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USMLE Step 1 > Microbiology - General Bacteriology, Gram Positive , Mycobacteria > Flashcards

Microbiology - General Bacteriology, Gram Positive , Mycobacteria Flashcards

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USMLE® Step 1 flashcards
1
Q

What structures are unique to gram-positive organisms?

A

Lipoteichoic acid (combination of lipids and techoic acid)

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2
Q

What structures are unique to gram-negative organisms?

A

Endotoxin/LPS (outer membane)

Periplasm

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3
Q

Peptidoglycan

A

gives rigid support, protects against osmotic pressure

composed of sugar backbone with peptide side chains cross-linked by transpeptidase

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4
Q

Cell wall/cell membrane (gram-positives)

A

major surface antigen.

Peptidoglycan for support. Lipoteichoic acid induces IL-1 and TNF

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5
Q

Outer membrane (gram negatives)

A

site of endotoxin (lipopolysaccharide [LPS]); major surface antigen

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6
Q

Plasma membrane

A

site of oxidative and transport enzymes

-made of phospholipid bilayer

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7
Q

Ribosome

A

protein synthesis

- made up of 50S and 30S subunits

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8
Q

Periplasm

A
  • unique to gram negatives
  • space between cytoplasmic membrane and outer membrane in gram-negative bacteria
  • contains many hydrolytic enzymes, including B-lactamases
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9
Q

Capsule

A

protects against phagocytosis

-composed of polysaccharide (except Bacillus anthracis, which contains D-glutamate)

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10
Q

Pilus/fimbria

A

mediate adherence of bacteria to cell surface; sex pilus forms attachment between 2 bacteria during conjugation
- made of glycoprotein

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11
Q

Flagellum

A
  • used for motility

- composed of protein

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12
Q

Spore

A

resistance to dehydration, heat, and chemicals
- keratin-like coat; dipicolinic acid
peptidoglycan

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13
Q

Plasmid

A

contains a variety of genes for antibiotic resistance, enzymes, and toxins

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14
Q

Glycocalyx

A

mediates adherence to surfaces, especially foreign surfaces (e.g. indwelling catheters)
- composed of polysaccharide

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15
Q

Pleomorphic bacteria

A

Ricksettsiae (Giemsa)

Chlamdyiae (Giemsta)

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16
Q

Branching filamentous bacteria

A

Actinomyces

Nocardia (weakly acid fast)

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17
Q

Bacteria with no cell wall

A

Mycoplasma (does not gram stain)

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18
Q

Bacteria with unusual cell membranes/walls

A

Mycoplasma - contains sterols and have no cell wall

Mycobacteria - contain mycolic acid. High lipid content

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19
Q

Bacteria that don’t Gram stain well

A

“These Rascals May Microscopically Lack Color”

TREPENOMA (too thin)
RICKETTSIA (intracellular parasite)
MYCOBACTERIA (high lipid content in cell wall detected carbolfuscin)
MYCOPLASMA
LEGIONELLA
CHLAMYDIA
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20
Q

Culture for H. influenza

A

Chocolate agar with factors V (NAD+) and X (hematin)

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21
Q

Culture: N. gonorrhoeae, N. meningitidis

A 
Thayer Martin (or VPN) media
- Vancomycin inhibits gram positive, Polymixin inhibits gram negative organisms except Neisseria, and Nystatin (inhibits fungi)
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22
Q

Culture for B. pertussis

A

Bordet-Gengou (potato) agar

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23
Q

Culture for C. diptheriae

A

Tellurite plate, Loeffler’s media

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24
Q

Culture: M. tuberculosis

A

Lowenstein-Jensen agar

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25
Q

Culture: M. pnuemoniae

A

Eaton’s agar

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26
Q

Lactose-fermenting enterics culture

A

Pink colonies on MacConkey’s agar

  • fermentation produces acid, turning colony pink.
  • E.coli is also grown on EMB as colonies with green metallic sheen
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27
Q

Legionella culture

A

Charcoal yeast extract agar buffered with cysteine and iron

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28
Q

Fungi culture

A

Sabouraud’s agar

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29
Q

Obligate aerobes

A

use an oxygen dependent system to generate ATP

“Nagging Pests Must Breathe”
- Nocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bacililis

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30
Q

Obligate anaerobes

A

anaerobes “Can’t Breathe Air”

