Emerging and Unusual Gram-Negative Infections in Cystic Fibrosis

Jane C. Davies, M.B.Ch.B., M.R.C.P., M.R.C.P.C.H., M.D.; Bruce K. Rubin, M.Engr., M.D., M.B.A., F.R.C.P.C.


Semin Respir Crit Care Med. 2007;28(3):312-321. 

In This Article

Achromobacter (Alcaligenes) Xylosoxydans

Although "A. xylosoxidans," a motile, gram-negative bacillus, has been recognized for many years as being capable of causing infection in persons with CF, the proper nomenclature of this species has presented an ongoing challenge. The species has been consecutively named Achromobacter xylosoxidans, Alcaligenes denitrificans subsp. xylosoxidans, and Alcaligenes xylosoxidans subsp. xylosoxidans.[55] Most recently, the name Achromobacter xylosoxidans was again proposed but this has not been uniformly accepted. Thus the species is currently correctly called either Achromobacter xylosoxidans or Alcaligenes xylosoxidans. Correct identification can be difficult with many of these organisms because the biochemical tests in common use are less reliable; researchers have suggested alternatives, including fluorescence in situ hybridization[56] and polymerase chain reaction (PCR)-based assays.[57]

Incidence in CF seems to vary from center to center, and the organism commonly coexists with other airway pathogens. Because infection is so often transient, detection and reported rates of infection are strongly influenced by the frequency of sputum culture. Data from the Cystic Fibrosis Foundation National Registry indicate that in 1996 1.9% of U.S. CF patients were infected with A. xylosoxidans; however, this species was detected by a core laboratory in 8.7% of 595 patients enrolled in the 6-month TSI clinical trials during approximately the same time period. A recent study by Tan and colleagues indicates that 13 (2.3%) of 557 patients in their pediatric and adult CF units were chronically infected with this organism; a further 31 (5.6%) patients were intermittently colonized.[58] Ronne Hanson et al identified a subgroup of their infected patients who were characterized by rapidly rising levels of specific anti-A. xylosoxidans antibodies who did experience a more rapid decline in lung function after infection than controls, although the group as a whole were not significantly affected.[59] With regard to acquisition, there is little evidence that it is acquired by patient-to-patient cross infection.[41,60] Persistence seems to be variable once the lung is infected, from transient to up to 6 years in one patient. Based on the available evidence it does not seem that infection with A. xylosoxidans contributes greatly to clinical deterioration in CF patients. The organism is also encountered outside the context of CF,[61] leading to bacteremia, meningitis, pneumonia, endocarditis, peritonitis, osteomyelitis, urinary tract infection, and endophthalmitis. Most infections are nosocomially acquired, with neonates, burn victims, and other immunocompromised patients being at greatest risk. As with many other CF pathogens, A. xylosoxidans are frequently resistant to multiple antibiotics.[62] In cases where treatment may be warranted based on the clinical situation, antibiotics that demonstrate the greatest activity in vitro include minocycline, imipenem, meropenem, piperacillin, and piperacillin-tazobactam. Combinations of antibiotics that have shown additive activity include chloramphenicol plus minocycline, and ciprofloxacin plus either imipenem or meropenem.


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.