ABSTRACT. A total of 328 cloacal swabs and 163 footpads of wild birds were investigated for the presence of salmonellae. All 19 isolates from cloacal swabs were serotyped as Salmonella Typhimurium susceptible to all five conventional antimicrobial agents (ampicillin, chloramphenicol, streptomycin, oxytetracycline and nalidixic acid) tested. In contrast, 15 salmonellae isolated from footpads included S. Muenhen, S. Virchow, S. Bareily and S. Bovismorbificans, including S. Typhimurium; these non-Salmonella Typhimurium isolates showed multiple drug resistance. KEY WORDS: Salmonella, wild bird.

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. A case of Staphylococcus aureus intramammary infection (IMI) on a Japanese dairy farm was monitored for 9 months. S. aureus isolates from cows and environmental samples consisted of specific strains with sequence types 352 and 705, as determined by multilocus sequence typing. Clonal strains of these sequence types are isolated from cows worldwide, indicating that they are adapted to the bovine environment. These results explain why many IMI cases are persistent and lead to subclinical mastitis. The strain isolated from milk was identical to those isolated from the cows' bodies and cows carrying S. aureus, milking units, personnel, heifers and cats in the dairy barn. These locations and factors should be emphasized as sources and routes of strains causing IMI.