Immunology: Basic Clinical Microbiology 5

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Agents that cause human disease:

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1. Bacteria: prolaryote
2. Virus
3. Fungi: yeast & molds
4. Parasites: protozoa & helminths

*bacteria, fungi & parasites = cellular
*viruses are NOT cellular

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2 Fundemental Cell Types

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1. Eukaryotes: fungi & parasites
-true nucleus
-nuclear membrane & use mitotic apparatus
-organelles
-chitin (fungi)
-membrane contains sterols
-non motile

2. Prokaryotes: bacteria
-nucleoid: single circular DNA
-lack nuclear membrance & mit. apparatus
-cell wall (peptidoglycans)
-bacteria motile (flagella)
*virus = non cellular

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Classification of Bacteria Shape

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-Cocci (balls)
-Bacilli (rods)
-Spirochetes (spirals)
-Pleomorphic (varies from 3 basic shapes)

*arrangement also important:
-diplococci: cocci in pairs (pneumococcus)
-chains: streptococci
-grapelike cluster: staphylococci

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Size of Bacterial Cells

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-range from 0-2.5mm
-smallest bacteria = mycoplasma (~same size of largest virus Poxvirus)
-largest bacteria = bacillus (~same size of yeast (candida) and RBCs)

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Gram Stain

What stains:
Gram -
Gram +

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1. Crystal Violet (blue stain): stick to thick peptidoglycan layer of gram +)
2. Wash: water & iodine sol'n
-iodine forms complex w/ crystal violet (gram +)
3. Wash: water & decolorize w/ alcohol & acetone (extracts crystal violet from thin walled gram -)
4. Counterstain with Safranin (red dye)

Gram -: Safranin
Gram +: Crystal Violet

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Cell Wall

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-outermost component common to all bacteria (gram -/+)
*exception = mycoplasma
-multilayered structure located external to cytoplasmic membrane
-composed of inner peptidoglycan surrounded by an outer mem = capsule
-layer = repeating disaccharides w/ 4 aa in side chain extending from each
-aa chain covalently bind to other aa from neighbors (stable cross-linked structure

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Cell Wall of Gram +

Cell Wall of Gram -

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-much thicker
-Teichoic Acid: surface receptors only found in + = fibers of polysaccharides that act as surface Ag (serologic ID)

1. inner cytoplasmic mem lipid layer
2. periplasmic space: filled w/ gel containing proteins & enzymes called beta-lactamases (degrade antibiotics)
3. thin peptidoglycan layers (NO TEICHOIC ACID)
4. unique outer cell mem: LPS: contains lipid A

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LPS

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lipoplolysaccharide: only in gram -
-3 covalently linked components:
1. outer carb chain of 1-50 oligosaccharide unit (Ag determinates O-Ag)
2. center core polysaccharide
3. Lipid A (endotoxin): released in blood when gram - lysed & responsible for endotoxic fever & shock
-destruction of BV: acts as sythetic thromboplastin (starts blood clot pathway)

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Acid-Fast Bacteria

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-Mycobacteria (TB, MAI, Leprosy): unusual cell wall
-high [mycolic acids] in cell wall resist ecolorization w/ acid alcohol after being stained w/ carbofuchsin

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Capsule

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-protective gelatinous walls that surround cell mem of both gram -/+
-composed of simple sugar residues that are secreted by bacteria that coat outer wall
-enables bacteria to be more virulent bc macrophages & neutrophils unable to phagocytize capsule
-sugar component vary from 1 bacterium to anotther (serologic)
-these sugars used as Ag in certain vaccines (opsonization)

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2 Tests to Identify Capsule Bacteria:

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1. India Ink Stain: not taken up from capsule, stain goes up right next to capsule
-ID fungus cryptococcus (opportunistic)
-#1 cause of meningitis in aids patient
-tropism for 2 parts of body: lungs (pneumonia) & brain (meningitis)

2. Quelling Rxn: pneumococcus
-mixed w/ antiserum (Ab to capsule) & methylene blue = capsule will swell

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Flagella

Spirochetes

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-long, whip-like appendages that move bacteria towards nutrients: attracted to chemotaxis
-extend from cell mem of: Vibrio cholera (single) but E. Coli & Proteus mirabilis (peritrichous flagella) = UTIs
-shigella = NO flagella

-move by using axial filament: wraps around spiral-shaped cell to produce undulating motion

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Pili (Fimbrae)

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-straight hair-like filaments that extend from cell wall
-shorter than flagella
-found mostly on gram - organisms
-fxn as adherence factors (adhesins); vital to cause disease
-ex: N. gonorrhea (helps bind to cervical cells; stays longer)

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1. E. coli and Campylobacter jejuni

