Abstract
In many countries including Japan, the status of emerging antimicrobial resistance among Serratia spp. and Citrobacter spp. in companion animals remains unknown because these genera are rarely isolated from animals. In this study, 30 Serratia spp. and 23 Citrobacter spp. isolates from companion animals underwent susceptibility testing for 10 antimicrobials. Phenotypic and genetic approaches were used to identify the mechanisms of extended-spectrum cephalosporins (ESC). Subsequently, ESC-resistant Citrobacter spp. strains underwent multilocus sequence typing and pulsed-field gel electrophoresis (PFGE). A significantly higher rate (34.8%) of ESC resistance was observed in Citrobacter spp. isolates than in Serratia spp. isolates (0%). ESC resistance was detected in five C. freundii strains, two C. portucalensis strains, and one C. koseri strain. All of the ESC-resistant Citrobacter spp. strains harbored CMY-type and/or DHA-type AmpC β-lactamases. Three C. freundii strains harbored the CTX-M-3-type extended-spectrum β-lactamases. Notably, the three blaCTX-3-producing and two blaCMY-117-bearing C. freundii strains (obtained from different patients in one hospital) had the same sequence type (ST156 and ST18, respectively) and similar PFGE profiles. We believe that ESC-resistant Citrobacter spp. are important nosocomial pathogens in veterinary medicine. Therefore, infection control in animal hospitals is essential to prevent dissemination of these resistant pathogens.
Highlights
The genera of Serratia and Citrobacter, belonging to the Enterobacteriaceae family, are opportunistic nosocomial pathogens and cause a wide spectrum of human infections [1,2]
The bacterial species of our collection were identified by several conventional methods and determined by MALDI-TOF MS and recN phylogeny
We conclusively determined 23 Citrobacter spp. isolates based on recN phylogeny as follows: C. freundii (n = 9), C. koseri (n = 6), C. portucalensis (n = 6), and C. europaeus (n = 2) (Figure 1)
Summary
The genera of Serratia and Citrobacter, belonging to the Enterobacteriaceae family, are opportunistic nosocomial pathogens and cause a wide spectrum of human infections [1,2]. In companion animals, these genera are rarely associated with infections such as pneumonitis, urinary tract infection, myocarditis, septicemia, and intravenous catheter site infection [3]. The emergence of multidrug resistance—notably, resistance to extended-spectrum cephalosporins (ESC)—among Serratia spp. and Citrobacter spp. is a worldwide concern to human medicine [1]. In many countries including Japan, the status of emerging antimicrobial resistance among Serratia spp. and Citrobacter spp. in companion animals remains unknown
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