Application and Evaluation of the Matrix-Assisted Laser Desorption Ionization Time of Flight Mass Spectrometry Method to Identify Moraxella bovoculi and Moraxella bovis Isolates from Cattle

Moraxella bovis is a gram-negative bacterium and an etiologic agent of infectious bovine keratoconjunctivitis (IBK). IBK is associated with corneal ulceration, opacity (edema), photophobia, lacrimation, and epiphora. Moraxella bovoculi has been proposed as another causative agent in IBK, although M. bovis is still considered to have the greatest impact. M. bovis is an opportunistic pathogen that causes infection when irritation to the cornea occurs. Flies are major vectors although aerosols can also be another route. Three types of treatment are observed: topical, subconjunctival, and systemic. Reduced weight gain and decreased milk production cause a negative impact on the cattle industry. Identification of M. bovis and M. bovoculi can be performed using biochemical or DNA-based approaches, both of which may be time consuming and inconsistent between laboratories. A comparative evaluation of M. bovoculi and M. bovis identification was conducted using matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry with a database provided by Bruker Daltonics (BDAL database), the BDAL database supplemented with spectra generated in this study (UNL VDC database), and with polymerase chain reaction restriction fragment length polymorphism typing (PCR-RFLP). M. bovoculi (n=250) and M. bovis (n=18) isolates from cattle with or without IBK were used. MALDI-TOF MS using the UNL VDC database correctly identified 100% (250/250) of M. bovoculi and 94% (17/18) of the M. bovis isolates making it the most effective identification methodology for M. bovis and M. bovoculi isolates from cattle