Bacteria can enhance their survival by attaching to inanimate surfaces or tissues, and presenting as multicellular communities encased in a protective extracellular matrix called biofilm. There has been pronounced interest in assessing the relationship between the antibiotic resistant phenotype and biofilm-production in clinically-relevant pathogens. The aim of the present paper was to provide additional experimental results on the topic, testing the biofilm-forming capacity of Escherichia coli isolates using in vitro methods in the context of their antibiotic resistance in the form of a laboratory case study, in addition to provide a comprehensive review of the subject. In our case study, a total of two hundred and fifty (n = 250) E. coli isolates, originating from either clean-catch urine samples (n = 125) or invasive samples (n = 125) were included. The colony morphology of isolates were recorded after 24h, while antimicrobial susceptibility testing was performed using the Kirby-Bauer disk diffusion method. Biofilm-formation of the isolates was assessed with the crystal violet tube-adherence method. Altogether 57 isolates (22.8%) isolates were multidrug resistant (MDR), 89 isolates (35.6%) produced large colonies (>3 mm), mucoid variant colonies were produced in 131 cases (52.4%), and 108 (43.2%) were positive for biofilm formation. Biofilm-producers were less common among isolates resistant to third-generation cephalosporins and trimethoprim-sulfamethoxazole (P = 0.043 and P = 0.023, respectively). Biofilms facilitate a protective growth strategy in bacteria, ensuring safety against environmental stressors, components of the immune system and noxious chemical agents. Being an integral part of bacterial physiology, biofilm-formation is interdependent with the expression of other virulence factors (especially adhesins) and quorum sensing signal molecules. More research is required to allow for the full understanding of the interplay between the MDR phenotype and biofilm-production, which will facilitate the development of novel therapeutic strategies.
Keywords: Escherichia coli; antibiotic resistance; biofilm formation; colony morphology; crystal violet; literature review; urinary tract infections; virulence.