title: Quaternary Ammonium Compound Resistance of Klebsiella Pneumoniae and Klebsiella Quasipneumoniae Strains Isolated from the International Space Station
Creators: name: Sushenko, Natasha
Publisher: name: University of Nevada, Las Vegas
publisherIdentifier: https://ror.org/0406gha72
publisherIdentifierScheme: ROR
Year: 2024

description: The International Space Station (ISS) has been continuously inhabited for twenty-three years and harbors a diverse population of microorganisms under conditions of microgravity, elevated radiation, and relative isolation, including Biosafety Level 2 (BSL-2) opportunistic pathogens. To sanitize surfaces on the ISS, astronauts use a combination of four antimicrobial quaternary ammonium compounds (QACs). As the stresses of space flight are known to stimulate virulence and antimicrobial resistance in bacteria, the frequent use of QAC disinfectants on the ISS is of concern to NASA. This not only poses risks to astronauts during future long-term space travel, but there is also a concern that these hypervirulent and multidrugresistant strains will be returned to Earth by astronauts.For my master’s thesis, I studied strains of Klebsiella pneumoniae and Klebsiella quasipneumoniae, opportunistic BSL-2 pathogens that were isolated from the interior surface microbiome of the ISS, with particular emphasis on how these ISS-adapted strains differ from an Earth-origin type strain when exposed to QACs. This thesis consists of four chapters: Chapter 1, an introduction and literature review; Chapter 2, a description of the complete genome of a strain of Klebsiella quasipneumoniae isolated from the ISS, which was published in 2022 in Microbial Resource Announcements; Chapter 3, a study of the responses of both ISS- and Earth-origin strains of Klebsiella to QAC exposure; and Chapter 4, a conclusion. 
The first research chapter (Chapter 2) consists primarily of in silico work to complete the genome of Klebsiella quasipneumoniae subsp. similipneumoniae strain IF3SW-P1, isolated from the ISS; this included assembly and annotation of the genome based on long-read Oxford Nanopore Technology sequencing data. The completed genome was then analyzed for the presence of putative virulence and antimicrobial resistance genes. The second research chapter (Chapter 3) consists of experimental approaches to study the responses to QAC disinfectants by both ISS- and Earth-origin strains of Klebsiella. This work included determining the minimum inhibitory concentration (MIC) of QACs for each strain before conducting viability assays at both sub-lethal and standard QAC concentrations. These viability assays included viability qPCR using the viability dye PMAxx, and fluorescence microscopy conducted using LIVE/DEAD BacLight viability dyes. This work showed significant differences in the response of the two ISS-origin strains of Klebsiella, as well as differences between the ISS-origin strains and the Earth-origin type strain, in both the amount of QACs required to inhibit growth of the strains and in the responses of the strains after exposure to lethal QAC concentrations. This suggests the ISS-origin strains, which are frequently exposed to QACs in the ISS environment, may be less susceptible to QACs.