Figure 3. Pulsed-field gel electrophoresis of three pairs of Pseudomonas aeruginosa isolates obtained from three patients from nasogastric tubes (lanes 2, 4, 6) and from oropharynx (lanes 3, 5, 7). Lane 1 shows the λ marker size (New England Biolabs, Eldan, Rosh Ha’ain, Israel). cussed in this study exist everywhere. Similar studies from other long-term-care facilities could provide further evi- dence. Acknowledgments We thank Mel Rosenberg for helpful professional advice and Yehuda Ben Shaul and Yacob Delarea for performing scan- ning electron microscopy. Dr. Leibovitz is a specialist in internal medicine and geri- atrics and director of a skilled nursing ward at Shmuel Harofe Hospital, Geriatric Medical Center, affiliated with the Sackler School of Medicine, Tel-Aviv University. His present subject of clinical research is the mucosal orifices of frail elderly patients. References 1. Donlan RM. Biofilms: Microbial life on surfaces. Emerg Infect Dis 2002;8:881–90. 2. Leibovitz A, Plotnikov G, Habot B, Rosenberg M, Segal R. Pathogenic colonization of the oral flora in frail elderly patients fed by naso-gastric tube or percutaneous entero-gastric tube. J Gerontol Biol Sci Med Sci 2003;58A:52–5. 3. Pollack M. Pseudomomas aeruginosa. In: Mandell GL, Bennett JE, Dolin R, editors. Principles and practice of infectious disease. Edinburgh: Churchill Livingstone, Ltd; 2000. 4. Sauer K, Camper AK, Ehrlich GD, Costerton JW, Davies DG. Pseudomonas aeruginosa displays multiple phenotypes during devel- opment as a biofilm. J Bacteriol 2002;184:1140–54. RESEARCH 5. Whiteley M, Bangera MG, Bumgarner RE, Parsek MR, Teitzel GM, Lory S, et al. Gene expression in Pseudomonas aeruginosa biofilms. Nature 2001;413:860–4. 6. National Committee for Clinical Laboratory Standards. Performance standards for antimicrobial susceptibility testing. M100-S11. Wayne (PA): The Committee; 2001. 7. Warner LA. Lemon-glycerine swabs should be used for routine oral care. Critical Care Nurse 1986;6:82–3. 8. D’Agata E, Venkataraman L, DeGirolami P, Samore M. Molecular epidemiology of ceftazidime-resistant gram-negative bacilli in a non- outbreak setting. J Clin Microbiol 1997;35:2602–5. 9. Tenover FC, Arbeit RD, Goering RV, Mickelsen PA, Murray BE, Persing DH, et al. Interpreting chromosomal DNA restriction patterns produced by pulsed-field gel electrophoresis: criteria for bacterial strain typing. J Clin Microbiol 1995;33:2233–9. 10. Valenti WM, Trudell RG, Bentley DW. Factors predisposing to oropharyngeal colonization with gram-negative bacilli in the aged. N Engl J Med 1978;298:1108–11. 11. Irwin RS, Whitaker S, Pratter MR, Millard CE, Tarpey JT, Corwin RW. The transiency of oropharyngeal colonization with gram-negative bacilli in residents of a skilled nursing facility. Chest 1982;81:31–5. 12. Scannapieco FA, Stewart EM, Mylotte JM. Colonization of dental plaque by respiratory pathogens in medical intensive care patients. Crit Care Med 1992;20:740–5. 13. Terpenning MS, Taylor GW, Lopatin DE, Kerr CK, Domingues BL, Loesche WJ. Aspiration pneumonia: dental and oral risk factors in an older veteran population. J Am Geriatr Soc 2001;49:557–63. 14. Palmer LB, Albulak, Fields S, Filkin AM, Simon S, Smaldone GC. Oral clearance and pathogenic oropharyngeal colonization in the eld- erly. Am J Respir Crit Care Med 2001; 164:464–8. 15. Martinez-Martinez L, Pascual A, Perea EJ. Effect of three plastic catheters on survival and growth of Pseudomonas aeruginosa. J Hosp Infect 1990;16:311–8. 16. Martinez-Martinez L, Pascual A, Perea EJ. Kinetics of adherence of mucoid and non-mucoid Pseudomonas aeruginosa to plastic catheters. J Med Microbiol 1991;34:7–12. 17. Limeback H. Implications of oral infections on systemic diseases in the institutionalized elderly with a special focus on pneumonia. Annals of Periodontology 1998;3:262–75. 18. Strausbaugh LJ, Crossley KB, Nurse BA, Thrupp LD. Antimicrobial resistance in long term care facilities. Infect Control Hosp Epidemiol 1996;17:129–40. 19. Brooun A, Liu S, Lewis K. A dose-response study of antibiotic resist- ance in Pseudomonas aeruginosa biofilms. Antimicrob Agents Chemother 2000;44:640–6. 20. Gorman SP, McGovern JG, Woolfson AD, Adair CG, Jones DS. The concomitant development of poly (vinyl chloride) related biofilm and antimicrobial resistance in relation to ventilator-associated pneumo- nia. Biomaterials 2001;22:2741–7. Address for correspondence: Arthur Leibovitz, Shmuel Harofe Hospital, Geriatric Medical Center, POB 2, Beer-Yaakov, Israel; fax: 972- 89237156, email: shmuelh@netvision.net.il Emerging Infectious Diseases • Vol. 9, No. 8, August 2003 959