A systematic analysis of beta-lactamases based on comparative proteomics has not been performed thus far. In this report, we searched for the presence of beta-lactam-related proteins in 591 bacterial proteomes belonging to 52 species that are pathogenic to humans. The amino acid sequences for 19 different types of beta-lactamases (ACT, CARB, CifA, CMY, CTX, FOX, GES, GOB, IMP, IND, KPC, LEN, OKP, OXA, OXY, SHV, TEM, NDM, and VIM) were obtained from the ARG-ANNOT database and were used to construct 19 HMM profiles, which were used to identify potential beta-lactamases in the completely sequenced bacterial proteomes. A total of 2877 matches that included the word "beta-lactamase" and/or "penicillin" in the functional annotation and/or in any of its regions were obtained. These enzymes were mainly described as "penicillin-binding proteins," "beta-lactamases," and "metallo-beta-lactamases" and were observed in 47 of the 52 species studied. In addition, proteins classified as "beta-lactamases" were observed in 39 of the species included. A positive correlation between the number of beta-lactam-related proteins per species and the proteome size was observed (R 0.78, P