Multiple factors contribute to the negative experience and disinterest of medical students on the perception of the Microbiology course [1]. In this paper, an Adaptive Serious Game is proposed as a more entertaining educational approach to motivate and to improve the performance of medical students on a Microbiology subject. To achieve that, a Bayesian Network model constructed from expert knowledge and a Role-Playing game design were proposed. To validate our proposal, a playability survey was applied to 36 college students. These students were divided in two groups for evaluating their performance with and without an adaptability feature. Overall, the results suggest the game is attractive, enjoyable and useful tool for learning. Moreover, the use of Bayesian networks contributes to the success performance ratio of the students.