Antimicrobial resistance of pathogenic NAD-dependent Pasteurellaceae from pigs

Actinobacillus pleuropneumoniae (App) and Haemophilus parasuis (Hps) are fastidious bacterial species commonly isolated in clinical specimens from pigs. App is associated with necrotizing pneumonia and Hps with polyserositis, arthritis and meningitis in pigs. The treatment has traditionally involved using beta-lactam antibiotics, to which the isolates of both pathogens have been almost universally susceptible. However, high frequencies of resistance to several groups of antibiotics, including beta-lactams, have emerged in some other countries, so currently the treatment has to be based on local knowledge. The aim of the study was to assess the prevalence of antimicrobial resistance of both App and Hps isolated from pigs in Poland.

A total of 133 App and 67 Hps strains isolated, from diseased pigs, between 2008 and 2015 were tested. A single isolate from the same farm was included. The strains were analyzed for their resistance to 11 antimicrobials using the microbroth dilution method (TREK D. S.). The obtained MIC (minimal inhibitory concentration) values were evaluated according to the criteria CLSI (clinical breakpoints, 2013).

Resistance of App isolates was found against 9 tested antimicrobials, reaching the highest values for tetracycline (30%), ampicillin and penicillin (6% each), erythromycin (4.5%), enrofloxacin (2.3%), tiamulin (1.5%), trimethoprim/sulphamethoxazole, spectinomycin and ceftiofur (0.8% and one strain, each). The significant proportion – 90% and 60 % isolates – had a reduced susceptibility to erythromycin and tetracycline, respectively. No resistance against amoxicillin/clavulanic acid and florfenicol was detected.

Resistance of Hps isolates was found against 8 tested antimicrobials, reaching the highest values for tetracycline (17.1%), enrofloxacin (13.2%), trimethoprim/sulphamethoxazole, ampicillin and penicillin (9.2% each), tiamulin and erythromycin (2.6% each). The significant proportion (90%) isolates had a reduced susceptibility to erythromycin only. No resistance against amoxicillin/clavulanic acid, ceftiofur and florfenicol was detected.

This study showed that Polish App and Hps strains had similar trends of the resistance. So far the isolates of App and Hps have full susceptibility to amoxicillin with clavulanic acid as well as florfenicol. App isolates have very limited degree of resistance to ceftiofur. The pathogenic NADdependent Pasteurellaceae have a limited to moderate degree of resistance to natural and semisynthetic penicillins, which are commonly used for treatment. Our results also showed a higher level of resistance to enrofloxacin and sulfamethoxazole/trimethoprim combination in Hps, than App strains.

Disclosure of Interest: None Declared.