Projects in the Criss Lab

Neisseria gonorrhoeae survives exposure to human neutrophils, but the mechanisms underlying this process are poorly understood.  We are using a combination of cell biology, molecular biology, bacterial genetics, and biochemistry to reveal these mechanisms.  Since N. gonorrhoeae is an obligate human pathogen, we use primary human neutrophils that are cultured to mimic the physiological state of neutrophils in the genitourinary tract of people with gonorrhea.  We also have a collaboration with the Virginia Department of Health to collect neutrophils and associated bacteria from people with acute gonorrhea, which will provide in vivo relevance to our in vitro system.

Gram stain of urethral gonorrheal exudate, showing neutrophils with associated gonococci. From Johnson and Criss, Frontiers in Microbiology 2011.

Some of our research questions include:

  1. How does N. gonorrhoeae survive inside human neutrophils? Analysis of neutrophils from patients with acute gonorrhea has suggested that the bacteria can live inside these otherwise antimicrobial cells.  We have developed fluorescence-based microscopy assays for quantifying bacterial survival inside and outside of human neutrophils over time, which we are using to investigate where, when and how N. gonorrhoeae persists inside neutrophils.
  2. How does N. gonorrhoeae resist neutrophil antimicrobial activities? To date we have identified two N. gonorrhoeae gene products that defend the bacteria from neutrophils.  We are examining the roles of additional selected bacterial gene products in their ability to defend N. gonorrhoeae from neutrophils and neutrophil-derived antimicrobial products.
  3. How does N. gonorrhoeae suppress the neutrophil oxidative burst? Although neutrophils can generate reactive oxygen species (ROS) as part of their antimicrobial arsenal, we found that infection with certain strains of N. gonorrhoeae inhibits neutrophils from producing ROS.  We are interested in mapping the bacterial and host factors that participate in this process.
  4. How do Neisserial opacity-associated (Opa) proteins modulate N. gonorrhoeae interactions with human neutrophils? The Opa proteins are a family of similar yet distinct outer-membrane proteins that interact with human heparan sulfate proteoglycans and/or carcinoembryonic antigen-related cell adhesion molecules.  Each gene encoding an Opa protein is phase-variable, so a single N. gonorrhoeae bacterium can express no, one, or several Opa proteins.  We are collaborating with Linda Columbus in the Department of Chemistry at UVA to explore the structure-function relationship between individual Opa proteins and human cells (, using recombinant Opa proteins re-folded into liposomes and comparing their behavior to N. gonorrhoeae expressing the same Opa proteins.  This research is being funded by a Seed Award from the UVA nanoSTAR Institute (
Thin-section transmission electron micrograph of N. gonorrhoeae-infected neutrophil.

Thin-section transmission electron micrograph of N. gonorrhoeae-infected neutrophil.


Human neutrophils bind and engulf N. gonorrhoeae. Bound bacteria are red/yellow, engulfed bacteria are green.

Human neutrophils bind and engulf N. gonorrhoeae. Bound bacteria are red/yellow, engulfed bacteria are green.



opa colony

Opacity phenotypes of colonies of N. gonorrhoeae. Arrows point to colonies of bacteria expressing Opa proteins. From Ball and Criss, Journal of Bacteriology 2013.