Antimicrobial Resistance and Cytotoxicity of Citrobacter spp. in Maanshan Anhui Province, China

Abstract

<b>Objectives:</b><i>Citrobacter</i> spp. especially <i>Citrobacter freundii</i>, is frequently causing nosocomial infections, and increasingly becoming multi-drug resistant (MDR). In this study, we aimed to determine the genetic diversity and relationships of <i>Citrobacter</i> spp. from diarrheal patients and food sources, their antimicrobial resistance profiles and <i>in vitro</i> virulence properties. <b>Methods:</b> Sixty two <i>Citrobacter</i> isolates, including 13 <i>C. freundii</i>, 41 <i>C. youngae</i> and eight <i>C. braakii</i> isolates, were obtained from human diarrheal patients and food sources. Multilocus Sequence Typing (MLST) of seven housekeeping genes and antimicrobial susceptibility testing using the broth microdilution method according to CLSI recommendations were carried out. Adhesion and cytotoxicity to HEp-2 cells were performed. PCR and sequencing were used to identify <i>bla</i>_CTX-M, <i>bla</i>_SHV, <i>bla</i>_TEM and <i>qnr</i> genes. <b>Results:</b> The 62 isolates were divided into 53 sequence types (STs) with all STs being novel, displaying high genetic diversity. ST39 was a predominant ST shared by 5 <i>C. youngae</i> strains isolated from four foods and a diarrheal patient. All isolates were resistant to cefoxitin, and sensitive to imipenem, meropenem and amikacin. The majority of <i>Citrobacter</i> isolates (61.3%) were MDR of three or more antibiotics out of the 22 antibiotics tested. Two <i>C. freundii</i> isolates each carried the <i>bla</i>_TEM-1 gene and a variant of <i>qnrB77</i>. Three <i>Citrobacter</i> isolates each carried <i>qnrS1</i> and <i>aac(6')-Ib-cr</i> genes. Seven isolates that showed strong cytotoxicity to HEp-2 cells were MDR. <b>Conclusions:</b><i>Citrobacter</i> spp. from human and food sources are diverse with variation in virulence properties and antibiotic resistance profiles. Food may be an important source of <i>Citrobacter</i> species in transmission to humans. <i>C. freundii</i> and <i>C. youngae</i> are potential foodborne pathogens.