In Mexico, the main causal agents of hospital infections are the species of Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli and Klebsiella pneumoniae; whose strains are usually multiresistant to antibiotics. In view of this situation, new antimicrobials are required, with structures and mechanisms of action different from current commercial antibiotics and, in the future, new drugs to counteract the infections caused by these microorganisms. The foregoing has led to the investigation of new antimicrobial substances from plants considered popular medicinal. These plants have a wide range of chemicals, whose active ingredients can be useful as a medicine and can be found in their entire structure or only in some sections. Therefore, this work evaluated in vitro the bactericidal activity of ethanolic extracts from red mangle bark, garlic clove, onion and lemon peel in multi-resistant gram-negative bacteria.