Correlation between ability of Ornithobacterium rhinotracheale to agglutinate red blood cells and susceptibility to fosfomycin.

Twenty five freeze-dried isolates of Ornithobacterium rhinotracheale were used for the determination of minimum inhibitory concentrations (MIC) against the antibiotic fosfomycin (Fosbac, produced by Bedson SA, consisting of a 25% mixture of fosfomycin). The same isolates were tested for their ability to haemagglutinate chicken red blood cells. Ten of the 25 isolates were found to be susceptible to fosfomycin (MIC values below 128 ug/ml). All of these isolates were able to agglutinate red blood cells. This is the first report on the ability of O. rhinotracheale to agglutinate red blood cells. The remaining 15 isolates were resistant to fosfomycin (MIC values above 128 ug/ml). Only five of these isolates were found to have the ability to agglutinate red blood cells. There appears to be a correlation between the ability of O. rhinotracheale isolates to agglutinate red blood cells and their susceptibility to fosfomycin. The ability of certain isolates of O. rhinotracheale to agglutinate red blood cells, raises the questions of differences in virulence between the isolates which can agglutinate red blood cells and those which cannot and the use of this ability to agglutinate red blood cells as an alternative method for serotyping O. rhinotracheale.