The prevalence of Shiga toxin-producing Escherichia coli (STEC) in Japan was examined by using stool samples from 87 calves, 88 heifers, and 183 cows on 78 farms. As determined by screening with stx-PCR, the prevalence was 46% in calves, 66% in heifers, and 69% in cows; as determined by nested stx-PCR, the prevalence was 100% in all animal groups. Of the 962 isolates picked by colony stx hybridization, 92 isolates from 54 farms were characterized to determine their O serogroups, virulence factor genes, and antimicrobial resistance. Of these 92 isolates, 74 (80%) could be classified into O serogroups; 50% of these 74 isolates belonged to O serogroups O8, O26, O84, O113, and O116 and 1 isolate belonged to O serogroup O157. Locus of enterocyte effacement genes were detected in 24% of the isolates, and enterohemorrhagic E. coli (EHEC) hlyA genes were detected in 72% of the isolates. Neither the bundle-forming pilus gene nor the enteropathogenic E. coli adherence factor plasmid was found. STEC strains with characteristics typical of isolates from human EHEC infections, which were regarded as potential EHEC strains, were present on 11.5% of the farms.

A total of 15 strains of Mycoplasmawere examined for in vitro sensitivity to 22 commonly used antibiotics and 9 nitrofurans. They were strains of Mycoplasma mycoides var. mycoides, M. mycoides var. capriy M. hyorhinis, M. suipneumoniae (hyopneumoniae), M. granularum, M. cams, M. pulmonis, M. arthritidiSy M. neurolyticum, M. gallisepticum, and M. laidlawii, all of which were isolated from various animals, except for one strain of M. laidlawii which was isolated from sewage. The sensitivity was determined by observing inhibition of growth in the agar and broth dilution systems. Amongall the mycoplasmasexamined, there were no markeddifferences in susceptibility to these drugs, with the exception of erythromycin and oleandomycin. Anti-tumor antibiotics, i. e., actinomycin D and mitomycin C, were the most active of all the agents. Tylosin, bottromycin, spiramycin and tetracycline followed them in activity. Kasugamycin, polymyxin B and colistin were noninhibitory. M.suipneumoniaeå , which is known as the etiological agent of swine enzootic pneumonia (SEP), and other species of respiratory mycoplasmas of swine were compared with regard to minimuminhibitory concentrations (MIC) upon these drugs. The sensitivity of M. suipneumoniae to the drugs used was similar to that of other mycoplasma. Amongthe new nitrofurans tested, drugs with high activity against the mycoplasma were discovered. Manystudies have been made previously on the sensitivity of various mycoplasmas to antimicrobial drugs. Because of the high host specificity of mycoplasmas, strains derived from the same individual host species were chiefly used in such studies.

A total of 151 strains of Mycoplasma hyorhinis isolated from porcine lung lesions (weaned pigs, n = 71, and finishers, n = 80) were investigated for their in vitro susceptibility to 10 antimicrobial agents. Thirty-one strains (28 from weaned pigs and 3 from finishers) showed resistance to 16-membered macrolide antibiotics and lincomycin. The prevalence of the 16-membered macrolide-resistant M. hyorhinis strain in weaned pigs from Japanese herds has approximately quadrupled in the past 10 years. Several of the 31 strains were examined for mutations in the 23S ribosomal RNA (rRNA). All field strains tested showed a transition of A to G at position 2059 of 23S rRNA-rendered Escherichia coli. On the other hand, individual tylosin-and lincomycin-resistant mutants of M. hyorhinis were selected in vitro from the susceptible type strain BTS7 by 3 to 9 serial passages in subinhibitory concentrations of each antibiotic. The 23S rRNA sequences of both tylosin and lincomycin-resistant mutants were compared with that of the radical BTS7 strain. The BTS7 mutant strain selected by tylosin showed the same transition as the field-isolated strains of A2059G. However, the transition selected in lincomycin showed mutations in domains II and V of 23S rRNA, G2597U, C2611U in domain V, and the addition of an adenine at the pentameric adenine loop in domain II. The strain selected by lincomycin showed an additional point mutation of A2062G selected by tylosin. KEY WORDS: antimicrobial susceptibility, macrolide resistance, Mycoplasma hyorhinis, 23S ribosomal RNA, tylosin. J. Vet. Med. Sci. 67(8): 795-800, 2005 Mycoplasma hyorhinis, which causes arthritis, pleuritis, peritonitis, pericarditis, and polyserositis, is frequently isolated from the upper respiratory tract and tonsils of young pigs [3, 4]. It is also reported as a causal agent of otitis media [13]. It has often been isolated from pigs with por-cine reproductive and respiratory syndrome (PRRS) [8, 19]. No vaccines have been available to control the spread of M. hyorhinis within herds. Thus, at present, chemotherapeutic control is the most practical way to minimize the economic losses caused by M. hyorhinis infection. There have been several reports examining the susceptibility of M. hyorhinis to antimicrobial agents [1, 2, 6, 9, 10, 20, 24]. Over the course of a decade in Japan, we detected isolates of M. hyorhinis and M. hyosynoviae that were resistant to 16-membered macrolides, such as tylosin and josamycin [9, 10]. A few reports describe macrolide resistance in swine mycoplasmas in European countries [1, 6]; however, no macrolide-resistant M. hyorhinis has been detected in the US. [24]. Alterations in the ribosomal proteins of L4 and L22 [16, 23] and rRNA [22] have been reported as the mechanism of resistance to macrolides in Escherichia coli. In addition, structural modifications of erythromycin by phosphorylation [14], glycosylation [7], and lactone ring cleavage by erythromycin esterase [15] have been reported as the mechanisms of resistance of many bacterial species to e...

ABSTRACT. Polymerase chain reaction (PCR) systems were developed for detection of 3 pathogenic bovine mycoplasmas, Mycoplasma alkalescens (Mak), M. bovigenitalium (Mbg) and M. bovirhinis (Mbr). The primers were selected from the sequences of the 16S rRNA from each of the mycoplasmas. Neither the Mbg-PCR system nor the Mbr-PCR system showed cross-amplification among 24 bovine, caprine-ovine and human mycoplasma species (including Acholeplasma and Ureaplasma species) tested. The Mak-PCR system showed cross-amplification with M. canadens ATCC29418 T (T=type strain). The sensitivity of each PCR system to detect the proper mycoplasma was 10 3 colony forming units (CFU) when a pure culture was tested, and 2 × 10 3 CFU when the mycoplasma culture was spiked into a calf nasal swab sample. The target mycoplasmas in a clinical nasal swab sample that could be detected by the direct plate method could also be detected by these PCR systems. -KEY WORDS: bovine mycoplasma, Mycoplasma alkalescens, M. bovigenitalium, M. bovirhinis, PCR