Lipopolysaccharide subtypes of Haemophilus influenzae type b from an outbreak of invasive disease.

Thirty isolates of Haemophilus influenzae type b were obtained during an outbreak of invasive H. influenzae type b disease and were classified by the electrophoretic profile of their lipopolysaccharide (LPS). The LPS was extracted by a rapid micromethod and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and silver staining. The isolates could be divided into 1 of 14 subtypes based on the profile of two to four bands. No subtype was predominant. However, all isolates obtained from duplicate sites of the same individual were of the same subtype. Isolates obtained from two patients (6 weeks apart) who attended the same day-care center differed in LPS subtype but were identical in their major outer membrane protein electrophoretic profile. Nasopharyngeal cultures were obtained from healthy children, their immediate families, and employees of the day-care center. Of 13 H. influenzae isolates examined from these contacts, only 1 was type b, which was obtained from a day-care worker and had the same LPS subtype and major outer membrane protein electrophoretic profile as one of the disease isolates. The remaining nasopharyngeal isolates were untypable, and most, but not all, were different in LPS pattern. Thus, LPS subtyping of H. influenzae type b may be useful in examining the predominance or transmission of a strain during an outbreak and may distinguish some strains not differentiated by outer membrane protein pattern.