Cytotoxicity of Mycoplasma pneumoniae Membranes

Pathogenesis of Mycoplasma pneumoniae: An update

Genus Mycoplasma, belonging to the class Mollicutes, encompasses unique lifeforms comprising of a small genome of 8,00,000 base pairs and the inability to produce a cell wall under any circumstances. Mycoplasma pneumoniae is the most common pathogenic species infecting humans. It is an atypical respiratory bacteria causing community acquired pneumonia (CAP) in children and adults of all ages. Although atypical pneumonia caused by M. pneumoniae can be managed in outpatient settings, complications affecting multiple organ systems can lead to hospitalization in vulnerable population. M. pneumoniae infection has also been associated with chronic lung disease and bronchial asthma. With the advent of molecular methods of diagnosis and genetic, immunological and ultrastructural assays that study infectious disease pathogenesis at subcellular level, newer virulence factors of M. pneumoniae have been recognized by researchers. Structure of the attachment organelle of the organism, that mediates the crucial initial step of cytadherence to respiratory tract epithelium through complex interaction between different adhesins and accessory adhesion proteins, has been decoded. Several subsequent virulence mechanisms like intracellular localization, direct cytotoxicity and activation of the inflammatory cascade through toll-like receptors (TLRs) leading to inflammatory cytokine mediated tissue injury, have also been demonstrated to play an essential role in pathogenesis. The most significant update in the knowledge of pathogenesis has been the discovery of Community-Acquired Respiratory Distress Syndrome toxin (CARDS toxin) of M. pneumoniae and its ability of adenosine diphosphate (ADP) ribosylation and inflammosome activation, thus initiating airway inflammation. Advances have also been made in terms of the different pathways behind the genesis of extrapulmonary complications. This article aims to comprehensively review the recent advances in the knowledge of pathogenesis of this organism, that had remained elusive during the era of serological diagnosis. Elucidation of virulence mechanisms of M. pneumoniae will help researchers to design effective vaccine candidates and newer therapeutic targets against this agent.

Mycoplasma pulmonis inhibits electrogenic ion transport across murine tracheal epithelial cell monolayers

Murine chronic respiratory disease is characterized by persistent colonization of tracheal and bronchial epithelial cell surfaces by Mycoplasma pulmonis, submucosal and intraluminal immune and inflammatory cells, and altered airway activity. To determine the direct effect of M. pulmonis upon transepithelial ion transport in the absence of immune and inflammatory cell responses, primary mouse tracheal epithelial cell monolayers (MTEs) were apically infected and assayed in Ussing chambers. M. pulmonis-infected MTEs, but not those infected with a nonmurine mycoplasma, demonstrated reductions in amiloride-sensitive Na+ absorption, cyclic AMP, and cholinergic-stimulated Cl- secretion and transepithelial resistance. These effects were shown to require interaction of viable organisms with the apical surface of the monolayer and to be dependent upon organism number and duration of infection. Altered transport due to M. pulmonis was not merely a result of epithelial cell death as evidenced by the following: (i) active transport of Na+ and Cl-, albeit at reduced rates; (ii) normal cell morphology, including intact tight junctions, as demonstrated by electron microscopy; (iii) maintenance of a mean transepithelial resistance of 440 omega/cm2; and (iv) lack of leakage of fluid from the basolateral to the apical surface of the monolayer. Alteration in epithelial ion transport in vitro is consistent with impaired pulmonary clearance and altered airway function in M. pulmonis-infected animals. Furthermore, the ability of M. pulmonis to alter transport without killing the host cell may explain its successful parasitism and long-term persistence in the host. Further study of the MTE-M. pulmonis model should elucidate the molecular mechanisms which mediate this reduction in transepithelial ion transport.

Purification and characterization of Mycoplasma penetrans Ca2+/Mg2+-dependent endonuclease

The major nuclease from Mycoplasma penetrans has been purified to homogeneity. The enzyme seems to be present as a membrane-associated precursor of 50 kDa and as a peripheral membrane monomeric polypeptide of 40 kDa that is easily removed by washing of cells with isotonic buffers and in the aqueous phase upon Triton partitioning of Triton X-114-solubilized protein. The 40-kDa nuclease was extracted from M. penetrans cells by Triton X-114 and phase fractionation and was further purified by chromatography on Superdex 75 and chelating Sepharose (Zn2+ form) columns. By gel filtration, the apparent molecular mass was 40 kDa. The purified enzyme exhibits both a nicking activity on superhelical and linear double-stranded DNA and a nuclease activity on RNA and single-stranded DNA. No exonuclease activity was found for this enzyme. This nuclease required both Mg2+ (optimum, 5 mM) and Ca2+ (optimum, 2 mM) for activity and exhibited a pH optimum between pH 7 and 8 for DNase activity. It was inhibited by Zn2+, Mn2+, heparin, sodium dodecyl sulfate, and chelator agents such EDTA and EGTA, but no effect was observed with ATP, 2-mercaptoethanol, N-ethylmaleimide, dithiothreitol, nonionic detergents, phenylmethylsulfonyl fluoride, and iodoacetamide. Nuclease activity was inhibited by diethylpyrocarbonate at both pH 6 and 8 and by pepstatin, suggesting the involvement of a histidine and an aspartate in the active site. When added to human lymphoblast nuclei, the purified M. penetrans endonuclease induced internucleosomal fragmentation of the chomatin into oligonucleosomal fragments. On the basis of this result, and taking into account the fact that M. penetrans has the capacity to invade eucaryotic cells, one can suggest, but not assert, that produced Ca2+/Mg2+-dependent endonuclease may alter the nucleic acid metabolism of host cells by DNA and/or RNA degradation and may act as a potential pathogenic determinant.

