Molecular Epidemiology of Nosocomial Colonization and Infection due to Stenotrophomonas (Xanthomonas) maltophilia at a Tertiary Care Hospital.

J.YAO*, J. CONLY, J. BURT, M. GARCIA, M. KRAJDEN, and J. BRUNTON.

Dept. Of Microbiology, The Toronto Hospital, and University of Toronto, Ontario, CANADA.


S. maltophilia (Sm) remains a challenge in hospital infection control practice due to its multi-
drug resistance and propensity to colonize and cause serious infections in hospitalized patients. Since 1990 there has been a consistent 2- fold increase (10.9 vs 5.3 isolates per month) in the number of Sm isolated at our institution, with the majority of isolates (64.5%) being respiratory in origin. During the first 10 months of 1993, a total of 109 non-duplicate Sm were isolated, with 75 (69%) isolates originating from the intensive care units (ICU). The ICU environmental and health care worker handwashing cultures yielded 10 Sm isolates from environmental sources (ventilatory equipment and sink drains) only. DNA macrorestriction analysis by pulsed-field gel electrophoresis of these strains revealed unique DNA profiles from 2 environmental isolates, each of which was clonally related to 19 and 11 of the clinical strains, respectively. Of these 30 clinical strains, 24 (80%) strains were from ICU patients. The remaining 8 environmental strains showed DNA restriction profiles that were concordant with those of one or more clinical isolates. The majority of the non-ICU isolates had unique DNA band patterns.

Without any temporal relationship between the collection of environmental and clinical isolates,
our data suggest a common environmental reservoir as a potential source for the continued occurrence of colonization and infections due to Sm, particularly in the ICU. The epidemiology of colonization and infections with Sm in our institution is complex, and the mechanisms of transmission remain uncertain.

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