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Antibiotics ineffective in reducing S. aureus in ventilated patients
Antibiotics are ineffective both in reducing Staphylococcus aureus in the lower airway and preventing ventilator-associated tracheobronchitis and pneumonia in ventilated patients, according to findings published in Clinical Infectious Diseases.
“S. aureus seems to be in competition for colonization with the normal repiratory flora,” researchers wrote. “To improve patient outcomes, alternative or adjunct therapies to antibiotic treatment are urgently needed.”
The study included 48 patients staying at Lahey Hospital and Medical Center in Burlington, Massachusetts, between May and December of 2010.
Twenty-one of the patients were colonized with MRSA, and 27 were colonized methicillin-susceptible S. aureus (MSSA). All patients were treated with “appropriate” anti-staphylococcal antibiotics for at least 2 days.
Of the 18 patients with MRSA treated with vancomycin, only one experienced reduced bacterial burden. The other three patients with MRSA received linezolid, which did not yield a microbiological response.
Of the 15 patients with MSSA treated with vancomycin, nine did not respond. The remaining six received vancomycin along with one or two other antibiotics and showed bacterial counts with a decreasing tendency, from heavy to light.
Of the 39 patients colonized only by S. aureus, 13 were diagnosed with ventilator-associated tracheobronchitis (VAT) and 15 with ventilator-associated pneumonia (VAP). Five of those initially diagnosed with tracheobronchitis progressed to pneumonia.
The researchers also noted that heavy colonization occurred in 60% of patients at 4 days post-intubation and in 92% in the first 8 days.
They pointed out some studies have shown that cytotoxin-neutralizing antibodies, in combination with antibiotics for MRSA and MSSA, could be an alternative treatment.
“Several clinical studies are ongoing with S. aureus toxin–neutralizing antibodies that have the potential to address the question of whether this alternative approach offers benefits for ventilated patients by preventing S. aureus VAP, and improving disease outcome and mortality rates,” they wrote.
In a related editorial, Jason P. Burnham, MD, and Marin H. Kollef, MD, both from Washington University School of Medicine, said the patients’ nonresponse to treatment in the study could be explained by “biofilm formation or the presence of bacterial persisters/small colony variant S. aureus.” Small colony variant S. aureus, they said, “are inert to multiple antibiotics and have been associated with worse outcomes and recurrent infections.”
Burnham and Kollef noted a number of different approaches to the prevention of S. aureus VAP and VAT, including nebulized antibiotics and vaccines, but agreed with the researchers that better therapeutic options are “urgently needed.” – by Joe Green
Disclosures: Three of the researchers are employees and shareholders of Arsanis, and Kollef is a principal investigator for the company. Burnham reports no relevant financial disclosures.