  • Clostridium
  • Bacteroides
  • Actinomyces
  • lack catalase and/or superoxide dismutase and are susceptible to oxidative damage.
  • generally foul smelling (short chain fatty acids) are difficult to culture and produce gas in tissue (carbon dioxide and hydrogen gas)
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31
Q

Encapsulated bacteria

A
  • positive Quelling reaction - if encapsulated bug is present, capsule swell when specific anticapsular antisera are added
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32
Q

Name encapsulated bacteria

A

“SHiNE SKiS

Streptococcus pneumonia
H. influenzae type B
Neisseria meningitidis
Escheria coli
Salmonella
Klebsiella pneumonia
Strep agalactiae (Group B strep)
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33
Q

Obligate intracellular

A 
Rickettsia, Chlamydiae (can't make own ATP)
Stay inside (cells), it's Really Cold
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34
Q

Facultative intracellular

A 
"Some Nasty Bugs May Live FaculitiveLY"
Salmonella
Neisseria
Brucella 
Mycobacterim 
Listeria
Francisella
Legionella
Yersinia
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35
Q

Catalase-positive organisms

A

Catalase degrades hydrogen peroxide before it can be converted to microbicidal products by enzyme myeloperoxidase.

Examples: Pseudomonas, Listeria, Aspergillus, Candida, E.coli, S. aureus, Serratia

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36
Q

People susceptible to infection by catalase positive organisms

A

People with chronic granulomatous disease (NADPH oxidase deficiency) have recurrent infections with these microbes because they degrade the limited hydrogen peroxide

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37
Q

Vaccines

A
  • for those containing polysaccharide capsule antigens, a protein is conjugated to polysaccharide antigen to promote T-cell activation and class switching.
  • a polysaccharide antigen can’t be presented to T cells, thus only M antigens would be presented
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38
Q

Transformation

A

ability to take up naked DNA (i.e. from cell lysis) from environment.

  • feature of SHiN (S. pneumoniae H. influenzae Neisseria)
  • Any DNA can be used. Adding deoxyribonuclease to medium will degrade naked DNA
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39
Q

Conjugation (F+ x F-)

A

F+ plasmid contains genes required for sex pilus and conjugation.
Bacteria without this plasmid are termed F-.
Plasmid (dsDNA) is replicated and transfered through pilus from F+ cell.
NO TRANSFER OF CHROMOSOMAL genes

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40
Q

Conjugation (Hfr x F-)

A

F+ plasmid can be incorporated into bacterial chromosomal DNA, termed high-frequency recombination (Hfr) cell.
Replication of incorporated plasmid DNA may include some flanking chromosomal DNA.

Transfer of plasmid and chromosomal genes

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41
Q

Transposition

A

Segment of DNA that can “jump” (excision and reintegration) from one location to another, can transfer genes from plasmid to chromosome and vice versa.
When excision occurs, may include some flanking chromosomal DNA, which can be incorporated into plasmid and transferred to another bacterium

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42
Q

Generalized Transduction

A

“packaging” event. Lytic phage infects bacterium, leading cleavage of bacterial DNA. PArts of bacterial DNA may become packaged into viral capsid. Phage infects anoter baceterium, transferring these genes.

  • RECIPIENT ACQUIRES BACTERIAL DNA BUT NO VIRAL DNA
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43
Q

Specialized Transduction

A

“Excision” event.
Lysogenic phage infects bacterium; viral DNA incorporates into bacterial chromosome.
When phage DNA is excised, flanking bacterial DNA may be excised with it. DNA is packaged into phage viral capsid and can infected another bacterium)

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44
Q

Genes for following toxins encoded in lysogenic stage

A 
Shig-A like toxin
Botulinium toxin
Cholera toxin
Diptheria toxin
Erythrogenic toxin of Strep pyogenes

** When times are good, virus leaves bacteria alone but under stress, virus acts up

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45
Q

Gram + positive bacteria, Novobiocin resistant

A

Staphylococci Saprophyticus

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46
Q

Gram + cocci, novobiocin sensitive

A

STAPHYLOCOCCI epidermidis

47
Q

Gram + cocci, Optochin resistant

A

STREP viridans

48
Q

Gram + cocci, Optochin sensitive

A

STREP pneumoniae

49
Q

Gram + cocci, Bacitracin resistant

A

Group B strep (Strep agalactiae)

50
Q

Gram + cocci, Bacitracin sensitive

A

Group A strep (Strep pyogenes)

