S. aureus infections in CF highly resistant to most antibiotics: Review

Most effective for this staph infection: vancomycin and teicoplanin

Andrea Lobo, PhD avatar

by Andrea Lobo, PhD |

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Antibiotic resistance is high among cystic fibrosis (CF) patients infected with Staphylococcus aureus (S. aureus), according to a recent study.

There was “high resistance to most of the antibiotics studied,” researchers say, with the highest observed for the antibiotics erythromycin and clindamycin, while the lowest resistance was seen with vancomycin and teicoplanin.

The study, “Prevalence of antibiotic resistance of Staphylococcus aureus in cystic fibrosis infection: A systematic review and meta-analysis,” was published in the Journal of Global Antimicrobial Resistance.

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Meta-analysis to determine antibiotic resistance of S. aureus infections

CF is caused by mutations in the CFTR gene, which provides instructions for making a protein channel that normally regulates the flow of chloride ions in and out of cells.

CFTR mutations lead to a missing or dysfunctional protein, resulting in impaired flow of water and salts, and the production of thick and sticky mucus. The accumulation of mucus in the body’s organs leads to most CF symptoms.

In the lungs, mucus can clog the airways and lead to difficulty breathing and inflammation. It is also a fertile environment for the growth of bacteria that cause chronic infections.

Chronic lung infections caused by methicillin-resistant S. aureus (MRSA) are thought to exacerbate the symptoms and the decline of lung function in patients living with CF. Studies have shown that the incidence of MRSA in CF patients is significantly higher than that of methicillin-sensitive S. aureus (MSSA).

Researchers in China have now conducted a review and meta-analysis (which pools results from multiple studies) to determine antibiotic resistance of S. aureus in CF infections. Results of a total of 19 studies were pooled. In those studies, 3,394 isolates from CF patients in 10 countries from four continents were analyzed.

The analyses of antibiotic resistance were conducted separately according to two different guidelines — the Clinical and Laboratory Standards Institute (CLSI) and European Committee on Antimicrobial Susceptibility Testing (EUCAST).

A random-effects model — which assumes that the effects being estimated are not identical, but follow some distribution — was used to estimate the pooled prevalence of resistance for each antibiotic.

The high levels of antibiotic resistance observed are worrisome and indicate the need to monitor antibiotic use.

Using the CLSI guideline, erythromycin had the highest resistance rate (77%), followed by clindamycin (51%), while vancomycin (1%) and teicoplanin (0%) had the lowest resistance.

Also, the resistance to some antibiotics was significantly higher in MRSA than in MSSA infections. These included ciprofloxacin (64.9% vs. 34.4%), clindamycin (62.92% vs. 28.95%), erythromycin (84.59% vs. 56.79%), and gentamicin (42.94% vs. 8.16%).

The results were similar when based on EUCAST, with erythromycin also showing the highest resistance rate (73%), followed by clindamycin (63%), while vancomycin and teicoplanin had the lowest (0%).

Using this guideline, MRSA had a significantly higher resistance than MSSA to ciprofloxacin (75.83% vs. 18.93%), clindamycin (74.23% vs. 45.57%), erythromycin (84.68% vs. 35.79%), linezolid (3.43% vs. 0.28%), gentamicin (23.92% vs. 8.73%), rifampin (21.35% vs. 2.26%), and tetracycline (31.04% vs. 5.13%).

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Two methods used to determine antibiotic resistance

When the researchers analyzed subgroups by year — 2008 to 2015 and 2015 to 2021 — only linezolid showed significant differences, specifically an increase in antibiotic resistance over time.

“This suggests that this antibiotic should be more controlled to prevent increased resistance,” the researchers wrote.

The included studies used two methods to determine antibiotic resistance in S. aureus isolates: the disk diffusion method, in which a paper disk saturated with antibiotic is incubated with bacteria; or the broth dilution method, in which containers with identical volumes of antibiotic are incubated with a known number of bacteria.

According to the CLSI guideline, the method used to study antibiotic resistance did not impact the results. However, using EUCAST, significant differences were found with ciprofloxacin (dilution method: 18.45% vs. disk diffusion: 36.02%), clindamycin (71.91% vs. 46.56%), and cotrimoxazole (10.69% vs. 1.96%).

“Vancomycin and teicoplanin were CF patients’ most effective treatment options, although the highest antibiotic resistance to erythromycin and clindamycin was observed,” the team wrote. “The high levels of antibiotic resistance observed are worrisome and indicate the need to monitor antibiotic use.”

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