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S Levisohn

Publications and source records attributed to S Levisohn.

31 records · Page 2Linked to original sources
PubMed1985

Evaluation of cytopathologic changes induced in chicken tracheal epithelium by Mycoplasma gallisepticum in vivo and in vitro.

Changes in tracheal epithelial surfaces induced by Mycoplasma infection in vivo and in vitro included release of mucous granules followed by exfoliation of ciliated and nonciliated epithelial cells. Light microscopy, scanning electron microscopy, and transmission electron microscopy confirmed that the loss of cilia from individual cells was infrequent. Epithelial cells typically lost their intercellular connections, rounded up, exfoliated, and then lysed--giving rise to a population of cellular organelles, such as mitochondria and cilia intermixed with mucus to form the exudate found within the tracheal lumen. Repair of the epithelial surface was effected by basilar epithelial cells differentiating and filling in the spaces formed by exfoliated cells. These cells were hypertrophied, nonciliated at 14 days after infection in vivo, and covered with microvilli. In sectioned material obtained during the infection, there was increasing epithelial thickness due to cellular infiltration and edema. Tracheal rings in vitro showed similar changes to those seen in vivo, except that exfoliation was more severe and occurred earlier. In addition, there were no cellular infiltration due to the lack of a vascular supply and only a small amount of mucus due to the smaller number of mucous cells available to release into the tracheal lumen.

Animals↗
PubMed1984

Early stages in the interaction between Mycoplasma gallisepticum and the chick trachea, as related to pathogenicity and immunogenicity.

Mycoplasma strains, which occur naturally or as the result of laboratory manipulation, differ markedly in biological properties such as pathogenicity, infectivity, transmissibility, and immunogenicity. These properties are clinical expressions of a series of complex interactions between the mycoplasma organisms and the host. We have focused on the early interactions occurring at the level of the tracheal mucosa, with the intent of identifying Mycoplasma gallisepticum strains possessing a combination of properties suitable for use in a live vaccine. The ability of a strain to colonize the chick trachea was evaluated by reisolation from the infected organ, expressed as infective dose (ID50). In addition to studies in the live chick, we have employed an in vitro model system for the study of adherence of the mycoplasmas to human red blood cells (RBC). Several strains that colonized the chick trachea were studied, multiplying profusely in close proximity to the epithelial surface, but producing only moderate or transient tissue damage in vivo. Adherence in vivo occurred via the "bleb" region of the M. gallisepticum organisms. A serological response was elicited by colonizing pathogenic or nonpathogenic M. gallisepticum but not by strains that were found by other methods to be readily eliminated from the tracheal surface.

Adhesiveness↗
PubMed1981

Antibiotic sensitivity patterns in field isolates of Mycoplasma gallisepticum as a guide to chemotherapy.

Control of Mycoplasma gallisepticum (Mg) infection in commercial poultry flocks has sometimes been achieved by the intensive use of antibiotics. In some cases, a single drug, tylosin tartrate, has been used repeatedly in prophylactic and therapeutic applications. It appears that this selective pressure can lead to the emergence of strains with reduced sensitivity to tylosin. This was observed in Mg strains isolated in 1978 from turkey breeding flocks repeatedly treated with tylosin, but not in isolates from acute disease outbreaks. Moreover, in a study of four recent outbreaks of mycoplasma respiratory disease in poultry, some of the Mg strains isolated in each of the outbreaks showed reduced sensitivity to tylosin and, at the same time, to spiramycin. This suggests that the buildup of these strains in the general pool of Mg is playing an increasingly significant role in clinical outbreaks. Periodic in vitro antibiotic sensitivity testing of field isolates of mycoplasma is indicated as a means of monitoring the impact of mass medication programs and as a guide to therapeutic treatment.

Animals↗
PubMed1981

Vaccination of chickens with nonpathogenic Mycoplasma gallisepticum as a means for displacement of pathogenic strains.

Attempts to solve the problem of Mycoplasma gallisepticum (Mg) infection of poultry by a combination of eradication and antibiotic treatment have at best met with only partial success. As a result of the continuing economic burden of the disease, there has been a renewed interest in vaccination as a tool in the control of Mg. A particularly pressing problem exists in the commercial egg industry, where the occurrence of MG infection of layer hens at the onset of egg production leads to a marked depression in productivity. Vaccination with the F strain of Mg has been demonstrated to efficacious in the alleviation of this problem, and the procedure is widely employed in the USA. Under field conditions of vaccination the F strain was found to be virtually nonpathogenic, although challenge experiments show that it retains some pathogenicity. The strain is carried in the trachea of vaccinated layers for as long as one year, but only spreads slowly. A specific serological response to Mg is produced in response to vaccination. To some extent, this response is dose dependent, but it is quantitatively less than that produced by virulent strains introduced by the same route. It has been suggested that the continued presence of a nonvirulent Mg in the upper respiratory tract, and the concomitant local immunological response, may prevent infection by field strains of Mg. In fact, judicious vaccination procedures appear to lead to the displacement of pathogenic Mg by the vaccine strain. By these means, it may be possible to eradicate Mg from flocks while maintaining production.