51
Q

Alpha hemolytic bacteria

A
  • form green ring around colonies on blood agar
52
Q

Beta hemolytic bacteria

A
  • form clear area of hemolysis on blood agar. Including following organisms:
  • Staph aureus
  • Strep pyogenes
  • Strep agalactiae (Group B strep)
  • Listeria monocytogenes
53
Q

Staph aureus

A

gram + cocci, catalase +, coagulase +

  • yellow colonies, Beta hemolytic
  • protein A binds Fc portion of IgG to prevent complement fixation and phagocytosis
54
Q

Infections caused by S. aureus

A
  • inflammatory disease (skin infections, organ ABSCESS, pneumonia)
  • Toxic Shock Syndrome (TSST-1)
  • Rapid onset food poisoning (enterotoxins within)
  • MRSA - resistant to B-lactams b/c of altered penicillin binding proteins
  • Acute bacterial endocarditis (common in IV drug users)
  • Scalded skin syndrome
55
Q

S. aureus food poisoning

A

due to ingesting of PREFORMED toxin

56
Q

TSST

A
  • associated with S. aureus
  • super-antigen that binds to MHC II and T-cell receptor, resulting in polyclonal T-cell actvation
  • Presents as fever, rash, desquamation, end organ failure
57
Q

Staphylococcus epidermidis

A

gram + cocci, catalase +, coagulase -
Novobiocin sensitive

  • produces biofilms on catheters and prosthesis
  • component of normal skin flora, contaminates blood cultures
  • 10 - 20% UTIs in females
58
Q

Streptococcus pneumoniae

A

Gram + diploccoci, Encapsulated
Catalase -, ALPHA hemolytic
IgA protease, Capsule resists phagocytosis
Optichin SENSITIVE

– no virulence without capsule
Toxins: Pneumolysin O - puts pores in pulmonary cells

59
Q

Infections associated with S. pneumoniae

A

“MOPS”

Meningitis - (esp. > 60 years old)
Otitis media (in children)
Pneumonia (in adults)
Sinusitis

60
Q

Pneumococcus

A

associated with “rusty” sputum, sepsis in sickle cell anemia and splenectomy

61
Q

Viridins group streptococci

A 
gram + cocci, catalase - 
alpha hemoltic
bile soluble 
Quelling reaction
optichin RESISTANT
  • normal flora of oropharynx and cause dental caries and SUBACUTE endocarditis
62
Q

Subacute Endocarditis

A
  • associated with Strep viridans, Group D Strep

- attacks DAMAGED valves, usually by Group A Strep, by making glycocalyx

63
Q

Sx of subacute endocarditis

A
  • Janeway lesions
  • Osler’s nodes
  • Roth’s spots (in retina)
  • Splinter hemorrhages under fingernals
    ECG shows vegetations on mitral valve
  • can be shown with dental appointments or rheumatic fever as a child
64
Q

Strep pyogenes (Group A Strep)

A

gram + cocci, calatase -
Beta hemolytic
Bacitracin sensitive

Diagnosed by ASO titer

65
Q

Pyogenic infections associated with S. pyogenes

A

Pharyngitis, Impetigo, Cellulitis

66
Q

Toxin-mediated infections associated with S. pyogenes

A

Scarlet fever, Toxic Shock-Like Syndrome, Necrotizing Fascitis

67
Q

Virulence factors associated with S. pyogenes

A
  1. Streptokinase (converts plasminogen to plasmin) –> fibrinolysis
  2. M protein - resists phagocytosis
  3. Hyaluronidase - breaks down connective tissue
  4. DNAse: digests DNA
68
Q

Immunogenic infections associated with S. pyogenes

A

Rheumatic fever, Acute Glomerulonephritis

69
Q

JONES criteria to diagnose rheumatic fever

A 
J-oints
O-bvious signs
N-odules (subcutaneous)
E-rythema marginatum (targetoid lesions)
Syndham's chorea
70
Q

Scarlet fever

A
  • associated with S. pyogenes
  • scarlet rash sparing face
    strawberry (scarlet) tongue, scarlet throat
71
Q

Streptococcus agalactiae (Group B Strep)

A

gram + positive, Beta hemolytic
Bacitracin resistant
- colonizes vagina, causes pneumonia, meningitis, and sepsis (mainly in babies)

