Compound Screening and Growth Curves v1
Authors: Goller Carlos 
Published: March 2023

Overview The bacterial genus Delftia was named for the city of Delft in the Netherlands, where the species type was isolated and for the Delft research groups that had a critical role in the early development of bacteriology. Species of Delftia have since been isolated all over the world in different environments and have been known to cause infections in humans.1Delftia are gram-negative rod-shaped aerobes. Species of Delftia are often resistant to several compounds, including the common disinfectant chlorhexidine,2 most antibiotics in the aminoglycoside group,3 and heavy metals.4 One of Delftia’s most surprising talents is its ability to concentrate heavy metals like gold.5 Biofilms found on gold deposits suggest that these bacteria are responsible for their formation.6 Known species of Delftia include D. acidovorans, D. tsuruhatensis, D. deserti, D. lucustris, and D. litopenaei. Refer to Figure 1 for an example of Delftia acidovorans colonies growing on tryptic soy agar (TSA). Where are Delftia spp.found? Delftia spp. are commonly isolated from aquatic environments such as lakes7 and wastewater8 and are thought to be ubiquitous. Because of their affinity for aquatic environments, Delftia have been identified in organisms and objects frequently found in these environments, such as mosquitoes9 and birds’ feathers.10Delftia aren’t just aquatic microbes, though. These bacteria have been identified in unexpected places like desert soil11 and contact lens cases.12 An Opportunistic Pathogen Species of Delftia have been known to cause various infections in healthy and immunocompromised people. Many of these infections are (IV) line-related,13,14 but other infections have occurred due to intravenous drug use.3Delftia were also implicated in eye inflammation related to contact lens use.12 NC State students and staff have even found Delftia DNA in surveys of kitchen sinks performed by students in the BIT 477/577 Metagenomics lab module! Our Project We will set up a series of high-throughput (HT) assays to test whether different gold chloride concentrations inhibit the growth of different Delftia strains. Gold chloride has been explored for its antibacterial properties15. However, Delftia spp. have a unique non-ribosomal peptide that helps relieve gold toxicity by producing delftibactin5. Bacterial strains will be grown in 96-well plates to test multiple concentrations of gold chloride and antibiotics and the effect of miniaturization of the assay. We will set up plates in the first lab session to test several strains at multiple doses with numerous replicates. Plates will incubate for one day at 30ºC before assessing cell viability using a stain for metabolic activity, PrestoBlue®. This approach can be adapted to screen active compounds from a high-throughput screening (HTS) campaign. For this first compound screen, we will focus on the effects of automation and miniaturization on assay reproducibility. We will test gold chloride concentrations in a twelve-point dose-response curve. At the end of this experiment, you can determine which concentrations are inhibitory by calculating the percent growth inhibition and IC50. We will compare the susceptibility of various Delftia strains.