Antibiotic resistance profiles of microplastics associated microbial communities in the Adriatic Sea

Introduction. Plastics have gradually become a global environmental pollution problem with a significant impact on human and animal health. Their large dispersion in the marine environment generates microplastics (MPs) which also release nanoplastics with effects on living organisms. The aim of this study was: i)to identify MPs and their associated microorganisms in the sea sediments of the Regional Natural Reserve Sentina (Adriatic Sea) and ii)to evaluate the antibiotic susceptibility patterns of the microbial communities. Materials and Methods. Beach transects, parallel to the shoreline where the waves break, has been identified for the samplings. Each sample was in three replicas at three different positions of the transect (0, 15, and 30 meters). A protocol to perform microplastics isolation from sand sediments, suitable for biological samples and based on plastic floating in high salinity water, has been optimized. On floating microplastics, DNA isolation was performed with DNeasy PowerSoil Pro Kit (QIAGEN) for the shotgun metagenomic analysis. Isolated aerobic and anaerobic cultivable microorganisms have been identified by MALDI-TOF MS (Bruker). Susceptibility to a panel of 14 human and veterinary antibiotics, belonging to 12 different categories, was assessed by Kirby-Bauer and E-test methods. Results. From sea sediments, the increased seawater density allowed plastics floating and through filtration, different kind of plastic materials, such as polyethylene, polypropylene, poly-methyl acrylate and poly-vinyl chloride were found. The metagenomics results are currently under processing and analysis. By microbial cultivation and MALDI-TOF MS identification, different bacterial species (n=29), both Gram -ve (55.2%) and Gram +ve (44.8%), have been isolated from the samples enriched in microplastics. Some bacteria are promising for the involvement in plastic degradation, such as Lysinobacillus fusiformis, Exiguobacterium sp., Pseudomonas oleovorans. Other bacteria are potentially pathogens, like Clostridium septicum, Clostridium novyi, Shewanella putrefaciens. Only the 17.2% of bacteria, Exiguobaterium sp., Halomonas aquamarina, Paenibacillus brevicompactum, Lactobacillus fuchuensis, Providencia rettgeri, resulted susceptible to all human and veterinary antibiotics. Higher percentages of resistance were observed for penicillins (85.7%) and monobactams (80.9%), in Gram +ve and Gram -ve, respectively. Althought not significant, a resistant pattern was recorded for carbapenems in Gram +ve (28.6%) and Gram -ve bacteria (61.9%, P=0.0532). Significant higher resistances for tetracyclines (64.3%, P=0.0166) were observed for Gram +ve microorganisms. Discussion and Conclusions. The MPs may work as a vehicle of phenotypic resistant microorganisms in the Adriatic Sea environment.