Tigecycline Resistance: A Unique Approach
Tigecycline, a glycylcycline antibiotic, combats bacterial resistance through mechanisms distinct from older tetracyclines [1]. While both classes of drugs target the bacterial ribosome to inhibit protein synthesis, tigecycline's chemical structure allows it to overcome common tetracycline resistance pathways [2].
How Does Tigecycline Inhibit Bacterial Growth?
Tigecycline binds to the 30S ribosomal subunit, preventing the entry of aminoacyl-tRNA into the A site of the ribosome [3]. This binding event disrupts the translation process, thereby inhibiting bacterial protein synthesis and leading to cell death [3].
What Resistance Mechanisms Do Other Tetracyclines Face?
Older tetracyclines primarily rely on two mechanisms to inhibit bacterial growth: blocking tRNA binding to the ribosome and preventing ribosomal translocation [4]. However, bacteria have evolved ways to circumvent these actions. The most common resistance mechanisms involve efflux pumps that actively transport tetracyclines out of the bacterial cell, and ribosomal protection proteins that bind to the ribosome and dislodge the tetracycline, allowing protein synthesis to continue [4].
How Does Tigecycline Evade Common Resistance Mechanisms?
Tigecycline's structural modifications enable it to evade these primary resistance mechanisms [2].
Efflux Pumps and Tigecycline
While efflux pumps are a major challenge for older tetracyclines, tigecycline is generally a poor substrate for many of these efflux systems [5]. This means that bacteria that have developed resistance to tetracyclines via increased efflux pump activity may still be susceptible to tigecycline [5].
Ribosomal Protection and Tigecycline
Tigecycline's binding to the ribosome is stronger and less easily disrupted by ribosomal protection proteins compared to older tetracyclines [2][6]. This enhanced binding affinity allows tigecycline to maintain its inhibitory effect even in the presence of these proteins, which are a key mechanism of resistance against other tetracyclines [6].
Can Bacteria Become Resistant to Tigecycline?
Despite its advantages, resistance to tigecycline can emerge. This often involves mutations in genes related to the bacterial cell envelope, such as those affecting the expression of efflux pumps or porins, which can reduce intracellular tigecycline accumulation [7]. Overexpression of specific efflux pumps, like TetA and TetK, has also been implicated in tigecycline resistance in some bacterial species [7]. Additionally, modifications to the 16S rRNA binding site on the ribosome can also confer resistance [6].
Sources
1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3974084/
2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7804568/
3. https://www.nejm.org/doi/full/10.1056/NEJMra062059
4. https://pubmed.ncbi.nlm.nih.gov/17452956/
5. https://www.sciencedirect.com/science/article/pii/S147330990670367X
6. https://pubmed.ncbi.nlm.nih.gov/16081246/
7. https://www.ajicjournal.org/article/S0196-6553%2807%2900496-0/fulltext