Quinolone resistance-determining regions of gyrA and parC in Pasteurella multocida strains with different levels of nalidixic acid resistance.

Pasteurella multocida causes sporadic or epidemic diseases among different animal species, including focal and systemic infections in humans. Penicillin is the drug of choice for treatment of Pasteurella infections, but third-generation cephalosporins and fluoroquinolones are a good alternative for betalactamase-producing strains or for allergic patients (1, 10). Quinolone resistance in gram-negative bacteria is increasing, with different mutations occurring in the quinolone resistance-determining regions (QRDR) of the gyrA and parC genes, one of the main causes of resistance (3, 5–9). In an attempt to determine if this mechanism also occurs in P. multocida, both QRDR were isolated and sequenced from six isolates from animal (PM25 and its derivative PM1024) and human clinical (16Q, 14Q, and 15Q) origins (Table 1). All strains