Abstract
Despite strengthened antimicrobial therapy, biofilm infections of Acinetobacter baumannii are associated with poor prognosis and limited therapeutic options. Assessing antibiotics on planktonic bacteria can result in failure against biofilm infections. Currently, antibiotics to treat biofilm infections are administered empirically, usually without considering the susceptibility of the biofilm objectively before beginning treatment. For effective therapy to resolve biofilm infections it is essential to assess the efficacy of commonly used antibiotics against biofilms. Here, we offer a robust and simple assay to assess the efficacy of antibiotics against biofilms. In the present work, we carefully optimized the incubation time, detection range, and fluorescence reading mode for resazurin-based viability staining of biofilms in 96-well-plates and determined minimal biofilm eradication concentrations (MBECs) for A. baumannii isolates from patients with chronic infection. By applying this assay, we demonstrated that antibiotic response patterns varied uniquely within the biofilm formation of various clinical samples. MBEC-50 and 75 have significant discriminatory power over minimum inhibitory concentrations for planktonic suspensions to differentiate the overall efficiency of an antibiotic to eradicate a biofilm. The present assay is an ideal platform on which to assess the efficacy of antibiotics against biofilms in vitro to pave the way for more effective therapy.
Highlights
Every medical procedure that depends on antibiotics to fight infections can become compromised by antibiotic resistance
The amount of fluorescent resorufin produced was linearly proportional to the viable bacterial cell concentrations in both planktonic and biofilm growth conditions (Fig. 1a)
A linear range was observed between 104–108 colony forming units (CFU) per biofilm (R2 = 0.952), while significant fluorescent signal was detected when bacteria concentrations were
Summary
Every medical procedure that depends on antibiotics to fight infections can become compromised by antibiotic resistance. Among the bacteria that are alarmingly prevalent are multi-drug resistant Acinetobacter baumannii, which cause some 60% of hospital-acquired or nosocomial infections[1]. These bacteria have become prevalent in communities, causing ventilator associated pneumonia, blood stream and a variety of skin and tissue infections, in both healthy and immune-compromised individuals[1,2]. It is well recognized that, a simple, rapid antimicrobial susceptibility test for biofilms is crucial for better clinical decision making to control chronic biofilm infections with appropriate antibiotic therapy[12,17,18]
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