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Low-virulence Citrobacter species encode resistance to multiple antimicrobials
C Pepperell1, J V Kus, M A Gardam
1The Centre for Infection and Biomaterials Research, Hospital for Sick Children Research Institute. Departments of Surgery. Medicine, University of Toronto, Toronto, Ontario, Canada.
Antimicrobial Agents and Chemotherapy
|October 18, 2002
Summary
Multidrug-resistant Citrobacter species, including cefpodoxime-resistant strains, are common colonizers in transplant patients. These bacteria carry resistance genes, posing a potential threat for future antimicrobial resistance development.
Area of Science:
- Microbiology
- Infectious Diseases
- Antimicrobial Resistance
Background:
- Citrobacter species are gram-negative bacteria, typically commensals, but can cause nosocomial infections in immunocompromised individuals.
- These bacteria often exhibit cephalosporin resistance due to beta-lactamase overexpression.
- Multidrug-resistant Enterobacteriaceae (MDRE) are a growing concern, particularly in vulnerable patient populations.
Purpose of the Study:
- To investigate the prevalence and characteristics of multidrug-resistant Citrobacter species in solid-organ transplant patients.
- To identify the genetic mechanisms conferring antimicrobial resistance in these strains.
- To assess the clinical significance of Citrobacter colonization in this patient cohort.
Main Methods:
- Pulsed-field gel electrophoresis (PFGE) was used for strain typing.
- Genetic analysis, including PCR and DNA sequencing, was performed to identify resistance genes.
- Phenotypic testing evaluated antimicrobial susceptibility profiles.
- Clinical data was reviewed to determine infection rates.
Main Results:
- Nearly half of MDRE-colonized transplant patients carried cefpodoxime-resistant Citrobacter strains (C. freundii, C. braakii, C. amalonaticus).
- Extended-spectrum beta-lactamase (ESBL) genes (SHV-5, SHV-12) were identified in 26% of strains.
- Resistance to aminoglycosides (28%), trimethoprim-sulfamethoxazole (31%), and fluoroquinolones (8%) was observed.
- Class I integrons, encoding resistance to aminoglycosides and/or trimethoprim, were found, including novel instances in C. braakii and C. amalonaticus.
Conclusions:
- Multidrug-resistant Citrobacter species are prevalent colonizers in solid-organ transplant recipients.
- These strains harbor significant antimicrobial resistance genes, including ESBLs and integrons.
- Despite high colonization rates, clinical infections were infrequent, suggesting low virulence but potential for future resistance gene accumulation and evolution.