Emerging Threats in Citrobacter Nosocomial  Infections: Mechanisms of Virulence and  Resistance

Ramya  Ramadoss; Balasubramanian  Moovarkumudalvan; Divya  Lakshmanan; Pradeep   J; Bilal  M I; Suresh Kumar  Saravanan

Ramya Ramadoss Mahatma Gandhi Medical Advanced Research Institute, MGMARI, Sri Balaji Vidyapeeth, Deemed to be University, Puducherry, India
Balasubramanian Moovarkumudalvan Mahatma Gandhi Medical Advanced Research Institute, MGMARI, Sri Balaji Vidyapeeth, Deemed to be University, Puducherry, India
Divya Lakshmanan Mahatma Gandhi Medical Advanced Research Institute, MGMARI, Sri Balaji Vidyapeeth, Deemed to be University, Puducherry, India
Pradeep J Mahatma Gandhi Medical Advanced Research Institute, MGMARI, Sri Balaji Vidyapeeth, Deemed to be University, Puducherry, India
Bilal M I Mahatma Gandhi Medical Advanced Research Institute, MGMARI, Sri Balaji Vidyapeeth, Deemed to be University, Puducherry, India
Suresh Kumar Saravanan Mahatma Gandhi Medical Advanced Research Institute, MGMARI, Sri Balaji Vidyapeeth, Deemed to be University, Puducherry, India

Keywords: Nosocomial infections, Opportunistic pathogens, Citrobacter, Antimicrobial resistance, Carbapenemase

Abstract

Citrobacter species, especially Citrobacter freundii, have emerged as important nosocomial pathogens over the past decade. Rising rates of multidrug resistance (including extended-spectrum beta-lactamases (ESBLs) and carbapenemases) and documented hospital outbreaks have heightened clinical concern. This review consolidates recent literature on the aspects of epidemiology, clinical manifestations, virulence and resistance mechanisms in hospital-acquired Citrobacter infections. Most Citrobacter infections are nosocomial infections,
with urinary tract, bloodstream, and intra-abdominal infections being predominant. Citrobacter species possess multiple virulence factors like adhesins, fimbriae, biofilm capability and Type VI secretion systems
(T6SS), that facilitate colonisation, persistence and host interaction. Intrinsic chromosomal AmpC beta-lactamases and increasing acquisition of plasmid-mediated ESBLs and carbapenemases along with tripartite efflux pumps drive the emergence of multidrug-resistant (MDR) phenotypes. Environmental reservoirs for Citrobacter species and mobile genetic elements increase nosocomial transmission. Therapeutic management is increasingly challenging with emergence of newer beta -lactam/beta-lactamase inhibitor combinations. Siderophore cephalosporins could be potential inhibitors for carbapenemase-producing isolates, though interpretation of susceptibility testing remains essential. Effective nosocomial infection prevention requires strict adherence to hand hygiene, intubation device care, decontamination of hospital environment, and antimicrobial stewardship. Despite growing awareness, substantial knowledge gaps persist, particularly regarding molecular mechanisms behind virulence, optimal treatment pathways to reduce resistant infections,
and cost-effective surveillance strategies. Citrobacter species is an emerging opportunistic pathogen with a dual challenge of virulence and resistance. This emphasizes the urgency to prioritize genomic surveillance, diagnostics and stewardship-informed therapies to address the clinical and public health impact.
Keywords: Nosocomial infections, Opportunistic pathogens, Citrobacter, Antimicrobial resistance, Carbapenemase

DOI: https://doi.org/10.24321/0019.5138.202640

How to cite this article:
Ramadoss R, Moovarkumudalvan B, Lakshmanan D, Pradeep J, Bilal M I, Saravanan S K. Emerging Threats in Citrobacter Nosocomial Infections: Mechanisms of Virulence and Resistance. J Commun Dis. 2026;58(2):143-151.

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