Implementation of convolutional neural networks for microbial colony recognition

Initial classification of microorganisms based on visual identification of colonies remains challenging for skilled microbiologists and is influenced by the proficiency and subjective interpretation of professionals. To overcome these challenges, we applied deep learning to microbial colony recognition to provide microbial data to microbiologists to assist in clinical classification. Photographs of clinically isolated microbial colonies were captured to produce a 48 × 48 pixel colony data set, which was divided into training, validation, and test data sets. Eight convolutional neural networks (CNNs) were adapted to the colony classification task. The classification performance of the models was evaluated based on accuracy, precision, recall, and F1 score. The data set included five categories, namely gram-negative bacilli, gram-positive cocci, Candida, Aspergillus, and background of blood agar medium, with corresponding labels of 0, 1, 2, 3, and 4, respectively; each category contained 1,000 images. Among the trained CNNs, AlexNet showed the lowest performance, with an accuracy of 93.40%, whereas GoogLeNet had the highest performance, with an accuracy of 98.80%. MobileNet and ShuffleNet were more than 98% accurate. GoogLeNet misclassified only 6 of the 500 images in the test data set, and the algorithm was extremely capable of identifying both clinical and standard strains that were not included in the data set. The various trained CNNs demonstrated excellent performance in microbial colony recognition. These data-driven CNNs are expected to provide auxiliary decision-making tools for microbiologists.IMPORTANCECurrently, the classification of microorganisms is highly subjective because it is dependent upon the skill level of the microbiologist. In this study, we used deep learning for microbial colony recognition to provide objective information to guide the identification of microbial colonies. We used photographs of clinically isolated microbial colonies divided into training, validation, and test data sets. Eight convolutional neural networks (CNNs) were applied, and the classification performance of each model was evaluated using accuracy, precision, recall, and F1 scores. Our study confirmed that CNNs can classify colonies into four broad categories: gram-negative bacilli, gram-positive cocci, Candida, and Aspergillus, with excellent predictive performance. Our method does not require specialized photographic equipment and exhibits high generalization performance, even for unknown bacteria.