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Microbiology Exam 1 > General Bacteriology + Gram Positive > Flashcards

General Bacteriology + Gram Positive Flashcards

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1
Q

Bacteria are grouped and named based on their…

A
  • Morphological differences
  • Biochemical/metabolic differences
  • Immunologic characteristics
  • Genetic characteristics
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2
Q

All organisms have a name with two parts, consisting of ____ and _____

A
  • Genus

- Species

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3
Q

What are the three major shape categories of bacteria?

A
  • Cocci (coccus)– spherical, oval
    • Typically arranged in clusters or chains
  • Bacilli (bacillus)– rods
    • May be straight or curved
    • Short bacilli – coccobacilli
  • Spiral – comma shaped, s-shaped, or true spiral
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4
Q

What are the steps to performing a gram stain?

A

1) Smear the substance onto a slide (sputum, drainage, etc)
2) Heat it to fix the bacteria to the slide
3) Pour on crystal violet stain (blue dye) and wait 60 sec
4) Wash off with water and add iodine solution and wait 60 sec
5) Wash off with water and add ethyl alcohol or acetone to decolorize
6) Add safranin to counterstain (red dye), wait 30 sec and wash off with water

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5
Q

What give gram positive bacteria their color?

A
  • Very thick peptidoglycan
  • Extensive cross-linking
  • Holds on to purple/blue color = Gram stains blue
  • Allows low molecular weight compounds to come through
  • Substances that target the cytoplasmic membrane (like PCN) can pass through
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6
Q

What give gram negative bacteria their color?

A
  • Thinner – much less peptidoglycan
  • Simple cross-linking
  • Blue gets washed away, red gets absorbed = Gram stains red
  • Does block low molecular weight compounds
  • It has an outer membrane of lipopolysacharide (LPS)
  • LPS contains lipid A – toxic to humans
  • Lipid A is known as the “gram-negative endotoxin”
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7
Q

What are two examples of bacteria that do not stain well? What technique is used instead?

A
  • Mycobacterium tuberculosis has extra lipids that cause it to resist uptake of stains –> Acid-fast
  • Treponema pallidum are too thin to be seen without special lighting of microscope –> Gram negative
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8
Q

What is the bacterial cell wall made of?

A

Peptidoglycan

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9
Q

What is transpeptidase?

A
  • Enzyme that creates the linkage formation of the cell wall

- Located in the cell membrane

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10
Q

What does the antibiotic penicillin inhibit?

A

Transpeptidase

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11
Q

What are the classic COCCI Gram-Positives bacteria?

A

1) Streptococcus – forms strips of cocci
- A (Group A strep) Streptococcus pyogenes
- B (Group B strep) Streptococcus agalactiae
- Streptococcus viridans
- Streptococcus pneumoniae
2) Enterococcus– forms strips of cocci
- D Enterococci
3) Staphylococcus – forms clusters of cocci
- Staphylococcus saprophyticus
- Staphylococcus aureus
- Methicillin-resistant Staphylococcus aureus (MRSA)
- Staphylococcus epidermidis

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12
Q

What are the classic BACILLI Gram-Positives bacteria?

A

1) Bacillus – spore-forming
- Bacillus cereus
- Bacillus anthracis
2) Clostridium – spore-forming
- Clostridium botulinum
- Clostridium tetani
- Clostridium perfringens
- Clostridium difficile
3) Corynebacterium – not spore-forming
- Corynebacterium diptheriae
4) Listeria – not spore-forming
- Listeria monocytogenes

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13
Q

What are the classic Gram-Nevative bacteria?

A
  • Most GN organisms are rods or pleomorphic. 1 cocci + 1 spirochete
    1) Neisseria - Diplococci
  • Neisseria meningitis
  • Neisseria gonorrhoeae
  • Moraxella catarrhalis
    1) Spirochete
  • Treponema pallidum
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14
Q

Define virulence.

A
  • Virulence – the degree of an organism’s pathogenicity

- Virulent organism – one that can cause disease

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15
Q

What determines virulence?

A

Virulence factors, such as…

  • Presence of certain cell structures (Flagella, Pili, Capsules, Endospores, Biofilms)
  • Bacterial endotoxin (lipid A)
  • Bacterial exotoxins
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16
Q

Describe flagella, pili, and capsules.

