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Pseudomonas aeruginosa

Is there a danger of getting Pseudomonas aeruginosa when treated Staphylococcus aureus?
Dear questionner

Thank you for your question. Staphylococcus aureus is a common pathogen in CF and is detected in the sputum of many children with CF. There are different approaches to treatment of Staphylococcus aureus. Some centres include short term antibiotic courses in response to a positive sputum culture, other centres use antibiotics therapy only if the sputum culture is associated with clinical symptoms. Other CF centres use prophylactic treatment from diagnosis to reduce the prevalence of Staphylococcus aureus infection. Especially with the latter approach there are some concerns about increased risk of bacterial resistance and Pseudomonas aeruginosa infection. There are some studies that have looked at this. A Cochrane review found no difference in groups of continuous prophylactic versus intermittend (given as required) antibiotic treatment for Staphylococcus aureus in P. aeruginosa infection, however there seemed to be a trend towards lower P. aeruginosa isolation rates in the prophlaxis group after 2-3 years of treatment and a trend towards a higher isolation after 4-6 years.
The current research seems to suggest that the safety of prophylactic, broad spectrum, oral cephalosporins for treatment of Staphylococcus aureus is questionable and the main safety concern raised is selection for P.aeruginosa infection with the use of broad spectrum antibiotics such as cephalexin.There is currently no evidence to suggest that a narrow spectrum antibiotic, such as flucloxacillin (widely used in the UK) increases the incidence of P.aeruginosa infection. We hope this answers your question and we would encourage you to discuss any issues you have with your CF doctor.

Prof Judy Bradley
Prof Stuart Elborn

Smyth AR, Walter S. "Prophylactic anti-staphylococcal antibiotics for cystic fibrosis.", Cochrane Database Syst Rev. 2012 Dec 12;12:CD001912. doi: 10.1002/14651858.CD001912.pub2.
The question of a higher incidence of P. aeruginosa colonization addresses the continous anti-staphyloccocal prophylaxis, not the acute therapy of the finding of S. aureus. In the latter case, it may even be vice versa, as S. aureus "has been thought to be a predecessor of later infection by P. aeruginosa" (1).

Some more cited details from the above mentioned Cochrane database review may be interesting here:


We included four studies, totaling 401 randomised participants aged zero to seven years on enrolment. Fewer children receiving anti-staphylococcal antibiotic prophylaxis had one or more isolates of Staphylococcus aureus. There was no significant difference between groups in infant or conventional lung function. We found no significant effect on nutrition, hospital admissions, additional courses of antibiotics or adverse effects. There was no significant difference in the number of isolates of Pseudomonas aeruginosa between groups, though there was a trend towards a lower cumulative isolation rate of Pseudomonas aeruginosa in the prophylaxis group at two and three years and towards a higher rate from four to six years. As the studies reviewed lasted six years or less, conclusions cannot be drawn about the long-term effects of prophylaxis.

Anti-staphylococcal antibiotic prophylaxis leads to fewer children having isolates of Staphylococcus aureus, when commenced early in infancy and continued up to six years of age. The clinical importance of this finding is uncertain. Further research may establish whether the trend towards more children with CF with Pseudomonas aeruginosa, after four to six years of prophylaxis, is a chance finding and whether choice of antibiotic or duration of treatment might influence this.

D. d'Alquen

(1) Döring et al in the Journal of Cystic Fibrosis 11 (2012) 461-479: “Treatment of lung infection in patients with cystic fibrosis: Current and future strategies”