Investigation of Drug ResistantAcinetobacter baumannii Virulence Factors Implicated in Intracellular Survival Within Differentiated THP-1 Cells

Abstract Introduction/Objective Acinetobacter baumannii is a nosocomial opportunistic pathogen that is usually associated with mucosal infections such as pneumonia, urinary tract infections or sepsis and less commonly with more severe illnesses such as meningitis, wound infection, or necrotizing fasciitis. Of late, A. baumanniihas been flagged by the CDC as an urgent threat due to multidrug-resistant properties it has acquired, making it a major concern to public health. Due to a sparsity of information on the virulence factors of immune evasion, it has been difficult to understand how this bacterium is able to gain a foothold and cause severe infections. We sought to study how necrotizing fasciitis-associated strains of A. baumannii interact with human macrophages to assess their capabilities in evasion of the host immune response. Methods/Case Report To this end, extensively drug resistant A. baumannii was isolated at two timepoints (strains NFAb-1 and NFAb-2) from a patient over the course of a lethal necrotizing fasciitis infection that led to sepsis. The intracellular survival of these two strains was compared with each other, as well as to the type strains, ATCC 19606 and ATCC 17978, within a human macrophage-differentiated monocyte cell line, THP-1. Survival studies were complemented with quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR) to investigate expression of potential bacterial virulence factors, Catalase E (KatE), Phospholipase C (PLC), Outer membrane protein A (ompA), and Pilus A (PilA), that could contribute to immune evasion. Results (if a Case Study enter NA) The intracellular survival assay demonstrated enhanced survival and bacterial growth of NFAb-1 and NFAb-2 within macrophages compared to ATCC 19606 and 17978. Examining gene expression, KatE, PLC, and OmpA didn’t show any significant differences between the bacterial strains, while the PilA gene had much higher expression in NFAb-1 and NFAb-2 compared to ATCC 19606 and 17978. Conclusion This data establishes these nectrotizing fasciitis-causing A. baumannii strains are more likely to sruvivie a macrophage-mediatied immune response and expression of pilus-assocated genes may play a role in these interactions. our studies demonstrate a need to further investigate A. baumannii mechanisms of virulence to understand its ability to evade the immune response in hopes of understanding and combating infections.