Microbiology - General Bacteriology, Gram Positive , Mycobacteria Flashcards Preview

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

Flashcards in Microbiology - General Bacteriology, Gram Positive , Mycobacteria Deck (113):
1

What structures are unique to gram-positive organisms?

Lipoteichoic acid (combination of lipids and techoic acid)

2

What structures are unique to gram-negative organisms?

Endotoxin/LPS (outer membane)
Periplasm

3

Peptidoglycan

gives rigid support, protects against osmotic pressure

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

4

Cell wall/cell membrane (gram-positives)

major surface antigen.

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

5

Outer membrane (gram negatives)

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

6

Plasma membrane

site of oxidative and transport enzymes
-made of phospholipid bilayer

7

Ribosome

protein synthesis
- made up of 50S and 30S subunits

8

Periplasm

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

9

Capsule

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

10

Pilus/fimbria

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

11

Flagellum

- used for motility
- composed of protein

12

Spore

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

13

Plasmid

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

14

Glycocalyx

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

15

Pleomorphic bacteria

Ricksettsiae (Giemsa)
Chlamdyiae (Giemsta)

16

Branching filamentous bacteria

Actinomyces
Nocardia (weakly acid fast)

17

Bacteria with no cell wall

Mycoplasma (does not gram stain)

18

Bacteria with unusual cell membranes/walls

Mycoplasma - contains sterols and have no cell wall
Mycobacteria - contain mycolic acid. High lipid content

19

Bacteria that don't Gram stain well

"These Rascals May Microscopically Lack Color"

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

20

Culture for H. influenza

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

21

Culture: N. gonorrhoeae, N. meningitidis

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

22

Culture for B. pertussis

Bordet-Gengou (potato) agar

23

Culture for C. diptheriae

Tellurite plate, Loeffler's media

24

Culture: M. tuberculosis

Lowenstein-Jensen agar

25

Culture: M. pnuemoniae

Eaton's agar

26

Lactose-fermenting enterics culture

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

27

Legionella culture

Charcoal yeast extract agar buffered with cysteine and iron

28

Fungi culture

Sabouraud's agar

29

Obligate aerobes

use an oxygen dependent system to generate ATP

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

30

Obligate anaerobes

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)

31

Encapsulated bacteria

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


32

Name encapsulated bacteria

"SHiNE SKiS

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

33

Obligate intracellular

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

34

Facultative intracellular

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

35

Catalase-positive organisms

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

36

People susceptible to infection by catalase positive organisms

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

37

Vaccines

- 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

38

Transformation

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

39

Conjugation (F+ x F-)

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

40

Conjugation (Hfr x F-)

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

41

Transposition

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

42

Generalized Transduction

"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

43

Specialized Transduction

"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)

44

Genes for following toxins encoded in lysogenic stage

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

45

Gram + positive bacteria, Novobiocin resistant

Staphylococci Saprophyticus

46

Gram + cocci, novobiocin sensitive

STAPHYLOCOCCI epidermidis

47

Gram + cocci, Optochin resistant

STREP viridans

48

Gram + cocci, Optochin sensitive

STREP pneumoniae

49

Gram + cocci, Bacitracin resistant

Group B strep (Strep agalactiae)

50

Gram + cocci, Bacitracin sensitive

Group A strep (Strep pyogenes)

51

Alpha hemolytic bacteria

- form green ring around colonies on blood agar

52

Beta hemolytic bacteria

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

53

Staph aureus

gram + cocci, catalase +, coagulase +
- yellow colonies, Beta hemolytic
- protein A binds Fc portion of IgG to prevent complement fixation and phagocytosis

54

Infections caused by S. aureus

- 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

S. aureus food poisoning

due to ingesting of PREFORMED toxin

56

TSST

- 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

Staphylococcus epidermidis

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

Streptococcus pneumoniae

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

Infections associated with S. pneumoniae

"MOPS"

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

60

Pneumococcus

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

61

Viridins group streptococci

gram + cocci, catalase -
alpha hemoltic
bile soluble
Quelling reaction
optichin RESISTANT

- normal flora of oropharynx and cause dental caries and SUBACUTE endocarditis

62

Subacute Endocarditis

- associated with Strep viridans, Group D Strep
- attacks DAMAGED valves, usually by Group A Strep, by making glycocalyx

