Prevalence of β-lactam antibiotic resistance of Escherichia coli isolated from a neonatal intensive care unit

Abstract

Introduction: Escherichia coli (E. coli) causes infections in neonates admitted to neonatal intensive care units (NICUs). Although β-lactam antibiotics are commonly used for neonatal infectious diseases, E. coli has exhibited resistance to them. Therefore, we investigated the resistance of E. coli strains isolated from a NICU to β-lactam antibiotics. Methods: E. coli isolates were collected from patients admitted to a NICU from 2020–2023. The clinical characteristics of the patients were analyzed. The antimicrobial susceptibility was determined using the agar dilution method, and the distribution of β-lactamase genes was analyzed using PCR. Conjugation experiments were conducted to analyze the horizontal transferability of resistance genes on plasmids. Genomic DNA was extracted for whole genome sequencing, construction of plasmid physical maps, locating resistance genes, and analyzing flanking regions and the resistance gene-related sequences. Results: Throughout the study period, 110 distinct E. coli strains were collected. Among these, 62 cases presented strains with high minimum inhibitory concentrations (MIC) associated with conditions such as ventilator-associated pneumonia (35/62), catheter-associated urinary tract infection (14/62), necrotizing enterocolitis (7/62), skin infection (1/62), and neonatal septicemia (5/62). Resistance of E. coli isolates to seven β-lactam antibiotics ranged from 2.73–56.36%. In 62 strains (56.36%, 62/110), six genotypes (11 sub-genotypes) of 111 β-lactamase genes were identified. Conjugation experiments revealed two transconjugants carrying the blaKPC-2 gene and two carrying the blaOXA-1 gene, exhibiting resistance to carbapenems and other β-lactams. The plasmids of four strains were successfully conjugated and transferred to recipient E. coli C600. PCR of the transconjugant resistance genes revealed that two carried a blaKPC-2 gene with a MIC increased up to 32-fold relative to the recipients, and the other two carried a blaOXA-1 gene with a 32-fold increased MIC. For isolate ECK03 carrying blaKPC-2, blaCTX-M-64, blaCTX-M-65, and blaTEM-1, sequencing results showed that blaKPC-2, blaCTX-M-64, and blaTEM-1 were harbored on a 114-kb pECK03_KPC-2 plasmid, whereas two identical blaCTX-M-64 genes were harbored in E. coli isolate ECF13. Conclusion: These findings highlight the existence of E. coli β-lactam resistance within NICU populations, emphasizing the need for continual monitoring of β-lactamase isolates to facilitate effective antibiotic selection.