Animals↗
PubMed1973

Isolation, ultrastructure and antigenicity of Mycoplasma gallisepticum membranes.

The cell membrane of Mycoplasma gallisepticum was isolated by lysing the cells with digitonin. Chemical and density-gradient analyses and electron microscopy showed the isolated membranes to be relatively free of cytoplasmic contaminants. The density of the membranes exceeded that of other mycoplasma membranes, indicating a higher protein content. Small vesicular extensions seen in the sectioned membranes were interpreted as empty blebs.The isolated membranes, but not the cytoplasmic fraction, elicited in chickens the production of growth-inhibiting, agglutinating and haemagglutination-inhibition antibodies to M. gallisepticum in titres resembling those obtained by injection of whole cells. The peak of the serological response varied with the serological test employed. The rapid slide-agglutination test became positive as early as 3 days after the first injection of only 50 mug. of membrane protein. The haemagglutination-inhibition antibody titre reached its peak at about 10 days after the first injection, while that of the growth-inhibiting antibodies was reached only at about 25 days. The addition of adjuvant to the membrane antigen did not improve the production of the growth-inhibiting antibodies in chickens, but it produced some improvement in rabbits. Our results support the thesis that the chief immunogens of M. gallisepticum reside in the cell membrane of this organism.

Agglutination Tests↗
PubMed1967

Regulation of extracellular protease production in Bacillus cereus.

Both sporulation and protease production can be inhibited by growing Bacillus cereus T in a medium containing a high concentration of a mixture of amino acids. Mutants selected for the ability to sporulate in this inhibitory medium were found to produce high levels of protease in the normal and inhibitory media. Comparison of the mutant and wild-type enzymes by gel electrophoresis and heat inactivation suggested that they were identical. One of the mutants proved to be a purine-requiring auxotroph. Reversion to prototrophy resulted in the loss of the capacity to sporulate in the inhibitory medium and loss of the ability to produce large amounts of protease. Mutants capable of producing high levels of protease and of sporulating in the inhibitory medium were also found when selecting for a purine, pyrimidine, or lysine requirement or for the capacity to sporulate in the presence of a high concentration of glucose. Protease production could be considerably delayed in the purine auxotrophs or completely inhibited in the pyrimidine auxotrophs by growing the cells in a medium containing the inhibitory mixture of amino acids plus hypoxanthine for the former or a pyrimidine for the latter. The fact that a variety of metabolic alterations could lead to excessive protease production suggested that a common catabolic or biosynthetic intermediate was involved in the control of the production of this enzyme(s).

Amino Acids↗
PubMedDate not supplied

Molecular epidemiologic investigations of Mycoplasma gallisepticum conjunctivitis in songbirds by random amplified polymorphic DNA analyses.

An ongoing outbreak of conjunctivitis in free-ranging house finches (Carpodacus mexicanus) began in 1994 in the eastern United States. Bacterial organisms identified as Mycoplasma gallisepticum (MG) were isolated from lesions of infected birds. MG was also isolated from a blue jay (Cyanocitta cristata) that contracted conjunctivitis after being housed in a cage previously occupied by house finches with conjunctivitis, and from free-ranging American goldfinches (Carduelis tristis) in North Carolina in 1996. To investigate the molecular epidemiology of this outbreak, we produced DNA fingerprints of MG isolates by random amplification of polymorphic DNA (RAPD). We compared MG isolates from songbirds examined from 1994 through 1996 in 11 states, representing three host species, with vaccine and reference strains and with contemporary MG isolates from commercial poultry. All MG isolates from songbirds had RAPD banding patterns identical to each other but different from other strains and isolates tested. These results indicate that the outbreak of MG in songbirds is caused by the same strain, which suggests a single source; the outbreak is not caused by the vaccine or reference strains analyzed; and MG infection has not been shared between songbirds and commercial poultry.

Animals↗
PubMedDate not supplied

Ribosomal RNA gene probes to detect intraspecies heterogeneity in Mycoplasma gallisepticum and M. synoviae.

Intraspecies genotypic heterogeneity among strains of Mycoplasma gallisepticum and M. synoviae was tested using genomic fingerprints with a ribosomal RNA (rRNA) gene probe. The organism's DNA was digested by a restriction endonuclease, electrophoresed, transferred to a nitrocellulose sheet, and hybridized with 32P-labeled pMC5 plasmid carrying the highly conserved rRNA genes of M. capricolum. The resulting hybridization patterns indicated a degree of genotypic heterogeneity among M. gallisepticum strains more pronounced than among the M. synoviae strains tested. Most importantly, the live vaccine F strain of M. gallisepticum could be distinguished from virulent field isolates of this species, enabling the detection and identification of the F strain in areas in which vaccination with this strain has taken place. Genomic fingerprints with an rRNA gene probe can thus be added to the battery of tools useful in taxonomy at the intraspecies level and in epidemiology of mycoplasmosis in poultry.

