Gemella morbillorum -Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes

Gemella morbillorum -Introduction, Morphology, Pathogenicity, Lab Diagnosis, Treatment, Prevention, and Keynotes


Gemella morbillorum” is a species within the genus Gemella, which is part of the natural flora of the human body, particularly in the oral cavity and upper respiratory tract. Here are some key points about this bacterium:

  1. Gram-Positive Cocci: Like other members of the Gemella genus, it is a gram-positive bacterium, meaning it retains the crystal violet stain used in Gram staining and appears purple under a microscope.
  2. Habitat: It is commonly found in the human mouth and throat and is usually harmless in these locations.
  3. Opportunistic Pathogen: Although typically non-pathogenic, Gemella morbillorum can cause infections in certain situations, especially in individuals with compromised immune systems or underlying health conditions.
  4. Infections Caused: It has been associated with various infections, including infective endocarditis (an infection of the inner lining of the heart), bacteremia (presence of bacteria in the blood), and infections in other body sites, particularly following dental procedures or in patients with prosthetic devices.
  5. Diagnosis and Treatment: Diagnosis typically involves culturing the bacteria from clinical samples and identifying it using biochemical tests. Treatment usually includes antibiotics, with the specific choice guided by the susceptibility profile of the isolate.
  6. Morphology: Under the microscope, it appears as small, round cocci, often in pairs or short chains.


The morphology of “Gemella morbillorum,” a species of bacteria commonly found in the human oral cavity and upper respiratory tract, is characterized by several distinct features:

  1. Shape: It is a cocci, meaning it has a spherical shape. This is typical of many bacteria that are part of the normal flora in the human body.
  2. Arrangement: Under the microscope, these bacteria often appear in pairs or short chains. This arrangement can help differentiate them from other cocci in microbiological analysis.
  3. Gram Stain Reaction: As a gram-positive bacterium, Gemella morbillorum retains the crystal violet stain during the Gram staining process, appearing purple or blue under a microscope. This is indicative of a thick peptidoglycan layer in its cell wall.
  4. Size: The cocci are generally small, usually around 0.5 to 1.0 micrometers in diameter.
  5. Non-Motility: These bacteria are non-motile, meaning they do not have the capability to move independently.


Gemella morbillorum, although typically a part of the normal human flora, can act as an opportunistic pathogen under certain conditions. This means it has the potential to cause disease primarily in individuals with compromised immune systems or other predisposing factors. Here’s an overview of its pathogenicity:

  1. Infective Endocarditis: One of the most significant infections associated with Gemella morbillorum is infective endocarditis, an infection of the inner lining of the heart, particularly affecting the heart valves. It has been reported in medical literature as a causative agent in some cases of endocarditis, especially in patients with pre-existing heart conditions or prosthetic heart valves.
  2. Bacteremia: It can also cause bacteremia, which is the presence of bacteria in the bloodstream. This can occur following dental procedures or other situations where the bacteria might enter the bloodstream.
  3. Other Infections: In addition to endocarditis and bacteremia, Gemella morbillorum has been implicated in various other types of infections, such as septic arthritis (infection in the joints), meningitis, and infections of the respiratory tract, though these are less common.
  4. Virulence Factors: The specific virulence factors of Gemella morbillorum are not as well characterized as in more aggressive pathogens. However, like many opportunistic bacteria, its ability to cause disease is often related to the host’s immune status and the presence of predisposing factors.
  5. Diagnosis and Treatment Challenges: Infections caused by G. morbillorum can be challenging to diagnose due to the bacterium’s slow growth and similarities to other more common pathogens. Treatment typically involves antibiotics, but the exact regimen can vary based on the site of infection and antibiotic susceptibility testing results.
  6. Opportunistic Nature: It’s important to note that while it is a part of normal human flora and does not usually cause disease in healthy individuals, it can be a significant pathogen in vulnerable populations, such as those with compromised immune systems, underlying heart disease, or after invasive procedures.

Lab Diagnosis

The laboratory diagnosis of Gemella morbillorum infections involves several steps that are typical for identifying and characterizing bacterial pathogens. Here’s an overview of the process:

  1. Sample Collection: Appropriate clinical specimens are collected depending on the suspected site of infection. This could include blood samples for bacteremia or endocarditis, joint fluid for septic arthritis, or cerebrospinal fluid for meningitis.
  2. Gram Staining: It is a Gram-positive bacterium. In a Gram stain test, it appears as purple or blue spherical cells (cocci), often in pairs or short chains.
  3. Culture: The samples are cultured on standard bacteriological media. G. morbillorum grows well on blood agar and chocolate agar. It is a facultative anaerobe, so it can grow under both aerobic and anaerobic conditions. The colonies are typically small to medium-sized, non-hemolytic, and may have a smooth, glistening appearance.
  4. Biochemical Identification: Gemella morbillorum is catalase-negative and usually negative for oxidase. It can be differentiated from other Gram-positive cocci like Streptococci and Staphylococci using additional biochemical tests. Typical identification tests include bile solubility and PYR tests, where it usually shows negative results.
  5. Molecular Techniques: For more precise identification, molecular techniques such as polymerase chain reaction (PCR) and sequencing (like 16S rRNA gene sequencing) can be used. These methods are particularly helpful when conventional culture and biochemical methods are inconclusive.
  6. Antibiotic Susceptibility Testing: Once Gemella morbillorum is identified, testing its susceptibility to various antibiotics is crucial to guide effective treatment.
  7. Interpretation of Results: The identification of G. morbillorum must be interpreted in the context of the clinical presentation. Since it is part of the normal flora, its presence must be correlated with clinical signs and symptoms to confirm its role as a pathogen.


