Characterization of classic and atypical serogroup O :11 Aeromonas : evidence that the surface array protein is not directly involved in mouse pathogenicity

A number of different techniques were used to analyse classic and atypical serogroup O:11 Aeromonas isolates. Five of seven atypical O:11, S layer-negative strains lacking a homogeneous LPS side-chain pattern exhibited varying degrees of mouse pathogenecity. One virulent atypical strain (AH-77) synthesized a surface array protein (SAP) but was unable to anchor it to the cell surface in an intact form, presumably due to a defect in its LPS architecture. Proteinase K digestion to remove the SAP, or growth at elevated temperatures (42 degrees C) to reduce the proportion of SAP synthesized from classic O:11 S layer-positive strains, did not alter their LD50 values in outbred mice. In addition, a spontaneous mutant, AS-180-1, that was S layer-negative was as virulent as the parental S layer-positive strain in the mouse model. These results suggest neither the SAP nor the characteristic serogroup O:11 homogeneous LPS side-chain pattern are directly involved in mouse pathogenicity.