  • produces CAMP factors which enlarges hemolysis formed by S. aureus
72
Q

Treatment of pregnant women positive for Group B Strep

A
  • Screen pregnant women at 33 - 37 weeks

INTRAPARTUM penicillin prophylaxis

73
Q

Causes of meningitis in babies < 3 months

A
  • Group B Strep
  • Listeria monocytogenes
  • E. coli
74
Q

Group D Strep (Enterococci)

A

Gram +, catalase -
Gamma hemolytic (no hemoylsis)
Can grow in 6.5% NaCl and bile

  • Enterococus faecalis and E. faecium are normal colonic flora that are penicllin G resistant
75
Q

Infections associated with Enterococci (Group D Strep)

A

** enters bloodstream where mucosal barrier is disrupted (e.g. bedsore) –> can colonize heart valves
UTI
Biliary infections
Subacute endocarditis

76
Q

Vancomycin Resistant Enteroccoci

A

important cause of nocosomial infection

77
Q

Streptoccocus bovis (Group D Streptococci)

A

colonizes the gut
- can cause bacteremia and subacute endocarditis in colon cancer patients

  • Bovis in blood = cancer in colon
78
Q

Corynebacterium diphtheriae

A

Gram + rods

  • causes diphtheria via exotoxin encoded by B-prophage.
  • Potent exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2
79
Q

Lab diagnosis of C. diptheriae

A

Based on gram-positive rods with metachromatic (blue and red) granules and Elek’s test for toxin

Toxoid vaccine prevents diptheria

80
Q

Spores

A
  • some bacteria can form spores at the end of stationary phase when nutrients are limited.

Spores are highly-resistant to head and chemicals. Have dipicolonic acid in their core.
Have no metabolic activity
Must autoclave to kill spores (as is done to surgical equipment) by steaming at 121 C

81
Q

C. tetani

A

Gram +, spore-forming, obligate anaerobic bacilli

  • produces tetanospasm, an exotin causing tetanus
  • Tetanus toxin (and botulinum toxin) are proteases that cleave releasing proteins for neurotransmitters
82
Q

Tetanospasm toxin

A

causes tetanic paralysis (blocks glycine and GABA release [inhibitory neurotransmitter]) from Renshaw cells in spinal cord.

Causes spastic paralysis, trismus (lockjaw), and risus sarcondicus

83
Q

C. botulinum

A

Gram +, spore-forming, obligating anaerobic bacilli

  • produces PREFORMED, heat-labile toxin that inhibits ACh release at NMJ, causing botulism
  • diseases is caused by ingestion of preformed toxin.
  • babies, ingestion of spores in honey causes disease
84
Q

C. perfringens

A

gram +, obligate anaerobe bacilli

produces alpha toxin (“lecthinase” - phospholipase that can cause myonecrosis (gangrene) and hemolysis

85
Q

C. difficile

A

gram +, obligate anaerobe bacilli
produces 2 toxins

  • Secondary to antibiotic use (clindamycin or ampicillin)
86
Q

Treatment of C. difficile

A

Metronidazole or Oral vancomycin

87
Q

C. difficile toxins

A

Toxin A, enterotoxin, binds to the brush border of gut.

Toxin B, cytotoxin, destroys the cytoskeletal structures of enterocytes, causing pseudomembranous colitis

88
Q

Anthrax

A

caused by Bacillus anthracus, a gram +, spore-forming rod that produces anthrax toxin.

Only bacterium with a polypeptide capsule (contains D-glutamate)

89
Q

Cutaneous anthrax

A

contact –> black eschar (painless ulcer) ; can progress to bacterermia

Black skin lesion - black eschar (necrosis) surrounded by edematous ring. Caused by lethal factors and edema factors

90
Q

Pulmonary anthrax

A

inhalation of spores –> flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock

Woolsorter’s disease - inhalation of spores from contaminated woool

91
Q

Bacillus cereus

A

Gram + rod
causes food poisoning. Survives cooking rice. Keeping rice warm results in germinationof spores and enterotoxin formation

  • causes reheated rice syndrome
92
Q

Types of reheated rice syndrome (Bacillus cereus)

A

Emetic type - usually seen in rice & pasta (nausea and vomiting within 1-5 hrs) from cerulide (preformed toxin)

Diarrheal type - causes watery, non-bloody diarrhea and GI pain in 8 - 18 hours

93
Q

Listeria monocytogenes

A
  • Gram + bacilli, non-spore forming
    facultative intracellular microbe
    -acquired by ingesting unpasteurized milk/cheese and deli meats or by vaginal transmission during birth
  • form “actin rockets” by which they move from cell to cell. Characteristic tumbling motility
94
Q

