MICROBIO 3.5 - GRAM + RODS (BACILLI)

Gram-Positive Bacteria Overview

• Gram-positive bacteria are categorized based on shape into bacilli (rods), cocci (spheres), and branching filaments.

Bacillus

• Gram-positive Bacilli are Aerobic or Anaerobic.
• Aerobic species include Listeria, Bacillus, and Corynebacterium.
• Anaerobic species include Clostridium.

Bacillus Overview

• Bacillus species typically appear as single rods, paired rods, or chains of rods.
• Most Bacillus species are motile with flagella, with B. anthracis as an exception.
• B. anthracis is non-hemolytic, its name meaning "charcoal."
• B. cereus exhibits beta-hemolysis and is described as "wax-like."

Bacillus Anthracis

• Non-motile Bacillus anthracis is typically found in soil and animal products.
• The capsule is made of polypeptide w/D-glutamic acid
• Exotoxins produced include Edema toxin and Lethal toxin.
• Treatment includes Ciprofloxacin/doxycycline plus antitoxins.
• Virulence factors include a unique capsule that evades phagocytosis and exotoxins, edema, and lethal.
• The unique capsule is made of D-glutamic acid
• The exotoxins are edema (EF) and lethal (LF).
• Edema factor increases intracellular cyclic adenosine monophosphate (cAMP).
• Lethal factor is a protease that activates mitogen-activated protein kinases (MAPK).
• B subunit- protective antigen(PA) that binds to host cells.
• A subunit- combines with PA to form active toxins.
• Treatment for Anthrax includes vaccine (where endemic), US military mandatory and Fluoroquinolone (Ciprofloxacin) PLUS antitoxins.

Types of Anthrax

• Cutaneous anthrax is the most common and least dangerous form, often sourced from animals or IV drugs.
• Inhalation anthrax is the most lethal form.
• Gastrointestinal anthrax affects the upper and lower gastrointestinal tract, causing lesions and ulcers.
• Cutaneous anthrax shows a necrotic eschar and edema.
• Inhalation anthrax early symptoms are nonspecific, including fever, cough, and myalgias, late symptoms show mediastinal lymph node enlargement, edema, and respiratory failure.
• Gastrointestinal anthrax shows upper lymphadenopathy and lower ulcerative lesions.

Bacillus Cereus

• Mobile and Beta-hemolytic Bacillus Cereus is common, environmentally ubiquitous
• Symptoms of Bacillus Cereus contracted from food poisoning include emetic and diarrheal forms.
• Emetic form sources from rice with heat-stable toxins with symptoms like Nausea, abdominal cramps, vomiting with quick incubation.
• Diarrheal form sources from meat and vegetables caused by heat-labile enterotoxin with symptoms like Nausea, abdominal cramps, watery diarrhea and longer incubation.
• Ocular infection and severe pneumonia are less common
• Ocular infection is treated with Clindamycin/Vancomycin.

Corynebacterium Diphtheriae

• "Coryne" means club, and the bacteria shows club-shaped formations arranged in L or V shapes.
• Non-spore-forming and non-motile
• Airborne transmission and human-to-human spread
• Colonizes oropharynx/skin of asymptomatic carriers.
• Virulence factor is diphtheria toxin where Genes for toxins are introduced via lysogenic bacteriophages and Inactivates host cell protein synthesis.
• A subunit stops cell protein synthesis.
• B subunit is a binding domain a + translocation domain
• Binding domain binds heart & nerve cells.
• Translocation region facilitates toxin entry.
• Prevention: Vaccination (DPT) and RX: Antitoxin test for hypersensitivity
• Respiratory Diphtheria symptoms are Fever, Sore throat, and Adenopathy.
• Microbiology shows Club-shaped; "L" or "V" formations with Volutin (polyphosphate) granules and Stains Metachromatically.
• Complications include airway obstruction, myocarditis and cranial neuropathies.

Listeria Monocytogenes

• Listeria monocytogenes is a facultative intracellular anaerobe that doesn't form spores and has unique tumbling motility.
• It grows easily in cold temperatures.
• Listeriosis is caused by Listeria monocytogenes.
• Symptoms include Febrile gastroenteritis & meningitis.
• Particularly dangerous for immunocompromised, pregnant women, & elderly
• Outbreaks associated with dairy products & deli meats.
• High mortality rate from meningitis.
• No vaccine available; prevention is difficult.
• Symptoms in healthy adults include flu-like symptoms.
• Symptoms in immunocompromised adults include Meningitis,
• Causes neonate death, organ damage, Meningitis
• Virulence factors are Internalin A, Internalin B, Listeriolysin O, Actin assembly-inducing protein.
• Internalin A finds receptors on host enterocytes
• Internalin B finds receptors on host endothelial cells, fibroblasts, & enterocytes,
• Listeriolysin O helps escape from vacuoles. Microbial evasion of the phagolysosome to the cytosol
• Actin assembly-inducing protein (ActA) facilitates intra- & intercellular movement via "comet tails"
• Listeriosis pathogenesis includes; Ingestion of L. monocytogenes-contaminated foods, Internalins facilitate entry into enterocytes in GI tract, Actin tails/ActA push bacteria out of enterocytes & into macrophages, where replication occurs
• Parasitized macrophages disseminate bacteria throughout body and can cross the blood-brain barrier leading to meningitis,
• Invasive infections are treatable with β-Lactam (e.g. ampicillin) and Aminoglycoside (gentamicin).

