When individual human cells were cultured in the microgravity environment of spaceflight in the 1990s, scientists noticed that they started to aggregate and organize as structures that resembled the native tissue from which the cells were derived. This was very different to cells grown under normal gravity conditions, that sediment to the bottom of the culture dish, precluding tissue development. This finding triggered great interest by tissue engineers, and resulted in the use of the microgravity research platform to engineering tissue-like or organotypic models (1).
this principle, NASA engineers have developed a spaceflight-inspired culture
system: continuously rotating cylindrical bioreactors, called the rotating wall
vessels (RWV), re-creating conditions analogous to continuous suspension in
space. The RWV system therefore replicates aspects of the microgravity environment
of space right here on the surface of the Earth. Since then, the RWV system has
been exploited by many researchers worldwide to generate cell culture models
that are more reflective of the parental tissue, including models of the lung,
colon, small intestine, bladder, female reproductive tract, and brain. These
organotypic models have been used in a wide variety of biomedical and
biotechnological fields, including (but not limited to) tissue homeostasis and
organogenesis, regenerative medicine, cancer, environmental pollution, and
infectious diseases. They all have one common aim: to mimic the human tissues
and organs as closely as possible, and obtain biologically relevant results
that are meaningful for human health and response to therapeutics.
As a microbiologist, I am interested in using RWV-derived organotypic models of the lung to investigate how cells of the lung can influence the efficacy of antimicrobial agents against bacterial pathogens. Why is this so important? We all know that antibiotics are becoming less and less effective against pathogens, both in the lab, and in the patient.
An important example is patients with cystic fibrosis (CF). These patients are chronically infected with bacteria in their lungs, and can experience exacerbations – sudden drops in lung function, leading to hospitalisation, and immediate treatment with antibiotics. In acute cases such as these, it is critical for the doctors to choose the right antibiotic for treatment. A sputum sample containing the infecting bacteria is collected from the patients, and the antibiotic susceptibility of the isolated bacteria must be tested in the lab. The problem is that antibiotics chosen based on conventional laboratory assays do often not lead to clinical improvement in CF patients. In fact, a 5-year prospective study found that antibiotics given to CF children based on available laboratory tests did not result in better health outcomes (2). Then the question becomes: why is there such a big difference between the efficacy of antibiotics in the lab and in the patient? And can we find ways to improve this correlation? These are the questions that I have been trying to answer, using RWV technology to create models of human tissue, that would behave similarly to the organs of the whole organism.
We know that in the lungs of CF patients, bacteria grow as biofilms, groups of bacteria that stick together through a self-produced matrix, making them difficult to treat. Our collaborative team at Ghent University, Arizona State University, and the University of British Columbia, found that epithelial cells of the lung modify the activity of antibiotics against bacterial biofilms (3). Surprisingly, lung cells make some antibiotics, specifically the aminoglycosides, even more proficient at getting rid of biofilms. These findings show that the environment in which bacteria encounter antibiotics can also influence their susceptibility to them, a result that might have been missed using traditional methodologies. The RWV’s ability to recreate biologically functional 3D tissue models analogous to the human body is critical to these studies.
It goes without saying that there are other factors in the lung that influence antibiotic activity, and that the more physiological factors are incorporated in laboratory assays, the more relevant the experimental outcome is likely to be for the patient. Our results offer new insights on why antibiotics might be less efficacious in the complex lung environment, and why other potentially effective antibiotics might be missed using conventional assays that do not consider lung environmental factors. Understanding the underlying basis of the discrepancy between the activity of antibiotics in the lab and in the patient may lead to improved diagnostic approaches and pave the way towards novel means to boost antibiotic activity.
Nickerson CA, Pellis NR, Ott CM. Eds., Effect of Spaceflight and Spaceflight Analogue Culture on Human and Microbial Cells (Springer New York, 2016).
Hurley, MN, Ariff AH, Bertenshaw C, Bhatt J, Smyth AR. Results of antibiotic susceptibility testing do not influence clinical outcome in children with cystic fibrosis. J Cyst Fibros, 2012. 11(4): p. 288-92.
Crabbé A, Liu Y, Matthijs N, Rigole P, De La Fuente-Nùñez C, Davis R, Ledesma MA, Sarker S, Van Houdt R, Hancock RE, Coenye T, Nickerson CA. Antimicrobial efficacy against Pseudomonas aeruginosa biofilm formation in a three-dimensional lung epithelial model and the influence of fetal bovine serum. Sci Rep, 2017. 3(7): p. 4332.
Aurélie Crabbé graduated with a Ph.D. in Bioscience Engineering at the Vrije Universiteit Brussel in 2009, for her work entitled “Novel insights in Pseudomonas aeruginosa metabolism and pathogenesis by low fluid-shear culturing”.
In 2010, Aurélie worked at the Center for Infectious Diseases and Vaccinology at Arizona State University, focusing on engineering three-dimensional lung tissue culture models that mimic aspects of the in vivo architecture, function and multicellular complexity, under the tutelage of Prof. Cheryl Nickerson. Aurélie also applied 3-D lung models for studying host cytotoxicity to bacterial toxins, and host-associated biofilm formation of the opportunistic pathogen Pseudomonas aeruginosa.
Aurélie was awarded an Odysseus fellowship from the Fund for Scientific Research Flanders (FWO) to initiate her own research line at Ghent University starting October 2014. Her project focuses on investigating the role of host-microbiome interactions in P. aeruginosa biofilm formation and resistance to conventional and novel antimicrobial agents.