Distribution of antibiotic resistant bacteria that are human pathogens and tritagonists in waterways
Thesis DisciplineCellular and Molecular Biology
Degree GrantorUniversity of Canterbury
Degree NameMaster of Science
Rivers draining agricultural and urban areas carry greater levels of antibiotic resistant Escherichia coli than rivers in unpolluted environments. The number and diversity of antibiotic resistant E. coli were measured in two Cantabrian rivers. Silver Stream (Māori: Whirinaki) is drains land that is used agriculture, and Avon River (Māori: Ōtākaro) draina urban environments. The rivers were sampled three times between January and November 2017. E. coli were enumerated on E. coli selective medium with or without supplementation of the antibiotics ciprofloxacin, ampicillin, rifampicin or chloramphenicol.
In summary, 60% of the E. coli isolates from Avon River grew on ampicillin, 1% on chloramphenicol and 1% on ciprofloxacin containing media. About 60% of the E. coli initially isolated on 1 μg/mL ciprofloxacin from Avon River grew on ciprofloxacin at or above 16 μg/mL, almost five times higher than the clinical breakpoint concentration.
Approximately 70% of randomly selected E. coli first isolated from Avon River on TBX medium with antibiotic supplementation were resistant to two or more antibiotics. Of the ciprofloxacin resistant isolates, 98% also grew on ampicillin, 33% on chloramphenicol, 88% on tetracycline, 54% on trimethoprim, 37% on gentamycin and 19% on kanamycin. In contrast, only 30% of Silver Stream isolates were resistant to at least two antibiotics. Fewer than 1% were resistant to ciprofloxacin or chloramphenicol.
The statistical analysis of this survey demonstrated that the two rivers accumulate different amounts of antibiotic resistant E. coli and that isolates from the two rivers are resistant to different concentrations of antibiotic.
The cause of resistance, or differential retention of resistant bacteria, is unknown. A whole genome sequencing of 50 randomly selected isolates from the two rivers was used to identify the resistance genes and alleles.