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New bacteria in cystic fibrosis

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In recent years new, or relatively new, bacterial isolates have been obtained from patients with cystic fibrosis (CF). They include Burkholderia cepacia, Stenotrophomonas maltophilia, Achromobacter xylosidans, and Mycobacterium avium complex. Three papers in Thorax have added to knowledge about the occurrence and clinical significance of the first two of these organisms.

S maltophilia (previously known as Pseudomonas, or Xanthomonas, maltophilia) is a Gram-negative, non-fermenting rod found in the airways of CF patients and with widespread antibiotic resistance. Its importance as a pathogen has been unclear. A cohort study based on the US CF Foundation National Patient Registry (CH Goss and colleagues.

) has shown no correlation between S maltophilia colonisation and progression of lung disease. Among 20 755 patients aged 6 years or older (median age at entry 13.8 years) 2739 (13%) had at least one positive culture for S maltophilia. Patients colonised with the organism had worse lung function (FEV1 adjusted for sex, height, and age) but S maltophilia positivity did not influence the rate of decline in lung function after adjustment for confounding factors. The effect of treatment for S maltophilia needs to be assessed.

Organisms of the Burkholderia cepacia complex can cause serious lung infection in CF patients. There are nine B cepacia complex species, the commonest of which is B cenocepacia. The ET12 strain of B cenocepacia has been isolated from patients in Canada and the UK but the PHDC strain has been confined to the USA. Now workers in Ghent, Belgium (T Coenye and colleagues.

) have examined 796 B cenocepacia isolates and found that on randomly amplified polymorphic DNA (RAPD) typing, 19 European isolates were similar to 14 US reference isolates for the PHDC strain. Rep-PCR using the BOX-A1R primer (BOX-PCR) confirmed that the European isolates (from eighteen recent clinical samples from CF patients in France and Italy and one urine sample in the UK from 1964) were of the same clone as the PHDC strain. The PHDC strain is present on both sides of the Atlantic ocean.

Researchers at a Manchester centre for adults with CF (AM Jones and colleagues.

) have studied the two most common species (genomovars) of the B cepacia complex—B cenocepacia and B multivorans. Forty-nine patients had been infected with either B cenocepacia (33) or B multivorans (16). Chronic infection ensued in 31/33 and 8/16 respectively. One-year survival among patients chronically infected with B cenocepacia was reduced compared with their Pseudomonas aeruginosa-infected controls (80% vs 100%) whereas among patients infected with Bmultivorans survival was the same as among their P aeruginosa-infected controls (100%). The rates of 5-year survival were 67% vs 85% (B cenocepacia vs P aeruginosa) and 75% vs 75% (B multivorans vs P aeruginosa).

S maltophilia is not associated with more rapid decline in lung function; B cenocepacia strain PHDC has crossed the Atlantic; and B cenocepacia, but not B multivorans, is associated with reduced survival compared with P aeruginosa.