Naoya Kikuchi

Development of an appropriate PCR system for the reclassification of Streptococcus suis.

Thirty-five serotypes of Streptococcus suis (serotypes 1-34 and serotype 1/2) have so far been described on the basis of their polysaccharide capsular antigens. However, in the last decade, some serotype reference strains have been reexamined for their taxonomic status, and the reference strains of serotypes 20, 22, 26, 32, 33, and 34 may be different from taxon S. suis. In the present study, we developed a novel PCR method targeting the recombination/repair protein (recN) gene of S. suis, designated recN PCR, which corresponds to the current reclassification of this bacterium. We compared its specificity with other PCR methods for S. suis, and the results obtained confirmed its specificity. In addition, the detection limits of recN PCR were similar among all the reference strains of authentic S. suis, indicating that the recN PCR gave reliable results against bacterial strains and isolates used in this study. Therefore, recN PCR described in the present study will be a useful tool for the identification of authentic S. suis, and can also be used in epidemiological studies on this bacterium.

Phylogenetic Positions and Assignment of Swine and Ovine Corynebacterial Isolates Based on the 16S rDNA Sequence

The nucleotide sequences of the 16S ribosomal RNA gene (rDNA) of swine and ovine corynebacterial strains were determined. The sequences of the strains that identified as Corynebacterium pseudotuberculosis by their biochemical characteristics were homologous with each other. The phylogenetic position of C. pseudotuberculosis strains was closest to C. ulcerans and next closest to C. diphtheriae. The nucleotide sequence of another swine isolate, SC8, was similar to that of a recently proposed species, C. seminale, and a non‐validated species, “C. glucuronolyticum,” with about 0.01 to 0.02 evolutionary distances. Analysis of the predicted secondary structure of the 16S rRNA molecule agreed with the close phylogenetic relationships between C. pseudotuberculosis and C. ulcerans and between C. seminale and strain SC8.

Plasmid profiles of Klebsiella pneumoniae isolated from bovine mastitis

Plasmids of Klebsiella pneumoniae strains isolated from mastitic milk of cows were detected, and the epidemiological significance of their profiles was investigated. Of 47 K. pneumoniae isolates, 41 (87.2%) possessed plasmid(s). Although the molecular size of the plasmids ranged from 1.9 to 140 megadaltons (Md), the 125 Md plasmid was predominant (31/41, 75.6%). There was a great diversity in the plasmid profiles, however, no correlation was found between the plasmid profiles and capsular types of Klebsiella or the source of strains (dairy farms), except for one farm. All isolates obtained from cows on that farm possessed the 125 Md plasmid and their capsular type was 9.

Isolation of Corynebacterium pseudotuberculosis from the cervical canal of clinically normal sows

Two isolates from the cervical canal of clinically normal sows were indistinguishable from Corynebacterium pseudotuberculosis in their biochemical properties and genetic homology by DNA-DNA hybridisation. Furthermore, three sheep inoculated with one of the isolates developed typical lesions of caseous lymphadenitis and gave antibody responses specifically to C pseudotuberculosis.

Capsule types of Klebsiella pneumoniae isolated from the genital tract of mares with metritis, extra-genital sites of healthy mares and the genital tract of stallions

A survey of K. pneumoniae was performed on cervical swabs, feces and nasal swabs of mares and on samples from the genital tract of stallions from 1980 to 1986 in south-western Hokkaido, Japan. K1 was the predominant type (79 of 88, 89.8%) in the metritis cases due to K. pneumoniae in mares of racing breeds. The same type was isolated from semen and swabs of the fossa glandis of 6 of 20 (30.0%) of the stallions of racing breeds. Heavily encapsulated and less heavily encapsulated K1 strains were isolated from the stallions. Mares bred to stallions carrying heavily encapsulated strains developed metritis, while those bred to stallions carrying less heavily encapsulated strains did not. K39 was isolated from cervical swabs solely from metritis-infected mares of draft breeds and not from any mares of the racing breeds examined. Untypable strains were isolated from cervical swabs in 7 of 88 (8.0%) metritis cases of mares of racing breeds and from semen in 7 of 19 (36.8%) stallions of racing breeds and they were predominant in feces (19 of 21, 90.5%) and nasal swabs (3 of 4, 75.0%) of healthy mares of racing breeds.

Distribution of Corynebacterium renale among apparently healthy rats

We examined the distribution of Corynebacterium renale, a causative agent of urinary calculus, in clinically normal rats at 6 animal facilities in Japan. Swabs of the vulva and vaginal vestibule or prepuce of the rats were cultured for isolation of the organisms. C. renale has been isolated at only one animal facility, where cases of urinary calculus were reported several years ago. In this facility, 32% of female (43/135) and 22% of male (18/82) rats, 4-28 weeks old, were positive for C. renale. In contrast, 92 female and 169 male rats at other facilities without a history of the disease were negative for the organisms.