Aerobic Gram Positive Rods (Non-Branching & Branching - Pt. 2

Overview:
- Listeria species are non-branching, gram-positive rods.
- Listeria monocytogenes is a non-sporulating gram-positive rod.
- Grows well on blood agar plates and chocolate agar.
Natural Habitat & Infection:
- Widespread in nature, primarily infects animals.
- Limited exposure to humans; primarily found in dairy products and processed meats.
Diseases Caused:
- In humans: can lead to stillbirth or neonatal death.
Transmission:
- Through contaminated foods, particularly for healthy individuals.
- Risky foods include cheese, ice cream, hot dogs, lunch meats, coleslaw, and chicken.
- Pregnant women exhibit mild flu-like symptoms but can have serious repercussions for the fetus, including premature labor or septic abortion.
Motility Identification:
- On direct wet mount: end-to-end tumbling appearance.
- In semi-solid media (such as MIL): umbrella-like motility seen.
Cold Enrichment Technique:
- Enhances recovery of Listeria monocytogenes due to its ability to grow at low temperatures.
- Specimen inoculated into nutrient broth and incubated in the fridge for several weeks to months.
Severe Infections:
- Occur in immunocompromised individuals and the elderly, leading to septicemia or meningitis.
Treatment:
- Antibiotics used include penicillin and aminoglycosides.

Overview:
- Non-branching, gram-positive rod, often causing zoonotic infections.
Infection Transmission:
- Typically from abrasion or puncture wounds, particularly from animal exposure.
- Common in individuals with occupational exposure (e.g., fish handlers).
Clinical Presentation:
- Causes skin infections, cellulitis, and erysipeloid formation.
- Erysipeloid: localized infection at the inoculation site, characterized by painful swelling on hands or fingers; typically self-limiting, healing in 3-4 weeks.
Microbiological Characteristics:
- Gram positive or gram variable rod, often appears as long filaments on gram stain.
- Colonies on blood agar are non-hemolytic and pinpoint after 24 hours.
- Grows well on blood agar and chocolate agar; requires CO₂ for growth.
Resistance:
- Resistant to salting, pickling, and smoking processes.
Environmental Presence:
- Survives in soil, water, and plant material.
Systemic Conditions:
- Septicemia association with endocarditis; diffuse cutaneous infections are uncommon.
Treatment:
- Penicillin is the recommended antibiotic.

Overview:
- Non-branching gram-positive rods, natural inhabitants of the vagina, mouth, and gastrointestinal tract.
Physiological Role:
- Maintain proper pH balance in vaginal secretions, producing an acidic environment that inhibits pathogenic bacterial growth.
- Present in probiotics.
Microscopical Appearance:
- Long-chained rods observed in gram stains.
Growth Characteristics:
- Grows well on sheep blood agar and chocolate agar; requires CO₂ enrichment.
- Often appears alpha-hemolytic on blood agar, resembling Streptococci in morphology.
Identification Steps:
- Colony morphology observation, gram stain morphology check, and catalase test (catalase negative).

Overview:
- Non-branching gram-positive rod, a natural inhabitant of the vagina.
Clinical Implications:
- Can lead to bacterial vaginosis (BV), characterized by increased vaginal discharge and a pH greater than 4.5.
Diagnostic Techniques:
- Wet mounts of vaginal fluid to identify clue cells: large epithelial cells with gram-variable coccobacilli along edges.
- Whiff Test: Adding potassium hydroxide to vaginal discharge; a positive result is indicated by a characteristic fishy odor, suggestive of BV.
Infection Risks:
- Infections are uncommon but can occur in postpartum endometritis, septic abortion, and associated with cesarean births.
Microscopical Appearance:
- Stains as gram-variable; appears as pinpoint and non-hemolytic on media, growing well on blood agar and chocolate agar, requiring CO₂ enrichment for optimal growth.

Overview:
- Includes Nocardia, Streptomyces, and Rhodococcus species, characterized by gram-positive properties with branching filamentous forms.
- Growth morphology varies with strains and media.
- Can be aerobic, facultative anaerobes, or obligate anaerobes.
Common Growth Attributes:
- May exhibit dry or mucoid colonies, and appearance may be wrinkled or adhered to the agar.
Acid-Fastness:
- Some organisms can be partially acid-fast, depending on the strain and culture conditions.

Overview:
- Gram-positive, branched, beaded rods that are aerobic and partially acid-fast.
Natural Habitat:
- Normal inhabitants of soil and water; involved in the decomposition of plant material.
Clinical Presentations:
- Infections commonly occur in immunocompromised patients; most notably Nocardia asteroides.
- Routes of infection include:
- Pulmonary: via inhalation of organisms from soil.
- Cutaneous: mycetomas (chronic localized infections), lymphocutaneous infections, skin abscesses, or cellulitis.
Microbiological Characteristics:
- Requires non-selective media, and growth may take 3-6 days.
- Modified Thayer Martin agar can enhance growth by inhibiting contaminants.
Staining Characteristics:
- Appears branched and beading in gram stain; partial acid-fastness indicates retention of the primary stain with weak acid decolorization.

Overview:
- Non acid-fast, large diverse group of gram-positive branching filamentous rods, typically found in soil.
Infection Risks:
- Acquired via trauma; seen particularly in immunocompromised individuals (e.g., HIV).
Clinical Presentations:
- Can lead to mycetoma infections of cutaneous tissue, resulting in swelling and draining sinuses.

Overview:
- Anaerobic gram-positive, branching and filamentous rods, leading to progressively invasive infections.
Common Infections:
- Mixed oral infections, abdominal infections, periodontal disease, soft tissue infections, and actinomycosis.

Overview:
- Found in soil; infections in humans are rare.
Infection Risks:
- Primarily seen in immunocompromised patients (e.g., AIDS).
- Lung infections account for approximately 80% of cases, often associated with contact with farm animals or fecal debris.