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

Abstract

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.

Keywords

• Cytotoxicity
• Lead
• Zinc
• Manganese
• Cell culture infection