Mannheimia haemolytica is the main pathogen contributing to pneumonic pasteurellosis in sheep. The aim of this study was to investigate the antimicrobial resistance levels in M. haemolytica isolates from the lungs of slaughtered sheep and to examine the genetic resistance mechanisms involved. A total of 256 M. haemolytica isolates, 169 from lungs with pneumonic lesions and 87 from lungs without lesions, were analyzed by the disk diffusion method for 12 antimicrobials, and the whole genome of 14 isolates was sequenced to identify antimicrobial resistance determinants. Levels of phenotypic resistance ranged from <2% for 10 antimicrobials (amoxicillin, amoxicillin-clavulanic, ceftiofur, cefquinome, lincomycin/spectinomycin, gentamicin, erythromycin, florfenicol, enrofloxacin, and doxycycline) to 4.3% for tetracycline and 89.1% for tylosin. Six isolates carried tetH genes and four isolates carried, in addition, the strA and sul2 genes in putative plasmid sequences. No mutations associated with macrolide resistance were identified in 23 rDNA sequences, suggesting that the M. haemolytica phenotypic results for tylosin should be interpreted with care in the absence of well-established epidemiological and clinical breakpoints. The identification of strains phenotypically resistant to tetracycline and of several resistance genes, some of which were present in plasmids, highlights the need for continuous monitoring of susceptibility patterns in Pasteurellaceae isolates from livestock.

Acinetobacter is one of the most relevant pathogenic and nosocomial bacterial genus in human medicine. However, in veterinary medicine, and especially in Spain, there are very few studies about the impact and frequency of infections due to this genus. The main objective of this study was to characterise Acinetobacter isolates analysed at the Complutense Veterinary Teaching Hospital of the Complutense University of Madrid, with special emphasis on detecting antimicrobial resistance. A total of 23 isolates obtained from different animal species and samples over a 27-year period, were included in the study. Identification was made by using MALDITOF, VITEK-2, whole-genome sequencing and a chromogenic medium. Antimicrobial susceptibility was interpreted according to CLSI guidelines using the Kirby-Bauer disk diffusion and broth microdilution method. The proportion of clinical isolates identified as Acinetobacter spp. at the HCV-UCM was 0.3%. The frequency of AMR was low, though 30.8% of the isolates were classified as multidrug-resistant. Two isolates with the highest MIC for temocillin carried the tet(X) gene, and two isolates had mutations in both gyrA and parC QRDR regions. The results of this study suggest that, in Spain, antimicrobial resistance in Acinetobacter isolates of veterinary origin might not be yet widespread.

Acinetobacter is one of the most relevant pathogenic and nosocomial bacteria in human medicine. However, in veterinary medicine, particularly in Spain, there are very few studies on the impact and frequency of infections due to this genus. The main objective of this study was to characterise Acinetobacter isolates recovered at the Complutense Veterinary Teaching Hospital of the Complutense University of Madrid (HCV-UCM), with special emphasis on detecting antimicrobial resistance. A total of 23 isolates obtained from different animal species and samples over a 25-year period were included in the study, based on their identification as Acinetobacter by VITEK-2. Identification was made by using MALDI-TOF, VITEK-2, whole-genome sequencing (WGS) and a chromogenic medium. WGS confirmed that 13 of the 23 isolates belonged to Acinetobacter spp. Antimicrobial susceptibility was interpreted according to CLSI guidelines using the Kirby–Bauer disk diffusion and broth microdilution method. The proportion of clinical isolates identified as Acinetobacter spp. at the HCV-UCM was 0.3%. Of these, 15.4% (2/13 isolates) were classified as multidrug-resistant. Two isolates with the highest MIC for tigecycline carried the tet(X) gene, and two isolates harboured mutations in both gyrA and parC QRDR regions. The results of this study suggest that, in this hospital, antimicrobial resistance among Acinetobacter isolates may not yet be widespread.