Staph Bacteria Infection Linked to Worse Lung Function in CF

More exacerbations seen in those infected with staph vs. Pseudomonas bacteria

Margarida Maia, PhD avatar

by Margarida Maia, PhD |

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Young patients with cystic fibrosis (CF) who have a lung infection caused by Staphylococcus bacteria may have worse lung function and more exacerbations than those who are infected with Pseudomonas bacteria, a Brazilian study has found.

The study, “Lower airway microbiota and decreasing lung function in young Brazilian cystic fibrosis patients with pulmonary Staphylococcus and Pseudomonas infection,” was published in the journal PLOS One.

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CF causes an abnormally thick and sticky mucus to build up in certain organs of the body, such as the lungs. This mucus can block the airways and make it harder for patients to breathe. It also can trap germs such as bacteria and make infections more likely.

Pseudomonas aeruginosa is one of the most common types of bacteria infecting the lungs of patients with CF, but studies have shown that the entire lung microbiota may shift as the disease progresses. The lung microbiota refers to the collection of all germs living in the windpipe (trachea) and the lungs.

Sometimes, people living with CF experience a sudden worsening of their symptoms, called an exacerbation. When this happens, the lungs may stop working as they should and some bacteria may thrive and grow as a layer, called a biofilm, to form a tight-knit community. Bacteria growing as a biofilm are hard to treat with antibiotics.

To find out how the microbiota may change in CF, a team of researchers in Brazil used a method called 16S rRNA sequencing to identify which bacteria were present in samples of sputum. The sputum is mucus that is brought up from the lungs by coughing.

The study included 34 patients (17 men and 17 women) with a diagnosis of CF. Their ages ranged from 8 to 23 years, and their sputum was collected at the beginning of the study, and after 42 and 84 days.

S. aureus and P. aeruginosa most prevalent in sputum samples

A bacteria culture test, in which the bacteria in the sputum are grown in the lab, revealed that the most common type of bacteria was Staphylococcus aureus (47%), followed by P. aeruginosa (16%). “S. aureus is more prevalent at an earlier age,” the researchers noted. One-quarter (25%) of the samples of sputum grew both S. aureus and P. aeruginosa bacteria.

The 16S rRNA sequencing revealed a total of 226 different groups of bacteria, of which 155 were present in all samples of sputum in each of the three sampling days. The most common genera of bacteria were the Veillonella, Prevotella, Haemophilus, Pseudomonas, Staphylococcus, Streptococcus, Serratia, Neisseria, and Porphyromonas.

S. aureus or P. aeruginosa accounted for more than half of the bacteria in 40 of the samples of sputum. These bacteria were tested for their ability to grow as a biofilm in the lab, and all were able to do it.

To understand how these bacteria may be linked to lung function, the researchers divided the samples into those richest in Staphylococcus or Pseudomonas bacteria.

Spirometry, a test that measures how well the lungs are working, revealed a wide range of lung function. Forced vital capacity (FVC), a measure of how much air is breathed out in a forced breath, ranged from 31% to 152%. Forced expiratory volume in one second (FEV1), which measures the amount of air that is breathed out during the first second of the forced breath, ranged from 26% to 157%.

Patients who were infected with Staphylococcus bacteria had lower FVC and FEV1 than those who were infected with Pseudomonas bacteria, indicating worse lung function. Moreover, the more prevalent Staphylococcus bacteria were over Pseudomonas bacteria, the lower the FVC and FEV1.

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The researchers also found that Staphylococcus-infected patients had a lower body mass index (BMI, an estimate of total body fat) than those infected with Pseudomonas (18.1 vs. 19.4 kilograms per square meter).

Staphylococcus-infected patients “were underweight,” the team wrote, adding that “clinical condition was consistent with the results of pulmonary [lung] function.”

“Overall, children and young patients infected with Pseudomonas usually have a lower BMI than children infected with genus Staphylococcus, but this does not occur when the patient is already being monitored and receiving medication,” the researchers wrote.

Five patients in the Staphylococcus group and one in the Pseudomonas group had acute breathing difficulties and required antibiotics as part of their treatment, meaning they were experiencing an exacerbation. This was consistent with the findings of lung function and BMI.

A deeper look into the data of 16S rRNA sequencing revealed a number of genes involved in how Staphylococcus bacteria get around antibiotics to become resistant to them. In Pseudomonas, there were many genes involved in virulence, or how the bacteria release substances that cause harm to their host.

These findings “provide a valuable contribution to the knowledge in the field,” the researchers concluded. They noted the small size of the patient group and its variability as study limitations.