Animals↗
PubMedDate not supplied

A quantitative study of single and mixed infection of the chicken trachea by Mycoplasma gallisepticum.

The interaction between Mycoplasma gallisepticum (MG) and the tracheal mucosa of the young chicken was studied. The use of a selective plating method permitted differentiation between a pathogenic tylosin-resistant strain (227) and a less pathogenic tylosin-sensitive vaccine strain (F). Both MG strains adhered to the tracheal mucosa and colonized equally well. In mixed infection, the presence or absence of the second strain did not change the efficiency of colonization by either strain. When chickens were exposed to the vaccine strain 24 hr or 2 weeks before superinfection by the pathogen, there was no significant reduction in the efficiency of superinfection, despite the presence of 10(6) colony-forming units of MG strain F in the trachea. However, chickens had an increased ability to resist superinfection 5 weeks after exposure via the air sac. These results suggest that the biological mechanism underlying protection of F-strain-vaccinated chickens against adventitious infection by the homologous species does not involve competition for adherence sites or blockage by prior colonization.

Animals↗
PubMedDate not supplied

In ovo pathogenicity of Mycoplasma gallisepticum strains in the presence and absence of maternal antibody.

Mycoplasma gallisepticum (MG) strains showing marked variation in pathogenicity were examined for virulence in ovo. No correlation was found between in ovo pathogenicity and other in vivo or in vitro methods for pathogenicity evaluation. For certain highly pathogenic strains, there was a clear relationship between the titer of MG inoculated and the embryo mortality and time of death; an LD50 for these strains could be calculated by yolk-sac inoculation. However, not every strain that caused lesions in the respiratory tract in vivo caused embryo mortality. Less pathogenic strains that grow well and colonize the respiratory tract usually caused embryo mortality during the later stages of incubation, and there was no strict correlation between titer of inoculum and embryo mortality. It appeared that embryo death in these cases may have resulted from generalized stress due to mass multiplication of the MG. Embryo mortality due to virulent MG was completely blocked in eggs containing maternal antibody to MG, although the mycoplasma could be reisolated from the yolk-sac membrane of the live embryonated egg after 17 days of incubation. Attempts to mimic the effect of maternal antibody by injecting exogenous MG antiserum were not successful.

Animals↗
PubMedDate not supplied

Species identification of avian mycoplasmas by polymerase chain reaction and restriction fragment length polymorphism analysis.

Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analysis were used to detect and differentiate four pathogenic species (Mycoplasma gallisepticum, M. iowae, M. meleagridis, and M. synoviae) and ten nonpathogenic species of avian mycoplasma. A sequence of 1026 base pairs within the gene for 16S ribosomal RNA (16S rRNA) from avian mycoplasmas was successfully amplified by PCR with oligonucleotide primers (M16SPCR5' and M16SPCR3') common to all avian mycoplasmas tested. Restriction endonucleases (REs) with unique restriction sites, selected by computer-assisted analysis of known sequences of the amplified segment of avian mycoplasma, were then used to digest the PCR products. After electrophoresis of the resulting RE fragments, the RFLP patterns were compared. Combinations of up to six REs (HpaI, HhaI, HaeIII, HphI, FokI, and NlaIV) produced unique RFLP patterns by which the 14 species of avian mycoplasmas could be differentiated. The newly classified avian species M. imitans was also investigated by this method; M. imitans and M. gallisepticum gave identical RFLP patterns with the REs used in this study. The results obtained by the PCR and RFLP analysis were in agreement with current methods for species identification of avian mycoplasmas.

Animals↗
PubMedDate not supplied

Detection of Mycoplasma gallisepticum, M. synoviae, and M. iowae by multi-species polymerase chain reaction and restriction fragment length polymorphism.

A single set of oligonucleotide primers was designed from known 16S ribosomal RNA (rRNA) sequences of Mycoplasma gallisepticum (MG), M. synoviae (MS), and M. iowae (MI). This set of primers selectively amplifies a 780-base-pair DNA fragment within the 16S rRNA gene of MG, MS, and MI but does not amplify other avian mycoplasmas or other bacteria. The detection limit of the multi-species polymerase chain reaction (PCR) was approximately 100 mycoplasma (MG, MS, MI) colony-forming units per PCR reaction. The PCR product was differentiated by restriction fragment length polymorphism with the restriction enzymes HpaI, HpaII, and MboI. Preliminary results from field samples suggest that this technique could be a useful and rapid diagnostic test for the detection of these three pathogenic poultry mycoplasmas.

Animals↗