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Service de Réanimation Médicale et de Microbiologie A, CHU La Milèterie Poitiers cedex, France, ; Correspondence to: René Robert, MD, Service de Réanimation Médicale, CHU La Milèterie, 86021 Poitiers cedex, France; e-mail r.robert@chu-poitiers.fr
To the Editor:
We read with great interest the article of Marik and Careau (CHEST; January 1999).1 Despite specific care (rapid transport, adequate transport medium, and inoculation onto specific media under anaerobic conditions), only one anaerobic bacterium was isolated in this study, leading to the conclusion that anaerobic bacteria were not likely to be involved in these infections and that antibiotics effective against anaerobic bacteria may not be useful as empiric treatment in these situations. However, it is well known that the concentration of anaerobic bacteria in the oropharynx is higher than that of aerobic bacteria. These bacteria colonizing the oropharynx are responsible for nosocomial pneumonia. Thus the inability to isolate anaerobic bacteria in this study is surprising. Using specific transport and culture conditions, we could isolate a high percentage of anaerobic strains from protected brush specimens (PSB) in patients with ventilator-acquired pneumonia (VAP).2 These striking differences between the results of Marik and Careau and ours may be related to technical differences in the laboratory procedures used to recover anaerobic bacteria from PSB. First, we used freshly prepared meat yeast VL agar medium (Sanofi Pasteur; Marnes La Coquette, France) for anaerobic culture. This medium is prepared twice each week and is complemented with 8% sheep blood, menadione, and gentamicin, making this medium selective for anaerobes. Secondly, the anaerobic atmosphere was obtained in an oxoid jar with the Anaerogen Oxoid system (Oxoid; Basingstoke, England), which gives us better results than other tested systems (unpublished data). Finally, 2 of the 20 technicians in our laboratory are specifically assigned to the anaerobic bacteria department because of their skill in studying these bacteria.
Nevertheless, the potential interest of using antibiotics effective against anaerobic bacteria in patients with nosocomial pneumonia remains controversial.3 We recently reported that patients with VAP receiving well-adapted empiric antibiotherapy against anaerobic bacteria had a better outcome at D10.4 Furthermore, in a recent large study comparing the efficacy of ceftazidime vs piperacillin-tazobactam in ICU patients with VAP, mortality was lower in patients receiving piperacillin-tazobactam than in those receiving ceftazidime.5 Although anaerobic bacteria were not specifically investigated in this study, we can speculate that the mortality difference might be explained in part by a better activity of piperacillin-tazobactam than ceftazidime on anaerobes, which could have been associated with aerobic bacteria in patients with VAP.
In conclusion, because anaerobic bacteria are numerous in the oropharynx, and because colonized oropharyngeal content leads to nosocomial pneumonia, anaerobes associated with aerobic bacteria should be isolated in patients with VAP or aspiration pneumonia. Furthermore several arguments suggest taking into account these bacteria in the choice of empiric antibiotic therapy in patients with VAP.
References
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