Disk prediffusion is a reliable method for testing colistin susceptibility in porcine E. coli strains

Abstract

19During the last few years, acquired resistance to colistin in , but also in other 20 bacterial species, has been reported. It disk diffusion assay, suggesting acquired resistance in 15 strains (9.6 %). The E-test and disk 29 prediffusion assay generated results within acceptable levels compared to the reference agar 30 dilution assay. The categorical agreement with the results obtained the agar dilution 31 method were good to very good for all tests, except the disk diffusion assay. In conclusion, 32 current results suggest that, in addition to the E-test, the disk prediffusion test is a reliable, 33 alternative agar-based colistin susceptibility method for testing colistin susceptibility of 34 isolates in diagnostic bacteriology.

Use of colistin-containing products within the European Union and European Economic Area (EU/EEA): development of resistance in animals and possible impact on human and animal health

“…More recently, the pre-disk diffusion test has been used successfully in which colistin tablets are allowed an initial 2 h pre-diffusion before the isolate is added to the medium for another 18 h of incubation. Both this pre-disk diffusion test and the Etest give comparable results to MIC determination using the agar dilution technique [91]. The Etest has been shown to be unreliable in particular for Pseudomonas spp., Acinetobacter spp.…”

“…Different techniques, such as broth microdilution [89], agar dilution and Etest [90,91] have been used, but their accuracy is questionable because of the cationic properties of colistin [92]. The EUCAST clinical breakpoints for Enterobacteriaceae (E. coli and Klebsiella spp., but excluding Proteus spp., Morganella morganii, Providencia spp.…”

High prevalence of Salmonella enterica subsp. diarizonae in tonsils of sheep at slaughter

“…One reason for the resistant strains found in lambs can be that colistin is used for therapy in lambs but not in adult sheep (Gousia et al, 2011). Another reason can be that agar diffusion method gave false resistant results due to low diffusion of colistin into the agar (Boyen et al, 2010). The reason for the sensitive strains found in ewes can be that Luque et al (2009) used 50 μg/disk instead of 25 μg/disk.…”

Polymyxins: Antibacterial Activity, Susceptibility Testing, and Resistance Mechanisms Encoded by Plasmids or Chromosomes

“…However, resistance to colistin has increasingly been reported (10%) among porcine-pathogenic E. coli strains in Belgium (63), and the emergence of resistance has been described for cattle (64). Moreover, some recent data revealed the possibility of horizontal transmission from farm animals to humans in Asia (65).…”