Antimicrobial susceptibility of Pasteurella multocida isolated from sheep and pigs in Spain - Short communication

Pathological analysis and etiological assessment of pulmonary lesions and its association with pleurisy in slaughtered pigs

The intensification of pig farming has posed significant challenges in managing and preventing sanitary problems, particularly diseases of the respiratory complex. Monitoring at slaughter is an important control tool and cannot be overstated. Hence, this study aimed at characterizing both macroscopical and microscopical lesions and identifying the Actinobacillus pleuropneumoniae (APP), Mycoplasma hyopneumoniae (Mhyo), and Pasteurella multocida (PM) associated with pleurisy in swine. For this, a selected slaughterhouse in São Paulo State underwent a thorough examination of carcasses on the slaughter line, followed by lung sampling. The carcasses and lungs underwent macroscopical examination and were classified according to the score of pleurisy and lung samples were allocated into five groups, being: G0: score 0 - no lesions; G1: score 1; G2: score 2; G3: score 3; and G4: score 4. In total, 217 lung fragments were collected, for the histopathological evaluation and detection of the following respiratory pathogens: APP, Mhyo, and PM by qPCR. The results demonstrated that Mhyo and APP were the most prevalent etiological agents (single and co-identification) in lung samples, in different scores of pleurisies, while bronchopneumonia and bronchus-associated lymphoid tissue (BALT) hyperplasia lesions were the most frequent histopathological findings. Positive correlations were found between the quantification of APP DNA with 1) the score of pleurisy (R=0.254); 2) with the score of lung consolidation in all lung lobes (R=0.181 to R=0.329); and 3) with the score of lung consolidation in the entire lung (R=0.389). The study brings relevant information regarding the main bacterial pathogens associated with pleurisy in pigs and helps with understanding the relationship between the abovementioned pathogens and their impact on the respiratory health of pigs.

Antimicrobial Susceptibility and Resistance Mechanisms in Mannheimia haemolytica Isolates from Sheep at Slaughter

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.

First study on capsular serotypes and virulence factors of Pasteurella multocida isolates from Phan Rang sheep in Vietnam

Background and Aim: Pasteurella multocida is considered as a main factor mediating pneumonic pasteurellosis in ruminants, including sheep. It is also a current threat to Phan Rang sheep in Vietnam. This study aimed to characterize P. multocida isolated from Phan Rang sheep, their antibiotic resistance profile, and the prevalence of some virulence-associated genes of these strains. Materials and Methods: Bacteria were isolated on brain heart infusion, 10% sheep blood agar plates, and screened by biochemical tests. The polymerase chain reaction technique was used with specific primers to identify P. multocida, the presence of virulence-associated genes, and serotypes of isolates. Antimicrobial susceptibility and biofilm formation of isolates were examined using the disk diffusion method and crystal violet-based method, respectively. Results: A total of 41 P. multocida strains were isolated from 485 samples from clinically sick and healthy sheep. Of the isolates, 58.53% were serotype A, 9.75% were serotype B, and 31.71% were serotype D. Healthy animals were infected with serotype D only. All 15 virulence genes were identified in all strains isolated from clinically sick sheep, while strains isolated from healthy sheep carried 11/15 virulence genes tested. Among virulence-associated genes exbB, exbD, tonB, ompA, oma87, fimA, hgbA, and nanB were detected in over 90% of isolates, whereas hgbB, nanH, tbpA and pfhA were less frequent. Interestingly, pmHAS and tadD were highly prevalent in capsular type A strains, whereas the toxA gene was detected in capsular type D strains only. All of the isolated strains were fully susceptible to enrofloxacin, ciprofloxacin, neomycin, and ofloxacin. About 92.68% were susceptible to chloramphenicol and 90.24% to amikacin, but there was high resistance to erythromycin, tetracycline, and amoxicillin. Our results reveal that 53.65% of 41 isolates could produce biofilm, whereas 46.34% could not. Conclusion: Pasteurella multocida from Phan Rang sheep possess many virulence genes and resistance to several common antibiotics such as erythromycin, tetracycline, and amoxicillin. The results are an important warning regarding antibiotic resistance of P. multocida.

