Nasal swabs of 293 calves were examined for Mycoplasma. The samples were collected from calves affected with respiratory diseases on 71 farms in various parts of Japan between 1996 and 1997. Mycoplasma bovirhinis was isolated from 47 of 293 calves (16.0%). Mycoplasma alkalescens, M. bovis, M. arginini, M. bovigenitalium and Acholeplasma spp. were isolated from 19 (6.5%), seven (2.4%), four (1.4%), four (1.4%) and 18 (6.1%) calves, respectively. Pasteurella multocida and P. haemolytica were isolated from 60% of Mycoplasma-positive calves. However, other bacteria were not isolated from calves. To evaluate the antimicrobial susceptibility of their isolates, 68 M. bovirhinis, 21 M. alkalescens and 10 M. bovis strains were examined for 12 antimicrobial agents. All isolates showed higher susceptibility to tiamulin than to the other drugs used in the study. However, erythromycin had no effect on any of the Mycoplasma strains studied. The field isolates were less susceptible than the type strains to some drugs, such as spiramycin, oxytetracycline and tylosin.

ABSTRACT. Mycoplasma alkalescens, M. bovigenitalium, M. bovirhinis and M. bovis were directly detected from milk specimens by a polymerase chain reaction (PCR) when milk specimens were centrifuged and treated with mycoplasmal lysis buffer. The sensitivity of this PCR method was 110 to 1,400 colony forming units (CFU). This method was useful for the detection of mycoplasmas in milk specimens from cows at an early stage of mycoplasmal mastitis since a small amount of mycoplasma could be detect in milk without culture. The results were available within 12 hr, which is faster than conventional culture techniques. M. bovirhinis was detected in more than 70% of mastitic milk specimens when mycoplasmas were detected in milk specimens from 30 cows with mastitis by this PCR method. KEY WORDS: mastitis, mycoplasma, PCR.J. Vet. Med. Sci. 63(6): 691-693, 2001 Mycoplasma mycoides subsp. mycoides, M. bovis, M. alkalescens, M. bovigenitalium, M. dispar and others are the causative agents of several diseases in cows and calves, such as mastitis, pneumonia, arthritis, genital disorders and abortions [1,3,6,12,15]. M. bovirhinis is a troublesome agent as a secondary invader in respiratory diseases, and it is the mycoplasma that is the most common isolate from the nasal cavity of cattle with respiratory disease [8]. Since the diseases are largely resistant to chemotherapy [6,24], it is necessary to have rapid and reliable diagnostic methods to detect the agents at an early stage, so that effective control measures can be introduced in time. However, current methods for the detection of mycoplasmas are restricted to culture and serology, and both of these diagnostic methods are time consuming, laborious and difficult. Isolation and identification of mycoplasmas may take weeks, and few laboratories have the capabilities required to routinely culture mycoplasmas. Serodiagnosis requires the demonstration of increasing antibody titers that are reached only ten to fourteen days after the onset of clinical symptoms [19]. Consequently, the pathogen cannot be detected during the incubation period. Moreover, the serological cross reactions among the mycoplasma species are a critical problem [19]. Therefore, the absence of practical and rapid detection methods and resistance to therapy hamper the effective control of mycoplasma infections.Gonzalez [7] and Hatanaka et al. [9] reported cases of mycoplasmal mastitis caused by M. bovis derived from the nasal secretion of cows with pneumonia, emphasizing the relationship between mycoplasmal pneumonia and mastitis. During 1996-1997, we performed nationwide research on the isolation of mycoplasma from the nasal secretions of calves with respiratory diseases, and the result was that a strain of mycoplasma was isolated from about 30% of calves with respiratory diseases. The majority of the isolates consisted of the following 4 species, M. alkalescens, M. bovigenitalium, M. bovirhinis and M. bovis (Data not shown). Therefore, we restrict discussion to these four species in this study.The purpose of...

Quinolone-resistant (QR) mutants of Mycoplasma bovirhinis strain PG43 (type strain) were generated by stepwise selection in increasing concentrations of enrofloxacin (ENR). An alteration was found in the quinolone resistance-determining region (QRDR) of the parC gene coding for the ParC subunit of topoisomerase IV from these mutants, but not in the gyrA, gyrB, and parE gene coding for the GyrA and GyrB subunits of DNA gyrase and the ParE subunit of topoisomerase IV. Similarly, such an alteration in QRDR of parC was found in the field isolates of M. bovirhinis, which possessed various levels of QR. The substitution of leucine (Leu) by serine (Ser) at position 80 of QRDR of ParC was observed in both QR-mutants and QR-isolates. This is the first report of QR based on a point mutation of the parC gene in M. bovirhinis.