63

Sx of subacute endocarditis

- 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

Strep pyogenes (Group A Strep)

gram + cocci, calatase -
Beta hemolytic
Bacitracin sensitive

Diagnosed by ASO titer

65

Pyogenic infections associated with S. pyogenes

Pharyngitis, Impetigo, Cellulitis

66

Toxin-mediated infections associated with S. pyogenes

Scarlet fever, Toxic Shock-Like Syndrome, Necrotizing Fascitis

67

Virulence factors associated with S. pyogenes

1. Streptokinase (converts plasminogen to plasmin) --> fibrinolysis

2. M protein - resists phagocytosis

3. Hyaluronidase - breaks down connective tissue

4. DNAse: digests DNA

68

Immunogenic infections associated with S. pyogenes

Rheumatic fever, Acute Glomerulonephritis

69

JONES criteria to diagnose rheumatic fever

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

70

Scarlet fever

- associated with S. pyogenes
- scarlet rash sparing face
strawberry (scarlet) tongue, scarlet throat

71

Streptococcus agalactiae (Group B Strep)

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

Treatment of pregnant women positive for Group B Strep

* Screen pregnant women at 33 - 37 weeks
INTRAPARTUM penicillin prophylaxis

73

Causes of meningitis in babies < 3 months

- Group B Strep
- Listeria monocytogenes
- E. coli

74

Group D Strep (Enterococci)

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

Infections associated with Enterococci (Group D Strep)

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

76

Vancomycin Resistant Enteroccoci

important cause of nocosomial infection

77

Streptoccocus bovis (Group D Streptococci)

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

- Bovis in blood = cancer in colon

78

Corynebacterium diphtheriae

Gram + rods
- causes diphtheria via exotoxin encoded by B-prophage.
- Potent exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2


79

Lab diagnosis of C. diptheriae

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

Toxoid vaccine prevents diptheria

80

Spores

- 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

C. tetani

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

Tetanospasm toxin

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

C. botulinum

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

C. perfringens

gram +, obligate anaerobe bacilli
produces alpha toxin ("lecthinase" - phospholipase that can cause myonecrosis (gangrene) and hemolysis

85

C. difficile

gram +, obligate anaerobe bacilli
produces 2 toxins


- Secondary to antibiotic use (clindamycin or ampicillin)

86

Treatment of C. difficile

Metronidazole or Oral vancomycin

87

C. difficile toxins

Toxin A, enterotoxin, binds to the brush border of gut.
Toxin B, cytotoxin, destroys the cytoskeletal structures of enterocytes, causing pseudomembranous colitis

88

Anthrax

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

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

89

Cutaneous anthrax

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

Pulmonary anthrax

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

Bacillus cereus

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

- causes reheated rice syndrome


92

Types of reheated rice syndrome (Bacillus cereus)

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

Listeria monocytogenes

- 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

Infections caused of Listeria monocytogenes

Amnionitis, Septicemia, and Spontaneous abortion in pregnant women

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

95

Treatment of Listeria monocytogenes

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

96

Actinomyces

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

Nocardia

Gram + AEROBE
- acid fast
- found in soil
- Causes pulmonary infections in immunocompromised and cutaneous infections after trauma in immunocompetent

Tx: sulfonamides

98

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

- infects hilar nodes
- Ghon focus (usually in mid zone of lung)
- deposits in LOWER lobes

99

Outcomes of primary tuberculosis

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

Secondary tuberculosis

- partially immune/ hypersensitized host (usually adult)
- reinfection is cavitary lesion (usually in UPPER lobes)

101

Extrapumonary tuberculosis

- due to secondary TB
- CNS (parenchymal tuberculoma or meningitis)
- Vertebral body (Pott's disease)
- Lymphadenitis
- Renal
- GI

102

Mycobacterium tuberculosis

TB
- often resistant to multiple drugs
- include fever, night sweats, weight loss, and hemoptysis

103

Cord factor

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

Sulfatides inhibit phagolysosome fusion

104

M. kansaii

pulmonary TB-like symptoms

105

M. avium- intracellulare

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

106

Leprosy (Hansen's disease)

- 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

Two forms of Hansen's disease

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

Treatment of Hansen's disease

LEPROMATOUS - 6 MONTH course of dapsone and rifampin

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

109

Lactose fermenting bacteria

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

Penicillin and gram negative bugs

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

Neisseria

Gram - negative diplococci
Fermenst glucose and produces IgA proteinase

N. MeningGoCocci - ferments Maltose and Glucose

N. Gonorrrhoae - ferments Glucose

112

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

C. diptheriae

113

Lancefield grouping is based on what?

differences in the C carbohydrate on bacterial cell wall