Mixed bacterial responses to dust exposure in an A549 eukaryotic co-culture

Oxidative stress, biofilm-formation and activity responses of P. aeruginosa to microplastic-treated sediments: Effect of temperature and sediment type

Climate change and plastic pollution are the big environmental problems that the environment and humanity have faced in the past and will face in many decades to come. Sediments are affected by many pollutants and conditions, and the behaviors of microorganisms in environment may be influenced due to changes in sediments. Therefore, the current study aimed to explore the differential effects of various microplastics and temperature on different sediments through the metabolic and oxidative responses of gram-negative Pseudomonas aeruginosa. The sediments collected from various fields including beaches, deep-sea discharge, and marine industrial areas. Each sediment was extracted and then treated with various microplastics under different temperature (-18, +4, +20 and 35 °C) for seven days. Then microplastics were removed from the suspension and microplastic-exposed sediment samples were incubated with Pseudomonas aeruginosa to test bacterial activity, biofilm, and oxidative characteristics. The results showed that both the activity and the biofilm formation of Pseudomonas aeruginosa increased with the temperature of microplastic treatment in the experimental setups at the rates between an average of 2-39 % and 5-27 %, respectively. The highest levels of bacterial activity and biofilm formation were mainly observed in the beach area (average rate +25 %) and marine industrial (average rate +19 %) sediments with microplastic contamination, respectively. Moreover, oxidative characteristics significantly linked the bacterial activities and biofilm formation. The oxidative indicators of Pseudomonas aeruginosa showed that catalase and glutathione reductase were more influenced by microplastic contamination of various sediments than superoxide dismutase activities. For instance, catalase and glutathione reductase activities were changed between -37 and +169 % and +137 to +144 %, respectively; however, the superoxide dismutase increased at a rate between +1 and + 21 %. This study confirmed that global warming as a consequence of climate change might influence the effect of microplastic on sediments regarding bacterial biochemical responses and oxidation characteristics.

Impact of metal exposure on environmentally isolated Serratia marcescens' growth, oxidative-stress resistance, biofilm formation, and proliferation in eukaryotic co-culture models

Environmental metals can be noxious to the surrounding biota, indirectly impact freshwater habitats, and also impact microbiological communities. In this study, zinc (Zn) (55.5 mg/kg), manganese (Mn) (863.4 mg/kg) and lead (Pb) (17.5 mg/kg) levels measured in Houston watershed flood plain soil samples were higher than environmental agencies' thresholds. To investigate the effects of metal exposures, an environmentally isolated Serratia marcescens (SME), etiological agent of endocarditis and respiratory infections, and its reference strain (SMR) were exposed to Pb, Zn, and Mn, and subsequent oxidative stress responses and biofilm production were measured. Not surprisingly, SME was less sensitive to all 3 metal exposures than was SMR. Interestingly, SME produced increased biofilm and was more resistant to oxidative stress in the presence of Zn and Pb than SMR. In a 6 h lung infection model using BAES-2B cells, SME exhibited greater proliferation than SMR in all metal challenges. Similarly, in our HT29 gut infection model, SME out-proliferated SMR when challenged with Pb and Mn following the 6 h infection. Taken together, SME was better able to withstand environmental stressors than SMR, suggesting increased virulence potential of this opportunistic human pathogen.

Klebsiella spp. isolates from Houston bayous exhibit increased resistance to lead exposure and possess enhanced virulence potential

Houston watersheds are susceptible to microbial contamination as well as chemical contaminations from bordering industrial facilities. Bacterial loads in various Houston bayous were determined, and pathogenic Gram-negative bacteria were isolated for characterization. Isolates included Klebsiella aerogenes and Klebsiella pneumoniae. To determine whether environmental exposures to lead (Pb), measured in our Houston bayou samples, resulted in bacterial adaptations, we compared growth kinetics, biofilm production, oxidative stress resistance, and eukaryotic co-culture growth of environmentally isolated K. aerogenes and K. pneumoniae to their respective commercially acquired reference strains. Interestingly, the K. aerogenes environmental isolate displayed significantly better growth than the reference strain in the presence of 50 ppb of Pb. Unexpectedly, we did not observe any differences in biofilm production of the aforementioned strains when challenged with a range of Pb (0.5-50 ppb). However, when comparing our K. pneumoniae environmental isolate to its reference strain, there were significantly higher levels of biofilm produced by the environmental isolate when challenged with Pb concentrations of 10 and 50 ppb. When grown in eukaryotic cell co-culture with either BAES 2B lung cells or CCD 841 colon epithelial cells in the presence of 20 ppb Pb, the environmental isolates of K. aerogenes and K. pneumoniae had a significantly higher fold-increase over 6 h than their respective reference strains. Taken together, the environmentally isolated Klebsiella spp. appeared to be more Pb-tolerant than their respective reference strains, a possible environmental adaptation. Such enhanced tolerance can promote environmental persistence and increase the possibility of causing human disease.