Gabriela Delgado, Juan Carlos Valdez, Nadia Gobbato, Silvia Orosco, Pablo Saguir, Clara Silva, Marcela Ortiz Mayor, Luis Herrera, Mirta Rachid, Nilda Noemi Arias, Ana Trejo


Bacterial populations and inammation in the airways have been suggested as the main causes of cystic brosis (CF) pulmonary exacerbation. In
this work we studied the interactions of pathogenic bacteria Pseudomonas aeruginosa (Pae) and of Burkholderia cepacia complex (BCC) with the
oropharyngeal ora Streptococcus milleri group (SMG) isolated from the sputum of a CF patient with pulmonary exacerbation. We investigated the
virulence of single and mixed bacteria by evaluating the in vitro production of pyocyanin by spectrophotometric analysis and of rhamnolipids by
haemolysis and growth inhibition of Bacillus subtilis. Elastase production was analyzed in a mucus-like medium with the addition of
polymorphonuclear leukocytes (PMN) or DNA. Also, necrosis and netosis induced by bacteria in PMN were measured by ow cytometry and
spectrouorometry, respectively. Bacterial infections in a murine experimental model were analyzed.
Combinations of Pae with BCC and SMG enhanced pyocyanin and rhamnolipids production (p<0.01). Pae and BCC induced the highest elastase
release from PMN, but it was lower when SMG was added (p<0.05). Highest PMN necrosis levels were induced by the mixture of SMG, BCC, and
Pae (p<0.01). Pae was the major inducer of PMN netosis, followed by BCC and SMG. When Pae was combined with BCC and/or SMG, netosis
was reduced. Netosis correlated with elastase values.
In mouse models, infections combining SMG with Pae increase pulmonary inammation.
Commensal strains can increase the virulence of pathogenic bacteria. The exact role of Netosis and elastase in polymicrobial infections remains to
be determined.


Cystic Fibrosis, Polymicrobial Infection, Streptococcus Milleri, Neutrophils, Netosis.

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