Clostridium Overview

• Clostridium species are rapidly growing and obligate anaerobes, surviving in intestinal tracts, sewage, water, and soil.
• Spore-forming bacteria, with spores being dormant and highly resistant cells preserving genetic material, typically forming in times of extreme stress.
• Chemical disinfectants do not kill spores only sterilization with high heat/pressure can kill bacteria and spores.
• Motile
• Includes C. difficile, C. tetani, C. perfringens, and C. botulinum.

Clostridium Difficile

• Also known as C. diff
• Virulence factors: Toxin A attracts neutrophils and releases cytokines, increasing intestinal wall permeability and Toxin B destroys cytoskeletal integrity.
• Causes pseudomembranous colitis, where yellowish-white exudate forms on the colon's mucosal surface.
• Treated with Metronidazole or vancomycin (glycopeptide).
• A relapse after colitis is treated with fecal transfer.

Clostridium Tetani

• Clostridium tetani, also known as Tetanus, has a distinctive tennis-racket shape during spore formation.
• Virulence factor is Tetanospasmin, a heat-labile neurotoxin that blocks inhibitory neurotransmitters
• Causes Neuronal excitatory activity to be upregulated
• Causes Tetanolysin, oxygen-labile hemolysin.
• Spastic paralysis is a "tetanic triad" with includes lockjaw (trismus), grimace (risus sardonicus), and extreme back extension (opisthotonos).
• Local tetanus manifests as a persistent spasm localized around an area of injury.
• Cephalic tetanus affects cranial nerves (rare, but more likely to cause death).
• Maternal/neonatal tetanus arises specifically during medical or spontaneous abortion and delivery, spreading from the umbilical stump (if the mother wasn't immunized).
• Treatment involves wound debridement, metronidazole & antitoxins.
• Prevention involves a tetanus vaccine.

Clostridium Botulinum

• Clostridium botulinum, also known as Botulism
• One of its virulence factors is a Botulinum Exotoxin A-G- this is a "Miracle poison"
• A, B, and E are the most common human infections
• Spores enter canned goods and produce toxins.
• Neurotoxins are absorbed in the gut.
• These block of acetylcholine release at peripheral motor junctions
• Symptoms include Bulbar palsy, difficulty swallowing, weak jaw & face, and progressive loss of speech/weak tongue.
• Also causes Descending flaccid paralysis, respiratory failure death, wound botulism in high IV drug users, and infant botulism (floppy baby syndrome.)
• Treatment involves metronidazole or penicillin, and antitoxins, respiratory support, gastric irrigation
• Prevention involves boiling home-canned goods for 5+ minutes, discarding damaged/bulging cans, and not giving infants honey

Clostridium Perfringens

• Virulence factors: Alpha toxins
• Alpha toxins cause hemolysis, vascular leakage, liver toxicity, & cardiac dysfunction
• Enterotoxins (superantigen) alter intestinal membrane permeability in good poisoning.
• Soft tissue infections (cellulitis, fasciitis, myositis, myonecrosis)
• Myonecrosis (gas gangrene)- LIFE THREATENING disease that destroys muscle tissues.
• Bacterial metabolic activity produces gas bubbles which appear purpleish-black bulges under the skin
• Treatment consists of tissue debridement & penicillin or clindamycin requiring ~1/5 amputation
• Food poisoning-abdominal cramps, watery diarrhea without fever or vomiting
• Treatment- usually self-limiting; rehydration therapy
• Prevent properly storing & heating food before eating.

Gram Positive Filamentous Rods

• Gram Positive Filamentous Rods consists of Actinomyces Israelii and Nocardia Spp.

Actinomyces Israelii

• It Is anaerobic slow growth, low virulence
• Common colonizers of the oral cavity & resp. Tracts
• Invades deeper tissues after oral trauma/surgery
• Colonies have "sulfur granules" - Bacteria + Calcium phosphate form "molar-like" colonies
• Prevention through proper oral hygiene and prophylactic antibiotics.
• Treatment through Rx: Drainage/surgical debridement + Penicillin.
• Leads to: Granulomatous lesions, abscesses w/"sulfur granules" in pus and Cytopathology: "dust bunnies"

Nocardia Spp.

• Nocardia Spp. is weakly acid-fast, delicate beads, aerobic, and catalase-positive
• It is a Slow growth bacteria
• Source: Soil
• Immunocompromised
• Virulence Factors leads to = Evasion of Phagocytic Destruction Via ROS protection and Survival & Replicate w/in Macrophages
• Treatment with Trimethoprim-sulfamethoxazole and amikacin or Trimethoprim-sulfamethoxazole with imipenem/cephalosporin
• Most common as Pulmonary Diseases where Abscesses and necrosis develop occur- and Can disseminate from lungs.
• Also can cause CNS inections and Cutaneous infections