A

-Flagella: Protein filaments that move the bacterium around
-Pili: Straight filaments arising from bacterial cell wall
-Capsules: Protective gel-like wall around the cell wall
Major function – protection from immune system
Ex: Streptococcus mutans – makes a gel in the presence of sugar = cavities

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17
Q

Describe the clinical correlation of antibodies directed towards bacterial capsules.

A

-They bind to the capsule (opsonization) and our macrophages and neutrophils can then bind to and digest the bacteria

  • Example: Streptococcus pneumoniae has a capsule
  • A vaccine against Streptococcus pneumoniae contains antigens and causes an immune response against the antigens, triggering the production of antibodies
  • These antibodies then protect the individual from future infections
18
Q

Describe endospores

A
  • Metabolically dormant structures produced by some bacteria (Resistant to heat, cold, drying, and chemicals)
  • Form when there is a shortage of nutrients
  • Can lie dormant for years

-Formed by only 2 types of bacteria, both gram-positive
Bacillus
Clostridium

19
Q

Describe biofilms (glycocalyx, slime layer).

A
  • Extracellular polysaccharide network
  • Protects bacteria from attack by antibiotics and the immune system
  • Allows bacteria to bind to prosthetic devices (such as IV catheters)

-Staphylococcus epidermidis
Known to cause bacteremia, catheter-related sepsis, and infection of prostheses

20
Q

Describe endotoxin in Lipid A

A
  • Piece of outer membrane of the lipopolysaccharide (LPS) of gram-negative bacteria
  • Released when the bacterial cell undergoes lysis – part of the cell that fragments off
  • Can also be steadily shed from living bacteria
21
Q

What is the clinical correlation of septic shock?

A
  • Common, deadly response to both gram-negative and gram-positive infection
  • Bacteremia – bacteria in the bloodstream (w/ or w/out symptoms)
  • Sepsis – bacteremia that causes a systemic immune response to the infection
22
Q

Describe exotoxins.

A
  • Proteins secreted by bacteria
  • Can cause severe disease manifestations

-Botulism toxin, tetanus toxin (neurotoxins) made by Clostridium
Act on nerves and motor end plates to cause paralysis or contraction

-Cholera toxin (enterotoxin) made by Vibrio cholerae
Massive diarrhea in cholera

23
Q

Describe GENERAL streptococci characteristics and how they are categorized.

A
  • Line up like a strip
  • “catalase-negative”
  • Alpha-hemolytic streptococci = partially lyse RBCs
  • Beta-hemolytic streptococci = lyse RBCs completely
  • Non-hemolytic streptococci = cannot lyse RBCs
  • Classified by the presence of a carbohydrate antigen on their cell wall. Named A through U (Lancefield antigen)
  • There are more than 30 different species of Streptococci, but only 5 are significant human pathogens
24
Q

Give me streptococcus pyogenes details.

A
  • Group A beta-hemolytic streptococci
  • Clinical correlation: Streptococcal pharyngitis
  • Classic strep throat
  • Rapid strep test (RADT) – rapid antigen detection test
  • Can detect group A carbohydrate antigen in minutes
  • Penicillin treats it effectively
25
Q

What are the streptococcus agalactiae details?

A
  • Group B beta-hemolytic streptococci
  • 25% of women carry this bacteria vaginally
  • Can be passed to a baby during vaginal delivery
  • Can cause neonatal meningitis, pneumonia, and sepsis
  • Pregnant women are screened for GBS at 35-37 weeks’ gestation
26
Q

Yo… Group D Streptococci details.

A
  • Can be alpha or non-hemolytic
  • Enterococci (Enterococcus = genus)
  • Normal bowel flora in humans
  • Common infecting agents in UTIs, biliary tract infections, bacteremia, endocarditis (SBE)
27
Q

Streptococcus pneumoniae details.

A
  • Diplococci
  • Pneumonia and meningitis in adults
  • Otitis media in children
  • Major virulence factor is its polysaccharide capsule
  • Antigenic - antibodies can neutralize it
  • 35% of strains are high antibiotic resistance
28
Q

Streptococci viridans details.

A

-Dental plaque, tongue, and saliva
-Most are alpha-hemolytic
Cause 3 major types of infections
1) Dental infections
- Streptococcus mutans – dental caries
2) Endocarditis
3) Abscesses

29
Q

Describe GENERAL Staphylococci characteristics and how they are categorized.

