Anaerobic

T’his issue of Chest (see page 69) contains an interesting article by Pena Grinan and colleagues in which 50 patients with lung abscess underwent percutaneous lung aspiration for bacteriologic studies and cytology. This raises the question as to when this procedure may be indicated in the non-study situation. The bacteriology of anaerobic pulmonary infections (pneumonitis, necrotizing pneumonia, lung abscess and/or empyema) has been studied extensively, al­though additional studies are certainly indicated now in view of the advances that have been made in anaerobic bacteriology (use of anaerobic chambers, prereduced media, new selective media, newly de­scribed organisms, etc) and significant changes in taxonomy of the anaerobes. The study cited, however, adds nothing to available information. Elements of the normal oropharyngeal flora are the key pathogens in community-acquired disease. Anaerobes (Gram-neg­ative rods [various Bacteroides, Porphyromonas and Fusobacterium species] and Gram-positive cocci [Pep- tostreptococcus]) and viridans group streptococci pre­dominate. The В fragilis group is found in 7 percent of such infections and other beta-lactamase producing anaerobes are more common. In hospital-acquired aspiration pneumonia, nosocomial pathogens that col­onize hospitalized patients may be involved in infec­tion along with the organisms noted above; included would be Staphylococcus aureus, various Enterobac- teriaceae, and Pseudomonas aeruginosa.

In view of the resistant bacteria that may be encountered at times, it would seem desirable to obtain definitive bacteriologic studies in patients who are quite ill, especially those with necrotizing pneu­monia. There are reasons to hesitate to do this, however—-the difficulty in obtaining reliable speci­mens, the time required to perform these studies, and the cost. Since the source of the infecting organisms in these patients is almost always the upper airways, the specimen must be collected so as to avoid indige­nous and colonizing organisms. To culture delicate anaerobes, the specimen must be placed under anaer­obic conditions promptly; this is difficult with certain procedures used to obtain specimens. Empyema fluid provides a reliable specimen in sufficient volume so that it can be placed into an anaerobic transport vial or tube. Transtracheal aspiration, when not contrain- dicated, is this writers choice when empyema fluid is not available. Percutaneous transthoracic aspiration typically provides a very small specimen. In the study cited above, however, the authors attached a syringe to the sampling needle and obtained specimens of good volume; use of a transport vial might have improved the results, even with a short transport period. The above technique would not yield sufficient specimen in infections other than lung abscess. The telescoping plugged double catheter technique using a bronchial brush as the sampling device results in a tiny specimen that is difficult to place under anaerobic conditions promptly. Experience with quantitative culture of bronchoalveolar lavage fluid is limited. The time and cost issues can be averted by assuming that resistant anaerobes are present, and treated accord­ingly (or by assuming they are not in patients who are not very ill and changing to more potent therapy if the response is not adequate); culture for aerobic and facultative bacteria only will yield results quickly and cheaply; the issue of specimen collection remains an important one.
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As to therapy, the primary approach is use of antimicrobial agents, except in patients with empy­ema, who require drainage procedures. Open drainage with rib resection and breakdown of loculations may be required in advanced, refractory cases. Initial antimicrobial therapy should be empiric, based on the usual bacteriology encountered, whether or not the infection is hospital-acquired, susceptibility patterns of nosocomial pathogens from the hospital involved, prior therapy that may have led to selection of antibi­otic-resistant strains, and information from Gram stain of a reliable sputum or other appropriate specimen. Therapy can then be modified as needed, based on the patient s response and information obtained in the first 18-24 hours from cultures. Drugs essentially always active against anaerobes include imipenem, ticarcillin/clavulanate, ampicillin/sulbactam, metroni­dazole plus penicillin, and chloramphenicol. The first three agents listed are generally active vs S aureus except for the methicilHn-resistant type; they (partic­ularly the first two) also have significant activity against Gram-negative non-anaerobic rods. Cefoxitin and clin­damycin are quite active against most anaerobes; addition of penicillin would be helpful in the case of clindamycin. Penicillin G, itself, is still useful in many patients with anaerobic pulmonary infection, but should not be used as sole therapy in patients who are quite ill. These various suggested regimens for the anaerobic component of the infecting flora should be supplemented, as indicated, to cover other types of organisms known or anticipated to be present.

As to cytologic studies, this writer would favor bronchoscopy as the definitive procedure.