Application of O-serotyping in a study of Providencia rettgeri (Proteus rettgeri) isolated from human and nonhuman sources

A somatic (O) antigen serotyping scheme for Providencia rettgeri (Proteus rettgeri) was modified to exclude O-type strains recently reclassified as urea-positive Providencia stuartii and was extended to include new serotypes to provide for serotyping on the basis of 93 O-antigens. Isolates from two hospitals, five public health laboratories, and nonhuman sources (polluted water and frogs) were serotyped. The 112 isolates collected from a large general hospital over a 99-month period were distributed among 42 O-serotypes. No serotype showed significant predominance that would suggest the occurrence of human strains that are more prone than others to cause human infections, but in an institution experiencing cross-infection, 11 of the 22 (50%) isolates belonged to one serotype. The 54 isolates from the five public health laboratories belonged to 33 serotypes, 15 of which were found also among hospital isolates. All but 5 of 99 frog isolates were typable, and the 94 typable isolates were separated into 25 serotypes. Each of the four isolates from polluted water samples was of a different serotype. Sixteen of the serotypes found in frogs and three found in water were also identified among human isolates.