1009. Biofilm Formation in Acinetobacter Baumannii Clinical Isolates

Abstract

Abstract Background Multidrug resistant Acinetobacter baumannii (MDR-Ab) is a Gram-negative bacterium known for causing severe nosocomial infections, attributed in part to its formation of biofilm. Siderophore is a virulence factor known to support biofilm formation by regulating iron availability. In this study, we screened 44 isolates of MDR-Ab from our Gram-negative repository to determine the strains that phenotypically form biofilm and produce siderophore. The results were compared to Pseudomonas aeruginosa PAO1, which produces both biofilm and siderophore. Methods Isolates were grown overnight in minimal M9 medium supplemented with casamino acids and hydroxyquinones at 37°C. Bacterial cells were normalized (to OD 600=0.01) and a standard diluted 10-3 tube was used in the study. A 96-well plate was inoculated with 100 microliters of each isolate in quadruplicates. This process was repeated in Tygon tubes with 50 microliters of each isolate in triplicates. The plate and Tygon tubes were incubated statically for 48 hours at 30°C and then stained with crystal violet. The contents were dissolved in 33% glacial acetic acid and analyzed by spectrophotometry to measure biofilm formation. Siderophore secretion was measured in supernatants with Chrome Azurol S (CAS) reagent and production was observed on CAS agar plates. Results High levels of biofilm formation were observed in 8 strains of MDR-Ab in the 96-well plate (3, 4, 9, 22, 61, 1010, 1012, 1022) and 6 strains in Tygon tubes (3, 4, 16, 66, 1002, 1010) (Fig. 1). There was minimal siderophore production in MDR-Ab isolates compared to PAO1 in both the 96-well plate and Tygon tubes (Fig. 2). Only 4 strains lacked siderophore production on CAS agar and were inversely negative for the secretion in medium. Figure 1 Biofilm formation in a 96-well plate and Tygon tubes (A) High levels of biofilm formation were observed in MDR-Ab strain numbers 3, 4, 9, 22, 61, 1010, 1012, 1022 in the 96-well plate. (B) High levels of biofilm formation were observed in MDR-Ab strain numbers 3, 4, 16, 66, 1002, 1010 in Tygon tubes. Figure 2 Degree of siderophore production in a 96-well plate and Tygon tubes Siderophore production of MDR-Ab was limited compared to PAO1 after inoculation in a 96-well plate (A) and in Tygon tubes (B). Conclusion Many strains of MDR-Ab readily form biofilm. Overall siderophore production is lower in MDR-Ab compared to consistent production by PAO1, but this does not appear to affect MDR-Ab’s ability to form biofilm. Unlike in PAO1, biofilm formation in MDR-Ab may occur independently of siderophore production. This research serves as a basis for understanding future MDR-Ab biofilm elimination in patient catheters and indwelling devices. Disclosures All Authors: No reported disclosures