Use of molecular methods in biothreat preparedness
Year: 2017
Type: dissertation
Abstract: A biological threat is an epidemic or its threat caused by a microbe or biological material of a magnitude that would overwhelm healthcare services due to the contagiousness or wide distribution of infections. A biological threat can be naturally occurring, such as the West African Ebola epidemic of 2014-2016, or the consequence of an intentional release of a microbe or toxin. The aim of this thesis was to develop and use molecular methods in order to reliably and rapidly identify potential biological threat agents. The focus was on the detection and typing of biological threat agents, whether they are naturally occurring or intentionally released. Different molecular methods were used: polymerase chain reaction (PCR) to detect and differentiate pathogenic from non-pathogenic bacterial strains, 16S ribosomal RNA (rRNA) gene sequencing to investigate polymicrobial samples, and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) spacer comparison for bacterial strain typing. Cholera, a disease caused by Vibrio cholerae bacterium, is a major public health problem worldwide and a potential bioterrorism agent, according to the Centers for Disease Control and Prevention (CDC). In this thesis, an accurate PCR-based method was developed to detect V. cholerae strains: one assay for pathogenic strains and another for all V. cholerae strains. In addition, three different PCR platforms were compared. The PCR assays proved to be suitable for the reliable identification and differentiation of V. cholerae strains. The PCR platforms gave identical results, which indicate that the assays can be transferred between the platforms while maintaining sufficient sensitivity and specificity. Two 16S rRNA gene-based detection methods, using Sanger sequencing or pyrosequencing, were employed to study the presence of bacterial residues in carotid artery tissue samples and in livers of splenomegalic voles. The objectives were to observe the utility of the two methods and compare their performance. Both methods were found to be convenient approaches to detect and identify bacterial species present in different matrices and thus could be employed when investigating polymicrobial samples. In addition, the two methods gave similar results which emphasises the reliability of the methods and their results. The Yersinia genus includes three human pathogens; Y. pestis, the causal agent of plague and a potential biothreat agent, as well as Y. enterocolitica and Y. pseudotuberculosis, which commonly cause self-limiting enteritis. Due to the high level of DNA similarity between Y. pestis and Y. pseudotuberculosis, typing of Yersinia species and distinguishing them from each other has been challenging. Here, CRISPR spacers were used for typing Yersinia pseudotuberculosis complex strains. This method proved to be a promising tool, although the large diversity of different spacer sequences hindered the clustering of different strains. In addition, CRISPR data of Y. pseudotuberculosis and Y. pestis were compared to examine phylogenetic relationships, but surprising lack of shared spacers limited any further resolution from being made. In this thesis, molecular methods were developed and used to detect, identify, and type potential biological threat agents. PCR assays developed can be transferred to a field-deployable instrument and thus employed close to the patient, for example, during epidemics. PCR results were ready within a few hours, enabling a rapid and appropriate medical response. The 16S rRNA gene-based methods can be utilized in detection of biological agents, which are challenging or laborious to identify using traditional methods. The CRISPR-based sequencing method can be used for typing different strains of Y. pseudotuberculosis, if a comprehensive reference database is made available. DNA sequencing and recently next-generation sequencing have become powerful tools to identify and type biological agents. Sequencing methods can also be utilized in epidemiological investigations and source tracking. Different molecular methods have evolved recently and detection has become fast and more reliable. Rapid detection of microbes enables swift medical countermeasures, and accurate identification and typing methods facilitate the ability to distinguish a natural outbreak from an intentional release.
Source: Työväentutkimus Vuosikirja
Author: Katja A. Koskela
Language: English
Subfield: Microbiology (medical)
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2606962787