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Applied and Environmental Microbiology, April 2007, p. 2224-2229, Vol. 73, No. 7
0099-2240/07/$08.00+0     doi:10.1128/AEM.02099-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Novel Method for Rapid Assessment of Antibiotic Resistance in Escherichia coli Isolates from Environmental Waters by Use of a Modified Chromogenic Agar{triangledown}

A. J. Watkinson,1,2* G. R. Micalizzi,3 J. R. Bates,3 and S. D. Costanzo1

National Research Centre for Environmental Toxicology, 39 Kessels Road, Coopers Plains, Brisbane, Queensland, Australia 4108,1 Cooperative Research Centre for Water Quality and Treatment, PMB 3, Salisbury, South Australia, Australia 5108,2 Public Health Microbiology, Queensland Health Scientific Services, 39 Kessels Road, Coopers Plains, Queensland, Australia 41083

Received 5 September 2006/ Accepted 21 January 2007

We validated a novel method for screening Escherichia coli resistance to antibiotics in environmental samples using modified Difco MI agar (Becton Dickinson) impregnated with selected antibiotics (tetracycline, ampicillin, cephalexin, and sulfamethoxazole), termed MI-R. This method combines an existing rapid assessment technique for E. coli enumeration with clinical reference data for breakpoint analysis of antibiotic resistance and was developed to address issues encountered when clinical methods are used with environmental samples. Initial trials conducted using strains of E. coli with resistance to the selected antibiotics showed that this method was reproducible and accurate with respect to antibiotic resistance. Trials using wastewater effluent demonstrated the precision of the method, and the levels of resistance found in effluent were directly comparable to the levels of antibiotic resistance determined using the more traditional CLSI (formerly NCCLS) disk susceptibility test. All wastewater isolates growing on MI-R plates were confirmed to be resistant using the CLSI disk susceptibility test. Bacterial resistance to ampicillin (38% ± 4% overall), sulfamethoxazole, tetracycline (21% ± 3% overall), and ciprofloxacin (6% ± 1%) were found in wastewater effluent. A successful trial was also conducted with water collected from the Brisbane River, Australia. The levels of antibiotic resistance in E. coli ranged from 0 to 47% for ampicillin, from 0 to 24% for tetracycline, from 0 to 63% for sulfamethoxazole, and from 0 to 1% for ciprofloxacin, with the highest incidence of resistance associated with wastewater treatment plant discharges. This method has great potential for rapid and representative assessment of antibiotic resistance in E. coli and could allow increased sample analysis, resulting in greater confidence in spatial analysis in environmental studies.

* Corresponding author. Mailing address: National Research Centre for Environmental Toxicology, 39 Kessels Rd., Coopers Plains, Brisbane, QLD, Australia 4108. Phone: 61 7 3274 9004. Fax: 61 7 3274 9003. E-mail: a.watkinson{at}uq.edu.au.

{triangledown} Published ahead of print on 2 February 2007.

Applied and Environmental Microbiology, April 2007, p. 2224-2229, Vol. 73, No. 7
0099-2240/07/$08.00+0     doi:10.1128/AEM.02099-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Mariano, V., McCrindle, C. M. E., Cenci-Goga, B., Picard, J. A. (2009). Case-Control Study To Determine whether River Water Can Spread Tetracycline Resistance to Unexposed Impala (Aepyceros melampus) in Kruger National Park (South Africa). Appl. Environ. Microbiol. 75: 113-118 [Abstract] [Full Text]  
  • Watkinson, A. J., Micalizzi, G. B., Graham, G. M., Bates, J. B., Costanzo, S. D. (2007). Antibiotic-Resistant Escherichia coli in Wastewaters, Surface Waters, and Oysters from an Urban Riverine System. Appl. Environ. Microbiol. 73: 5667-5670 [Abstract] [Full Text]  


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