Microbiology: Gram Positive Bacilli Flashcards
1
Q
Commensal bacteria of the skin
A
- Propionibacterium (+B, An)
- Corynebacterium (+B, Ae)
- Staphylococcus epidermidis (+C, Ae)
2
Q
Commensal bacteria of the vagina
A
-Lactobacillus (+B, An)
3
Q
Commensal bacteria of the oropharynx
A
- Streptococcus (+C, Ae)
- Haemophilus (-B, Ae)
- Prevotella (-B, An)
- Veillonella (-C, An)
- Corynebacterium (+B, Ae)
4
Q
Commensal bacteria of the GI
A
-Bacteroides (-B, An)
5
Q
Pathogenesis of gram positive bacilli
A
- GP do not produce endotoxins
- Virulence factors can be acquired by plasmids or phage infection
- Pathology from L immune evasion, toxin production, and secondary host response
- Virulence factors: adhesins, exotoxins, exonzs, lysins
6
Q
Exotoxins of GP bacilli
A
- Expressed by both GP and GN bacilli
- Responsible for most of the pathogenic effects of a given species
- Can be either binary or non-binary
- Are not needed for growth
7
Q
Binary toxins
A
- Expressed by GP and GN bacilli (acquired extrachromally, by phage or plasmid)
- Have 2 domains, an A (activity) and B (binding)
- B domain directs the toxin to a specific cell type by binding to the cell surface receptor
- The A toxin then enters the cell to perform its function (often is ADP-ribosylating cellular targets)
- The two domains can be encoded on the same gene or different genes
- Cholera (-B) binary toxin inhibits Gs (GTP hydrolysis) pathway and activates AC
- Diptheria (+B) binary toxin inhibits protein synthesis through ADP-ribosylation of eEF2
8
Q
Diphtheria pathogenesis
A
- Spread from person contact of Corynebacterium diptheriae (aerobic), with expression of diphtheria toxin (binary toxin)
- This is normally found in oropharynx, pathogenic strains are infected w/ phage to express the toxin
- Infection of tonsils and pharynx and is characterized by formation of a pseudomembrane, where the toxin is absorbed into the blood
- Symptoms include malaise, sore throat, anorexia, fever
- W/o Rx toxin can lead to prostration (extremely weak), rapid pulse, pallor, coma and death
- Complications include myocarditis, neuritis (paralysis), respiratory insufficiency
9
Q
Diphtheria diagnosis (Dx)
A
- Based on clinical presentation (begin therapy w/o confirmatory cultures)
- Identification is based on cultures: growth on Loeffler medium and variable gram staining of club-shaped bacilli
- Is a reportable disease
10
Q
Listeriosis
A
- Caused by listeria monocytogenese, which is in soil and water and contaminates food products
- Not infective to healthy adults but are to immunocompromised (IC), elderly, pregnant women, young children
- Not killed by pasteurization, aerobic
11
Q
Pathogenesis of Listeriosis
A
- Grow intracellularly, produce LLO exotoxin (important for bacterial release from cells)
- Is capable of cell-cell transfer
- Internalin proteins allow entry into epithelia, uses the cell’s actin to move and “rockets” its way to neighboring cells (acquiring a double membrane)
- Manifests in neonates by disseminated abscesses and granulomas early on
- Later manifestation in neonates are meningitis or meningoencephalitis with sepsis
- In susceptible adults symptoms are usually meningitis or acute febrile gastroenteritis
- 20% mortality rate if untreated
12
Q
Dx of listeriosis
A
- Cultures of blood and CSF (GP coccobacilli)
- Reportable disease
13
Q
Sporulation
A
- Occurs in bacillus (GP aerobe) and clostridium (GP anaerobe) species
- Normally grow thing (vegetative) cells begin sporulation after receiving signals from the environment
- Spores have a complete copy of the genome, metabolically inert, resistant to most things
- Germinate in presence of moisture and nutrients
14
Q
Bacillus Anthracis life cycle
A
- High untreated mortality (90-100%) of anthrax is due to its life cycle
- Spores are the primary infectious agent depending on site of entry (cutaneous, GI, inhalation) but all forms of infection are life-threatening
- Spores are phagocytosed and germinate in phagosomes of macrophages
- Bacteria replicate intracellularly and are released after lysis of cell
- They can escape immune system due to capsule
- Exotoxin is produced at onset of bacteremia and is responsible for major pathogenic effects
15
Q
B. Anthracis exotoxin
A
- 2 types of binary toxins that share a same B domain (called PA, protective Ag)
- EF (edema factor) or LF (lethal factor) are the possible A domains for PA
- PA binds to cell membrane receptor and is cleaved by a protease, resulting in PA heptamerization (PA7) followed by binding of either LF or EF
- Receptors for PA are TEM8 and CMG2 (ATRX1/2)
- Once LF or EF bind to PA7, they are delivered into the cell
- EF is an AC, leading to increased cAMP production (PKA), water efflux, loss of water homeostasis and cell death
- LF is a Zn protease, w/ specificity for MAPK kinase1. Destruction of MAPK renders cell incapable of signal transduction. Leads to cell cycle disruption and cell death
- LF has highest toxicity in cardiac/smooth muscle. EF has highest toxicity in liver
- Used as bioweapon b/c: spores are effective dispersant, exotoxin has high lethality
