Microbiology: Gram Positive Bacilli Flashcards Preview

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Flashcards in Microbiology: Gram Positive Bacilli Deck (18):

Commensal bacteria of the skin

-Propionibacterium (+B, An)
-Corynebacterium (+B, Ae)
-Staphylococcus epidermidis (+C, Ae)


Commensal bacteria of the vagina

-Lactobacillus (+B, An)


Commensal bacteria of the oropharynx

-Streptococcus (+C, Ae)
-Haemophilus (-B, Ae)
-Prevotella (-B, An)
-Veillonella (-C, An)
-Corynebacterium (+B, Ae)


Commensal bacteria of the GI

-Bacteroides (-B, An)


Pathogenesis of gram positive bacilli

-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


Exotoxins of GP bacilli

-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


Binary toxins

-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


Diphtheria pathogenesis

-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


Diphtheria diagnosis (Dx)

-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



-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


Pathogenesis of Listeriosis

-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


Dx of listeriosis

-Cultures of blood and CSF (GP coccobacilli)
-Reportable disease



-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


Bacillus Anthracis life cycle

-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


B. Anthracis exotoxin

-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


Bacillus Cereus

-Aerobic, widely found in soil and environment, often spread through contaminated food (causing gastroenteritis)
-Can also infect penetrating wounds to the body (usually to eye)
-GI irritation can be of early form ( emetic, or food poisoning) and late form (diarrheal)
-Can become septic in IC patients


B Cereus emetic disease

-Symptoms are abdominal pain/discomfort, nausea, vomiting. These appear quickly (1-8 hrs) and resolve in a day
-Usually due to improperly cooked foods
-Bacteria contamination of foods leads to enterotoxin secretion, and subsequent toxin contamination of the food (pre-formed toxins)
-These enterotoxins are heat-stable and are not destroyed upon cooking, therefore killing the bacteria with cooking will still lead to intoxication and irritation of upper GI


B Cereus diarrheal disease

-Takes up to 24 hrs to appear, due to bacterial outgrowth in lower GI (from vegetative cells and spores)
-Symptoms are abdominal discomfort (pain/cramps) and diarrhea
-Absence of vomiting is noteworthy
-Growth of cells in colon leads to localized enterotoxin production, causing the diarrhea