Microbiology Final 2 Tahani

Introduction to Microbiology

• Lecture 20 covers pathogens like non-spore-forming Gram-positive rods (aerobic and anaerobic) and anaerobic gram-positive cocci.

Overview of Gram Positive Species

• Gram-positive species are categorized into rods and cocci, with spore-formers and non-spore-formers.
• Facultative anaerobes, as well as aerobic and anaerobic, are included.
• Specific examples of bacteria are listed, including Corynebacterium, Actinomyces, Propionibacterium, Lactobacillus, Bacillus, Clostridium, Bifidobacterium, Eubacterium, Micrococcus, Staphylococcus, Streptococcus, Gemella, and Peptostreptococcus.
• Important characteristics like catalase-positive/negative are noted for various species.

Overview of Bacteria

• Charts and diagrams visually illustrate the taxonomy of Gram-positive bacteria.
• Key characteristics such as motility, hemolysis, and antibiotic susceptibility are noted in the figures.
• Staphylococcus, Streptococcus, Corynebacterium, Clostridium, Listeria, and Bacillus are all separately presented, highlighting their distinguishing features.

Actinomyces

• Actinomyces are facultatively anaerobic or strictly anaerobic gram-positive rods.
• They grow slowly in culture and often cause chronic, slowly developing infections.
• Infections typically occur in the upper respiratory tract, gastrointestinal tract, and female genital tracts.
• Infections are usually endogenous, rather than communicable.
• They typically form filamentous forms or hyphae, resembling fungi in appearance.
• Common locations of infection include cervicofacial areas following dental procedures or oral trauma.
• Actinomycosis is the name given to the disease.
• Diagnosis, symptoms (including sinus tracts), and treatment are discussed in the context of disease management.

Nocardia

• Nocardia are strict aerobic rods that form branched filaments in tissues and culture.
• Distinguishable by their weakly acid-fast properties.
• Infections are generally exogenous, meaning caused by organisms that are not typically part of the normal human flora.
• Nocardia infections are commonly found in individuals with weakened immune systems.
• A key feature of Nocardia is a combination of aerial hyphae and acid-fastness, crucial for identification.
• This organism can cause severe infections (e.g., bronchopulmonary disease) following inhalation and occurs almost exclusively in immunocompromised patients.
• Nocardia is more commonly found in soil with high organic matter content, and more cases occur in the context of immunocompromised patients.

Lactobacillus

• Lactobacillus species are facultatively anaerobic or strictly anaerobic rods.
• They ferment to produce lactic acid.
• Commonly part of the normal flora in the mouth, stomach, intestines, and genitourinary tract, especially in the female genital tract.
• Rarely cause infections; indeed, some forms are used in probiotics and starter cultures for yogurt, cheese, sauerkraut, etc.
• Lactobacillus species can sometimes cause bacteremia or more severe conditions such as endocarditis in immunocompromised patients.

Propionibacterium

• Propionibacterium are small gram-positive rods.
• Found on skin, conjunctiva, external ear, and oropharynx, and female genital tract.
• The primary species is Propionibacterium acnes.
• Plays a role in acne pathogenesis and opportunistic infections in patients with prosthetic devices or intravascular lines.
• P. acnes colonization of the skin is necessary but not sufficient for the development of acne vulgaris, suggesting additional factors are critical for the expression of the disease.

Mobiluncus, Bifidobacterium, and Eubacterium

• Mobiluncus, Bifidobacterium, and Eubacterium are commonly found in areas like the oropharynx, large intestine, and vagina.
• Mobiluncus sometimes shows up in women with bacterial vaginosis, and is often an incidental finding.
• Mobiluncus have a gram variable or gram negative profile.
• Bifidobacterium and Eubacterium are commonly found in the oropharynx, intestine, and vagina.
• They are normally considered relatively benign contaminants of human specimens.

Non-spore-forming Aerobic Gram-Positive Rods

• This group includes Listeria monocytogenes, Corynebacterium diphtheriae, and others.
• Some are significant human pathogens (e.g., Listeria). Others include pathogens that commonly infect animals and can sometimes cause disease in humans (e.g. Erysipelothrix rhusiopathiae).
• Some are opportunistic pathogens (e.g., Corynebacterium jeikeium) and commonly affect people with weakened immune systems.

Listeria monocytogenes

• Listeria monocytogenes are short, non-branching, and gram-positive bacteria.
• Motile at room temperature but less motile at 37 degrees Celsius.
• Produces beta-hemolysis on sheep blood agar.
• A common cause of infection with a primary source being contaminated food leading to Foodborne Listeriosis.
• Pathogen can be transmitted from mother to child in utero.
• Most affected patient populations include neonates, the elderly, pregnant women, and others with weakened immune systems.
• It is a facultative intracellular pathogen.
• Key virulence mechanisms involve interacting with host cells via proteins, penetrating and multiplying within cells, and avoiding immune responses.

Corynebacterium diphtheriae

• Corynebacterium diphtheriae are irregularly staining, pleomorphic rods which are aerobic or facultatively anaerobic.
• They are ubiquitous in plants, animals, and humans.
• The primary virulence factor is diphtheria toxin (an A-B exotoxin).
• This toxin inhibits protein synthesis in host cells.
• Human-to-human transmission is the only known reservoir for the organism, typically via respiratory droplets and skin contact, and disease presentation begins with malaise and sore throat.

Anaerobic Gram-Positive Cocci

• Anaerobic gram-positive cocci are commonly found in the oral cavity, gastrointestinal tract, genitourinary tract, and skin.
• Infections typically happen when the bacteria spread from these locations to normally sterile regions within the body.
• Peptostreptococcus species are frequently found in subcutaneous abscesses, soft tissue infections, and diabetic foot ulcers, but also cause chronic infections with other pathogens.
• Often, infections with many Peptostreptococcus species are synergistic with other organisms.

Further Reading

• Recommended reading material includes Murray - Medical Microbiology 8th Edition, Section 4: Bacteriology, Chapter 21, and Chapter 31.

Test your knowledge about Actinomyces and related bacteria with this quiz. Explore key characteristics of infections they cause and identify true statements related to this genus. Perfect for microbiology students and professionals seeking to enhance their understanding of clinical specimens.