Clostridioides difficile Infection: Diagnosis and Treatment Challenges

Abstract

Clostridioides difficile is the most important cause of healthcare-associated diarrhea in the United States. The high incidence and recurrence rates of C. difficile infection (CDI), associated with high morbidity and mortality, pose a public health challenge. Although antibiotics targeting C. difficile bacteria are the first treatment choice, antibiotics also disrupt the indigenous gut flora and, therefore, create an environment that is favorable for recurrent CDI. The challenge of treating CDI is further exacerbated by the rise of antibiotic-resistant strains of C. difficile, placing it among the top five most urgent antibiotic resistance threats in the USA. The evolution of antibiotic resistance in C. difficile involves the acquisition of new resistance mechanisms, which can be shared among various bacterial species and different C. difficile strains within clinical and community settings. This review provides a summary of commonly used diagnostic tests and antibiotic treatment strategies for CDI. In addition, it discusses antibiotic treatment and its resistance mechanisms. This review aims to enhance our current understanding and pinpoint knowledge gaps in antimicrobial resistance mechanisms in C. difficile, with an emphasis on CDI therapies.

Keywords: Clostridioides difficile infection; cell cytotoxicity neutralization assay; drug-resistant pathogen; enzyme immunoassays; host immunity; nucleic acid amplification testing; recurrent C. difficile infection.

Figure 1

The diagram depicts the mechanisms by which C. difficile develops resistance to commonly utilized antibiotics in the treatment of CDI, encompassing vancomycin, metronidazole, fidaxomicin and rifamycins. (I) Vancomycin functions by tightly binding to the D-Ala-D-Ala C-terminus of uracil diphosphate-N-acetylmuramyl-pentapeptide, impeding the transglycosylation reaction responsible for incorporating late precursors into the developing peptidoglycan chain. This action inhibits the synthesis of the bacterial cell wall. Resistance to vancomycin in C. difficile is linked to mutations in the VanS_CD sensor histidine kinase and VanR_CD response regulator of the vanG operon-like gene cluster, vanG_CD. These mutations modify peptidoglycan precursors, altering the vancomycin binding site and contributing to the emergence of vancomycin resistance in C. difficile. (II) An additional mechanism contributing to vancomycin resistance is associated with a point mutation in MurG N acetylglucosaminyltransferase. This mutation impacts the conversion of peptidoglycan precursor lipid I to lipid II, a crucial step in bacterial cell wall synthesis. (III) Fidaxomicin exerts its bactericidal effects by inhibiting bacterial RNA polymerase, thereby disrupting transcription and subsequent protein synthesis. Resistance to fidaxomicin in C. difficile has been linked to induced mutations in the RNA polymerase subunit-β (rpoB). In contrast, rifamycins hinder bacterial RNA synthesis by binding to the β subunit of RNA polymerase, RpoB, at a distinct site and step of RNA synthesis compared to fidaxomicin. Rifamycin resistance is associated with mutations in the rifamycin resistance-determining region of rpoB, identified in clinical isolates of C. difficile. (IV) Metronidazole induces DNA strand breakage and cytotoxicity, leading to bacterial cell death. Resistance in C. difficile to Metronidazole may arise through mechanisms that impede the formation of the active drug form, potentially mediated by multigenetic processes associated with oxidoreductive and iron-dependent metabolic pathways.