A Predominant Clonal Thromboembolic Meningoencephalitis Group of Histophilus somni Assigned by Major Outer Membrane Protein Gene Sequencing and Pulsed-Field Gel Electrophoresis

Vaginitis with purulent vaginal discharge caused by artificial insemination using frozen Histophilus somni-contaminated semen

In April 2020, two cows in Japan, developed reproductive disorders accompanied by vaginitis with purulent discharge within 3 days of artificial insemination (AI) with the same lot of frozen semen. Histophilus somni was isolated from the vaginal swabs of both cows as well as from the same lot of frozen semen used for the AI. This incident marks the first reported case of H. somni infection in cattle through AI. The major outer membrane protein gene sequences and pulsed-field gel electrophoresis profiles of the isolates were identical. Moreover, we investigated the antimicrobial activity of 12 frozen semen straws against an H. somni isolate using a disk diffusion test. These straws were sourced from five AI centers and included the same lot of semen used for the AI. Although the composition of semen diluents from individual AI centers is not publicly available, both the same lot of frozen semen used in the AI and other lots produced by the same manufacturer showed lower antimicrobial activity than semen from other manufacturers. These results strongly suggest that the two vaginitis were caused by AI using H. somni-contaminated frozen semen because of insufficient antimicrobial activity to inhibit bacterial growth. The minimum inhibitory concentrations of the six antimicrobials recommended for addition to frozen semen in isolates were below the recommended concentrations, suggesting that proper addition could have prevented this incident. This highlights the importance of conducting periodical checks on the antibacterial activity of frozen semen to prevent the transmission of pathogens via AI.

Antimicrobial resistance and associated genetic background of Histophilus somni isolated from clinically affected and healthy cattle

Histophilus somni, a member of the Pasteurellaceae family, causes various diseases, including thrombotic meningoencephalitis and respiratory diseases. Here, 166 isolates recovered from Japanese cattle with various diseases between the late 1970s and the 2010s were subjected to susceptibility testing against 14 antimicrobials (ampicillin, amoxicillin, cefazolin, ceftiofur, kanamycin, streptomycin, nalidixic acid, enrofloxacin, danofloxacin, florfenicol, erythromycin, tylosin, oxytetracycline, and fosfomycin). The proportions of antimicrobial-resistant/intermediate isolates were low in the total isolates, with resistance rates ranging from 0% for ceftiofur and florfenicol to 13.2% for ampicillin. However, relatively high minimum inhibitory concentrations (MICs) and resistance/intermediate rates were observed in the isolates from cattle with respiratory diseases; i.e., 21/53 isolates (39.6%) showed resistance or intermediate to one or more antimicrobials for treatment of respiratory diseases, and the resistance/intermediate rates to oxytetracycline, kanamycin, ampicillin, amoxicillin, nalidixic acid, and danofloxacin were 28.3, 24.5, 24.5, 13.2, 1.9, and 1.9%, respectively. Isolates with high MICs tended to possess antimicrobial resistance genes, which may confer antimicrobial resistance phenotypes. In particular, all isolates with MICs of ampicillin/amoxicillin, kanamycin, and oxytetracycline ≥2 μg/mL, ≥512 μg/mL, and ≥4 μg/mL possessed bla_{ROB − 1}, aphA-1, and tetH/tetR, respectively, whereas isolates whose MICs were lower than the above-mentioned values did not possess these resistance genes. These results suggest that the resistance genes detected in this study are primarily responsible for the reduced susceptibility of H. somni strains to these antimicrobials. As integrative and conjugative element (ICEs)-associated genes were detected only in genetically related isolates possessing antimicrobial resistance genes, ICEs may play an important role in the spread of resistance genes in some genetic groups of H. somni strains.

Histophilus somni myocarditis and leptomeningitis in feedlot cattle: case report and occurrence in South America

We investigated deaths in a group of feedlot steers in Argentina. The main findings in 3 steers autopsied were pulmonary congestion and edema, necrotizing myocarditis, pericarditis, suppurative leptomeningitis, and bronchopneumonia. Histophilus somni was detected by bacterial culture and immunohistochemistry in the hearts of the 3 animals. Partial sequences of the 16S rRNA gene of a H. somni isolate had 99% similarity with other H. somni sequences in GenBank. Most reports of H. somni septicemia in cattle originate from North America and western Europe. There is scant information about cardiac histophilosis in South America. A survey of diagnostic laboratory personnel in 7 South American countries documented various forms of bovine histophilosis in Argentina, Brazil, Uruguay, and Venezuela.

Establishment of a suspension array for Pseudomonas aeruginosa O-antigen serotyping

Pseudomonas aeruginosa (P. aeruginosa) is widespread in the environment. It readily infects hospital and immunocompromised patients. Traditional biochemical and immunological diagnoses of P. aeruginosa infection cannot meet clinical demands. The variability of O-antigens is the primary basis for the serotyping schemes of many gram-negative bacteria, which is the most widely used method for pathogenic epidemiological purposes. In this study, we developed a suspension array that can accurately diagnose and identify 19 different P. aeruginosa O-antigen serotypes except O15, whose O-antigen gene cluster has not been characterized. In this assay, wzx/wzy genes were selected as the sero-specific gene for 18 serotypes other than O6, for which the glycosyltransferase gene wbpP was utilized. Meanwhile, the wzy_β gene was added to separate O2/16 from O5/18/20, and the insertion sequence (IS) in wzx was used to separate O17 from O11. Eighty-two clinical isolates were screened to test our assay. A total of 65 isolates (79.3%) could be serotyped, and the result were confirmed to be correct by sequencing. Sensitivity analysis indicated that at least 5 ng DNA or 10³ CFU cells could be detected using our suspension array. To our knowledge, this is the first report on serotyping P. aeruginosa by suspension array and may be of great value in the clinical diagnostics of P. aeruginosa infection.