The treatment of infections caused by Gemella morbillorum typically involves antibiotic therapy, with the specific regimen tailored based on the type and severity of the infection, as well as the patient’s overall health and antibiotic susceptibility of the bacterium. Key points regarding the treatment include:

  1. Antibiotic Therapy: It is generally susceptible to a range of antibiotics. Common choices include:
    • Penicillin and Penicillin Derivatives: These are often the first line of treatment, especially for serious infections like endocarditis.
    • Cephalosporins: May be used, especially in patients who are allergic to penicillin.
    • Vancomycin: Useful in treating patients with penicillin allergies or in cases of resistant strains.
    • Macrolides and Clindamycin: Can also be effective, depending on the antibiotic susceptibility profile.
  2. Culture and Sensitivity Testing: It’s crucial to perform culture and sensitivity testing to determine the most effective antibiotic, as resistance patterns can vary.
  3. Duration of Treatment: The length of antibiotic therapy can vary. For instance, treating endocarditis may require prolonged antibiotic therapy for several weeks.
  4. Management of Underlying Conditions: Addressing any predisposing factors, such as underlying heart conditions or compromised immune systems, is an important aspect of treatment.
  5. Surgical Intervention: In some cases of infective endocarditis, particularly when there are complications like heart valve damage, surgical intervention might be necessary alongside antibiotic treatment.
  6. Monitoring and Follow-up: Regular monitoring during and after treatment is essential to ensure the effectiveness of the therapy and to manage any potential side effects.


Preventing infections caused by Gemella morbillorum, like other opportunistic pathogens, primarily involves maintaining good general health and specific preventive measures for at-risk individuals. Here are some strategies:

  1. Good Oral and Dental Hygiene: Regular dental check-ups and good oral hygiene practices, such as brushing and flossing, are crucial. This reduces the risk of oral bacterial infections that could potentially spread.
  2. Prophylactic Antibiotics for High-Risk Procedures: Individuals with a history of cardiac issues or prosthetic heart valves may require prophylactic antibiotics before undergoing dental or surgical procedures that have a risk of introducing bacteria into the bloodstream.
  3. Manage Underlying Health Conditions: Effectively managing any chronic conditions, especially those that affect the immune system, can help reduce the risk of opportunistic infections.
  4. Sterile Techniques in Medical Settings: Proper insertion and maintenance of intravenous lines and catheters using sterile techniques can minimize the risk of bloodstream infections.
  5. Infection Control Practices: In healthcare settings, strict adherence to infection control practices, such as hand hygiene and proper sterilization of instruments, is essential to prevent the spread of infections.
  6. Awareness and Education: Being informed about the risks and transmission methods of opportunistic pathogens is important, especially for healthcare providers and individuals with pre-existing health conditions.


Gemella morbillorum is a notable species within the Gemella genus, primarily recognized for its role as an opportunistic pathogen in certain clinical contexts. Here are some keynotes about this bacterium:

  1. Natural Habitat: It is part of the normal flora in the human oral cavity and upper respiratory tract.
  2. Morphology: It is a Gram-positive cocci, often appearing in pairs or short chains under a microscope.
  3. Pathogenic Potential: While typically harmless as part of the normal flora, it can cause opportunistic infections, particularly in individuals with underlying health conditions or compromised immune systems.
  4. Infective Endocarditis: One of the most significant clinical associations of Gemella morbillorum is its role in infective endocarditis, especially in patients with pre-existing cardiac conditions or prosthetic heart valves.
  5. Other Infections: It can also be implicated in other infections, such as bacteremia, septic arthritis, and occasionally meningitis.
  6. Diagnosis: Laboratory diagnosis involves culturing the bacterium from clinical specimens, followed by Gram staining and biochemical testing.
  7. Antibiotic Treatment: Treatment typically involves antibiotics, with the regimen based on susceptibility testing due to variability in resistance patterns.
  8. Prevention Strategies: Preventive measures include maintaining good oral hygiene, prophylactic antibiotics for high-risk individuals undergoing certain medical or dental procedures, and managing underlying health conditions effectively.
  9. Healthcare Awareness: Awareness and proper infection control practices in healthcare settings are important to prevent nosocomial infections.

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