Ureaplasma diversum as a cause of reproductive disease in cattle

This article includes a brief review of the classification, habitat, and characteristics of the ureaplasmas, followed by a discussion of the pathogenesis, transmission, clinical syndromes, diagnosis, immunity, and treatment of Ureaplasma diversum infections in cattle.

Characterization of cytopathogenicity of aquarium seal mycoplasmas and seal finger mycoplasmas by light and scanning electron microscopy

Two recent mycoplasma isolates (one from an aquarium seal and one from a patient with the clinical entity known as seal finger) have been evaluated for cytopathogenicity in tracheal explant cultures. Examinations were performed in direct comparison to Mycoplasma phocidae, an isolate from an epidemic of seal pneumonia along the New England coast (USA) in 1979-1980. The study revealed similar inhibitory effects on ciliated tracheal epithelial cells and clumping of cilia by attached mycoplasmas; no exfoliation of respiratory epithelial cells was observed. In addition, cytopathic effects caused by the mycoplasmas were distinguished from effects of aging in non-infected explants under long-term in-vitro cultivation conditions. The general meaning of mycoplasmas in seals is discussed in detail in this paper.

Localization of an immunodominant 64 kDa lipoprotein (LP 64) in the membrane of Mycoplasma gallisepticum and its role in cytadherence

A 64 kDa lipoprotein (LP 64) haemagglutinin (pI 4.9-5.0) was isolated from the membrane of Mycoplasma gallisepticum. Triton X-114 phase partitioning has demonstrated that the hydrophobic nature of this haemagglutinin is due to a lipid portion of the molecule. Autoradiography of [3H]-palmitate-labelled M. gallisepticum revealed the presence of several additional lipoproteins. Immunoelectron microscopy demonstrated the localization of LP 64 to the base of the terminal structure. Densitometric scans of stained polyacrylamide gels of M. gallisepticum showed that LP 64 constitutes 1.7% of the total protein. Scans of immunoblots of M. gallisepticum indicate that LP 64 is highly immunogenic in chickens, accounting for 7.4% of the total serum IgG response at four weeks post-infection. A quantitative value for the IgG response to LP 64, relative to the percentage of total protein (the Relative Immunogenicity Index) was 4.4. LP 64 is conserved among several strains of M. gallisepticum, but its presence could not be detected in Mycoplasma synoviae. Antiserum raised to electroeluted LP 64 reacted specifically with this lipoprotein when assessed on either one- or two-dimensional immunoblots of M. gallisepticum. This antiserum, as well as Fab fragments, inhibited haemagglutination of chicken erythrocytes and inhibited the attachment of 14C-labelled M. gallisepticum to chicken tracheal epithelium in vitro by 62%.

Cytopathic effects of Mycoplasma pulmonis in vivo and in vitro

This study was performed to evaluate the cytopathic features resulting from Mycoplasma pulmonis infection of tracheal organ cultures compared to with those seen in in vivo infection and to use this system to determine possible differences in cytopathic effects in two M. pulmonis variants found to cause different diseases in vivo. The attachment of M. pulmonis to respiratory epithelium was similar in vivo and in vitro. Cytopathic effects seen in both systems were also similar in loss of tight junctions between cells and exfoliation of respiratory cells, resulting in exposure of the subepithelial layer. These similarities indicate that the observed tissue damage is initiated by the mycoplasmas rather than by immunologic host responses but does not exclude the possibility that host responses may subsequently contribute to the cytopathological events. Comparison of the effects of the two variants (one known to cause death in vivo) did not reveal differences in vitro. This suggests that host factors (not present in vitro) may account for differences in virulence. Detailed in vitro studies allowed the identification of the time frame corresponding to the in vivo infection and also revealed the limitations of the in vitro system.

Investigation of seal mycoplasmas for their cytotoxic potential on tracheal organ cultures of SPF and gnotobiotic rats

Eleven mycoplasma strains isolated from several organs of diseased seals during the seal epidemic in the Baltic and North Sea in 1988 and the seal epidemic along the New England coast in 1979-1980, were investigated for their cytotoxic potential by inoculation into tracheal organ cultures of SPF and gnotobiotic rats. The mycoplasma strains belonged to three different species. Administration of 2.0 x 10(2) to 4.5 x 10(7) colony forming units of all of the mycoplasma strains caused an inhibition of the ciliary activity and cytopathological changes within the epithelial cells appearing as bleb-like protuberances by observation with the inverted microscope. There was, however, a distinct difference in the strength of the cytopathological changes caused by the three mycoplasma species. Semi- and ultrathin sections of tracheal rings infected with the seal mycoplasma strain 852, observed by light and electron microscopy, revealed a heavy tissue injury of the tracheal epithelium and dumbbell-shaped mycoplasmas adhering to degenerated epithelial cells.

