Lineage, Antimicrobial Resistance and Virulence of Citrobacter spp

Abstract

<i>Citrobacter</i> spp<i>.</i> are opportunistic human pathogens which can cause nosocomial infections, sporadic infections and outbreaks. In order to determine the genetic diversity, <i>in vitro</i> virulence properties and antimicrobial resistance profiles of <i>Citrobacter</i> spp<b><i>.</i></b>, 128 Citrobacter isolates obtained from human diarrheal patients, foods and environment were assessed by multilocus sequence typing (MLST), antimicrobial susceptibility testing and adhesion and cytotoxicity testing to HEp-2 cells. The 128 Citrobacter isolates were typed into 123 sequence types (STs) of which 101 were novel STs, and these STs were divided into five lineages. Lineages I and II contained <i>C.</i> <i>freundii</i> isolates; Lineage III contained all <i>C.</i> <i>braakii</i> isolates, while Lineage IV and V contained <i>C.</i> <i>youngae</i> isolates. Lineages II and V contained more adhesive and cytotoxic isolates than Lineages I, III, and IV. Fifty-one of the 128 isolates were found to be multidrug-resistant (MDR, ≥3) and mainly distributed in Lineages I, II, and III. The prevalence of quinolone resistance varied with Lineage III (<i>C.</i> <i>braakii</i>) having the highest proportion of resistant isolates (52.6%), followed by Lineage I (<i>C.</i> <i>freundii</i>) with 23.7%. Seven <i>qnrB</i> variants, including two new alleles (qnrB93 and qnrB94) were found with Lineage I being the main reservoir. In summary, highly cytotoxic MDR isolates from diarrheal patients may increase the risk of severe disease.