Abstract
The ability of Pseudomonas aeruginosa to form biofilm during a long-term infection makes it difficult to treat patients correctly. The current clinical antimicrobial susceptibility testing methods are based on the study of planktonic strains. A standardized protocol to analyze the antimicrobial susceptibility in biofilms is necessary for routine laboratories. The aims of this study were to develop a simple biofilm model and to study the antimicrobial susceptibility of P. aeruginosa strains in biofilm growth. Different artificial sputum media, and aerobiosis and microaerobiosis conditions were analyzed using a microtiter plate method and P. aeruginosa PAO1 as reference strain. Planktonic and biofilm antimicrobial susceptibility to cefepime, imipenem, azithromycin, gentamicin, tobramycin, and ciprofloxacin were determined in clinical and non-clinical P. aeruginosa strains. The Synthetic Cystic Fibrosis Medium was proposed as a good medium. The biofilm greatly increased the resistance to tested antimicrobials, except for azithromycin. Cefepime and imipenem showed poor anti-biofilm effect while tobramycin, gentamicin, and ciprofloxacin showed good activity in some strains. Azithromycin showed a better activity in biofilm than in planktonic state when aerobic conditions were used. This study establishes useful information to test antimicrobial susceptibility in P. aeruginosa biofilms, and includes possible antimicrobial options to treat long-term infected patients.
Highlights
Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen with great ability to survive under a variety of environmental conditions
The aim of this study was to develop a simple biofilm model based on the use of a medium that mimics the sputum of the patients for studying P. aeruginosa biofilm, and to use it to analyze the biofilm antimicrobial susceptibility in a collection of seven P. aeruginosa strains from different origins, antimicrobial susceptibility, and biofilm capacity
P. aeruginosa PAO1 strain was more resistant to all tested antimicrobials in biofilm than in planktonic state except in the case of azithromycin
Summary
Pseudomonas aeruginosa is an opportunistic Gram-negative pathogen with great ability to survive under a variety of environmental conditions This microorganism is one of the most relevant causes of severe human nosocomial infections, especially in immunocompromised patients. The development of biofilm, organized bacterial communities embedded in an extracellular polymeric matrix attached to surfaces, is currently recognized as one of the major determinants in persistent infections [1]. This bacterial species shows resistance to a high number of antimicrobials due to several intrinsic mechanisms and either as a consequence of mutations or by acquiring genetic material from other bacteria. One of the major outstanding issues in Antibiotics 2020, 9, 880; doi:10.3390/antibiotics9120880 www.mdpi.com/journal/antibiotics
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