Document Type


Date of Award



College of Science, Engineering, and Technology (COSET)

Degree Name

Ph.D. in Environmental Toxicology

Committee Chairperson

Jason A Rosenzweig

Committee Member 1

Maruthi Sridhar Bhaskar

Committee Member 2

Maruthi Sridhar Bhaskar

Committee Member 3

Shishir Shishodia,

Committee Member 4

Daniel Virceanue

Committee Member 5

Hyun-Min Hwang


Bacterial environmental isolates, Co-Infection Assay, Eukaryotic co-culture, Heavy metal Pb, Houston bayous, Klebsiella species.


Houston watersheds and air ecosystems are susceptible to microbial contamination and chemical contaminations from bordering industrial facilities. We sought to evaluate bacterial loads in various Houston bayous, and settled indoor household dust, and isolate pathogenic Gram-negative bacteria for characterization. Isolates included Klebsiella aerogenes and Klebsiella pneumoniae. The specific objectives of the study are (1) Determine bacterial loads and Pb toxicant levels in Houston area watersheds and indoor dust samples; (2) Identify down selected bacterial isolates from environmental samples using ribotyping 16S ribosome RNA and BIOLOG MicroStation identification; (3) Compare environmentally and reference Klebsiella spp. for growth rate, kinetic activity, biofilm production, oxidative stress resistance, and eukaryotic co-culture system. All 17 down-selected colony isolates (including 6 Gram-positive isolates) were identified (using ribotyping and BLAST analysis) and included three human enteric pathogens: K. pneumoniae, K. aerogenes, and Serratia marcescens. We characterized the Mustang Bayou K. pneumoniae and Dickinson Bayou K. aerogenes as pathogenic isolates for all downstream applications. To determine whether exposure to metal contaminants found in Houston watersheds promoted adaptations in the environmental isolates, both the environmental and reference strains were exposed to various Pb concentrations. Pb levels were elevated in bayou water samples exceeding THH criteria of 1.15 ppb and approaching the actionable levels of 15 parts per billion (ppb) limits on drinking water. Only the 50 ppb Pb challenge significantly slowed bacterial growth for all four strains evaluated, while the K. pneumoniae environmental isolate appeared less sensitive to Pb exposure than its reference strain. We exhibited increased resistance to antibiotic chemotherapeutics: ampicillin, gentamicin, streptomycin, penicillin, tetracycline, and erythromycin. Interestingly, Environmental Stains Klebsiella spp. Isolates were slightly more resistant to gentamycin, streptomycin, and tetracycline than their reference strains. For our Biofilm formation, when comparing our K. pneumoniae environmental isolate to the reference strain, there were significantly higher biofilm levels produced by the ecological isolate when challenged with Pb concentrations of 10 and 50 ppb. Determine the effects of Pb- dose-dependent exposure on eukaryotic primary lung Beas-2B and CCD 841 gut cells. We found Pb dose-dependent exposure elicits cytotoxic effects on epithelial lung and gut cells and induces apoptosis measured at 3-, 6-, and 12-hours exposure periods. The cytotoxicity increased at high Pb concentrations level and generated apoptosis effects on Beas-2B, CCD 841 were recorded up to 80% and 60%, respectively, at 12 hours exposure time. When grown in eukaryotic cell co-culture with Beas-2B lung cells and CCD841 gut primary cells in the presence of 20 ppb Pb, Conversely, the K. pneumoniae environmental isolate had a significantly higher fold-increase over 6 hr. in a BAES 2B co-culture than its surrogate counterpart—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. Keywords: environmental isolate, eukaryotic co-culture, lung, and gut infection



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