Phenotypic and Genotypic Characterisation of AmpC-Producing SPICE Organisms from Clinical Isolates in a Tertiary Care Center

Abstract

Background: AmpC Beta -lactamases are a major resistance mechanism in Gram-negative bacteria, especially SPICE organisms (Serratia, Pseudomonas, Indole-positive Proteus, Citrobacter, and Enterobacter species). Their inducible nature and resistance to cephalosporins complicate treatment, while detection remains challenging. This study aimed to characterize AmpC producers using phenotypic and genotypic methods.
Methods: A prospective observational study was conducted at Saveetha Medical College from August 2024 to January 2025. Fifty non-duplicate SPICE isolates from pus, urine, blood, and respiratory samples were included. Cefoxitin screening followed by the cefoxitin-cloxacillin double-disc synergy test was used for phenotypic detection. Multiplex PCR targeting six AmpC genes (blaDHA, blaACT, blaACC, blaCMY, blaCIT, blaFOX) was performed.
Results: Of 50 isolates, 11 (22%) were AmpC producers. PCR identified blaCMY (45.5%) as the most common gene, followed by blaDHA (27.3%) and blaCIT (18.2%). Three isolates showed phenotypic positivity but no amplification, suggesting uncommon variants. Pseudomonas aeruginosa was the predominant isolate, with pus as the main specimen source (60%).
Conclusion: AmpC producers were detected in 22% of SPICE isolates, with blaCMY being most prevalent. Combining phenotypic and genotypic methods enhances detection accuracy and supports appropriate antimicrobial stewardship

DOI: https://doi.org/10.24321/0019.5138.202635

How to cite this article:
Pyenthamizh, Bhaumik N, Lavanya. Phenotypic and Genotypic Characterisation of AmpC-Producing Spice Organisms From Clinical Isolates in a Tertiary Care Center. J Commun Dis. 2026;58(2):105-111.