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Screening for Antibiotic-Resistance Genes and Class 1 Integrons in Commensal Bacteria in Agricultural and Other Environments and their Potential Transfer to Pathogenic Bacteria


Antibiotic resistance in pathogenic bacteria causes difficulties in effectively treating some bacterial
infections. Bacteria may acquire resistance genes through Class 1 integrons under environmental
pressures. Integrons have been widely reported in clinical isolates and isolates from food animals.
Recently, the presence of integrons in urban and pristine areas has drawn attention to the transfer of
resistance genes between integron-associated settings. Investigating the presence of Class 1 integrons
in agricultural and other environments could help us recognize resistance gene reservoirs and their
movements among ecosystems in response to various pressures. <P>

Objectives were: <BR/>
1. To assess the distribution of antibiotic resistance genes and Class 1 integrons in animal fecal samples
and agricultural environment samples; non-farm environment samples were tested as well, for
comparison. The obtained information should provide a better understanding of the potential
reservoirs for antibiotic resistance genes present in farm and other environments. <P>

2. For commensal isolates that were Class 1 integron-positive, conjugation experiments were
conducted in the samples in which the Class 1 integron-positive isolates were originally present to
estimate their potential transfer to pathogenic bacteria under various conditions.

More information

Findings: Levels of total and antibiotic resistant bacteria were similar in samples of soil, feces and water from cattle operations and city locations. Class 1 integrons were found in fecal and water samples from farms and city locations, as well as in soil, unused animal feed, compost and manure. This indicates that mobile antibiotic resistance genes are present in both cattle operations and non-farm environments. This study revealed that integron-positive commensal bacteria in cattle operations do not play an important role in the rapid spread of antibiotic resistance. However, one bacterial isolate from dog feces in a city dog park transferred its Class 1 integron to Escherichia coli O157:H7. The presence of antibiotic resistance genes in both cattle operations and non-farm environments suggests that antibiotic resistance is a complex ecological issue. Activities in cattle operations do not exert more obvious pressure than urban activities on the selection of Class 1 integron antibiotic resistance. Our findings highlight the need for comprehensive studies in various environments to determine the type and level of selection pressure and its effect on the development, persistence and transmission of antibiotic resistance.

Sofos, John
Colorado State University
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