Background: Pasteurella multocida is responsible for significant economic losses in pigs worldwide. In clinically diseased pigs, most P. multocida isolates are characterised as subspecies multocida, biovar 2 or 3 and capsular type A or D; however, there is little information regarding subspecies, biovars, and other capsular types of P. multocida isolates in Korea. Here, we provided information covering an extended time period regarding P. multocida in pigs with pneumonia in Korea using phenotypic and genotypic characterisations and data associated with the minimum inhibitory concentrations.
Results: The overall prevalence of P. multocida between 2008 and 2016 was 16.8% (240/1430), with 85% of the P. multocida isolates (204/240) coinfected with other respiratory pathogens. Of the 240 isolates, 166 were included in this study; all of these P. multocida isolates were characterised as subspecies multocida and the most prevalent phenotypes were represented by biovar 3 (68.7%; n = 114) and capsular type A (69.9%; n = 116). Additionally, three capsular type F isolates were identified, with this representing the first report of such isolates in Korea. All biovar 1 and 2 isolates were capsular types F and A, respectively. The virulence-associated gene distribution was variable; all capsular type A and D isolates harboured pmHAS and hsf-1, respectively (P < 0.001), with type F (biovar 1) significantly correlated with hsf-1 (P < 0.05) and pfhA (P < 0.01), biovar 2 highly associated with pfhA and pmHAS, and biovar 3 significantly correlated with hsf-1, pmHAS, and hgbB (P < 0.001), whereas biovar 13 was related only to hgbB (P < 0.05). The highest resistance rate was found to be to oxytetracycline (63.3%), followed by florfenicol (16.3%).
Conclusions: P. multocida subspecies multocida, biovar 3, and capsular type A was the most prevalent isolate in this study, and our findings indicated the emergence of capsular type F in Korea. Moreover, prudent use of oxytetracycline and florfenicol is required because of the identified high resistance rates. Further studies are required for continuous monitoring of the antimicrobial resistance, prevalence, and epidemiological characterisation of P. multocida, and experimental infection models are needed to define the pathogenicity of capsular type F.
Keywords: Antimicrobial resistance; Biovar; Capsular type; Pasteurella multocida; Virulence-associated gene.