A
  • Nose is the main site of colonization
  • Seen in clusters on gram stain
  • Catalase-positive: Allows them to survive attack by neutrophils
  • Beta-hemolytic
  • Coagulase test: Done in labs to help identify which species of Staphylococci is growing
  • Staphyloccus aureus elaborates the enzyme coagulase is “coagulase positive” –> causing blood to clot
30
Q

Staphylococcus aureus details.

A
  • Coagulase positive
  • Produces a toxin
  • Causes abscesses, pyogenic infections (endocarditis, septic arthritis) and toxic shock syndrome
  • Also causes hospital-acquired pneumonia and surgical wound infections
  • Also folliculitis, cellulitis, impetigo and bacterial conjunctivitis
31
Q

Methicillin-resistant Staphylococcus aureus (MRSA) details.

A

-Most Staphylococci are resistant to penicillin due to production of penicillinase
-Has acquired multi-drug resistance
HA-MRSA
CA-MRSA

32
Q

Staphylococcus epidermidis details.

A
  • Normal body flora (skin)
  • Coagulase-negative
  • Sticks to anything foreign in the body (IVs, catheters, etc.)
33
Q

Staphylococcus saprophyticus details.

A
  • Coagulase negative
  • Found primarily in genital tract of women
  • Can ascend into bladder
  • A leading cause of UTIs
34
Q

Bacillus anthracis details.

A
  • Causes anthrax
  • Anti-phagocytic capsule
  • Anthrax primarily affects cows and sheep
  • Humans become exposed to spores when contacting infected animals, soil, or HIDES/WOOL
  • Cutaneous, pulmonary, and GI
  • Once the verry small spore is introduced to lungs, skin, or intestine, it makes toxins
  • High mortality associated with pulmonary inhalation
  • Most common route of entry is through skin
  • Exotocin causes tissue necrosis
35
Q

Bacillus cereus details.

A

-Motile
-No capsule
-Causes food poisoning
STEEMD, RE-HEATED RICE
-Bacteria then germinate in the food releasing toxin (enterotoxin)
-Nausea, vomiting, watery diarrhea

36
Q

Clostridium botulinum details.

A
  • Anaerobic
  • When foods are canned without proper sterilization, spores germinate in the food and make a toxin
  • Produces neurotoxin and descending, flaccid paralysis
  • Blocks release of acetylcholine
  • Smoked fish or home canned vegetables
  • Infants: honey contaminated with spores
37
Q

Clostridium tetani details.

A
  • Causes tetanus
  • Spores can follow skin trauma by any object
  • Spores found in soil and animal feces
  • Necrotic tissue forms anaerobic environment and exotoxin is released
  • Leads to sustained contraction of skeletal muscle (tetany or spastic paralysis)
  • LOCKJAW, opisthotonos, respiratory failure
  • Tetanus immune globulin – to neutralize the toxin
38
Q

Clostridium perfringens details.

A

-Gas gangrene
-Spores found in soil and mature in anaerobic conditions
-Produces a gas and releases exotoxins
3 classes of infection
1) Cellulitis – palpation reveals spongy, crackling consistency due to pockets of gas (crepitus)
2) Myonecrosis – associated with trauma into muscle
3) Diarrhea – spores germinate in food and results in watery diarrhea (meat, poultry, gravy)

39
Q

Clostridium difficile details.

A
  • Pseudomembranous colitis
  • Pathogen that causes antibiotic-associated diarrhea after a patient takes broad-spectrum antibiotics
  • Antibiotics eradicate normal flora allowing Clostirdium difficile to superinfect the colon
  • Releases exotoxins – severe diarrhea, abdominal cramping, and fever
  • Colonoscopy – red inflamed mucosa with white exudate (pseudomembranes)
  • Stool sample for toxin test to confirm
40
Q

Corynebacterium diptheriae details.

A
  • No spores
  • Causes diptheria
  • Colonizes pharynx and forms GRAY pseudomembran
  • Releases powerful toxin into blood damaging heart and neural cells
  • Treatment consists of antitoxin, penicillin, and DPT vaccine
41
Q

Listeria monocytogenes details.

A
  • No spores
  • Has flagella
  • Pregnant women – bacteria infects fetus
  • Acquired from ingestion of contaminated food (soft CHEESE and DELI MEAT)
  • Neonate – can also be acquired during birth causing neonatal meningitis

Microbiology Exam 1 (7 decks)

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