RESEARCH Pseudomonas aeruginosa and the Orophar yngeal Ecosystem of Tube-Fed Patients Arthur Leibovitz,* Michael Dan,* Jonathan Zinger,* Yehuda Carmeli,* Beni Habot,* and Rephael Segal* Emerging Infectious Diseases • Vol. 9, No. 8, August 2003 We evaluated whether elderly patients fed with naso- gastric tubes (NGT) are predisposed to Pseudomonas aeruginosa colonization in the oropharynx. Fifty-three patients on NGT feeding and 50 orally fed controls with similar clinical characteristics were studied. The tongue dorsum was swabbed and cultured. P. aeruginosa was iso- lated in 18 (34%) of the NGT-fed group but in no controls (p<0.001). Other gram-negative bacteria were cultured from 34 (64%) of NGT-fed patients as compared with 4 (8%) of controls (p<0.001). Antibiotic susceptibility of the oropharyngeal P. aeruginosa isolates was compared with that of isolates from sputum cultures obtained from our hos- pital’s bacteriologic laboratory. The oropharyngeal isolates showed a higher rate of resistance; differences were signif- icant for amikacin (p<0.03). Scanning electron microscope studies showed a biofilm containing P. aeruginosa organ- isms. The pulsed-field gel electrophoresis profile of these organisms was similar to that of P. aeruginosa isolates from the oropharynx. NGT-fed patients may serve as vectors of resistant P. aeruginosa strains. Treservoir for pathogenic microorganisms. It is the only he oral cavity has long been considered a potential normally accessible site in the body that has hard, non- shedding surfaces for microbial colonization. Those unique tissues allow the accumulation of extracellular products and the formation of biofilms that serve as culture media for bacteria and contribute to the development of antibiotic resistance (1). Within the mouth, distinct habi- tats provide different ecologic conditions including mucos- al surfaces, cheeks, palate, periodontal region, tongue, and abiotic structures (teeth). Ecologic conditions within the mouth may vary and change the ecosystem, facilitating the growth of pathogenic organisms. Patients on nasogastric tube (NGT) feeding are a grow- ing segment of the frail elderly population. We have recently reported an increased rate of gram-negative bacte- ria in the nasopharynx of these patients, including a high proportion of Pseudomonas aeruginosa (2). P. aeruginosa has a predilection for wet sites and respiratory equipment *Tel-Aviv University, Israel 956 and may create reservoirs that threaten hospitalized patients (3). The oropharynx of NGT-fed elderly patients may provide such an ecosystem and promote the coloniza- tion of P. aeruginosa. This colonization could be due to several factors such as the papillary structure of the dor- sum of the tongue, the lack of mastication and swallowing (eliminating their mechanical cleansing effect), and the tube itself. P. aeruginosa, a well-known biofilm-producing microorganism (4,5), may be exploiting the NGT to create a thriving habitat. The purpose of this study was to reconfirm the high incidence of P. aeruginosa isolations from the oropharynx of NGT-fed elderly patients, determine its antibiotic sus- ceptibility, and explore the possibility of biofilm formation on the feeding tube. If these assumptions are true, the oropharynx of NGT-fed patients could constitute a poten- tial reservoir for P. aeruginosa in long-term-care facilities. Methods This prospective cross-sectional comparative study was conducted in the four skilled nursing wards of a 158-bed geriatric hospital. Skilled nursing wards are licensed for providing care for nursing patients who also have an active disease requiring close medical supervision (e.g., NGT feeding, severe bed sores, advanced cancer, or hemody- namic instability). Eligible for the study were all patients who had been receiving NGT feeding for at least 2 weeks. The control group comprised matched orally fed patients, with no swallowing disturbances, who resided in the same wards. The orally fed patients received a regular solid hospital diet with occasional supplements. Excluded from both groups were patients who had received any antibiotic treatment up to 2 weeks before the study, patients with advanced cancer, and patients who had received chemotherapy or radiotherapy to the neck. Informed con- sent was obtained from the patients or their proxies. Cultures were obtained by applying sterile cotton swabs to the base of the tongue dorsum and rubbing the buccal mucosa. The sample was then placed in transport medium. Samples were taken in the morning, before breakfast and the daily oral cleansing procedure.