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Mycoplasma penetrans is generally accepted as an opportunist residing mainly in the urogenital tract and has primarily been detected in immunocompromised individuals. The ability of M. penetrans to invade non-phagocytic host cells is a feature that was de-scribed soon after the first isolation of the organism. Other characteristics like highly phase-variable immunodominant surface proteins, an ability to change shape, and a membrane-bound nuclease have also been described; however, the functions these factors have in the context of an infection are poorly understood. Additionally, other than a curious change in cell shape upon interacting with host cells prior to invasion, little is known about the lifecycle of M. penetrans during infection. In this work, new strains of M. penetrans apparently causing non-gonococcal urethritis (NGU) in immunocompetent men were isolated and characterized in an effort to understand what is necessary for these bacteria to overcome the obstacles of infecting a healthy host. The new strains demonstrated an extreme resistance to azithromycin, a common therapy for NGU. Cytotoxicity among the strains was consistent; however, the production of hydrogen peroxide was found to be higher in all of the new isolates compared to the HF-2 strain, derived from a patient with an immune disorder. Along with strain HF-2, each new strain of M. penetrans demonstrated the ability to break down extracellular DNA traps presented by cells of the innate immune system. Each of the newly isolated strains was found to adhere to host cells using sialic acid as the primary ligand. The efficiency of host cell invasion was found to vary across strains and did not correlate with either the ability of the bacteria to bind to eukaryotic cells or their speed during gliding motility. It is not known if cell shape plays a role in host cell invasion; however, the ability to change cell shape independent of a host was demonstrated in M. penetrans and its close relative, the poultry pathogen Mycoplasma iowae. This change in cell shape was found not to be a stress-related response, having no impact on the ability of the cells to grow, but rather a response to exposure to a particular set of metabolites found at elevated concentrations inside host cells. The change in cell shape was found to be rapid and required the bacteria to be metabolically active, having a slight impact on adherence and motility, a potential result of slightly shorter attachment organelle. |
