Answer :
A bacterial strain not susceptible to any tested antibiotics likely indicates antibiotic resistance, which can be intrinsic or acquired through genetic changes. This resistance necessitates antimicrobial susceptibility testing to identify effective treatments.
If a tested bacterial strain was not susceptible to any of the tested antibiotics, this might indicate a case of antibiotic resistance. This resistance occurs when bacteria evolve mechanisms to withstand the effects of antibiotics that are intended to kill them or inhibit their growth.
The lack of susceptibility could suggest intrinsic resistance, where the bacteria naturally possess genes that confer resistance, or acquired resistance, which can occur through various mechanisms such as mutation, transformation, and conjugation.
For instance, Gram-negative bacteria are intrinsically resistant to vancomycin due to their outer membrane that prevents the antibiotic from penetrating.
Moreover, overuse or misuse of antibiotics can lead to the selection of resistant strains, making infections harder to treat. This phenomenon has led to serious public health concerns, exemplified by multidrug-resistant organisms like MRSA (Methicillin-resistant Staphylococcus aureus).
Therefore, antimicrobial susceptibility tests (AST) are conducted in clinical settings to identify effective antibiotics for treating infections, which is crucial in prescribing the correct medication that the bacteria have not developed resistance against.
