RESUMEN
In this study, 18 Avibacterium paragallinarum isolates collected in Taiwan from 1990 to 2003 were serotyped and tested for resistance to antimicrobial agents. Serotyping revealed that 13 isolates were Page serovar A and 5 isolates were Page serovar C. More than 75% of the isolates were resistant to neomycin, streptomycin and erythromycin. The most common resistance pattern (15 isolates, 83.3%) was neomycin-streptomycin. Furthermore, 88.9% of the isolates were resistant to two or more antibiotics. About 72% of isolates contained plasmids (pYMH5 and/or pA14). Plasmid pYMH5 encoded functional streptomycin, sulfonamide, kanamycin and neomycin resistance genes and revealed significant homology to a broad host-range plasmid, pLS88. Plasmid pA14 encoded a putative MglA protein and RNase II, both of which might be associated with virulence. Furthermore, seven isolates showed haemocin activity. Plasmid pYMH5 is the first multidrug-resistance plasmid reported in A. paragallinarum and it may facilitate the spread of antibiotic-resistance genes between bacteria. The putative virulence plasmid pA14 and haemocin-like activity in A. paragallinarum indicate two possible mechanisms which might be responsible for the pathogenesis.
Asunto(s)
Antibacterianos/farmacología , Bacteriocinas/metabolismo , Farmacorresistencia Bacteriana Múltiple/genética , Haemophilus paragallinarum/efectos de los fármacos , Haemophilus paragallinarum/patogenicidad , Plásmidos/genética , Animales , Secuencia de Bases , Pollos , Recuento de Colonia Microbiana/veterinaria , ADN Bacteriano/química , Brotes de Enfermedades/veterinaria , Relación Dosis-Respuesta a Droga , Farmacorresistencia Bacteriana/genética , Amplificación de Genes , Infecciones por Haemophilus/epidemiología , Infecciones por Haemophilus/microbiología , Infecciones por Haemophilus/veterinaria , Haemophilus paragallinarum/genética , Pruebas de Sensibilidad Microbiana/veterinaria , Reacción en Cadena de la Polimerasa , Enfermedades de las Aves de Corral/epidemiología , Enfermedades de las Aves de Corral/microbiología , Serotipificación/veterinaria , VirulenciaRESUMEN
Inactivated vaccines of Avibacterium paragallinarum provide protection and reduce the economic losses caused by infectious coryza. However, inactivated bacterins provide protection only against the Page serovars included in the vaccine. In this study, we investigated the immunological properties of a functional recombinant haemagglutinin protein (rHagA) derived from a Taiwan isolate strain A9 as the immunogen for vaccination. The rHagA subunit vaccine protected 71% of immunized chickens against 10(10) colony-forming units (CFU) of viable A9. Vaccinated chickens which showed no clinical signs of coryza developed haemagglutination inhibition (HI) titers of 1:10 or greater. Haemagglutination (HA) of serovars A and C was not affected by the presence of rHagA specific antiserum. The HA of rHagA could only be induced against formaldehyde-fixed chicken red blood cells (FA-RBCs). These results suggested that HagA is a moderate immunogen and might not be a major haemagglutinin in vivo. However, HagA might be involved in haemagglutination when treated serovar C aggregates fixed RBCs in vitro.