Plasmid-mediated AmpC in Klebsiella pneumoniae and Escherichia coli from septicaemic neonates: diversity, transmission and phenotypic detection.

Objectives: Presence and dissemination of plasmid-mediated AmpC genes (pAmpCs) have made bacteria cephalosporin-resistant and assessment of their prevalence and diversity is essential. Coexistence of pAmpCs with New Delhi metallo-β-lactamase (bla) has facilitated their spread and NDM interferes with correct pAmpC phenotypic identification.

Methods: Assessment of pAmpCs in different species and sequence types (STs), co-transmission with bla and phenotypic detection were analysed among Klebsiella pneumoniae (n = 256) and Escherichia coli (n = 92) isolated from septicaemic neonates over 13 years.

Results: pAmpCs were present in 9% (30/348) of strains, 5% in K. pneumoniae and 18% in E. coli. pAmpC genes (bla and bla) were detected, bla and bla variants being predominant. Strains were resistant to most antimicrobials tested. bla and bla were dominant among E. coli (14/17) and K. pneumoniae (9/13), respectively. pAmpC-bearing strains belonged to diverse STs, including epidemic K. pneumoniae ST11 and ST147. Some strains co-harboured carbapenemase genes, bla (17/30) and bla (5/30). In 40% (12/30) of strains, pAmpC genes were transferred by conjugation, of which 8/12 exhibited co-transfer with bla. pAmpCs were frequently found in replicons as follows: bla with IncHIB-M, bla with IncA/C, bla with IncA/C, and bla with IncFII. The combination disk-diffusion test correctly detected pAmpC in 77% (23/30) of pAmpC-bearing strains. However, correct detection of pAmpC was higher in strains that did not harbour bla vs. those with bla (85% vs. 71%).

Conclusion: Presence of pAmpCs along with carbapenemases, linkage with multiple STs, and replicon types indicated their potential for spread. pAmpCs can go undetected in the presence of bla; hence, regular surveillance is required.