Antibiotic resistance significantly impacts surgeries and chemotherapy treatments by increasing the risk of infections that are difficult to treat. During surgery, patients are often given prophylactic antibiotics to prevent post-operative infections. However, the effectiveness of these antibiotics is compromised if bacteria are resistant, leading to higher rates of surgical site infections. Similarly, chemotherapy weakens the immune system, making patients more susceptible to infections. If these infections are caused by resistant bacteria, they become challenging to treat, potentially interrupting or complicating the course of chemotherapy. This necessitates a shift towards more aggressive and toxic treatment regimens, impacting patient recovery and healthcare outcomes.

Infections caused by antibiotic-resistant bacteria are more expensive to treat for several reasons. First, they often require the use of newer, more expensive antibiotics, which may have a narrower target range and are often reserved for severe cases. Second, these infections frequently necessitate longer treatment durations, increasing healthcare costs. Moreover, resistant infections often lead to complications, requiring additional medical interventions, extended hospital stays, and increased use of healthcare resources. Lastly, there is often a need for more intensive diagnostic testing to identify the specific type of resistance, further adding to the treatment costs.

Reversing antibiotic resistance in bacterial populations is theoretically possible but extremely challenging in practice. If the use of a specific antibiotic is significantly reduced or stopped, the selective pressure favouring resistant bacteria decreases. Over time, this could lead to a reduction in the proportion of resistant bacteria, as resistance mechanisms often incur a metabolic cost, potentially making resistant bacteria less competitive in the absence of antibiotics. However, this process is slow and complicated by the fact that bacteria can retain resistance genes for extended periods, even without antibiotic pressure. Additionally, the widespread nature of antibiotic use and resistance makes it difficult to effectively implement such measures on a large scale.

Biofilms, which are communities of bacteria living in a self-produced matrix of polysaccharides and proteins, play a significant role in antibiotic resistance. In biofilms, bacteria exhibit increased resistance due to multiple factors. The physical barrier of the biofilm matrix can impede the penetration of antibiotics. Additionally, bacteria in biofilms often have altered growth rates and metabolic states, which can reduce the efficacy of antibiotics that target actively dividing cells. The close proximity of cells within a biofilm also facilitates the transfer of resistance genes. As a result, infections involving biofilms are notoriously difficult to treat and are a major concern in clinical settings.

Bacteria can acquire antibiotic resistance genes from other bacteria through a process known as horizontal gene transfer (HGT). This occurs in three primary ways: conjugation, transformation, and transduction. Conjugation involves the direct transfer of DNA, usually plasmids, between bacteria through a structure called a pilus. Transformation is the uptake of free DNA fragments from the environment by a bacterial cell. Transduction happens when bacteriophages (viruses that infect bacteria) inadvertently carry genetic material from one bacterium to another. These processes enable bacteria to rapidly acquire and spread resistance genes, even between different species, significantly contributing to the spread of antibiotic resistance.