Amoeba-Associated Bacteria: Novel Causes of Ventilator-Associated Pneumonia?

Abstract & Commentary

Synopsis: Organisms that may only be isolated by using coculture with amoeba and that are present in hospital water supplies may be implicated in some cases of ventilator-associated pneumonia.

Source: La Scola B, et al. Amoeba-resisting bacteria and ventilator-associated pneumonia. Emerg Infect Dis. 2003. www.cdc.gov/ncidod/EID/vol9no7/03-0065.htm.

La Scola and colleagues in Marseilles prospectively evaluated the role of amoeba-associated bacteria (AAB) as potential etiologic agents of ventilator-associated pneumonia (VAP).

Environmental sampling, also performed, discovered 310 isolates, representing 10 individual species of AAB from 864 water samples, including many samples from the water taps in patient rooms. The most commonly isolated strains were Legionella anisa and Bosea massiliensi.

No AAB were isolated by cocultivation with Acanthamoeba polyphaga from bronchoalveolar lavage (BAL) specimens obtained from each patient both immediately after tracheal intubation and upon the appearance of pulmonary infiltrates. PCR detected DNA of L anisa and B massilensis only 1 time each in 66 BAL specimens from 30 patients. Both patients seroconverted to their respective isolates. They were among 12 of 30 who seroconverted to 1 AAB, mostly to L anisa and B massilensis. Seroconversion was statistically correlated with VAP and with the systemic inflammatory response syndrome.

Comment by Stan Deresinski, MD, FACP

La Scola et al speculate that their inability to recover AAB from BAL by cocultivation may have been due to the antibiotic therapy being received by most patients.

B massilensis is a Gram-negative, oxidase-positive bacillus that has not previously been associated with human disease. L anisa has previously been isolated from potable and other waters and has been associated with Pontiac fever and with a few cases of Legionnaire’s disease.1-3 The data reported here suggest that these 2 organisms, and perhaps other similar bacteria, may play a role in some cases of hospital-acquired pneumonia and that the hospital water supply may be their reservoir. It will be of interest to see if these results can be confirmed and extended.

References

1. McNally C, et al. Potential importance of Legionella species as etiologies in community acquired pneumonia (CAP). Diagn Microbiol Infect Dis. 2000;38:79-82.

2. Fenstersheib MD, et al. Outbreak of Pontiac fever due to Legionella anisa. Lancet. 1990;336:35-37.

3. Fallon RJ, Stack BH. Legionnaires’ disease due to Legionella anisa. J Infect. 1990;20:227-229.

Dr. Derenski is Clinical Professor of Medicine, Stanford; Associate Chief of Infectious Diseases, Santa Clara Valley Medical Center.