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Here we describe an additional type of bacterial migration in which bacterial cells migrate vertically across a non-nutritive solid surface carried by capillary forces. Unlike standard motility experiments, these were run on a glass slide inserted into a Falcon tube, partly immersed in a nutrient medium and partly exposed to air. Observations revealed that capillary forces initiated upward cell migration when biofilm was formed at the border between liquid and air. The movement was facilitated by the production of extracellular polymeric substances (EPS). This motility differs from earlier described swarming, twitching, gliding, sliding, or surfing, although these types of movements are not excluded. We therefore propose to call it "capillary movement of biofilm". This phenomenon may be an ecologically important mode of bacterial motility on solid surfaces.

The aim of this study was to determine the susceptibility of hospital and environmental Acinetobacter baumannii isolate biofilms on ceramics and glass to common disinfectants benzalkonium chloride and chlorhexidine. For this purpose we developed a new method for biofilm cultivation and quantification on ceramics. The biofilm bacteria were more resistant to disinfectants than the planktonic populations, as more than 50 % of the biofilm population and none of the planktonic population survived 5-minute exposure. Furthermore, biofilm populations on ceramic tiles were significantly more resistant than those on glass coverslips, even though the amount of biofilm was practically the same on ceramics and glass. The reason for reduced susceptibility of A. baumannii biofilms on ceramics may be related to surface/disinfection interactions. Our findings suggest that biofilms on ceramic surfaces can be an important source of A. baumannii infection in hospital environments.

Background: Acinetobacter baumannii is one of the most prevalent causes of severe hospital-acquired infections and is responsible for the dramatic increase in carbapenem resistance in Croatia in the last 5 years. Such data have encouraged multicenter research focused on the organism's ability to form biofilm, susceptibility to antibiotics, and particular genotype lineage., Methods: Biofilm formation in 109 unrelated clinical isolates of A. baumannii recovered in six cities of Southern Croatia was investigated. Genotyping was performed by pulsed-field gel electrophoresis and antibiotic profile was tested by applying the disc diffusion method and confirmed by determining the minimum inhibitory concentrations. The ability to form biofilm in vitro was determined from overnight cultures of the collected isolates on microtiter plates, after staining with crystal violet, and quantified at 570 nm after solubilization with ethanol. The statistical relevance was calculated in an appropriate program with level of statistical confidence., Results: There was no significant difference in biofilm formation due to the genotype lineage. Isolates collected from intensive care units (ICUs) and isolated from respiratory samples were more likely to create a biofilm compared with isolates from other departments and other samples. There was a significant difference in the ability to produce biofilm in relation to antibiotic resistance pattern. A large proportion of A. baumannii isolates that were resistant to ampicillin/sulbactam, carbapenems, and amikacin were found to be biofilm-negative. In contrast, isolates susceptible and intermediately susceptible to ampicillin/sulbactam, carbapenems, and amikacin were biofilm producers., Conclusion: Clinical isolates of A. baumannii from respiratory samples in ICUs with a particular susceptibility pattern are more prone to form biofilm.