Normal (formerly Propionibacterium avidum) is a gram-positive bacterium in human skin flora. It is commonly found in sebaceous bodily parts, including the face, scalp, and  

 upper chest. While it is generally considered a commensal bacterium, opportunistic pathogens can behave this way under certain circumstances. 

Epidemiological studies on Cutibacterium avidum are relatively limited compared to other bacteria, as its close relative has overshadowed it, Cutibacterium acnes (formerly known as Propionibacterium acnes), which is more extensively studied. However, here’s what is known about the epidemiology of Cutibacterium avidum: 

• Prevalence: Cutibacterium avidum is commonly found on human skin. It is estimated that around 90-100% of individuals carry this bacterium on their skin surfaces. 
• Body Sites: Cutibacterium avidum is predominantly found in sebaceous areas of the body. It colonizes areas with abundant sebaceous glands, including the face, scalp, chest, back, and upper arms. 
• Age and Gender: There are no significant differences in the prevalence of Cutibacterium avidum based on age or gender. It is found in individuals of all age groups and both sexes. 
• Pathogenicity: Cutibacterium avidum is a relatively less pathogenic bacterium than Cutibacterium acnes. However, it has been implicated in certain clinical conditions, such as prosthetic joint infections, osteomyelitis, and endocarditis, particularly in immunocompromised individuals or those with underlying medical conditions. 
• Antibiotic Resistance: Cutibacterium avidum is generally susceptible to commonly used antibiotics, including penicillins, macrolides, and tetracyclines. However, resistance to certain antibiotics, such as erythromycin and clindamycin, has been reported in clinical isolates. 

The bacterium belongs to the family Propionibacteriaceae. It is a part of the average human skin microbiota and can be found in various locations on the body, including sebaceous areas such as the face, chest, and back. 

Structure of Cutibacterium avidum: 

Cutibacterium avidum is a pleomorphic bacterium, meaning it can take on various shapes, including cocci (spherical), rods, and filaments. It is a non-spore-forming bacterium and lacks flagella for motility. The cell wall of Cutibacterium avidum consists of a peptidoglycan layer, which is responsible for its Gram-positive staining characteristics. 

Classification of Cutibacterium avidum: 

• Kingdom: Bacteria 
• Phylum: Actinobacteria 
• Class: Actinobacteria 
• Order: Propionibacteriales 
• Family: Propionibacteriaceae 
• Genus: Cutibacterium 
• Species: Cutibacterium avidum 

Cutibacterium was recently reclassified from the Propionibacterium genus, and Cutibacterium avidum was previously known as Propionibacterium avidum. This reclassification was based on genetic and phylogenetic studies. 

Cutibacterium avidum is one of several species within the Cutibacterium genus, including Cutibacterium acnes (formerly Propionibacterium acnes) and Cutibacterium granulosum (formerly Propionibacterium granulosum). These species share some similarities but have distinct characteristics and can play different roles in the human skin microbiome. 

there are four antigenic types of C. avidum based on their cell wall polysaccharides: A, B, C, and D. Type A is the most common and accounts for 75% of clinical isolates, followed by type B (15%), type C (5%), and type D (5%). The antigenic types are not related to the pathogenicity or antibiotic susceptibility of C. avidum. 

1. avidum is generally sensitive to a broad spectrum of antibiotics, such as β-lactams, fluoroquinolones, macrolides, and rifampin, although erythromycin and clindamycin resistance has been reported. Treatment of C. avidum infections may require surgical removal of infected devices or tissues in addition to antibiotic therapy.

 There are several antigenic types of Cutibacterium avidum unique antigenic determinant, cell wall antigens. These antigenic types include: 

• Type 1 antigenic type: This type is characterized by a unique antigenic determinant, a hexose sugar called raffinose. 
• Type 2 antigenic type: This type is characterized by a different antigenic determinant called cellobiose. 
• Type 3 antigenic type: This type is characterized by the absence of both raffinose and cellobiose and is the most common antigenic type of Cutibacterium avidum. 
• Type 4 antigenic type: This type is characterized by a different antigenic determinant called glucose. 
• Type 5 antigenic type: This type is characterized by, yet another antigenic determinant called mannose. 

Regarding antigenic types, Cutibacterium avidum could be better studied than other bacteria. The available information on antigenic types of Cutibacterium avidum is limited. However, it is known that Cutibacterium avidum possesses several surface antigens that can trigger immune responses. These antigens may vary among different strains or isolates of the bacterium. 

While Cutibacterium avidum is generally considered a commensal bacterium, meaning it usually coexists harmlessly with its human host, it has been implicated in certain clinical conditions. It has the potential to cause disease under certain circumstances. However, the pathogenesis of Cutibacterium avidum still has to be completely comprehended, and further study is needed to establish the specific mechanisms through which it causes illness. 

The following are some elements that might affect how Cutibacterium avidum develops into a pathogen: 

• Adhesion and colonization: Cutibacterium avidum possesses adhesion molecules on its surface, which enable it to adhere to the skin and colonize the sebaceous glands. This adherence is an essential initial step in establishing infection. 
• Sebum metabolism: Cutibacterium avidum can metabolize sebum, a lipid-rich substance produced by the sebaceous glands. This metabolism can produce various metabolic byproducts, such as fatty acids and lipases, which may affect skin inflammation and disease progression. 
• Immune evasion: Cutibacterium avidum can modulate the host immune response. It can produce enzymes, such as hyaluronidase, that may degrade components of the host immune system, impairing the immune response and allowing the bacterium to persist. 
• Biofilm formation: Cutibacterium avidum can form biofilms, complex communities of bacteria encased in a protective matrix. Biofilms provide a survival advantage to bacteria, making them more resistant to antimicrobial agents and immune defenses. Biofilm formation by Cutibacterium avidum may contribute to its persistence and chronicity in certain skin infections. 
• Role in acne: Cutibacterium avidum has been connected to acne, a widespread skin ailment that forms comedones (blackheads and whiteheads), pimples, and inflammatory lesions. It is believed that Cutibacterium avidum, along with other bacteria in the skin microbiota, contributes to the development of acne through a combination of factors, including sebum metabolism, inflammation, and immune responses. 

