Other Gram Positives

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Only bacterium with capsule composed of protein (poly D glutamic acid)

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Bacillus anthracis (anthrax)

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Most anthrax is ____________

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cutaneous

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Characteristics of Bacillus

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Diverse group of gram-positives forming bacilli. Classified as aerobic/facultative anaerobe. Spores are extremely tolerant to environmental stressors.

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Plasmids that encode virulence factors and capsule for bacillus anthracis

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PX01 and PX02

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What does the exotoxin released by B. anthracis do in cutaneous infections?

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Causes localized tissue necrosis, evidenced by a painless round black lesion with a rim of edema (malignant pustule)

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Cause of pulmonary anthrax

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Inhaled spores travel to lymph nodes and following 1-60day incubation, mediastinal hemorrhagic necrosis of lymph nodes leads to severe systemic infection.

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Plasmid pX01 codes for exotoxin containing 3 proteins that together produce systemic effects of anthrax. What are they?

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1) Edema factor (EF): active subunit with adenylate cyclase activity - causes edema, impairs neutrophils

2) Protective antigen (PA) - promotes entry of EF into phagocytic cells

3) Lethal factor (LF): zinc metalloprotease that inactivates MAPKKs. Stimulates macrophage to release TNFalpha and IL1β

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What does plasmid pX02 encode?

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Three genes necessary for synthesis of poly-glutamyl capsule that inhibits phagocytosis of bacteria

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Treatment of anthrax

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Ciprofloxacin or doxycycline

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Bacillus cereus: what diseases does it cause

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Food poisoning/intoxication (not infection). Generally self-limiting and over within 24 hours.

Also causes endophthalmitis

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Two forms of Bacillus cereus

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1) Short incubation emetic form: 1-6 hours after ingestion causes nausea and vomiting

2) Long-incubation diarrheal form (8-16 hours)

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Two types of toxin Bacillus cereus secretes

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1) Heat labile
2) heat stabile

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Heat-labile toxin of B. cereus: disease characteristics

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Nausea, abdominal pain, diarrhea. Lasts 12-24 hours. Longer incubation period.

Similar to enterotoxin of cholera (increased adenylyl cyclase)

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Heat-stable toxin of B.cereus:disease characteristics

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Caused by Cereulide, an emetic toxin.

Clinical syndrome similar to S. aureus food poisoining. Short incubation period (1-5 hours) followed by severe nausea and vomiting (limited diarrhea)

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Treatment for B. cereus food poisoning.

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No treatment (no antibiotics) because sickness is due to enterotoxin (preformed).

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Clostridium is (an/aerobic)

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anaerobic

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How can Clostridium be differentiated from Bacillus?

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Anaerobic culture (Clostridium is anaerobic, Bacillus is aerobic)

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Treatment for Clostridium Botulinum poisoning

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antitoxin (can only neutralize unbound free neurotoxin).

Penicillin

Hyperbaric O2

Supportive therapy, including respirator if needed.

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Infantile botulism associated with consumption of what food?

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Honey

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organism responsible for antibiotic associated pseudomembranous colitis (diarrhea)

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Clostridium difficile

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T/F Corynebacterium and listeria form spores

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F

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pathogen responsible for diphtheria

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Corynebacterium diphtheriae

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Main cause of human disease in listeria genus

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Listeria monocytogenes

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T/F listeria can grow at low temperatures (refrigerator temps)

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T.

This is one of the ways it's used to culture - cold inhibits growth of other bacteria.

Especially hardy for a non spore-former.

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Major virulence factor of listeria

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Listeriolysin O (LLO)

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What is the Listeriosis "list?"

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Pregnant women, neonates, meningitis in elderly and immunocompromised

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When does listeria infection in pregnancy occur and why?

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usually 3d trimester when cell-mediated immunity decreases

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How is Listeria acquired?

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Ingestion of contaminated foods (infected coleslaw, milk, cheese, butter, deli meats)

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Characteristics of most listeria infections

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Fever, general flulike syndrome

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treatment of listeria

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ampicillin and penicillin, trimethoprim-sulfamethoxazole

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T/F Antibiotics are given to treat all listeria patients

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False. Just pregnant women, infants, elderly, immunocompromized

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A dry scab or slough formed on the skin as a result of a burn or by the action of a corrosive or caustic substance.

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eschar

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endophthalmitis etiological agent

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Bacillus cereus

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T/F Listeria is an intracellular pathogen

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T. It's a cytosolic intracellular. It hijacks the host cytoskeleton to promote intracellular motility (actin comets)

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What is the cholesterol-dependent hemolysin necessary for escape from phagocytic vacuole

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Listeriolysin (LLO)

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Phospholipases help with listeria's escape from
primary and especially secondary vacuole. What are they?

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PI-PLC (aka PlcA). Degrades glycosyl-PI (GPI) anchors of euk. membrane proteins

PC-PLC (aka PlcB): promotes escape from 2ndary vacuole. In epithelial cells can allow escape from primary vacuole in absence of LLO)

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Form distinctive clumps known as "Chinese letter" but are non-branching

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Coryneforms/Diphtheroids

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Diphtheria: signs and symptoms

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Presents generally in children as low-grade fever with local inflammation of nasopharynx, followed by formation of characteristics adherent membrane over the throat and tonsils which can vary in color from blue-white to black.

Absorption of toxin leads to labored breathing, rapid heartbeat, coma and death in 6-10 days.

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Diphtheria: Treatment

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antibiotic therapy (Penicillin G or erythromycin) combined with diphtheria antitoxin therapy

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Diagnostic tests for diphtheria (mnemonic)

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potassium TELLURITE agar, Loeffler's coagulated blood serum.

TELL UR InTErn not to LOAF (loeffler's) around

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How do diphtheria vaccines work?

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prevent the ADP-ribosylation of "diphthamide" amino acid in host EF-2 that would inhibit translation and lead to host cell death

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What is major virulence factor of C. diphtheriae?

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Diphtehria toxin causes ADP-ribosylation of diphthamide (modified histamine) amino acid in host Elongation Factor-2 that causes inhibition of translation --> death of cell by apoptosis

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transcriptional repressor of gene expression

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DtxR

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Classic diphtheria sign

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pseudomembrane on throat/nasopharynx (thicker than Strep throat)