Characterization of small plasmids carrying florfenicol resistance gene floR in Actinobacillus pleuropneumoniae and Pasteurella multocida isolates from swine in China

Actinobacillus pleuropneumoniae and Pasteurella multocida are two important bacterial pathogens in swine industry. In the present study, resistance profiles of nine commonly used antibiotics of A. pleuropneumoniae and P. multocida isolates of swine origin from different regions of China were investigated by determination of minimum inhibitory concentrations (MICs). In addition, genetic relationship of the florfenicol-resistant A. pleuropneumoniae and P. multocida isolates was determined by pulsed-field gel electrophoresis (PFGE). The genetic basis of florfenicol resistance in these isolates were explored by floR detection and whole genome sequencing. High resistance rates (>25%) of florfenicol, tetracycline and trimethoprim- sulfamethoxazole were observed for both bacteria. No ceftiofur- and tiamulin- resistant isolates were detected. Furthermore, all the 17 florfenicol-resistant isolates (nine for A. pleuropneumoniae and eight for P. multocida) were positive for floR gene. The presence of similar PFGE types in these isolates suggested that clonal expansion of some floR-producing strains occurred in the pig farms from same regions. WGS and PCR screening showed that three plasmids, named pFA11, pMAF5, and pMAF6, were the cargos of the floR genes in the 17 isolates. Plasmid pFA11 exhibited novel structure and carried several resistance genes, including floR, sul2, aacC2d, strA, strB, and bla _{ROB - 1}. Plasmids pMAF5 and pMAF6 were presented in A. pleuropneumoniae and P. multocida isolates from different regions, suggesting horizontal transfer of the two plasmids are important for the floR dissemination in these Pasteurellaceae pathogens. Further studies of florfenicol resistance and its transfer vectors in Pasteurellaceae bacteria of veterinary origin are warranted.

Investigation of Macrolide Resistance Genotypes of Pasteurella multocida Isolates from Cattle and Small Ruminants

Macrolides are commonly used to control respiratory tract infections in ruminants, but the susceptibility of Pasteurella multocida strains has shown a decrease to macrolide antibiotics in the last decade. In this work we assessed the prevalence of macrolide resistance of 100 P. multocida isolates from ruminant hosts and studied the resistance genotypes with newly designed PCRs. Susceptibility to erythromycin and tilmicosin was tested using minimal inhibitory concentration (MIC) test strips. A newly designed PCR was used for the detection of macAB genes, and a PCR plus restriction enzyme-based technique was developed for detecting a 23S rRNA gene mutation at position 2059. Five bovine isolates with notably increased MICs (≥256 μg/mL for erythromycin and ≥32 μg/mL for tilmicosin) carried resistance genes msr(E) and mph(E) or the A2059G point mutation in the 23S rRNA gene. Over 73% strains from small ruminants and all bovine isolates were MacAB PCR positive. Bovine strains were less sensitive to macrolide antibiotics than isolates from small ruminants, and an increase in the prevalence of macrolide resistance in bovine P. multocida isolates has also been observed over time.

Comparison of PK/PD Targets and Cutoff Values for Danofloxacin Against Pasteurella multocida and Haemophilus parasuis in Piglets

Danofloxacin is a synthetic fluoroquinolone with broad-spectrum activity developed for use in veterinary medicine. The aim of this study was to evaluate the pharmacokinetic/pharmacodynamic (PK/PD) targets, PK/PD cutoff values and the optimum doses of danofloxacin against P. multocida and H. parasuis in piglets. Single dose serum pharmacokinetics was determined in piglets after intravenous and intramuscular administration of 2.5 mg/kg. Danofloxacin was well absorbed and fully bioavailable (95.2%) after intramuscular administration of 2.5 mg/kg. The epidemiological cutoff (ECOFF) values of danofloxacin from 931 P. multocida isolates and 263 H. parasuis isolates were 0.03 and 4 mg/L, respectively. Danofloxacin MICs determined in porcine serum were markedly lower than those measured in artificial broth, with a broth/serum ratio of 4.33 for H. parasuis. Compared to P. multocida, danofloxacin exhibited significantly longer post-antibiotic effects (3.18-6.60 h) and post-antibiotic sub-MIC effects (7.02-9.94 h) against H. parasuis. The mean area under the concentration-time curve/MIC (AUC24h/MIC) targets of danofloxacin in serum associated with the static and bactericidal effects were 32 and 49.8, respectively, for P. multocida, whereas they were 14.6 and 37.8, respectively, for H. parasuis. Danofloxacin AUC24h/MIC targets for the same endpoints for P. multocida were higher than those for H. parasuis. At the current dose of 2.5 mg/kg, the PK/PD cutoff (COPD) values of danofloxacin against P. multocida and H. parasuis were calculated to be 0.125 and 0.5 mg/L, respectively, based on Monte Carlo simulations. The predicted optimum doses of danofloxacin for a probability of target attainment (PTA) of > 90% to cover the overall MIC population distributions of P. multocida and H. parasuis in this study were 2.38 and 13.36 mg/kg, respectively. These PK/PD-based results have potential relevance for the clinical dose optimization and evaluation of susceptibility breakpoints for danofloxacin in the treatment of swine respiratory tract infections involving these pathogens.

