Chikelue, Calvin I.
Mize, Maximillion T.
Simecka, Jerry


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The contribution of Mycoplasma pneumoniae to infections leading to community-acquired pneumonia (CAP) makes it a prime bacterium to study for the development of protective vaccines against it. Despite this, the scant few vaccines researched and tested offer little to no immune protection. In order to further along development of a protective vaccine, the human immune response to M. pneumoniae infection needs to be appropriately deduced. Our lab seeks to develop a humanized mouse model for M. pneumoniae which can be used for observing the most likely human immune response to this bacterium. These preliminary experiments revolve around the investigating the infectivity and pathogenicity of three different strains: S1, M129, and UABPO1. Whichever strain exhibits the ability to cause severe disease within our test animals in comparison to the others will be the strain we utilize in our future studies. These strains were used to infect multiple groups of Balb/c mice which were observed over 14 day time period. At the conclusion of the time period, the mice were sacrificed and the lungs were scored for lung lesions and afterward, depending on the experimental group, the lungs were either homogenized for dilution plating or stored in fixative for histological staining. As of this point in our precursory experimentation, the UABPO1 strain has shown the most promising results in terms of its pathogenicity in comparison to the other experimental strains and may be the strain our lab will utilize in the future studies for developing the humanized mouse model. Purpose (a): Community-acquired pneumonia (CAP) is a lung disease caused by infection with a respiratory bacterium. M. pneumoniae, a major contributor to CAP infections, is a bacterium that invades and attaches to the airway epithelium causing damage to the host through the production toxic substances or Community Acquired Respiratory Distress Syndrome (CARDS) toxin. No commercial vaccine currently exists for the bacterium and tested vaccines have shown to be more immunopathologic rather than protective. To develop a protective vaccine, the immune response against M. pneumoniae must be better understood. Our research is focused on the development of a humanized mouse model for the study of the immune mechanisms that occur during and infection with M. pneumonia. Methods (b): Three strains are used in these preliminary experiments: S1, M129, and UABPO1. Whichever strain causes severe disease within mice will be used in the future experiments with the model. Groups of Balb/c mice were inoculated intranasally with 20 to 40 uL of bacteria from cultured stocks. A fourth control group was included. Infected animals were observed for 14 days and clinical signs were documented. At the end of period, the mice were sacrificed and lungs harvested and scored for lung lesions. Harvested lungs were either homogenized for dilution plating on agar or stored in fixation solution for histological staining. Results (c): Studies were done using older mice, different dosages of mycoplasmas, and incubating thawed bacterial stocks to allow the organism to recover from their frozen state prior to inoculation. Each of these changes appeared to increase disease severity. In particular, mice infected with UABPO1 strain of mycoplasma developed more severe disease compared with the other tested strains of mycoplasma. Conclusions (d): At this point in our studies, we have seen that UABPO1, in comparison with the strains of mycoplasma, may be the most promising for use in further experiments developing the humanized mouse model. Future experiments will observe bacterial load within infected animals at several different time points since it is possible that bacterial clearance is occurring during by the end of the 14 day time course. As well as repeat studies in immunodeficient and humanized mice.