In a world where bacteria are often associated with sickness and infection, it is crucial to recognize that not all of them are harmful. Our bodies are hosts to trillions of beneficial bacteria which contribute significantly to our health [1]. While many of these organisms reside in the gut, they also play vital roles in various other areas of our bodies.

The human gut is a diverse ecosystem comprising bacteria, viruses, fungi, and other microorganisms. This complex community, known as the gut microbiome, is highly unique to each individual and plays a fundamental role in our health [2]. Among the microorganisms in the gut, bacteria are prominent and can be “good” and/or “bad”, depending on the context or their environment. It is important to note that there is large variability from person-to-person, but for simplicity, we will refer to “good” and “bad” bacteria as organisms that help us or make us sick, respectively.  

“Good” bacteria are essential for maintaining a balanced gut microbiome. These microorganisms offer numerous benefits, including aiding in digestion, supporting the immune system, and promoting gut health [3]. These days, many people promote a healthy gut microbiome by ingesting probiotics, as highlighted in our previous article. 

One example of how “good” bacteria support our health relates to the absorption of nutrients and vitamins, for example by synthesizing vitamin B12, which is an essential factor for human health [4]. Vitamin B12, also known as cobalamin, is a water-soluble compound that plays a fundamental role in several key functions, such as the production of red blood cells, neurological function, and DNA synthesis [5]. Unlike many other vitamins, our bodies cannot produce vitamin B12 on their own. Instead, we rely on dietary sources and the activity of certain bacteria in our gut to obtain an adequate supply. Specific bacterial strains, including Bifidobacterium, Lactobacillus, Enterococcus, and Propionibacterium, contribute to the production of this factor [6]. They convert vitamin analogs found in animal-based foods into active, absorbable forms that our bodies can utilize. Therefore, in the absence of an animal-based diet, supplements are often recommended.

Beyond the gut, beneficial bacteria have a significant presence in various areas of our bodies, each playing a unique role in promoting our health. Some “good” bacteria, such as Lactobacillus reuteri and Streptococcus salivarius, reside in the oral cavity [7-9]. There, they play a crucial role in maintaining oral health by competing with “bad” bacteria for nutrients and colonization space or by producing lactic acid, thus inhibiting their growth. Therefore, they reduce the risk of dental cavities, gum disease, and bad breath [7]. Other “good” bacteria have essential roles in supporting the health of our body’s largest organ, the skin. One such example is Cutibacterium acnes, which contributes to the preservation of our skin’s protective barrier. This bacterium resides in the sebaceous glands and hair follicles and can be associated with acne when overgrown, for example during puberty when sebum production increases [8]. However, under normal conditions, the C. acnes plays a role in maintaining healthy skin by preventing the colonization of harmful or “bad” bacteria and modulating skin inflammation [9,10]. “Good” bacteria are also crucial for vaginal health. Bifidobacterium infantis and various Lactobacillus species are found in the vaginal tract [11,12]. They contribute to vaginal health by producing lactic acid, maintaining a low pH, and thereby preventing the overgrowth of harmful microorganisms. 

“Good” and “bad” bacteria exist in our microbiome in a delicate equilibrium, the disruption of which can cause health issues, for example, when “bad” bacteria overgrow. Staphylococcus epidermidis, a common “good” bacterial species found on our skin, prevents the colonization of harmful pathogens by occupying ecological niches on the skin, similar to C. acnes mentioned previously. However, the related bacterium, Staphylococcus aureus, causes “staph” on the face [13]. We also previously mentioned the beneficial mechanisms of Streptococcus salivarius, however, its close relative, Streptococcus pyogenes, can cause infections like strep throat, tonsillitis, or even more severe complications [14,15]. The presence of “good” bacteria is crucial to prevent overgrowths of these “bad” bacteria and safeguard our well-being. 

Maintaining a healthy microbiome ensures that “good” bacteria support various bodily functions and help maintain our vitality. So, the next time you think about bacteria, remember that not all of them are harmful; some are “good” and are essential to our health throughout the body.