2. Bordetella pertussis

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1. cannot cause diarrhea w/o adhesion to bind to intestinal epithelium

2. uses adhesin to bind ti ciliated respiratory cells & cause whooping cough

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Glycocalyx (slime layer)

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-polysaccharide coating secreted by bacteria
-covers surface & allows bacteria to adhere firm to various structures (skin, heart valves, catheters)
-mediates adherance of strep mutans to surface of teeth, imp roles in form of dental plaque (precursor to caries)

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Endospores

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-highly resistant structures made in adverse conditions
-metabolically dormant forms resistant to heat, cold, drying, & chem agents
- once formed spores have no activity & can remain dormant for years
-they form when nutrients are depleted & form inside the cell & contains bacterial DNA
-resistance mediated by dipicolinic acid: Ca ion chelator

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2 Genera of medically important bacteria that produce Spores:

Precauations to rid of spores.

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1. Genus Bacillus (Anthrax)
2. Genus Clostridium (Tetanus, Gas Gangrene, Botulism)

Autoclave: heat surgical instruments, steam under pressure, 121 degrees for 15 minutes

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Exotoxins

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-released by few gram -
-released by all major gram +
**exception listeria monocytogenes: produce LPS
-

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Neurotoxins

Enterotoxins

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exotoxins that act on nerves or motor endplates to cause paralysis
-ex: tetanus & botulism

act on GI tract to cause diarrhea by inhibiting NaCl resorption, active NaCl secrete & kill intestinal epith cells = osmotic pull of fluid into intestines

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2 disease cause by enterotoxins

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1. Infectious diarrhea: colonize & bind to GI tract, relase enterotoxin
-ex: V. Cholera: most sig. large dose cause 30-40 bowel mvmts per day (rice water diarrhea: nothing in Gi tract)
-E. Coli, C. Jejuni, Shigella

2. Food Poisoning: bacteria grow in food, enterotoxin ingesting result in diarrhea & vomitting for less than 24 hrs (Staph aureus)

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Endotoxin

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LPS: only in gram -
*exception: gram + listeria
-very toxic, released when bacteria undergo lysis
-not a protein excreted from cells, rather normal part of outer mem of gram -

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Endotoxin

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LPS: only in gram -
*exception: gram + listeria
-very toxic, released when bacteria undergo lysis
-not a protein excreted from cells, rather normal part of outer mem of gram -

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Normal Flora

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-various bacteria & fungi permanent residents of certain body sites: esp the skin, oropharynx, colon, & vagina
-CNS, blood, lower bronchi/aveoli, liver, spleen, kidnes, & bladder (free from)
-can become opportunistic: ex-taph epidermidis(found on skin, if reaches can damage artifical heart valves)

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Normal Flora of Intestinal Tract

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in normal fasting ppl: stomach contains few organisms because of low pH & enzymes
-small intestines: strp, lactobcailli, yests, C. albicans (large # of organism found in terminal ileum)
-colon major location of bacteria
~20% of feces consists of bacteria

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Carrier

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-indiv. harbors a potential pathogen (source of infection for others)
-asymptomatic infection or recovered but continues to carry it

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Throat

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Viridans Step inhibits strp pyogens
Neisseria inhibits neisseria meningitis
staph epidermis inhiits staph aureus

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#1 microorg. of UTIs

Imp cause of peritonitis: perforation of intestinal wall

Imp. cause of both

Cuase of hospital acquired infections

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E coli

B fragilis

Streptococcus (enterococcus) faecalis

P. aeruginosa (present in 10% of normal stool)

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Strep Viridans

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-strep mutans: found in large # in dental plaque, precursor to caries
-leading cause of subacute bacterial endocarditis (can enter during time of dental surgery & attach to damage heart valves

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Anaerobic Bacteria

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bacteriodes, fusobacterium, clostridium, & peptostreptococcus found in gingical crevices
-O2 concentrations low
-if aspirated = lung abcesses

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Eikenella Corrodens

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gram -
-part of normal oral flora, causes skin & soft tissue infection assoc w/ human bites & clench fist injuries

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Normal Flora of GU tract

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-vaginal flora of women = lactobacillus
-responsible for produce acid that keep pH of vagina low
-before puberty & after menopause: estrogen low = lactobacilli rare & vagina pH high --> prevent growth of potential pathogens
-suppression by Antibiotics lead to overgrowth of C. albicans
-20-25% women of child-bear age carry Group B Stretococci in vagina: can cause spsis & meningitis of newborn during passage of birth canal
-urine can be contaminated w/ staph epidermis & coliforms
-area around urethras of women & uncirumsised males = mycobacterium smegmatis (acid-fast organism)