The effects of Mycoplasma mobile 163 K on the ciliary epithelium of tracheal organ cultures

Mycoplasma (M.) mobile 163 K, isolated from the gills of a tench (Tinca tinca L.), was examined for cytotoxic capacities using tracheal organ cultures from gnotobiotic rats and gnotobiotic piglets in pH-controlled experiments (pH 7.2-7.6). The mycoplasmas caused an inhibition of the ciliary activity at incubation temperatures of 20, 25 and 30 degrees C. The strongest cilia stopping effect was observed at an incubation temperature of 25 degrees C, the optimal growth temperature of the mycoplasmas. No ciliostasis occurred at 37 degrees C. The number of the organisms did clearly affect the severity of ciliostasis in the range from 4.0 x 10(4) to 7.7 x 10(8) c.f.u. in rat as well as in porcine tracheal organ cultures. Toxic substances, secreted by the mycoplasmas into the culture medium, could not be detected. In histological investigations cytopathological changes were observed in the epithelial cells, apparent in the destruction and loss of cilia, cytoplasmatic vacuolization, swelling of mitochondria, peripheral orientation of the nuclear chromatin and detachment of epithelial cells from each other and the basal membrane. The final stage of the infection was characterized by complete exfoliation of the epithelial cells and the complete destruction of the multi-layer epithelium. The localization of the mycoplasmas attached to the ciliary epithelium was shown by scanning and transmission electron microscopy.

Interaction of Mycoplasma pneumoniae with HeLa cells

The susceptibility of HeLa cells to Mycoplasma pneumoniae-induced injury was examined. Infections were initiated with relatively low mycoplasma doses, carried out in a culture medium incapable of supporting M. pneumoniae replication in the absence of host cells, and monitored for up to 10 days. Under these conditions, a time- and dose-dependent decline in the number of viable host cells compared with that of uninfected controls was observed. The effect of M. pneumoniae infection on host cell macromolecular synthesis was also evaluated. At high doses of infection, synthesis of both protein and RNA declined rapidly relative to that in control cells. At lower doses there was a biphasic response in protein synthesis, which was substantially lower than that in the uninfected control by day 1 postinfection, returned to control levels by day 4 postinfection, and was again less than that in control cells by day 7 postinfection. In contrast, no transient recovery was observed in RNA synthesis, which declined very gradually over 7 days in infected HeLa cells compared with that in uninfected control cells. The ability of HeLa cells to support the proliferation of M. pneumoniae under these experimental conditions was demonstrated by quantitation of mycoplasma CFU in the nonpermissive medium in the presence or absence of HeLa cells. A negligible increase in the number of M. pneumoniae was observed over 4 days when HeLa cells were absent, while CFU increased by almost 20-fold when M. pneumoniae was cultured in the presence of HeLa cells. The susceptibility and response in macromolecular synthesis in M. pneumoniae-infected HeLa cells differed from that recently described for a nontransformed culture of hamster trachea epithelial cells under the same experimental conditions (Y.-Y. Chen and D.C. Krause, Infect. Immun. 56: 570-576, 1988), underscoring the importance of the choice of host cell for in vitro modeling of M. pneumoniae pathogenesis.

Parasitism of hamster trachea epithelial cells by Mycoplasma pneumoniae

Hamster trachea epithelial (HTE) cells were employed as a model system for Mycoplasma pneumoniae pathogenesis. To more closely mimic natural infection, M. pneumoniae was forced to rely upon host cells (as opposed to the growth medium) for nutrients, and infections were initiated with relatively low mycoplasma doses and monitored for extended time periods. A time- and dose-dependent decline in the viability of infected cells was observed; however, viability never declined below 50% of that in uninfected controls. Protein and RNA synthesis actually increased above control levels in infected cells, despite a concomitant decrease in viability. This response was pronounced at higher multiplicities of infection but was only transient at lower doses. In parallel studies in which a culture medium capable of supporting M. pneumoniae growth was used, loss of viability was accelerated. With a low-dose infection a transient increase followed by a precipitous decline in macromolecular synthesis was observed, relative to that in uninfected controls. At higher doses, however, macromolecular synthesis decreased dramatically and in proportion to the loss of viability. The requirement for HTE cells for mycoplasma growth under the experimental culture conditions was demonstrated by quantitating viable mycoplasmas in the culture medium in the presence or absence of HTE cells over 4 days. The increase in mycoplasma number was negligible in the absence of HTE cells, while a 30-fold increase was observed in the presence of HTE cells. These findings demonstrate the feasibility of long-term, low-dose studies of M. pneumoniae pathogenesis with trachea epithelial cells and a nonpermissive culture medium. This experimental system should facilitate the elucidation of the mechanism(s) responsible for host cell injury, and perhaps reveal how host cells respond to infection.

Ion transport and cadmium-induced inhibition of ciliary activity and induction of swelling of epithelial cells in mouse trachea organ culture

Swelling of epithelial cells and reduction of ciliary activity in mouse trachea organ culture occurred after incubation for 4 h with a rather low concentration of cadmium acetate (10 microM). Specific inhibitors of ion transport (Na+, K+, Cl-) such as furosemide, amiloride and ouabain did not mimic, abolish or increase the toxic effects induced by cadmium acetate. Exposure to cadmium acetate had no significant effect on electrolyte uptake (22Na+ and 86Rb+). These results suggest that the swelling of epithelial cells induced by cadmium acetate is not due to an osmotic swelling from an accumulation of electrolytes. Ba2+, known to have several biological properties in common with Ca2+, and to influence basolateral K+ flux, counteracted the toxic effects of cadmium acetate, whereas a more rapid and extensive swelling occurred with cadmium acetate in a medium without Ca2+. No effect on the uptake of 109Cd2+ was found with barium chloride, whereas in a medium without Ca2+ the Cd2+ uptake increased by 47%. Trifluoperazine (100 microM), a drug which in vitro binds tightly to calmodulin, imitated the toxic effects of 10 microM cadmium acetate. The combination of 10 microM cadmium acetate and 100 microM trifluoperazine resulted in an additive toxic effect. A possible mechanism for the cadmium acetate-induced swelling and inhibition of ciliary activity could, thus, be a disturbance of the regulatory activity of calmodulin.

