Impact of Coexistence Phenotype Between Staphylococcus aureus and Pseudomonas aeruginosa Isolates on Clinical Outcomes Among Cystic Fibrosis Patients

Abstract

Staphylococcus aureus (SA) is the major colonizer of the lungs of cystic fibrosis (CF) patients during childhood and adolescence. As patients age, the prevalence of SA decreases and Pseudomonas aeruginosa (PA) becomes the major pathogen infecting adult lungs. Nonetheless, SA remains significant and patients harboring both SA and PA are frequently found in the worldwide cohort. The overall impact of co-infection remains controversial. Furthermore, co-infecting isolates may compete or coexist. The aim of this study was to analyse if co-infection and the coexistence of SA and PA could lead to worse clinical outcomes. The clinical and bacteriological data of 212 Lyon CF patients were collected retrospectively, and patients were ranked into three groups, SA only (n = 112), PA only (n = 48) or SA plus PA (n = 52). In addition, SA and PA isolates from co-infected patients were tested in vitro to define their interaction profile. Sixty five percent (n = 34) of SA/PA pairs coexist. Using univariate and multivariate analysis, we confirm that SA patients have a less severe clinical condition than others, and PA induces a poor outcome independently of the presence of SA. Regarding co-infection, no significant difference in clinical outcomes was observed between patients with coexisting pairs and patients with competitive pairs. However, when compared to SA mono-infected patients, patients with coexisting pair presented higher frequency and length of hospitalizations and more exacerbations. We suggest that coexistence between SA and PA may be an important step in the natural history of lung bacterial colonization within CF patients.

How Bacterial Adaptation to Cystic Fibrosis Environment Shapes Interactions Between Pseudomonas aeruginosa and Staphylococcus aureus

“…The increased biofilm production of CF-adapted S. aureus isolates could also promote the formation of mixed-species biofilm with P. aeruginosa , although no direct correlation has yet been established. These hypotheses could explain (i) the high proportion of co-infected patients with S. aureus and P. aeruginosa in international cohorts ( Hubert et al, 2013 ; Limoli et al, 2016 ; Briaud et al, 2020 ), and (ii) the high proportion of isolates presenting a non-competitive interaction ( Briaud et al, 2020 ). Further investigations need to be conducted to confirm this model and fully understand the effects of S. aureus adaptation on its relationship with P. aeruginosa .…”

“…Bacterial enumerations performed during co-culture kinetics can thus easily reveal and quantify this phenomenon ( Miller et al, 2017 ; Cendra et al, 2019 ; Pallett et al, 2019 ; Figure 3A ). Less cumbersome procedures were nonetheless developed to assess interaction status between clinical CF isolates in large set of strains ( Figure 3B ; Baldan et al, 2014 ; Michelsen et al, 2014 , 2016 ; Limoli et al, 2017 ; Briaud et al, 2019 , 2020 ; Camus et al, 2020 ). Baldan and colleagues thus performed competition tests on plates during which a spot of P. aeruginosa culture is deposited on a lawn of S. aureus .…”

“…A P. aeruginosa spot is deposited in the center of the lawn and the plate is incubated 24 h. Competition is characterized by an inhibition halo of S. aureus growth in contact with the spot of P. aeruginosa , whereas S. aureus growth is not affected by P. aeruginosa during the coexisting interaction. Size of the inhibition halo can be measured ( Baldan et al, 2014 ; Briaud et al, 2019 , 2020 ; Camus et al, 2020 ). (C) P. aeruginosa streak is performed on a rich agar medium, after what a perpendicular S. aureus streak is added.…”

“…Another important feature of P. aeruginosa is its ability to interact with other CF microorganisms such as Aspergillus fumigatus , Candida albicans , and Staphylococcus aureus. S. aureus is also one of the most predominant pathogens in CF lungs and is detected simultaneously with P. aeruginosa in 20 to 50% of patients ( Limoli et al, 2016 ; Briaud et al, 2020 ). P. aeruginosa can exhibit particularly aggressive behavior toward S. aureus ( Michelsen et al, 2016 ).…”

“…This antagonistic interaction was the only one observed between the two species for a long time. However, P. aeruginosa strains with more tolerant behavior toward S. aureus have recently been isolated from chronic CF infections ( Baldan et al, 2014 ; Michelsen et al, 2016 ; Briaud et al, 2019 , 2020 ; Pallett et al, 2019 ; Camus et al, 2020 ). The establishment of such coexisting interaction between the two species seems to arise from their evolution in the lung ecosystem.…”