Antimicrobial susceptibility of Pasteurella multocida and Haemophilus parasuis isolates associated with porcine pneumonia

Pasteurella multocida and Haemophilus parasuis pig isolates obtained in the Czech Republic were tested for their susceptibility against selected antimicrobial agents by broth microdilution method between 2008 and 2011. A low degree of resistance was observed for ampicillin, amoxicillin/clavulanic acid, ceftiofur, tulathromycin, tilmicosin, florfenicol and enrofloxacin in 20 (6.0%), 15 (4.5 %), 2 (0.6%), 8 (2.4%), 13 (3.9%), 5 (1.5%) and 5 (1.5%) P. multocida isolates as well as for tiamulin, gentamicin, tulathromycin, tilmicosin and ampicillin in 2 (2.4%), 2 (2.4%), 3 (3.6%), 3 (3.6%) and 6 (7.2%) H. parasuis isolates. In addition, moderate level of resistance to tiamulin was found in 60 (18.1%) P. multocida isolates and high level of resistance for tetracycline was detected in 107 (32.2 %) P. multocida isolates and in 23 (27.7 %) H. parasuis isolates. Differences between resistance rates of P. multocida and H. parasuis were significant (P ≤ 0.5) only for tiamulin. These data confirmed that antimicrobial resistance is not very widespread among current porcine P. multocida and H. parasuis isolates in the Czech Republic. Antimicrobial resistance, minimal inhibition concentration, respiratory diseases, pigs Pasteurella multocida and Haemophilus parasuis are the causative agents of infectious diseases of porcine respiratory tract which cause major economic losses by their negative impact on the weight gain, feed conversion, and health status (Oliveira and Pijoan 2004; Shin et al. 2005). Antibiotic treatment is one of the commonly used measures for the control of pasteurellosis and H. parasuis infections but the use of antimicrobial agents leads to both selection and increase of resistance (Schwarz and Chaslus-Dancla 2001). Failure to treat infectious disease caused by resistant bacteria leads to increased morbidity and mortality (Kolar et al. 2010). Variations in the antimicrobial use for the control of bacterial pathogens in pigs from one country to another can contribute to evident differences in antimicrobial susceptibility of P. multocida and H. parasuis. In accordance with the recommendation of Schwarz et al. (2010) on the requirement of application of the same methodology and interpretive criteria (which would allow for re-evaluation of the original data if the interpretive criteria change over time), only a limited number of recent studies were conducted regarding the susceptibility of P. multocida and H. parasuis to antimicrobials with the use of microdilution method. Considering the lack of recent studies of antimicrobial susceptibility testing of P. multocida and H. parasuis within the European territory, the aim of this work was to examine a panel of various isolates obtained from different Czech locations to determine their susceptibility to selected antimicrobial agents by the broth microdilution method, in accordance with the guidelines issued by the Clinical and Laboratory Standards Institute (CLSI) in 2008. Materials and Methods