Pseudomonas putida are environmental reservoirs of antimicrobial resistance to β-lactamic antibiotics.

The adaptive flexibility of bacteria largely contributes to the emergence of antibiotic resistance, eventually leading to the predictable failure of current antimicrobial therapies. It is of utmost importance to improve current approaches and implement new ways to control bacterial growth and proliferation. A promising strategy lies in unraveling the antimicrobial resistance (AMR) dynamics in environmental reservoirs, namely in soil. Environmental microorganisms are antibiotic producers and generally also carriers of AMR mechanisms. Therefore, soil samples were collected from areas distinctly influenced by men: rural farms and urban fluvial shores. Globally, microbial communities collected in farms revealed the highest antibiotic resistance potential. Largely predominant Gram-negative isolates were further screened for their low susceptibility to β-lactamic agents, and found to belong to Pseudomonaceae family, with predominance of Pseudomonas putida (92 %). Minimal Inhibitory Concentration (MIC) was determined for five β-lactams and the distributive analysis of cefotaxime MIC performed, allowing the first report of Epidemiological Cut-OFF values for P. putida regarding such antibiotic. Hence, 46 % of the isolates from farms presented acquired resistance to cefotaxime, with fluvial strains presenting an acquisition of AMR in 22 % of the isolates. The response to β-lactams impact in P. putida is different from Pseudomonas aeruginosa's, the family type strain, showing that data determined for a species should only be extended to other bacteria with caution, even closely related. It becomes crucial to broaden present research, mainly focused on few pathogenic bacteria, to other microorganisms carrying relevant resistance tools or capable of genetic transfer to more virulent strains. Most available data on AMR so far has been obtained from studies performed in restricted clinical or veterinary context, showing the result of a strong selective pressure related to therapy but often disregarding the origin of the AMR mechanisms encountered. The strong impact that environmental microorganisms have (and probably already had in the past) on the evolution and spreading of AMR, is just beginning to be unveiled.