Assessment of animal diseases caused by bacteria resistant to antimicrobials: Swine

In this opinion, the antimicrobial-resistant bacteria responsible for transmissible diseases that constitute a threat to the health of pigs have been assessed. The assessment has been performed following a methodology based on information collected by an extensive literature review and expert judgement. Details of the methodology used for this assessment are explained in a separate opinion. A global state of play of antimicrobial resistant Escherichia coli, Streptococcus suis, Actinobacillus pleuropneumoniae, Pasteurella multocida, Glaeserella parasuis, Bordetella bronchiseptica, Staphylococcus aureus, Staphylococcus hyicus, Brachyspira hyodysenteriae, Trueperella pyogenes, Erysipelothrix rhusiopathiae, Streptococcus dysgalactiae, Mycoplasma hyosynoviae, Mycoplasma hyorhinis, Mycoplasma hyopneumoniae and Brachyspira pilosicoli has been provided. Among those bacteria, EFSA identified E. coli and B. hyodysenteriae with > 66% certainty as being the most relevant antimicrobial resistant bacteria in the EU based on the available evidence. The animal health impact of these most relevant bacteria, as well as their eligibility for being listed and categorised within the animal health law framework will be assessed in separate scientific opinions.

Virulence attitude estimation of Pasteurella multocida isolates in embryonated chicken eggs

A total of 220 birds of age ranging from 3 to 14 weeks old were collected from several backyards and different farms in Sharkia Governorate, Egypt, and surveyed for the presence of fowl cholera. Twenty Pasteurella multocida from chickens (15/145, 10%) and ducks (5/75, 6%) were bacteriologically isolated, and it was shown that the infection was significantly related to age and breed. Capsular typing, using multiplex polymerase chain reaction (PCR), demonstrated that all strains were type A (100%). Disk diffusion assay towards ten antimicrobials revealed high susceptibilities to amikacin, doxycycline, chloramphenicol, and neomycin with varying degrees. Doxycycline was effective at the lowest concentration (MIC 0.125-1 µg/ml). Multidrug resistance was detected with a percentage of 25%. Multidrug-resistant isolates (five isolates) were subjected to study their pathogenicity in embryonated chicken eggs (ECE). The results showed a variation in indices between different dilutions of the tested strains. The resulting pathogenicity indices showed significant differences (P < 0.05) according to the origin and dilution of the isolate. From the original inoculum to 10^-4 dilutions, the mortality of inoculated embryos occurred within 1-2 days with pathological findings, including maceration and lesions on chorioallantoic membrane (CAM). From dilutions ranging from 10^-5 to 10^-9, no death occurred until 7 days post-inoculation, but a variation in the lesions on CAM was observed. In conclusion, P. multocida serogroup A could be intensely pathogenic for mature chickens thus causing considerable economic losses, and PCR provides a suitable technique for early and rapid diagnosis of fowl cholera.

A single point mutation in the hyaC gene affects Pasteurella multocida serovar A capsule production and virulence

Pasteurella multocida (P. multocida) is a Gram-negative bacterium which causes diseases in poultry, livestock, and humans, resulting in huge economic losses. P. multocida serovar A CQ6 (PmCQ6) is a naturally occurring attenuated strain with a thin capsule. Thus, we aimed to explore why this strain is less virulent and produces less capsule compared with P. multocida serovar A strain CQ2 (PmCQ2). Analysis of capsular polysaccharide synthesis genes in PmCQ6 revealed that, compared with PmCQ2, there was only a single point mutation in the initiation codon sequence of the hyaC gene. To test whether this point mutation caused capsular deficiency and reduced virulence, we rescued this hyaC mutation and observed a restoration of capsule production and higher virulence. Transcriptome analysis showed that the hyaC point mutation led to a downregulation of capsule synthesis and/or iron utilization related-genes. Taken together, the results indicate that the start codon mutation of hyaC is an important factor affecting the capsule synthesis and virulence of PmCQ6.