Effects of Antibiotics onPseudomonas aeruginosaNK125502 andPseudomonas fluorescensMF0 Biofilm Formation on Immobilized Fibronectin

Innovative Perspectives on Biofilm Interactions in Poultry Drinking Water Systems and Veterinary Antibiotics Used Worldwide

Prudent use of antibiotics in livestock is widely considered to be important to prevent antibiotic resistance. This study aimed to evaluate the interactions between biofilms and veterinary antibiotics in therapeutic concentrations administrated via drinking water through a standardized experimental setup. In this context, two biofilms formed by pseudomonads (Pseudomonas (P.) aeruginosa or P. fluorescens) and a susceptible Escherichia (E.) coli strain were developed in a nutrient-poor medium on the inner surface of polyvinyl chloride pipe pieces. Subsequently, developing biofilms were exposed to sulfadiazine/trimethoprim (SDZ/TMP) or tylosin A (TYL A) in dosages recommended for application in drinking water for 5 or 7 days, respectively. Various interactions were detected between biofilms and antibiotics. Microbiological examinations revealed that only TYL A reduced the number of bacteria on the surface of the pipes. Additionally, susceptible E. coli survived both antibiotic treatments without observable changes in the minimum inhibitory concentration to 13 relevant antibiotics. Furthermore, as demonstrated by HPLC-UV, the dynamics of SDZ/TMP and TYL A in liquid media differed between the biofilms of both pseudomonads over the exposure period. We conclude that this approach represents an innovative step toward the effective evaluation of safe veterinary antibiotic use.

Milieu matters: An in vitro wound milieu to recapitulate key features of, and probe new insights into, mixed-species bacterial biofilms

Bacterial biofilms are a major cause of delayed wound healing. Consequently, the study of wound biofilms, particularly in host-relevant conditions, has gained importance. Most in vitro studies employ refined laboratory media to study biofilms, representing conditions that are not relevant to the infection state. To mimic the wound milieu, in vitro biofilm studies often incorporate serum or plasma in growth conditions, or employ clot or matrix-based biofilm models. While incorporating serum or plasma alone is a minimalistic approach, the more complex in vitro wound models are technically demanding, and poorly compatible with standard biofilm assays. Based on previous reports of clinical wound fluid composition, we have developed an in vitro wound milieu (IVWM) that includes, in addition to serum (to recapitulate wound fluid), matrix elements and biochemical factors. With Luria-Bertani broth and Fetal Bovine Serum (FBS) for comparison, the IVWM was used to study planktonic growth, biofilm features, and interspecies interactions, of common wound pathogens, Staphylococcus aureus and Pseudomonas aeruginosa. We demonstrate that the IVWM recapitulates widely reported in vivo biofilm features such as biomass formation, metabolic activity, increased antibiotic tolerance, 3D structure, and interspecies interactions for monospecies and mixed-species biofilms. Further, the IVWM is simple to formulate, uses laboratory-grade components, and is compatible with standard biofilm assays. Given this, it holds potential as a tractable approach to study wound biofilms under host-relevant conditions.

4-Hydroxybenzaldehyde sensitizes Acinetobacter baumannii to amphenicols

Bacterial metabolism modulated by environmental chemicals could alter antibiotic susceptibility. 4-Hydroxybenzaldehyde (4-HBA), which cannot support the growth of Acinetobacter baumannii, exhibited synergism only with amphenicol antibiotics including chloramphenicol (CAM) and thiamphenicol. Interestingly, this synergistic effect was not observed with other growth-supporting, structurally similar compounds such as 4-hydroxybenzoate. Transcriptomic analysis demonstrated that genes involved in protocatechuate metabolism (pca genes) and osmotic stress (bet genes) were significantly upregulated by 4-HBA and CAM treatment. The 14C-labeled CAM influx was lower in a pcaK1 (encoding a transporter of protocatechuate) deletion mutant and was higher in the pcaK1 overexpressing cells relative to that in the wild type upon 4-HBA treatment. Our kinetic data using 14C-labeled CAM clearly showed that CAM uptake is possibly through facilitated diffusion. Deletion of pcaK1 did not result in the elimination of CAM influx, indicating that CAM does not enter only through PcaK1. The amount of 4-HBA in the culture supernatant was, however, unaffected during the test conditions, validating that it was not metabolized by the bacteria. CAM resistant A. baumannii cells derived by serial passages through CAM-amended media exhibited lower level of pcaK1 gene expression. These results led us to conclude that the activation of PcaK1 transporter is probably linked to cellular CAM susceptibility. This is the first report showing a relationship between CAM influx and aromatic compound metabolism in A. baumannii.

Comparative adherence to human A549 cells, plant fibronectin-like protein, and polystyrene surfaces of fourPseudomonas fluorescensstrains from different ecological origin

The main objective of this study was to compare the adherence properties of four Pseudomonas fluorescens isolates from different ecological niches (human tissue, rhizosphere, drinking water, and cow milk). The substrates used to test P. fluorescens adherence were as follows: cultured human respiratory epithelial cells A549, immobilized plant fibronectin-like protein, and polystyrene. For all the experiments, bacteria were grown at 27 °C. The adherence assay to human cells was performed at 37 °C, whereas adherence to fibronectin and polystyrene was done at 27 °C. The four strains tested adhered to A549 cells but showed different adherence patterns. At 3 h, the milk isolate showed an aggregative adherence phenotype, whereas the three other isolates showed a diffuse adherence pattern. With a longer incubation time of 24 h, the aggregative pattern of the milk isolate disappeared, the adherence of the clinical strain increased, the adherence of the water isolate decreased, and morphological changes in A549 cells were observed with the clinical, water, and soil isolates. The four strains tested formed biofilms on polystyrene dishes. The clinical and milk isolates were the more efficient colonizers of polystyrene surfaces and also the more adherent to immobilized plant fibronectin-like protein. There was no relation between bacterial surface hydrophobicity and P. fluorescens adherence to the substrates tested. The main conclusions of these results are that P. fluorescens is an adherent bacterium, that no clear correlation exists between adherence and ecological habitat, and that P. fluorescens can adhere well to substrates not present in its natural environment.Key words: Pseudomonas fluorescens, adherence, biofilm, ecological niche, plant fibronectin-like protein, A549, polystyrene.