Effects of cadmium acetate and sodium selenite on mucociliary functions and adenosine triphosphate content in mouse trachea organ cultures

The effects of cadmium acetate and sodium selenite in mouse trachea organ culture have been studied separately and in combination. Ciliary activity, morphology, rate of total protein and glycoconjugate (i.e. glycoprotein and proteoglycan) synthesis/secretion and ATP content were investigated. Exposure to 10 microM cadmium acetate or 2000 microM sodium selenite resulted in a complete cessation of ciliary activity within 5 h. With cadmium acetate also a swelling of epithelial cells was observed. Sodium selenite (250-2000 microM) delayed by 2-3 h the inhibitory effect of cadmium acetate (5-20 microM) on ciliary activity. The rate of protein synthesis, as determined by incorporation of [3H]proline, was reduced by 13% and 44% at exposure for 4 h at 37 degrees C to 250 microM and 500 microM sodium selenite respectively, the effect being partly abolished by cadmium acetate. With 5 microM and 10 microM cadmium acetate the rate of glycoconjugate synthesis, as measured by incorporation of [3H]glucosamine, increased by 50% and 69%, respectively, after incubation for 4 h. This increase was partly reduced by sodium selenite. Neither cadmium acetate nor sodium selenite had any effect on the rate of total protein or glycoconjugate secretion. The ATP content in trachea rings was reduced by 48% and 54% after incubation for 4 h with 250 microM and 500 microM sodium selenite, respectively. No significant effect of cadmium acetate was found on ATP content. An antagonistic effect of sodium selenite and cadmium acetate in mouse trachea organ culture is suggested from the present experiments.

Nonspecific lymphocyte responses in F344 and LEW rats: susceptibility to murine respiratory mycoplasmosis and examination of cellular basis for strain differences

Mycoplasma pulmonis produces a mitogen which may play a role in the pathogenesis of murine respiratory mycoplasmosis in rats. Since LEW rats are more susceptible to this disease than F344 rats are, these two strains were used to examine a possible association between disease severity and the level of nonspecific lymphocyte stimulation by mitogens, including M. pulmonis membrane preparations. F344 and LEW spleen, lung, blood, and lymph node lymphocytes were exposed to various mitogens. LEW lymphocytes gave a significantly higher response to mitogenic stimulation, regardless of their anatomical source. These differences in lymphocyte responsiveness were primarily due to differences within the nonadherent cell population. Significantly higher numbers of W3/25+ (T helper) cells were found in LEW lymphoid populations, whereas no difference was found in MRC OX-8+ (T suppressor/cytotoxic) cells. These data suggest an association between disease severity and host responsiveness to nonspecific stimuli.

Isolation of a cytopathic factor from Mycoplasma hyopneumoniae

A cytopathic factor was isolated from M. hyopneumoniae VPP11 membranes. This factor had an isoelectric point of 6.2 and was capable of inducing cytopathic effect in MRC-5 human lung fibroblast culture at a concentration of 250 ng of protein per ml. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of this cytopathic factor showed a major band with a molecular weight of approximately 54,000.

Ciliary motility in brain ventricular system and trachea of hamsters

Ciliary beat frequency (CBF) in various parts of brain ventricular system, as well as in trachea of hamsters, was examined. Coronal sections of brain and tracheal rings were maintained in a thermostatically controlled perfusion chamber and CBF measured by a photoelectric system equipped with a fiber-optic probe. CBF (Hz) values of lateral ventricle, aqueduct and fourth ventricle were 27.9 +/- 4.6; 30.7 +/- 7.7 and 31.9 +/- 7.8 Hz, respectively. CBF in the third ventricle--19.8 +/- 7.1 Hz--was significantly lower than in other segments of ventricular system. CBF in choroid plexus cilia was very slow, 5-10 Hz, whereas in tracheal rings amounted to 13.7 +/- 3.1 Hz. Bovine cervical mucus and mucus stimulant reversibly inhibited CBF in brain but not in trachea. Brain cilia in contrast to those in trachea were not capable of transporting particles. In addition to demonstrating differences between tracheal and ependymal cilia, this work suggests that cilial motility plays a functional role in local mixing of cerebrospinal fluid, but does not relate to the bulk flow within the ventricular system.

Toxic properties of the Mycoplasma arthritidis ISR-1 membrane

Isolated membranes of Mycoplasma arthritidis ISR-1 possess toxic properties for rats, mice and chicken embryos. Reactions are dose-dependent. By intravenous injection of 20 mg of membrane protein, a lethal toxicity syndrome resembling shock is induced in Sprague-Dawley rats of 100 g body weight. Mice of approximately 20-g body weight show the same syndrome by intravenous injection of 15 mg of membrane protein. The lethal toxicity for chicken embryos increases from 10 to 80% after injection of 0.3 to 1.5 mg of membrane protein. The LD50 in chicken embryos was found to be 0.5 mg membrane protein. After administration of 10-15 mg of membrane protein, rats showed an increase in temperature from 38 to 41 degrees C within 5 h. Because of the difficulty in measuring the temperature in mice, loss of body weight was taken as the criterion for toxicity. Body weight was reduced up to 16% within 1 day after intravenous injection of 500 micrograms of membrane protein per g of body weight. For sheep red blood cells, M. arthritidis ISR-1 membranes were haemolytic in concentrations of 4 mg of membrane protein and higher. Intradermal injection of 1 mg of membrane protein into guinea-pigs resulted in red swelling reactions measuring approximately 10 mm in diameter 10 h after injection. For foetal rat skin fibroblasts, M. arthritidis ISR-1 membranes were toxic in concentrations from 1 micrograms (3H-uridine incorporation), 10 micrograms (14C-leucine incorporation) and 100 micrograms (3H-thymidine incorporation) of membrane protein.

