COVID-19, the illness that emerged in late 2019 and became a global pandemic, is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus. While SARS-CoV-2 is the direct cause, bacteria can still influence how the illness progresses.
Viruses Versus Bacteria
Bacteria are single-celled organisms with their own cellular structures, including a cell wall, DNA, and organelles. They carry out their own metabolic functions and reproduce independently through binary fission, where one cell divides into two.
Viruses, in contrast, are not considered living organisms because they lack the cellular machinery to reproduce on their own. They are much smaller than bacteria and consist of genetic material (DNA or RNA) encased within a protein shell called a capsid. To multiply, viruses must invade a living host cell and hijack its components to produce new viral particles.
Their distinct natures dictate how viruses and bacteria cause illness and are treated. Bacteria can cause harm, sometimes by producing toxic by-products. Bacterial infections are treated with antibiotics, which target bacterial structures or processes.
Viruses destroy host cells as they replicate and spread throughout the body. Antibiotics are ineffective against viruses because viruses lack the cellular structures that antibiotics target. Viral infections are often managed with supportive care to alleviate symptoms, or with antiviral medications designed to interfere with viral replication.
Bacterial Co-infections and Secondary Infections
While SARS-CoV-2 is a virus, bacteria can become relevant in COVID-19 cases through co-infections or secondary infections. A co-infection means simultaneous infection with SARS-CoV-2 and a bacterial pathogen. A secondary infection develops after the initial viral infection, often when the immune system is weakened or tissues are damaged.
COVID-19 can weaken the immune system, making individuals more susceptible to bacterial infections. Common bacterial infections observed in COVID-19 patients include pneumonia and bloodstream infections. For instance, Pseudomonas aeruginosa and Staphylococcus aureus can cause respiratory and skin infections, and are associated with hospital-acquired infections.
These bacterial infections can worsen patient outcomes. They can lead to more severe illness, prolonged hospitalization, and more complications. Such infections complicate treatment, requiring specific antibiotic interventions in addition to managing the viral illness.
Impact on the Body’s Bacterial Communities
COVID-19 and its associated treatments can impact the body’s natural bacterial communities, collectively known as the microbiome. The gut microbiota, a complex community of microorganisms residing in the digestive tract, is particularly susceptible. The SARS-CoV-2 virus can directly affect the gut microbiome, potentially through its interaction with the angiotensin-converting enzyme 2 (ACE2) receptor in the gut.
Studies show that COVID-19 patients often experience a reduction in overall bacterial diversity within their gut microbiome. This dysbiosis, or imbalance, can lead to a decrease in beneficial bacteria. Simultaneously, there can be an increase in opportunistic pathogens, bacteria that can become problematic when the immune system is compromised or the microbial balance is disturbed.
This disruption in the gut microbiota can have broader systemic consequences. It may contribute to a “leaky gut,” where increased intestinal permeability allows bacterial products and toxins to enter the bloodstream, exacerbating systemic inflammation. Alterations in the microbiome can also affect immune responses and have been linked to persistent gastrointestinal symptoms after COVID-19.
Antibiotic Use and Resistance
Antibiotics are ineffective against the SARS-CoV-2 virus itself, as COVID-19 is a viral infection. However, antibiotics have been frequently prescribed to COVID-19 patients, often due to concerns about bacterial co-infections or secondary infections, especially in hospitalized cases. For example, a high percentage of hospitalized COVID-19 patients received antibiotics.
The widespread and sometimes inappropriate use of antibiotics during the pandemic raises public health concerns, particularly regarding antimicrobial resistance (AMR). AMR occurs when bacteria, viruses, fungi, and parasites no longer respond to the medicines designed to kill them, making infections harder to treat. This natural process can be accelerated by the overuse or misuse of antimicrobial drugs.
When antibiotics are used unnecessarily, they do not benefit the viral infection and contribute to the spread of drug-resistant bacteria. This means common bacterial infections could become increasingly difficult or impossible to treat with existing medications. Using antibiotics only when a bacterial infection is suspected or confirmed is important to preserve their effectiveness for future use.