Background:Biofilms are communities of bacteria attached to the surfaces in an extracellular polymeric matrix which are associated with many chronic infections in humans. Acinetobacter spp. are emerging as a major cause of nosocomial infections and Acinetobacter baumannii is the predominant species associated with this kind of infections.Objectives:In the present study, the potential of biofilm formation of clinical isolates, A. baumannii, was assessed by using crystal violet method. Furthermore, susceptibility pattern of these strains to ciprofloxacin and imipenem was determined.Methods and Materials:Biofilm formation by 75 A. baumannii isolates was evaluated by using microtiter plate and tube methods and crystal violet staining. Tube method was carried out under static and shaking conditions. Then, the susceptibility of isolates to ciprofloxacin and imipenem was determined.Results:Results showed that in tube method under shaking, 22% of clinical isolates were strong biofilm producers while 23% of them were not able to form biofilms. In this experiment, 18% and 42% of isolates were considered as moderate and weak biofilm-forming strains, respectively. In microtiter plate tests, 18% of strains were strong-biofilm producers and 25% of them were notable biofilm producers. In this assessment, 10% and 47% were considered as moderate and weak biofilm-forming isolates, respectively. The susceptibility tests, using microdilution method, confirmed that 92% of these isolates were resistant and 6.6% were susceptible to ciprofloxacin, although these results for imipenem were 68% and 24%, respectively.Conclusions:It can be concluded that most of A. baumannii isolates can form biofilm in microtiter plate and tube. The results also verified that most of these isolates were resistant to ciprofloxacin and imipenem.

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Horizontal gene transfer is the one of the most important drivers of bacterial evolution. Transformation by uptake of extracellular DNA is traditionally not considered to be an effective mode of gene acquisition, simply because extracellular DNA are considered to degrade in a matter of days when it is suspended in e.g. seawater. Mineral surfaces are, however, known to preserve DNA in the environment, and sedimentary ancient DNA studies have solidified there are considerable amounts of fragmented DNA stored in sediments world-wide. Recently the age of stored DNA was increased to at least 2 ma highlighting that sediments represent a rich resource of past traits. It is well established that bacteria can acquire large kilobase DNA molecules adsorbed to mineral surfaces. Here we show that Acinetobacter baylyi can incorporate 60 bp DNA fragments adsorbed to a wide range of common sedimentary minerals. Our recorded transformation frequencies vary with mineral types and scales inversely with mineral surface charge and the ability of the mineral to immobilize the DNA in a liquid environment. We argue that the influence of mineral surface properties introduces interfacial geochemical processes as drivers for evolution and provide sedimentologic processes a central role in the evolutionary avenue of selection.

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