Abstract
Resistance to last-resort antibiotics is significant public health issue. Antibiotic use in animal husbandry may be a driver of resistance that can subsequently be disseminated via the food chain. This study sought to determine the level of polymyxin resistance in Gram-negative pathogens present in Australian poultry, particularly the presence of mobilizable mechanisms of polymyxin resistance. Cloacal swabs from 213 birds were taken in a point prevalence survey from six different farms at a Victorian chicken processing facility. Colistin resistant organisms were recovered by direct plating on CHROMagar COL-APSE media. Bacterial isolates were identified and analysed by MALDI-TOF, biochemical and genotypic assays. The 213 specimens yielded 57 (26.8%) colistin-resistant Gram-negative organisms, all of which have been previously described as exhibiting intrinsic resistance to polymyxin antibiotics. The most frequent organism was identified as Hafnia paralvei (40/57; 70%). Other colistin-resistant organisms included Aeromonas hydrophila (16%), Myroides odoratus (7%), Alcaligenes faecalis (5%), and Pseudochrobactrum spp (2%). No mobile colistin resistance (mcr) genes were detected. Polymyxin-resistant organisms are widely distributed in the food chain, with over a quarter of the birds tested yielding a polymyxin-resistant organism. However, strains containing mcr genes remain rare in Australian poultry.
Highlights
Polymyxin B and E are cationic antimicrobial peptides currently reserved as a last resort treatment for serious infections caused by multi-drug resistant Gram-negative bacteria (Poirel et al, 2017)
Other organisms which were recovered on CHROMagar COL-APSE media included Aeromonas hydrophila (n = 9; 16.1%), Alcaligenes faecalis (n = 3; 5.3%), and Myroides odoratus (n = 4; 7.1%)
Polymyxin resistant organisms were recovered from Australian poultry samples, all the organisms recovered have been previously described as intrinsically resistant to polymyxins
Summary
Polymyxin B and E (colistin) are cationic antimicrobial peptides currently reserved as a last resort treatment for serious infections caused by multi-drug resistant Gram-negative bacteria (Poirel et al, 2017). Colistin has been used in human and veterinary medicine for over 50 years, it has recently become increasingly important in the treatment of infections with carbapenem-resistant organisms where few treatment options remain. Enterobacteriaceae such as Serratia spp. and Proteus spp., as well as Gram-negative cocci such as Neisseria are well-known to be intrinsically resistant to colistin. Less has been documented about other intrinsically colistin-resistant organisms in the food chain. The increased reliance on this agent has forced us to reconsider how polymyxins are used, in light of the emergence of mobilisable colistin resistance.
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