 The human body has several defense mechanisms that help protect against Cuavidum and other microorganisms. Here are some of the host defenses involved in combating Cutibacterium avidum: 

• Physical barrier: The skin acts as a physical barrier, preventing the entry of microorganisms into the body. Cutibacterium avidum typically resides in has been connected to acne, a widespread skin ailment. 
• Sebum production: Cutibacterium avidum thrives in sebaceous areas of the skin, where it can utilize sebum (skin oil) as a nutrient source. However, sebum production also plays a role in host defense. Sebum contains antimicrobial substances, such as fatty acids, that have antimicrobial properties and can help control the growth of Cutibacterium avidum. 
• Normal skin flora: The skin is home to a diverse community of microorganisms, including various beneficial bacteria. The presence of normal skin flora can inhibit the growth of potential pathogens, including Cutibacterium avidum, by competing for resources and producing antimicrobial substances. 
• Immune system response: The immune system plays a crucial role in recognizing and eliminating invading microorganisms. Cutibacterium avidum can trigger an immune response, activating the skin’s natural defenses, often maintaining control over the stratum corneum, the skin’s topmost layer.
  
• Antimicrobial peptides: The skin produces various antimicrobial peptides, such as defensins and cathelicidins, with broad-spectrum antimicrobial activity. These peptides can target Cutibacterium avidum and help control its growth. 
• Inflammatory response: Inflammation is a standard host defense mechanism in response to infection or tissue injury. It helps recruit immune cells to the site of infection and facilitates the clearance of pathogens, including Cutibacterium avidum. 

Clinical manifestations of Cutibacterium avidum infections can vary depending on the site of infection. Here are some possible manifestations: 

• Skin and Soft Tissue Infections: Cutibacterium avidum may lead to infections of the skin and soft tissues, including abscesses, cellulitis, and wound infections. These infections often present with redness, swelling, pain, and possibly discharge or pus formation. 
• Surgical Site Infections: v. This can result in delayed wound healing, persistent or recurrent infection, and may require further medical intervention. 
• Device-Related Infections: Cutibacterium avidum has been associated with infections related to medical devices like prosthetic joints, catheters, or shunts. These infections can cause local symptoms such as pain, inflammation, and discharge at the site of the device. 
• Bacteremia: Cutibacterium avidum can enter the bloodstream and cause bacteremia in rare cases. Bacteremia is the condition in which bacteria in the blood lead to systemic symptoms such as fever, chills, rapid heartbeat, and general malaise. 

 The diagnosis of Cutibacterium avidum infection typically involves a combination of clinical evaluation, laboratory tests, and microbiological culture: 

• Clinical Evaluation: The doctor will examine the affected area and take a detailed medical history to assess the symptoms and potential risk factors for infection. Cutibacterium avidum infections can manifest as skin conditions, including acne, folliculitis, abscesses, and postoperative wound infections. 
• Microbiological Culture: To definitively identify Cutibacterium avidum, a sample is collected from the affected area. Can be done by swabbing the skin, obtaining a pus sample, or collecting a tissue biopsy. Next, a lab receives the material to perform a culture examination. And the isolation of the bacteria. The culture helps confirm Cutibacterium avidum’s presence and rule out other potential pathogens. 
• Gram Staining: Gram staining is commonly performed on the cultured sample to determine the Gram reaction and the bacterial morphology of Cutibacterium avidum. It appears as gram-positive cocci or short rods. 
• Biochemical Testing: Further testing, such as biochemical assays, can be conducted to confirm the identity of the isolated bacteria as Cutibacterium avidum. These tests may include catalase testing, oxidase testing, and other specific biochemical reactions. 

Controlling Cutibacterium avidum involves maintaining good skin hygiene and adopting practices that promote a healthy skin microbiome. Here are some general tips for controlling this bacterium: 

• Regular cleansing: Wash your skin regularly using a mild cleaner to remove extra oil and debris from dead skin cells. However, avoid over-washing; it can strip away the natural oils and disrupt the skin’s balance. 
• Avoid harsh products: Avoid using harsh soaps, detergents, and cosmetics that can irritate the skin and disrupt its microbiome. Look for products labeled as non-comedogenic or suitable for sensitive skin. 
• Moisturize: Keep your skin moisturized to maintain its natural barrier function. Opt for non-comedogenic moisturizers that do not clog pores. 
• Avoid excessive oil: Minimize heavy oils and greasy products on your skin, as they can provide a favorable environment for Cutibacterium avidum to thrive. 
• Don’t pick or squeeze acne lesions: Picking or squeezing acne can introduce more bacteria into the skin and worsen inflammation. It can also lead to scarring. Instead, use over-the-counter acne treatments or consult a dermatologist for appropriate treatment options. 
• Maintain a healthy lifestyle: Eating balanced food, maintaining hydration, obtaining sufficient rest, and controlling stress levels can contribute to overall skin health. 
• Seek professional advice: If you are experiencing persistent or severe acne or other skin conditions, it is advisable to consult a dermatologist. They can offer tailored advice and treatment choices based on your specific needs. 

• Clinical and Biological Features of Cutibacterium (Formerly Propionibacterium) avidum, an Underrecognized Microorganism – PMC (nih.gov)  
• Cutibacterium avidum – microbewiki (kenyon.edu)