Effect of diethylaminoethyl dextran on the growth of Mycoplasma in agar

Selective medium for culture of Mycoplasma hyopneumoniae

•

Systematic improvements to the medium for growth of Mycoplasma hyopneumoniae.

•

Development of selective medium for M. hyopneumoniae inhibitory to M. hyorhinis.

•

Improved colony size of M. hyopneumoniae.

•

Improved reproducibility of culture for use in genetic manipulations.

The fastidious porcine respiratory pathogen Mycoplasma hyopneumoniae has proven difficult to culture since it was first isolated in 1965. A reliable solid medium has been particularly challenging. Moreover, clinical and pathological samples often contain the fast-growing M. hyorhinis which contaminates and overgrows M. hyopneumoniae in primary culture. The aim of this study was to optimise the culture medium for recovery of M. hyopneumoniae and to devise a medium for selection of M. hyopneumoniae from clinical samples also containing M. hyorhinis. The solid medium devised by Niels Friis was improved by use of Purified agar and incorporation of DEAE-dextran. Addition of glucose or neutralization of acidity in liquid medium with NaOH did not improve the final yield of viable organisms or alter the timing of peak viability. Analysis of the relative susceptibility of M. hyopneumoniae and M. hyorhinis strains to four antimicrobials showed that M. hyopneumoniae is less susceptible than M. hyorhinis to kanamycin. This was consistent in all UK and Danish strains tested. A concentration of 2 μg/ml of kanamycin selectively inhibited the growth of all M. hyorhinis tested, while M. hyopneumoniae was able to grow. This forms the basis of an effective selective culture medium for M. hyopneumoniae.

Agarose soy casein digest medium for replacement of blood agar for potency determinations of live Pasteurella vaccines

Blood agar, prepared with Trypticase (BBL Microbiology Systems, Cockeysville, Md.) soy agar and 5% defibrinated bovine blood, is used for testing the potency of live Pasteurella multocida and Pasteurella haemolytica vaccines, but its potential for variation makes it undesirable to use in a standard assay method. Tests done with RPMI 1640 and Trypticase soy medium indicated that the benefits obtained by adding defibrinated blood to the Trypticase soy agar medium were more likely due to neutralization of toxic components than to the presence of transferrin or iron as growth factors. Reduction of toxic components in the Trypticase soy agar medium was accomplished by replacing agar with agarose and by autoclaving glucose as a separate solution to produce the replacement medium. The replacement medium was prepared by autoclaving three separate solutions--Trypticase soy broth without glucose; glucose; and agarose--cooling to 55 degrees C, and mixing and then pouring the mixtures into petri dishes. The growth obtained with this medium as judged by determination of the number of CFU and the colony sizes of P. multocida or P. haemolytica was equal to or better than those obtained with blood agar.

Intracage ammonia promotes growth of Mycoplasma pulmonis in the respiratory tract of rats

Ammonia (NH3) from soiled cage bedding is known to enhance the progression and severity of murine respiratory mycoplasmosis in rats. To test the hypothesis that NH3 directly or indirectly enhances the growth of Mycoplasma pulmonis in vivo, pathogen-free F344 rats were inoculated intranasally with 1 x 10(4) to 4 x 10(4) or 4 x 10(6) to 5 x 10(6) colony-forming units of M. pulmonis and exposed to less than or equal to 1.5 or 76 microgram of NH3 per liter (less than or equal to 2 or 100 ppm, respectively). Nasal passages, larynges, tracheas, and lungs from rats killed at intervals up to 28 days after inoculation were quantitatively cultured. Growth of M. pulmonis was much greater in NH3-exposed rats than in controls, particularly in those inoculated with the lower dose. Increases in M. pulmonis populations were more rapid in proximal airways than in distal airways. Serum immunoglobulin G and M antibody responses to M. pulmonis as measured by an enzyme-linked immunosorbent assay were greater in NH3-exposed rats. In other experiments, the nasal passages absorbed virtually all NH3 when the rats were exposed to less than 380 micrograms of NH3 per liter (500 ppm), indicating that NH3 induced increases in the numbers of organisms in the distal respiratory tract, probably by a secondary, rather than a direct, effect. Also, NH3 exposure did not inhibit pulmonary antibacterial activity as measured by clearance of radiolabeled Staphylococcus epidermidis. The growth of M. pulmonis in vitro was inhibited by 1 mM NH4+ added to the medium as NH4OH but not by NH4+ concentrations of 0.5, 0.1, or 0.01 mM, suggesting that NH3 increases growth indirectly through effects on the host.

In vitro susceptibility of Mycoplasma hyopneumoniae and Mycoplasma hyorhinis to fifty-one antimicrobial agents

By a tube dilution assay technique, 51 antimicrobial agents were singly tested against 9 strains of Mycoplasma hyopneumoniae and 1 strain of M. hyorhinis for the purpose of obtaining information useful for selecting an agent for testing in vivo against porcine mycoplasmal pneumonia. Based on determining minimal inhibitory concentrations and chemically grouping the agents into nine classes, all M. hyopneumoniae strains were found resistant to penicillins and peptides and susceptible to sulfonamides and tetracyclines, and, in other classes, were either susceptible or resistant depending on the particular agent being tested. Strains were susceptible to the same 33 of the 51 agents. Minimal inhibitory concentrations ranged from 0.06 to 9.20 mug/ml. M. hyorhinis was susceptible to 19 of the 33 agents that M. hyopneumoniae was susceptible to. Minimal inhibitory concentrations ranged from 0.03 to 8.10 mug/ml. All strains of M. hyopneumoniae differed from M. hyorhinis in that they were susceptible to cephaloglycin and nitrofurazone.

Mycoplasm suipneumoniae and Mycoplasma flocculare in comparative pathogenicity studies

Three field strains of Mycoplasma suipneumoniae each inoculated into 3 gnotobiotic piglets produced macro- and microscopic lung lesions typical of enzootic pneumonia in 8 of the animals. Under similar conditions 3 strains of M. flocculare produced typical macroscopic lung lesions in just 1 out of 9 animals. It is therefore concluded that M. flocculare is not of primary etiologic importance in the porcine enzootic pneumonia complex.

The frequency of successful reisolation from nasal cavities, lungs, and other tissues indicated that the lungs are the sole natural habitat for M. suipneumoniae, while for M. flocculare lungs as well as nasal cavities should be regarded as the natural habitat.

None of the organisms apparently spread via the blood stream. M. flocculare, but not M. suipneumoniae, induced histologic alterations of the nasal mucosa.