Molecular epidemiological characteristics of carbapenem-resistant Enterobacter cloacae complex
Authors: He Jing , Cheng Kuo , Sui Qian , Feng Junhua , Zhang Xiaoyu , Zhao Kaixuan , Wang Wei , Zhang Jinyan , Deng Yanli 
Published: December 2024

Background
To monitor the trend of antibiotic sensitivity changes in carbapenem-resistant Enterobacter cloacae complex (CR-ECC) at the Fourth Hospital of Hebei Medical University, evaluate the molecular epidemiological status of CR-ECC, analyze resistance genes and homology, explore the differential characteristics of virulence genes, and provide theoretical guidance and data support for the standardization of clinical anti-infective treatment and hospital infection prevention.
Results
CR-ECC first emerged in 2020, and by 2022, a total of 32 isolates had been identified. Among the Enterobacteriaceae, CR-ECC ranks second in prevalence, only after Klebsiella pneumoniae and Escherichia coli. Sputum was the most common source of isolates, with 14 cases constituting 43.75% of the total, followed by blood at 25.00% and urine at 12.50%. Ascites and secretions contributed fewer isolates, with only 2 cases each. The majority of these isolates were from the Intensive Care Unit (ICU), accounting for 53.13% of the total. The 32 CR-ECC exhibited a 100% resistance rate to piperacillin/tazobactam, cefotaxime, and imipenem, and a 78.13% resistance to aztreonam. Resistance to tobramycin, ciprofloxacin, and levofloxacin was comparatively lower, yet remained near 60%. The rate of resistance to sulfamethoxazole/trimethoprim exceeded 10%, while the resistance to amikacin was a mere 3.13%. No isolates displayed resistance to tigecycline or colistin. The 32 CR-ECC that produced carbapenemase belonged to 8 different sequence types (STs). Prominently, 18 isolates were identified as ST171, and 8 as ST1077. The predominant carbapenemase genotype was NDM-1, with 18 ST171 isolates additionally producing the OXA-1 carbapenemase. Five plasmid replication types were identified, including Col(pHAD28), IncC, IncHI2/IncHI2A, IncM1, and IncX3, with Col(pHAD28) and IncC being the most prevalent. The distribution of plasmid replication types correlated with the ST types. Six virulence genes were detected, with fimA, csgD, and entB being the most frequent, identified in a total of 31 isolates. This was followed by mrkD (29) and icmf (23), and a single isolate was identified for fyuA.
Conclusions
The detection rate of CR-ECC has exhibited an increasing trend over the past five years, impacting the respiratory system and intensive care population. The accurate and timely identification of CR-ECC is a crucial step in enhancing hospital infection prevention measures. Tigacycline, colistin, and amikacin demonstrate significant antibacterial activity against CR-ECC, while aztreonam exhibits certain sensitivity specifically towards CR-ECC strains that produce metallo-β-lactamases. Integrating antimicrobial susceptibility tests with carbapenemase detection can provide supplementary evidence to guide clinical anti-infective therapy. The predominant strain of CR-ECC at the Fourth Hospital of Hebei Medical University is ST171, which produces the NDM-1/OXA-1 carbapenemase. This strain features a plasmid replication type of Col(pHAD28) and harbors virulence genes including fimA, csgD, entB, mrkD, and icmf. There are notable differences in the biological information among CR-ECC strains of various ST types.