Effect of sodium selenite on the ciliary activity, adenosine triphosphate, and protein synthesis in mouse trachea organ cultures

Trachea from albino mice were cut transversely into nearly identical rings and incubated in medium 199 with Hanks salts and HEPES buffer at 37 degrees C. Sodium selenite at 0.5-5 mM depressed the ciliary activity. With 1 and 5 mM sodium selenite, a 50% reduction in the activity index was observed after approximately 5 and 1.5 h, respectively. The ATP content in trachea rings was reduced with 0.05-5 mM sodium selenite, and increasing concentrations gave decreasing amount of ATP after incubation for 4 and 21 h. The rate of protein synthesis as determined by incorporation of radioactive leucine was reduced with 0.5 and 2 mM sodium selenite. The synthesis was reduced quickly by 2 mM sodium selenite, which gave a 30% reduction after incubation for 1 h. It seems that the ATP levels may be used as the most sensitive indication of sodium selenite toxicity in mouse trachea.

Effects of heavy metals on structure, function, and metabolism of ciliated respiratory epithelium in vitro

Tracheal explants were used to evaluate the relative ciliostatic and cytotoxic potential of heavy metal salts (cadmium chloride, chromium chloride, nickel chloride, and copper sulfate). Explants from hamster, rat, and guinea pig were all sensitive to the metals, though guinea pig explants showed the greatest difference between the untreated and metal treated tissues. Dosage levels were 50, 100, and 500 microM, for 24 to 148 h. Cadmium caused the greatest degree of ciliostasis and cell necrosis. Copper was less toxic, and nickel and chromium caused marginal damage when tested at 100 microM or lower. In each instance, damage became detectable at approximately 24 to 48 h and was nearly stabilized by 72 h. A significant loss of ciliary motion was always accompanied by a decrease in metabolic activity (dehydrogenase activity and ATP content). Transmission and scanning electron microscopy revealed a severely necrotic epithelium after exposure to cadmium, with only subtle morphological alterations after exposure to other metals. With all of the treatments there was no overt structural damage to cilia and little alteration in membranes of cells remaining in the epithelium. Some coagulation or vacuolization was noted in cadmium and copper treated explants but most cellular organelles did not display obvious damage. The most significant changes in the tracheal epithelium exposed to heavy metal salts in vitro were a loss of ciliary motion and a decrease in total ATP content.

Cytotoxicity and ciliostasis in tracheal explants exposed to cadmium salts

Cadmium salts were examined for their biological effects on ciliated respiratory epithelium in hamster tracheal explants. Cadmium chloride and cadmium acetate both caused significant decreases in ciliary motion when tested at 100 micrograms M and above. Reductions in relative ciliary activity were dose-dependent and were first demonstrable at 8-32 hr. The decreased ciliary motion was accompanied by decreases in two key metabolic compound (ATP and dehydrogenase) which are normally associated with cell viability. Histopathological examination of cadmium-treated tissues showed an epithelium thinner than normal, with extensive vacuolization and few, if any, intact ciliated cells. The various biological effects exerted by cadmium are presented, along with potential mechanisms of pathogenesis for the observed ciliostasis and cytonecrosis. Decreases in adenosine triphosphate appear to play a critical role in the development of cadmium-related effects on cellular function and metabolism.

Comparison of ciliostasis by mycoplasmas in mouse and chicken tracheal organ cultures

The cilia-stopping effect of mycoplasmas of human and various animal origin in mouse and chicken tracheal organ cultures was studied. From the results in mouse tracheal organ cultures, the mycoplasma strains tested were divided into three groups: Mycoplasma pulmonis m53, M pulmonis JB, M. pulmonis OK, M. mycoides subsp. Mycoides PGl and M. Gallisepticum S6 showed a strong cilia-stopping effect; M. pulmonis PG22, M. mycoides subsp. capri PG3, M. meleagridis 19729, M. neurolyticum Type A and M. arthritidis PG6 showed a mild effect; and M. pneumoniae FH, M. salivarium Hup, M. hominis type 1-C and M. orale N-C human origin and Acholeplasma laidlawii PG8 showed a weak effect. On the other hand, in chicken tracheal organ cultures, only M. gallisepticum S6 showed a strong effect, M. meleagridis 19729 was affected to a lesser degree, and the other mycoplasma strains showed a weak or no effect. The results indicate that some murine and poultry mycoplasmas showed a cilia-stopping tendency in mouse and chicken tracheal organ cultures, respectively, while human mycoplasmas showed weak or little effect in both organ cultures. In mouse tracheal organ cultures, M. pulmonis m53 treated with heat, trypsin or formaldehyde, and the sterile filtrate of an m53 broth culture showed no cilia-stopping effect. The relationship of the pathogenicity of mycoplasmas for their natural hosts to that for cultured respiratory cells is discussed.