Infections caused of Listeria monocytogenes

A

Amnionitis, Septicemia, and Spontaneous abortion in pregnant women

Granulomatosis infantiseptica, neonatal meningitis, meningitis in immunocompromised patients; mild gastritis in healthy individuals

95
Q

Treatment of Listeria monocytogenes

A

Gastroenteritis usually self-limited
Ampicillin in infants
Immunocompromised patietns
Elderly in empirical treatment of meningitis

96
Q

Actinomyces

A

Gram + positive ANAEROBE

  • not acid fast
  • normal oral flora (say “AAH”)
  • causes oral/facial absceses that drain through sinus tracts
  • forms “yellow sulfur” granules

Tx: penicillin

97
Q

Nocardia

A

Gram + AEROBE

  • acid fast
  • found in soil
  • Causes pulmonary infections in immunocompromised and cutaneous infections after trauma in immunocompetent

Tx: sulfonamides

98
Q

Primary tuberculosis (infection of non-immune host/usually child)

A
  • infects hilar nodes
  • Ghon focus (usually in mid zone of lung)
  • deposits in LOWER lobes
99
Q

Outcomes of primary tuberculosis

A
  1. Heals by fibrosis –> tuberculin positive
  2. Progressive lung disease (HIV, malnutrition)
  3. Severe bacteremia –> Miliary tuberculosis
  4. Preallergic lymphatic or hematogenous dissemination –> possible reactivation in adult life
100
Q

Secondary tuberculosis

A
  • partially immune/ hypersensitized host (usually adult)

- reinfection is cavitary lesion (usually in UPPER lobes)

101
Q

Extrapumonary tuberculosis

A
  • due to secondary TB
  • CNS (parenchymal tuberculoma or meningitis)
  • Vertebral body (Pott’s disease)
  • Lymphadenitis
  • Renal
  • GI
102
Q

Mycobacterium tuberculosis

A

TB

  • often resistant to multiple drugs
  • include fever, night sweats, weight loss, and hemoptysis
103
Q

Cord factor

A

in virulent strains of Mycobacterium tuberculosis
- inhibits macrophage maturation ad induces release of TNF-alpha (surface glycolipids)

Sulfatides inhibit phagolysosome fusion

104
Q

M. kansaii

A

pulmonary TB-like symptoms

105
Q

M. avium- intracellulare

A

caues disseminated non TB disease in AIDS
- often resistant to multiple drugs
Prophylactic treatment with azithromyxin

106
Q

Leprosy (Hansen’s disease)

A
  • caused by Mycobacterium leprae
  • poorly Gram stained
  • prefers cooler areas of skin (skin and superficial nerves)
  • causes chronic disease with hypopigmentation and “stocking” loss sensation
  • in US, caused by armadillos
107
Q

Two forms of Hansen’s disease

A

LEPROMATOUS - presents diffuselt over skin and is communicable. Characterized by LOW cell mediated immunity with humoral Th2 response

TUBERCULOID - limited to hypoesthetic, hair less skin plaques, charcterized by HIGH cell mediated immuity with large Th1 type response

108
Q

Treatment of Hansen’s disease

A

LEPROMATOUS - 6 MONTH course of dapsone and rifampin

TUBERCULOID - dapsone, rifampin, and clofazmine for 2-5 YEARS

109
Q

Lactose fermenting bacteria

A

grow pink colonies on MacConkey’s agar

  • Citrobacter
  • Klebsiella
  • E. coli
  • Enterobacter
  • Serratis

E. coli produces B-galactosidase that breaks down lactose into glucose

110
Q

Penicillin and gram negative bugs

A

Gram-negative bacilli are resistant to penicillin G, but may be susceptible to ampicillin and amoxicillin.

  • Gram negative outer membrane layer inhinbits entry of penicillin G and vancomycin
111
Q

Neisseria

A

Gram - negative diplococci
Fermenst glucose and produces IgA proteinase

N. MeningGoCocci - ferments Maltose and Glucose

N. Gonorrrhoae - ferments Glucose

112
Q

Sx:
Gram + rod culture
Pseudomembranous pharyngitis (grayish- white membrane) with lymphadenopathy, myocarditis, and arrhythmias

A

C. diptheriae

113
Q

Lancefield grouping is based on what?

A

differences in the C carbohydrate on bacterial cell wall

USMLE Step 1 (34 decks)

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