Microbiology

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What is the gram staining process?

1. Crystal violet dye plus iodine stains all bacterial cell walls
2. Alcohol extracts blue dye from lipid rich, thin-walled gram-negative bacteria
3. Red dye counterstains decolorized gram-negative bacteria

Describe gram-positive bacteria

-Rich in peptidoglycan
-retain violet dye

Describe gram-negative bacteria

-Poor in peptidoglycan
-counterstain with red dye

What is Ziehl Neelson stain used for?

Acid fast bacteria (red)

What is India ink stains used for?

Cryptococcus

What is Geimsa stain used for?

Blood smears

What is PAS used for?

Glycogen, mucopolysaccharides

What is Prussian blue stain used for?

Iron

What is Congo red stain used for?

Amyloid

What is osmic acid stain used for?

Electron microscopy

normal flora of the skin?

Staphylococcus epidermis

Potential skin pathogens?

Staphylococcus aureus

Normal flora of the nasopharynx?

Streptococcus viridans, anaerobes

Potential pathogens of the nasopharynx?

S.pneumoniae
N.meningitidis
H.influenzae

Normal flora of the mouth?

Streptococcus viridans

Potential pathogens of the mouth?

Candida albicans

Normal flora of the colon?

E. coli

Potential pathogens of the colon?

B.fragilis, enterococci

Normal flora of the vagina?

Lactobacillus
streptococci

Potential pathogens of the vagina?

Candida albicans

Composes the inner layer of the cell wall of all bacteria?

Peptidoglycan
-thick in gram-positive
-thin in gram-negative
-exception = Mycoplasma

Techoic acid forms the outer layer of the cell wall of which type of bacteria?

Gram-positive

Lipopolysaccharide forms the outer layer of the cell wall of what type of bacteria?

Gram-negative
-outer cell membrane = lipid bilayer
-also contains porins

What is special about mycobacteria cell walls?

Contain mycolic acid

What is special about Mycoplasma cell walls?

-It has no cell wall; membrane only
-only bacterium whose membrane contains cholesterol

Does penicillin work against Mycoplasma pneumonia?

No, penicillin attacks peptidoglycan and there are none

How are exotoxin neutralized?

By antibodys

What type of bacteria produce exotoxins?

Both gram-positive and gram-negative bacteria

What type of bacteria produce endotoxins?

gram-negative only

Endotoxins

-lipopolysaccharides
-nonspecific
-TNF, IL-1 → shock, fever
-poor antigen
-heat-stable

exotoxins

-Polypeptides
-specific
-toxoid used as vaccines
-usually heat labile

Which toxin is responsible for blocking the release of lysine leading to muscle spasms?

Tetanus toxin

Which toxin is responsible for blocking the release of acetylcholine leading to muscle paralysis?

Botulinum toxin

Which toxin inhibits protein synthesis by ADP ribosylation of EF-2?

Diphtheria toxin

Which toxin causes hemoloysis, necrosis, and cell death?

Alpha toxin → staph aureus

Which bacteria is responsible for toxic shock syndrome toxin?

Staph aureus → induces cytokine that produce anaphylactic shock

Which toxin stimulates adenylate cyclase activating GS protein?

Cholera toxin

Which toxin stimulates adenylate cyclase inhibiting GI protein?

Pertussis toxin

What does the heat-stable E. coli enterotoxin do?

Stimulates at guanylate cyclase

Obligate aerobes

M tuberculosis
pseudomonas aeruginosa
nocardia

Microaerophilic bacteria

campylobacter jejuni
Brucella abortus

Obligate anaerobic bacteria

Clostridium
actinomyces

most common cause of the common cold?

Rhinovirus

most common cause of pharyngitis and laryngitis?

Viral >bacterial (beta hemolyzing streptococci)

most common cause of tonsillitis?

beta hemolyzing streptococci

most common cause of otitis media?

Streptococcus pneumoniae, Haemophilus influenza

most common cause of sinusitis?

Streptococcus pneumoniae, Staphylococcus aureus

most common cause of pneumonia in infants?

RSV

most common cause of pneumonia in young adults?

Mycoplasma

most common cause of pneumonia in the elderly?

Streptococcus pneumonia

most common causes of bacterial meningitis in neonates?

-E. coli
-strep agalactica (GBS)
-Listeria

most common cause of bacterial meningitis in adults?

Neisseria Meningitidis >strep pneumoniae

most common cause of bacterial meningitis in the elderly?

Streptococcus pneumoniae >Neisseria Meningitidis

most common cause of endocarditis?

S.viridans

most common cause of carbuncle?

S.aureus

most common cause of sepsis In a catheterized patient?

S.aureus, Candida

most common cause of sepsis in a burn patient?

Pseudomonas aeruginosa

most common cause of diarrhea in children?

Rotavirus

most common cause of diarrhea in adults in the US?

Campylobacter

most common cause of diarrhea in travelers?

E. coli, Shigella, Salmonella

most common causes of genital ulcers?

Herpes >syphilis

most common cause of urethritis?

Chlamydia > gonococcus

most common cause of cystitis?

E. coli

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