Michelle Paczosa & Joan Mecsas analyze mechanisms of bacterial pneumonia
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Klebsiella pneumoniae are a leading cause of nosocomial diseases in the USA and worldwide, including pneumonia, sepsis and urinary tract infections. This bacteria is abundant in the environment and is a commensal in the human mouth and intestine. These infections are particularly acute in people who have diminished immune defenses due to underlying conditions, such as cancers or diabetes. Severe diseases caused by these bacteria are rising due to an increased incidence of multi-antibiotic and pan-antibiotic resistant K. pneumoniae infections. Infections by these resistant bacteria are increasingly difficult to treat, and result in significantly increased patient morbidity and mortality. This problem is exacerbated by the decreased introduction of new and innovative antibiotics by pharmaceutical companies that would help fight these infections.
Michelle Paczosa, an Immunology PhD student working under the guidance of Joan Mecsas, PhD is focusing on understanding how gram-negative bacterial pathogens cause inactive neurtophlis, a key arm of the body's defense against infection and cause pneumonia. Building on work using Yersinia where she identified the surface proteins critical for Yersinia to function in lungs and how they mediate delivery of effector proteins into lung neutrophils, she is now focused on Klebsiella pneumoniae.
To determine virulence factors that K. pneumoniae requires for pneumonic infection, we performed a high-throughput genetic screen using a method called TnSeq to identify genes that are critical for K. pneumoniae infection in lungs. To do this, a large population of K. pneumoniae, where each bacterium contained a transposon insertion in a different part of their genome, was used to infect mice. After infection, the bacteria were harvested from the lungs and the insertion sites were determined by high-throughput sequencing. By comparing the frequency of each insertion mutant in the bacterial population recovered from lungs after infection to its frequency in the population before infection, we determined which genes are important during infection because genes present in low abundance after infection are likely to disrupt genes that are critical in the lung.
Because K. pneumoniae infection often occurs in immunosuppressed people, we also determined which genes are needed for K. pneumoniae growth in the absence of neutrophils by performing our screen in both healthy and neutrophil depleted mice. From this, we’ve identified candidate genes required during lung infection in mice in three different scenarios: only in the presence of neutrophils; in the presence or absence of neutrophils and in the absence of neutrophils. Our next steps will include confirming that these candidates are indeed important for K. pneumoniae to infect, survive and grow in lungs in vivo. We will also be collecting K.pneumoniae clinical isolates from patients in hospitals to determine if these genes are important in clinical strains and could serve as therapeutic targets.
Paczosa MK, Fisher ML, Maldonado-Arocho FJ, Mecsas J. 2014. Yersinia pseudotuberculosis uses Ail and YadA to circumvent neutrophils by directing Yop translocation during lung infection. Cell Microbiol. 16: 247-268.