Laboratory lessons in identifying Pasteurella bettyae

We discuss the phenotypic features of a clinically significant blood culture isolate that was ultimately identified as Pasteurella bettyae, with important laboratory learning points.

The blood culture from a female patient with septic shock from an unknown source grew a Gram-negative, oxidase-positive, coccobacillus that was initially identified by API® NH as Haemophilus influenzae (%ID=99.8; T=0.75). A respiratory source was therefore investigated for. The MALDI-TOF result, which was returned to the laboratory 4 weeks after blood culture became positive, revealed the isolate to be Pasteurella bettyae (score=2.305). P. bettyae is an unusual organism associated with gynaecological infections, such as Bartholin’s abscess. Local source control, such as incision and drainage of a Bartholin’s abscess, may accelerate resolution of sepsis. The laboratory misclassification of P. bettyae as H. influenzae using API® NH may lead to misidentification of the source of infection.

1. Correctly identifying P. bettyae as the cause of a Gram-negative coccobacillus bacteremia can prompt suspicion of a gynaecological source of sepsis.

2. P. bettyae and H. influenzae, as members of the same family Pasteurellaceae, have overlapping morphological and biochemical features that can lead to laboratory misclassification. A catalase test and x+v plates can clearly differentiate the isolates (discussed further in poster). It is recommended that laboratories perform both tests, with MALDI-TOF confirmation if possible, rather than rely solely on the result of an API® NH.