Inflammatory toxin from Mycoplasma bovis: isolation and characterization

An inflammatory toxin was extracted from Mycoplasma bovis with 75 percent aqueous ethanol. The toxin is a complex polysaccharide composed of glucose, glucosamine or galactosamine, and a heptose, is heat-stable, devoid of protein and lipid, and has a molecular weight of 73,000. The holotoxin in the cell membrane is a glycoprotein; however, it is the polysaccharide portion that is toxic. This inflammatory toxin increases vascular permeability and is capable of activating complement. Infusion of 0.9 milligram of toxin into the bovine udder resulted in the characteristic eosinophilic mastitis produced by Mycoplasma bovine.

Influence of the fusogenic agent polyethylene glycol on attachment of Mycoplasma pneumoniae to other cells

The effect of fusogenic agents on the interaction of Mycoplasma pneumoniae with human lung fibroblasts was evaluated. A 60-s exposure of the fibroblasts to polyethylene glycol (molecular weight 200; 10%) significantly increased attachment of mycoplasmas to the fibroblasts.

The mucociliary activity of the respiratory tract. I. Inhibitory effects of products of Pseudomonas aeruginosa on rabbit trachea in vitro

Bacteriological filtrates of three strains of Pseudomonas aeruginosa were compared with respect to inhibitory effect on ciliary movements and a quantitative difference was established between them. The cilia inhibitory effect was strictly concentration-dependent and was resistant to heating. The ciliotoxic effect disappeared from filtrates after chloroform extraction. The chloroform-extracted sediment ws dissolved in physiological saline and the solution revealed an inhibitory effect on cilia. Involvement of endotoxin is not probable, since E. coli endotoxin in a high concentration was not toxic. Partially purified Pseudomonas aeruginosa phenazine pigment as well as haemolysin inhibited ciliary activity and the effect was standardized in the present experimental system.

Antimycoplasmal activity of dimethylphenols in a tracheal explant culture system

Mycoplasma pneumoniae induces pneumonia-like symptoms in hamsters and causes ciliostasis and cytonecrosis in hamster tracheal explants. 2,4-Dimethylphenol and, to a lesser extent, its 2,3-, 2,5-, and 2,6-dimethylphenol isomers protected tracheal explants from these changes after exposure to virulent M. pneumoniae strain PI 1428. The effect was concentration, time, and isomer dependent. At concentrations of 10(-9) M or greater, 2,4-dimethylphenol completely prevented the morphological (loss of ciliated cells) and biochemical (decreased dehydrogenase activity) changes normally observed after exposure to M. pneumoniae. Apparently, 2,4-dimethylphenol interfered with an early event in the infection process. Complete protection required that it be present during the first 2 h of exposure of the explants to the infecting mycoplasmas. These xylenols may prove to be useful tools for helping to define the mechanisms of pathogenesis in certain respiratory infections.

Interaction of Mycoplasma pneumoniae with human lung fibroblasts: characterization of the in vitro model

The interaction of pathogenic Mycoplasma pneumoniae and host cells was studied in cell cultures of MRC-5 human lung fibroblasts. A comparison of results obtained with fibroblasts in a monolayer format and with hamster tracheal explant cultures indicated that the former can bind significantly larger numbers of mycoplasmas. In addition, the attachment was 96% specific, that is, mediated through a neuraminidase-sensitive receptor on the host cell. Uptake of mycoplasmas was directly related to the number of mycoplasma cells present in the inoculum, and attachment was virtually complete within a 30-min period at 37 degrees C. High doses of M. pneumoniae induced a marked cytopathic effect, whereas doses of less than or equal to 10(6) colony-forming units per ml produced grossly observable cell damage that was moderate and variable. Transmission electron microscopy studies indicated that attachment of M. pneumoniae to the surface of lung fibroblasts occurred with the specialized terminal structure or binding site oriented closest to the epithelial cell surface. The filamentous mycoplasma cells were spatially arranged in several configurations and were not limited to a vertical orientation. The advantages and disadvantages of human lung fibroblast monolayer cultures, in reference to other in vitro models are discussed. A new mycoplasma agar medium (G-200 agar) with a defined tissue culture base and 10% horse serum is also described.

Effect of cadmium acetate, copper sulphate and nickel chloride on organ cultures of mouse trachea

Tracheas from albino mice were excised and cut into rings approximately 1 mm thick. After preincubation overnight in Medium 199 with 5% calf serum, they were placed into fresh medium. Cadmium acetate, copper sulphate or nickel chloride was added separately or in combination, to a final concentration of 10--200 micron. Each metal was also added (10 micron) to serum-free Medium 199. The percentage (0--100) of the inner intact epithelium and the rate (0--4) of the ciliary beat in each ring were assessed before and during a 4-hour incubation period and multiplied to yield a relative activity index (0--400). Cadmium acetate at 10--100 micron depressed the ciliary activity significantly more than 10--100 micron copper sulphate (each level P less than 0.05). With 200 micron a 50% reduction of the activity index was observed after approximately 35 min. with cadmium acetate and 85 min. with copper sulphate. At 10--200 micron, cadmium acetate was significantly more suppressive than nickel chloride (each level P less than 0.05). When comparing the inhibitory effects of copper sulphate and nickel chloride a significant difference appeared at 10--100 micron (each level P less than 0.01), but not at 200 microm (P less than 0.05). With 200 micron nickel chloride a 50% reduction in the activity index was observed after 90 min. There was a tendency towards reduced toxicity of cadmium acetate when combined with copper sulphate and of copper sulphate when combined with nickel chloride. In serum-free medium metal toxicity was increased.

