey, UK. l.randall@bla.defra.gsi.gov.uk
Clouting
C S
CS
Gradel
K O
KO
Clifton-Hadley
F A
FA
Davies
R D
RD
Woodward
M J
MJ
D016573:Agrochemicals / Q000494:pharmacology*; D000822:Animal Husbandry; D000818:Animals; D002645:Chickens; D002939:Ciprofloxacin; D003510:Cyclohexanes; D004202:Disinfectants / Q000494:pharmacology*; D024901:Drug Resistance, Multiple, Bacterial; D004783:Environmental Microbiology; D004926:Escherichia coli / Q000235:genetics* / Q000302:isolation & purification; D006801:Humans; D008372:Manure; D008826:Microbial Sensitivity Tests
D016573:Agrochemicals; D003510:Cyclohexanes; D004202:Disinfectants; D008372:Manure; D002939:Ciprofloxacin