Natural infection of germfree rats with Mycoplasma pulmonis

Sterility testing of germ-free mouse colonies

In biomedical research, germ-free and gnotobiotic mouse models enable the mechanistic investigation of microbiota-host interactions and their role on (patho)physiology. Throughout any gnotobiotic experiment, standardized and periodic microbiological testing of defined gnotobiotic housing conditions is a key requirement. Here, we review basic principles of germ-free isolator technology, the suitability of various sterilization methods, and the use of sterility testing methods to monitor germ-free mouse colonies. We also discuss their effectiveness and limitations, and share the experience with protocols used in our facility. In addition, possible sources of isolator contamination are discussed and an overview of reported contaminants is provided.

The search for aliens within us: a review of evidence and theory regarding the foetal microbiome

The microbiome is believed to be established during the birthing process through exposure to the maternal microbiome and immediate external environment. The absence of a microbiome prior to birth is based on the sterile womb hypothesis, which was formulated at the beginning of the 20th century and is supported primarily by the culture-based approach in microbiological studies.Findings of bacterial presence in products of fertilization such as the placenta, amniotic fluid, foetal membranes, and umbilical cord blood in studies using next-generation DNA sequencing technologies began to challenge the sterile nature of the intrauterine environment during gestation. These studies have been mainly criticized by their approach to contamination and inconclusive evidence of viability. The implications of bacterial presence in utero are far reaching in medicine and basic sciences. If commensal bacteria exist in the foetus, antibiotic therapies in pregnancy particularly for asymptomatic cases will need to be re-evaluated. Experimental studies utilizing gnotobiology may also be impacted by a realignment of theory.This review of existing literature aims to provide insight into the existence of bacteria in utero, specifically the foetal microbiome through analysis of experimental evidence and theoretical concepts, and to suggest approaches that may further provide clarity into this inquiry.

Gnotobiotics and the Microbiome

This chapter provides an overview of germfree (GF), gnotobiotic (GN), and defined flora (DF) laboratory rats, relating their history, traditional and modern derivation procedures, the anatomy and physiology, and their use in the study of mammalian host–microbiome relationships. Extensive literature on the nutrition and physiology of GF rats and the expanding library of immunological reagents have increased the research utility of GF, GN, or DF rats. Such rats have been extensively used in metabolic experiments as nucleus seed stocks for the production of disease-free animals and as tools for infectious disease studies, among others. The chapter also presents research applications of GF rats that are particularly suitable for testing candidate viral carcinogens since they are uniquely free of all known viruses, for pathology studies in the distinguishing of primary mediation lesions from those associated with infections, and the study of the biological effects of radiation.

Isolation, propagation, and characterization of a newly recognized pathogen, cilia-associated respiratory bacillus of rats, an etiological agent of chronic respiratory disease

A Gram-negative, filamentous, rod-shaped bacillus which failed to grow in cell-free media was isolated in apparently pure culture from the bronchial scraping and washing of a laboratory rat suffering from chronic respiratory disease by inoculating embryonated chicken eggs via the allantoic route. None of the embryos died during 20 serial passages at weekly intervals. The bacillus was reisolated in embryonated eggs from cesarean-derived barrier-maintained N:SD(SD) rats 8 and 12 weeks after intranasal inoculation with 10th-passage allantoic fluid. The inoculated rats were housed in Horsfall-type units and remained free from other known respiratory pathogens, including mycoplasmas and murine viruses, throughout the study. The bacillus colonized the ciliated epithelial cells of the respiratory tract and caused a marked peribronchial infiltration and hyperplasia of mononuclear cells which progressed with time. The bacillus, ca. 0.2 micron wide by 4 to 6 micron long, stained very poorly with basic aniline dyes but was readily demonstrated with the Warthin-Starry silver technique. It was heat labile (56 degrees C for 30 min); spore forms were not observed. It withstood freeze-thawing and was successfully stored at -70 degrees C. Although no visible means of locomotion was observed with the electron microscope, a slow gliding motility, sometimes with bending and flexing of bacilli apparently adherent to the glass surface, was observed with phase microscopy. As an etiological agent of chronic respiratory disease of rats, this cilia-associated respiratory bacillus (tentatively designated the CAR bacillus) may be the first recognized gliding bacterium known to cause disease in a warm-blooded vertebrate.

Role of mitogenicity in pathogenicity of mycoplasmas for murine hosts

The mitogenicity and pathogenicity of Mycoplasma pulmonis were compared in two rat strains. Both the mitogenic and the pathologic effects induced by M. pulmonis membranes were more severe in Lewis rats than in Hooded rats, and were dependent on the mitogen doses used. It was concluded that the severity of lung lesions induced by M. pulmonis membranes correlated with the degree of mitogenic responses of the different rat strains to this organism. The roles of T- and B-cell mitogens in induction of pneumonia were studied in Hooded rats treated intranasally with either the T-cell mitogen concanavalin A or with M. neurolyticum membranes which stimulate the B-cell populations, or with both concanavalin A and M. neurolyticum. Results clearly showed that the individual B- and T-cell mitogens affected the lungs of treated animals. Nevertheless, the mitogenic co-stimulation of both B and T lymphocytes in rat lungs was necessary to obtain maximal development of interstitial lymphocytic pneumonia.

Comparison of methods for detection of Mycoplasma pulmonis in experimentally and naturally infected rats

Isolation, indirect immunofluorescence, an enzyme-linked immunosorbent assay (ELISA), and histopathological examination of tissues for characteristic lesions were evaluated for their efficiency in detecting Mycoplasma pulmonis infection in rats. Whereas all of the methods were efficient in naturally infected Sprague-Dawley rats, none of the methods consistently detected infection in F344 rats experimentally infected with low doses of the organism. In the experimental infections, however, the success rate of any method was directly related (P less than 0.05) to increasing inoculum dose and time postinoculation. Collectively, the data indicated that isolation of M. pulmonis was the most efficient single detection method and the nasopharyngeal duct was the best single site to culture, although sampling of multiple sites within the respiratory tract increased the rate of isolating the organism. The ELISA was understandably the least sensitive method in the low-dose, experimentally infected rats because of the time required for development of a detectable serum antibody response. Although each of the four methods identified a high percentage of naturally infected rats, the ELISA was the most efficient method in these animals as it was uniformly positive. The use of combinations of methods was found to increase the rate of detection of M. pulmonis infection in both experimentally and naturally infected rats.

Lymphocyte activation by various Mycoplasma strains and species

The capacity of various mycoplasma strains and species to induce lymphocyte transformation in vitro was studied. Of six strains of Mycoplasma pulmonis studied, five displayed mitogenic activity with rat lymphocytes. Among those M. pulmonis strains, our MP15 isolate and the Negroni strain exhibited particularly potent mitogenic capacity. The murine mycoplasmas M. neurolyticum and M. arthritidis shared this mitogenicity for rat lymphocytes. However, the human mycoplasmas M. fermentans, M. pneumoniae, M. hominis, M. orale, and Acholeplasma laidlawii did not activate rat lymphocytes. Lymphocytes obtained from germfree rats were activated to the same extent as those from animals bred under conventional conditions. The mitogenic potency exhibited by mycoplasma was not restricted to infective microorganisms, and preparations of killed mycoplasma particles exerted an extensive lymphocyte transformation. The data show that the mitogenic activity of mycoplasmas is not confined to a single mycoplasma isolate and that it acts in a nonspecific manner.