In the last years clinicians and researchers have realised that the interactions between microorganisms in polymicrobial infections (when a single patient is colonised/infected with two or more pathogens) are relevant for the progression of the disease. Contacts between pathogens can affect their fitness (how well they can grow inside us) and also impact on the response of our immune system. However, the research into this novel and extremely complex area is still in its infancy and we need to gain much more information before being able to understand what is going on in each specific condition. It is suspected that in some interactions the microorganisms may compete with each other, which is usually good for us. However, in other types of interactions the pathogens may help each other, which is of course detrimental for the patients. In the case of Aspergillus – Pseudomonas interaction it is still not completely clear which is taking place, a positive or a negative interaction.

Pseudomonas (mainly the species Pseudomonas aeruginosa) is a common bacterial pathogen and Aspergillus (mainly the species Aspergillus fumigatus) is the most common fungal pathogen of the human respiratory tract. Both organisms are able to grow in the lungs of immunosuppressed individuals and also of patients with certain underlying diseases, such as bronchiectasis, chronic obstructive pulmonary disease (COPD), hospital acquired pneumonia and cystic fibrosis. Since the awareness of the importance of polymicrobial infections is quite recent, there are not many reports of the incidence of co-infection with these two pathogens yet. One of the few, from the end of 2018, reported a prevalence of co-infection in cystic fibrosis patients of 15.8% (1). That means that almost sixteen percent of all cystic fibrosis patients may be co-infected with both Pseudomonas and Aspergillus… This is of course not trivial!

 Several studies carried out in various laboratories around the world would suggest that the interaction between Aspergillus and Pseudomonas is of competitive nature. That would indicate that they weaken each other during co-infection, which could mean good news for patients. However, there are also results, including some clinical evidence, that suggest the opposite, the pathogens could be helping each other in the human lungs. What seems clear is that having both pathogens is not good for the patients (2). Therefore, we need to understand how these microbes interact during co-infection to be able to decide which course of action is best, should we treat against both or only one? Which one first, or both at the same time?

To address these questions my research group, in the Manchester Fungal Infection Group, is trying to understand the specific interactions that take place between Aspergillus fumigatus and Pseudomonas aeruginosa under conditions that are similar to co-infection of the human lung.

We want to discover which interactions are the important ones. This will help us understand what is going on during co-infection and we can then use this knowledge to improve the management and treatment of patients.

Dr Jorge Amich | MRC Career Development Fellow

Manchester Fungal Infection Group (MFIG)

1. Zhao J, Cheng W, He X, Liu Y.2018. The co-colonization prevalence of Pseudomonas aeruginosa and Aspergillus fumigatus in cystic fibrosis: A systematic review and meta-analysis. Microb Pathog 125:122-128.

2. Reece E, Segurado R, Jackson A, McClean S, Renwick J, Greally P.2017. Co-colonisation with Aspergillus fumigatus and Pseudomonas aeruginosa is associated with poorer health in cystic fibrosis patients: an Irish registry analysis. BMC Pulm Med 17:70.

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