Role of cell-associated pathogen metabolism in infection of tracheal explants by Mycoplasma pneumoniae

The effect of environmental conditions on the relative pathogenicity of Mycoplasma pneumoniae for hamster tracheal explants was investigated. Organisms from the early stages of the growth cycle (e.g., day 1 to 2) were more effective in the induction of ciliostasis than were older cultures. Both the degree of ciliostasis and the speed of onset were affected. The type of explant culture medium also affected pathogenic potential. M. pneumoniae infection produced significantly greater ciliostasis and cytonecrosis in a "permissive" medium, i.e., one capable of supporting mycoplasma metabolism and replication, than in a "nonpermissive" medium. However, no adenine protection effect could be detected under permissive conditions, though it was quite striking when a nonpermissive medium was used as the post-infection explant medium. This suggests that the cell damage noted under permissive conditions may result from processes distinct from those operative in the actual host-parasite cellular interaction.

Immunofluorescence and electron microscopy of the attachment of Mycoplasma synoviae to chicken embryo fibroblasts

The techniques of immunofluorescence and of transmission and scanning electron microscopy were used to demonstrate the attachment of Mycoplasma synoviae to chicken embryo fibroblasts. Although the organisms colonized the surface of many of the cells, there was marked variation in the number of organisms associated with individual cells.

The mycoplasmas

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Role of adenine in pathogenesis of Mycoplasma pneumoniae infections of tracheal epithelium

Adenine sulfate and several related compounds were evaluated for their ability to retard the cytotoxic effect which normally accompanies M. pneumoniae infections of hamster tracheal explants. Adenine sulfate, at the 0.01 mM level, was found to exert a significant protective effect. Little or no ciliostasis or loss of cell viability was detectable when organ cultures were infected with 10(7) CFU of virulent M. pneumoniae in the presence of the adenine supplement. Mycoplasmas grew in broth and on plastic surfaces in the presence of adenine, and no significant diminution of growth rate or cell yield was detectable. Organisms adhered to the tracheal epithelial surface regardless of the presence or absence of adenine. When explants were incubated in the presence of 14C-(8)-adenine, rinsed, and then infected with M. pneumoniae, the adenine label could be recovered from the mycoplasmas 20 h after the infection. These data are compatible with the known nucleic acid requirement of mycoplasmas and with a model which ascribes a role for purine/pyrimidine competition and/or depletion in the infective process.

Cytopathogenicity of Mycoplasma hyopneumoniae in porcine tracheal ring and lung explant organ cultures alone and in combination with monolayer cultures of fetal lung fibroblasts

Porcine tracheal rings and lung explants alone and in combination with monolayer cultures of porcine lung fibroblasts (PLF) were separately inoculated with virulent strains of Mycoplasma hyopneumoniae and incubated at various times. The preparations were observed by bright-field, phase-contrast, and scanning electron microscopy. In PLF cultures, the strains at initial concentrations of 10(1.3) colony-forming units/ml increased within 3 days to 10(6) colony-forming units/ml, showed progressive clustering on the cells, and caused some sloughing. Introduction of a tracheal ring or lung explant into these mycoplasma-infected PLF cultures caused the explant to lose its epithelial ciliary motility. Eventually parts or whole cells of the respective ciliated epithelium were lost. Without infected PLF monolayers, the explants inoculated with M. hyopneumoniae were less susceptible to infection. When uninfected explants were incubated for 18 days or kept in stock for 2 months, they did not show the above changes. With 5 h postinoculation, M. hyopneumoniae cultures became intimately associated with the PLF culture, but when epithelial cell sloughing occurred, the mycoplasmal cells became dependent on the introduction of a fresh PLF monolayer or a tracheal or lung explant for survival.

Differences in the attachment of Mycoplasma pneumoniae cells and membranes to tracheal epithelium

Hamster trachea organ cultures were exposed to isolated membranes of Mycoplasma pneumoniae, PI 1428. Attachment, monitored by the uptake of tritiated membranes, was relatively insensitive to neuraminidase pretreatment, unlike the attachment of viable cells. Membrane attachment was optimal when explants were incubated with 50 to 100 micrograms of membrane protein per ml in minimal essential medium broth while gently being rotated (1 rpm) in a roller apparatus for 90 to 120 min at 37 degrees C. Saturation of the receptor sites with viable cells failed to inhibit subsequent membrane attachment. Induction of squamous metaplasia by extended cultivation of tracheal explants in a vitamin A-free medium reduced the content of ciliated cells without significantly affecting total cell viability, but did not alter the attachment of M. pneumoniae membranes. Collectively, the data indicate that the mechanism of attachment of M. pneumoniae membranes to respiratory epithelium is distinct from the receptor site-mediated attachment of M. pneumoniae cells.

Effect of squamous metaplasia on infection of hamster trachea organ cultures with Mycoplasma pneumoniae

An organ culture system for hamster trachea was developed for maintenance of the ciliated respiratory epithelium during periods of extended cultivation (i.e., greater than 20 days). Evaluation of five serum types showed that horse serum and fetal calf serum were best for the maintenance of epithelial ciliary activity and morphology. Rings that were opened on one side ("split rings") had the best maintenance of the ciliated epithelium as judged by the retention of ciliary activity and normal histological appearance after 3 to 4 weeks in culture. The in vitro induction of squamous metaplasia was achieved by cultivating explants in Waymouth MAB 87/3 (vitamin A-free) medium, without serum. This system allowed a direct comparison of the effects of Mycoplasma pneumoniae infection in two epithelial types, ciliated pseudostratified columnar and keratinizing squamous. Attachment of 14C-labeled mycoplasmas was more than twofold greater in the normal epithelium. Pretreatment of explants with neuraminidase decreased attachment for both squamous and pseudostratified epithelial surfaces to a similar basal level. Recovery of viable organisms from infected tissue of both epithelial types indicated that the organism titer remained essentially constant during the infection period, but was significantly higher for the pseudostratified ciliated epithelium. These results suggest that specific receptor sites for M. pneumoniae are markedly reduced by the induction of squamous metaplasia and, hence, appear to be specific for the normal respiratory surface containing goblet cells and pseudostratified, ciliated epithelial cells.

