title: Development of a selective culture medium for primary isolation of the main Brucella species.
abstract: Bacteriological diagnosis of brucellosis is performed by culturing animal samples directly on both Farrell medium (FM) and modified Thayer-Martin medium (mTM). However, despite inhibiting most contaminating microorganisms, FM also inhibits the growth of Brucella ovis and some B. melitensis and B. abortus strains. In contrast, mTM is adequate for growth of all Brucella species but only partially inhibitory for contaminants. Moreover, the performance of both culture media for isolating B. suis has never been established properly. We first determined the performance of both media for B. suis isolation, proving that FM significantly inhibits B. suis growth. We also determined the susceptibility of B. suis to the antibiotics contained in both selective media, proving that nalidixic acid and bacitracin are highly inhibitory, thus explaining the reduced performance of FM for B. suis isolation. Based on these results, a new selective medium (CITA) containing vancomycin, colistin, nystatin, nitrofurantoin, and amphotericin B was tested for isolation of the main Brucella species, including B. suis. CITA's performance was evaluated using reference contaminant strains but also field samples taken from brucella-infected animals or animals suspected of infection. CITA inhibited most contaminant microorganisms but allowed the growth of all Brucella species, to levels similar to those for both the control medium without antibiotics and mTM. Moreover, CITA medium was more sensitive than both mTM and FM for isolating all Brucella species from field samples. Altogether, these results demonstrate the adequate performance of CITA medium for the primary isolation of the main Brucella species, including B. suis.
authors.affiliation: Unidad de Sanidad Animal, Centro de Investigación y Tecnología Agroalimentaria (CITA), Gobierno de Aragón, Carretera de Montañana 930, 50059 Zaragoza, Spain.
authors.forename: M J
authors.initials: MJ
authors.lastname: De Miguel
authors.forename: C M
authors.initials: CM
authors.lastname: Marín
authors.forename: P M
authors.initials: PM
authors.lastname: Muñoz
authors.forename: L
authors.initials: L
authors.lastname: Dieste
authors.forename: M J
authors.initials: MJ
authors.lastname: Grilló
authors.forename: J M
authors.initials: JM
authors.lastname: Blasco
mesh_terms: D000818:Animals; D000890:Anti-Infective Agents / Q000494:pharmacology; D001431:Bacteriological Techniques / Q000379:methods*; D002002:Brucella / Q000187:drug effects / Q000254:growth & development / Q000302:isolation & purification*; D002006:Brucellosis / Q000175:diagnosis* / Q000662:veterinary*; D003470:Culture Media / Q000737:chemistry*; D006801:Humans; D012641:Selection, Genetic
chemical_list: D000890:Anti-Infective Agents; D003470:Culture Media