Environmental reservoirs of antibiotic resistant bacteria

After a year of nagging by Michiel I have finally put together my first post and hope to make this a regular occurrence!

A current research project is to investigate the prevalence of antibiotic resistant Enterobacteriaceae sp. in coastal bathing waters and associated freshwater streams and rivers.  Previous work by other researchers including work done by Gaze and collaborators at Warwick University, Greg Amos and Liz Wellington, has shown that waste water treatment plants introduce antibiotic resistant organisms into rivers. A key question is whether these environmental reservoirs lead to human exposure.

Water samples from bathing waters and associated freshwater sources were analysed during the 2012 bathing season by Lihong Zhang, Research Fellow. Samples were concentrated and plated onto non-selective plates and third generation cephalosporins (3GCs). We were particularly interested in CTX-M gene carriage, a group of genes that has emerged in opportunistic Gram-negative pathogens in recent years.


Cefotazime selective plates with 3GC resistant coliforms (pink) and E. coli violet (thanks to Matthew Purnell  and Junho Scott for photos (4th year special study unit medical students)

Preliminary results suggest that CTX-Ms are carried by approximately 1:1000 enteric bacteria in bathing waters and associated fresh waters, with prevalence higher in E. coli than other genera. Human exposure risk is likely to be a function of E. coli count, with higher risk associated with exposure to freshwater sources associated with bathing waters. Preliminary data also suggests that CTX-M gene diversity is high; whilst the majority of genes are CTX-M-15 and CTX-M-14 a significant minority belong to other genotypes and are currently being characterised.


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