Research Note: Antimicrobial resistance of Campylobacter species isolated from chickens near Ulaanbaatar city, Mongolia.

There has been no report on the prevalence of Campylobacter spp. in farm animals in Mongolia. To uncover the prevalence of Campylobacter spp. in chickens in Mongolia and their antimicrobial resistance, in this study, we isolated and characterized Campylobacter spp. from chickens in Mongolia. We collected 71 cloacal swabs of chickens from 5 farms including 4 layer farms and one broiler farm near Ulaanbaatar city and isolated 25 Campylobacter jejuni and 6 Campylobacter coli isolates. All isolates were resistant to tetracycline, and 3 C. coli isolates were resistant to erythromycin. The C. coli isolates possessed either the erm(B) gene or nucleotide substitution at nt 2,075 of 23S rDNA, both of which are known to be associated with erythromycin resistance. Sixteen of the 31 C. jejuni/C. coli isolates (51.6%) were resistant to nalidixic acid and fluoroquinolones. All the fluoroquinolone-resistant isolates possessed amino acid substitution from threonine to isoleucine at codon 86 (nucleotide substitution: ACA to ATA). Multilocus sequence typing and phylogenetic analyses showed a variation in C. jejuni/C. coli in chickens in Mongolia. In addition, some of the C. jejuni isolates seemed to be phylogenetically close to isolates in Asian and Oceanian countries. This is the first report on the characterization of antimicrobial resistance of Campylobacter spp. in farm animals in Mongolia and is valuable for implementation of measures for a prudent use of antimicrobials in farm animals.

Pathological and Immunohistochemical Analyses of Naturally Occurring Equine Glanders Using an Anti-BpaB Antibody.

Glanders is caused by the gram-negative bacterium Burkholderia mallei. In this study, we investigated the histopathology and immunohistochemical localization of B. mallei in natural cases of equine glanders. Four horses showing clinical signs of nasal discharge and multiple cutaneous nodules or papulae in the hindlimbs and abdomen were reported in Mongolia. They tested positive for B. mallei infection on complement fixation, Rose Bengal agglutination, and mallein tests. Gross and histological lesions observed in these cases were similar to those previously reported in equine glanders. Immunohistochemistry using a monoclonal antibody to B. mallei BpaB showed localization of the bacterial antigen in the cytoplasm of neutrophils, macrophages, epithelioid cells, and multinucleated giant cells in the pyogranulomas and abscesses in target organs. Some alveolar type II cells and bronchiolar epithelial cells also contained the antigen. These results suggest that the anti-BpaB antibody is useful for identifying B. mallei-infected cell types in naturally infected horses.

Seroprevalence of equine glanders in horses in the central and eastern parts of Mongolia.

Glanders is a contagious and fatal equine disease caused by the gram-negative bacterium Burkholderia mallei. B. mallei is prevalent among horse populations in Asia, the Middle East, and South America. More than four million horses have been registered in Mongolia in 2020. However, the recent prevalence of glanders has not been well investigated. In this study, we aimed to investigate the seropositivity of B. mallei in horse populations in Mongolia using the complement fixation test (CFT) and Rose Bengal plate agglutination test (RBT). We randomly collected blood samples from horses in central and eastern Mongolia between 2018 and 2019. Of 337 horses, 26 (7.7%) and 28 (8.3%) were seropositive using RBT and CFT, respectively. Interestingly, seropositivity in horses resulting from crossbreeding of Mongolian native horses with thoroughbred horses was higher than that in Mongolian native horses. Our observations suggest that equine glanders are still endemic to Mongolia.

Molecular epidemiological investigation of Brucella melitensis circulating in Mongolia by MLVA16.

Mongolia has a high incidence of brucellosis in human and animals due to livestock husbandry. To investigate the genetic characteristics of Mongolian B. melitensis, an MLVA (multi-locus variable-number tandem-repeat analysis)-16 assay was performed with 94 B. melitensis isolates. They were identified as B. melitensis biovar (bv.) 1 (67), 3 (10) and Rev. 1 vaccine strains (17) using a classical biotyping and multiplex PCR. In genotyping, three human isolates were grouped at 2 genotypes with sheep isolates, and it implies that B. melitensis are cross-infected between human and livestock. In the parsimony analysis, Mongolian B. melitensis isolates had high genetic similarity with Chinese strains, likely due to the geographical proximity, clustered distinctively as compared with other foreign isolates. B. melitensis Rev. 1 vaccine strains were divided into 4 genotypes with 92% similarity. In the analysis of Rev.1 strains, the risk of mutation of vaccine strain might not be overlooked. Animal quarantines should be strengthened to prevent the spread of Brucella species among adjacent countries.

Differential diagnosis of Brucella abortus by real-time PCR based on a single-nucleotide polymorphisms.

To diagnose brucellosis effectively, many genus- and species-specific detection methods based on PCR have been developed. With conventional PCR assays, real-time PCR techniques have been developed as rapid diagnostic tools. Among them, real-time PCR using hybridization probe (hybprobe) has been recommended for bacteria with high DNA homology among species, with which it is possible to make an accurate diagnosis by means of an amplification curve and melting peak analysis. A hybprobe for B. abortus was designed from a specific single-nucleotide polymorphism (SNP) on the fbaA gene. This probe only showed specific amplification of B. abortus from approximately the 14th cycle, given a melting peak at 69°C. The sensitivity of real-time PCR was revealed to be 20 fg/µl by 10-fold DNA dilution, and the detection limit was 4 CFU in clinical samples. This real-time PCR showed greater sensitivity than that of conventional PCR and previous real-time PCR based on Taqman probe. Therefore, this new real-time PCR assay could be helpful for differentiating B. abortus infection with rapidity and accuracy.