Vol. 17, No. 14
THE JOHNS HOPKINS MICROBIOLOGY NEWSLETTER
Monday, April 6, 1998
A. Provided by Marguerite Hawkins, Epidemiology and Disease Control Program, Division of Outbreak Investigation, Maryland Department of Health and Mental Hygiene
From March 26, 1998 through April 1, 1998, 5 outbreaks have been reported to the Maryland Department of Health and Mental Hygiene as follows: 1 influenza-like illness, 2 food- related gastroenteritis, 1 presumed viral gastroenteritis and 1 diarrheal illness, presumed typhoid related to travel to Mexico.
B. The Johns Hopkins Hospital: Information provided by Dr. Frank Holmes, Dept. of Pathology
Case History
A 65 year-old white male with a history of hypertension and moderate-to-severe chronic obstructive pulmonary disease underwent repair of an aortic aneurysm. His postoperative course was complicated by ventilator-dependence, requiring a tracheostomy, and feeding by percutaneous endoscopic gastrostomy tube placement. During his long hospital course in the intensive care unit, the patient was placed on multiple antibiotics, including vancomycin, imipenem, and amikacin, for lung infiltrates and persistent fevers. Multiple cultures taken by endotracheal suctioning grew Pseudomonas aeruginosa, which was susceptible to tobramycin and moderately-susceptible to ceftazidime, and Stenotrophomonas (Xanthomonas) maltophilia, which was resistant to all antibiotics except for sulfonamide and trimethoprim/sulfamethoxazole.
Stenotrophomonas (Xanthomonas) maltophilia
Originally called Pseudomonas maltophilia and later Xanthomonas maltophilia, this organism has now been placed separately within its own genus, Stenotrophomonas. It is a free- living, motile, gram-negative rod that is ubiquitous in the environment. In addition to being recovered from almost any clinical site, S. maltophilia can also be found as a contaminant in various inanimate objects, such as oxygen humidifier water reservoirs and cardiopulmonary bypass pumps. It occasionally causes opportunistic infections and is emerging as an important nosocomial pathogen, with an increasing number of nosocomial infections having been reported in recent years. Not only has infection increased, but the incidence of life-threatening infections is also significantly on the increase. In one study, a crude mortality rate of 43% was reported in all patients from whom the organism was cultured. Risk factors associated with death in these patients included placement in an intensive care unit, age older than 40 years, and a pulmonary source for the isolate.
S. maltophilia can cause a wide variety of disease, including pneumonia, bacteremia, endocarditis (typically associated with open heart surgery or intravenous drug use), cholangitis, urinary tract infection, conjunctivitis, mastoiditis, meningitis, and serious, traumatic or postoperative wound infections. The most common site of recovery is the respiratory tract, although in most patients these isolates do not appear to be clinically significant. The single most important predisposing factor for infection with S. maltophilia is a compromised immune system. In particular, mechanically-ventilated, intensive care unit patients receiving broad- spectrum antibiotics, especially imipenem, and having central venous catheters, are at increased risk of colonization and infection. In one study of cystic fibrosis patients, S. maltophilia had a prevalence rate of 10%, and, interestingly, all of the children were co-colonized with Pseudomonas aeruginosa.
Diagnosis
Stenotrophomonas maltophilia is a motile rod, which possesses multitrichous flagella. It can be easily distinguished from other pseudomonads by virtue of being lysine- and DNAse- positive and oxidase-negative. Rare strains have been found to be slowly oxidase-positive but have all of the other biochemical features characteristic of S. maltophilia. Colonies may appear pale yellow or lavender green on blood agar medium.
Treatment
An important feature in the rising incidence of infections caused by this organism might be its unique antibiotic susceptibility profile. It is inherently resistant to most of the commonly used antipseudomonal drugs, including aminoglycosides and many beta-lactam agents, and use of these drugs can favor colonization by the organism. All strains of S. maltophilia are resistant to imipenem by virtue of a zinc-containing penicillinase. In one study, patients treated with imipenem were 10 times more likely to be found among those infected with S. maltophilia than controls, and all of the fatal cases occurred in patients who had received imipenem. On the other hand, S. maltophilia is characteristically susceptible to trimethoprim-sulfamethoxazole, which is the antibiotic of choice in treating any infection caused by this microorganism.
References
Elting LS, Khiardoni N, Bodey GP, Fainstein V. Nosocomial infection caused by Xanthomonas maltophilia: a case-control study of predisposing factors. Infect Control Hosp Epidemiol 11:134- 138,1990.
Gladman G, Connor PJ, Williams RF, David TJ. Controlled study of Pseudomonas cepacia and Pseudomonas maltophilia in cystic fibrosis. Arch Dis Child 67:192-195,1992.
Marshall WF, Keating MR, Anhalt JP, Stekelberg JM. Xanthomonas maltophilia: an emerging nosocomial pathogen. Mayo Clin Proc 164:1097-1100,1989.
Morrison AJ, Hoffman KK, Wenzel RP. Associated mortality and clinical characteristics of nosocomial Pseudomonas maltophilia in a university hospital. J Clin Microbiol 24:853- 855,1986.
Spencer, RC. The emergence of epidemic, multiple-antibiotic-resistant Stenotrophomonas (Xanthomonas) maltophilia and Burkholderia (Pseudomonas) cepacia. J Hosp Infect 30 (Suppl):453-464,1995.