Interaction of virulent Mycoplasma pneumoniae with hamster tracheal organ cultures

Exposure of hamster tracheal organ cultures to virulent Mycoplasma pneumoniae leads to alterations in ribonucleic acid (RNA) and protein biosynthesis and metabolism of the respiratory epithelium. An examination of the turnover rates of RNA and protein in infected tracheal organ cultures indicates that the rates of degradation of both prelabeled host cell RNA and protein are similar to those of uninfected controls. Infected tracheal organ cultures shifted to a nonpermissive medium within 24 h after infection and further incubated in the nonpermissive medium for 72 or 96 h behaved as normal uninfected cultures in terms of metabolic precursor uptake. Under these conditions, mycoplasmas remained attached to the respiratory epithelium. Cell membranes prepared from virulent mycoplasmas by several procedures neither attached to nor altered the metabolic activity of tracheal cultures. These data indicate that the intimate contact between virulent mycoplasmas and the respiratory epithelium does not alone account for the subsequent interruption of host cell metabolism but must be accompanied by continued multiplication and biochemical function of attached mycoplasmas.

Microrespirometer chamber for determinations of viability in cell and organ cultures

The effects of chemical, physical, and infectious cytotoxic agents on primary and cultured cells were evaluated by measurements of oxygen uptake for various time periods. A newly developed respirometer used a Clark oxygen electrode in a 1.0-ml chamber, with provisions for constant mixing and for temperature control of both the sample and electrode chambers. The device was unique because the electrode and instrumentation were provided by a clinical blood-gas analyzer. Oxygen uptake by blank controls was negligible, whereas cells and tissue consumed oxygen at rates of approximately 1 to 5 mul/h in a dose- and temperature-dependent fashion. Cyanide, heat, and freeze-thaw lysis reduced the oxygen uptake to less than 0.6 mul/mg per h. Infection of trachea organ cultures with Mycoplasma pneumoniae significantly reduced relative ciliary activity, tetrazolium reduction capacity, and oxygen consumption in a coordinated fashion.

Pathogenicity factors of mycoplasmas

The pathogenicity of mycoplasmas is caused by several factors, e.g. exotoxin, toxic properties of membrane components, exoenzymes, peroxide, and immunological factors. The absence of a rigid cell wall and the small genome tend to influence the interactions between mycoplasmas and host tissue. Mycoplasmas do not have a cell wass and are therefore resistant to the action of the host's lysozymes. They appear in some patients to be immunologically inconspicuous and in other patients they have been reported to have an immuno-suppressive effect. Recently there have been reports of central nervous system disorders due to mycoplasma. The pathogenic factors involved in these reactions have not been elucidated. Other aspects of Mycoplasma pneumoniae pathogenicity are also discussed.

Quantitative reduction of 2,3,4-triphenyl tetrazolium chloride by hamster trachea organ cultures: effects of Mycoplasma pneumoniae cells and membranes

The ability of Mycoplasma pneumoniae cells and membranes to affect tetrazolium reduction by hamster trachea organ cultures was evaluated. Uninfected trachea explants reduced 2,3,5-triphenyl tetrazolium chloride (TTC) and nitro-blue tetrazolium when incubated at 37 C in the absence of air. Reduced tetrazolium salts (formazans) were extractable with acetone or ethylene glycol and could be quantitated spectrophotometrically. The optimal assay system involved the use of three or more tracheal rings incubated for 2 h in 0.12% TTC in Tyrode balanced salts supplemented with 1.2% sodium succinate. Formazan was extracted for 5 min with acetone, and the optical density (490 nm) was determined. Trachea explants with metabolic activity reduced or obliterated by freeze-thaw lysis, heat (56 C X 30 min), or cyanide (0.1 M NaCN X 30 min) had negligible ciliary activity and tetrazolium reduction activity (optical density at 490 nm [dry weight]). Tracheas exposed to mycoplasma cells or membranes also showed significantly decreased ciliary activity and tetrazolium reduction; e.g., only 5pc of the ciliary activity and reduction capacity remained after 5 days in culture when infected with M. pneumonia PI 1428 cells. The data indicate that the exposure of ciliated respiratory epithelium to mycoplasma cells or membranes results in diminished oxidative metabolism, and that the ability to reduce TTC to its formazan is correlated with relative ciliary activity.

Oxygen consumption by trachea organ cultures infected with Mycoplasma pneumoniae

Hamster trachea organ cultres were shown to consume measurable amounts of oxygen when incubated in a closed micro-chamber. Several simple and complex media were evaluated, and the optimal system involved incubating 2 to 4 mg of tracheal tissue in Tyrodes balanced salt solution at 37 C for 60 min, with oxygen activity measured with a Clark electrode. Tracheas infected with Mycoplasma pneumoniae showed a significantly lower oxygen utilitzation than did uninfected controls. The effect was dose dependent when levels of 105 to 107 colony-forming units per ml were used to infect the tracheal rings. Virulent mycoplasmas caused significant decreases in relative ciliary activity and oxygen utilization, whereas attenuated mycoplasmas reduced ciliary activity and oxygen utilization levels to a lesser extent.