Bailey & Scott's Diagnostic Microbiology: Advanced Clinical Microbiology Flashcards


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1

Mycobacteria, general characteristics

-Aerobic, Intracellular

-Nonmotile

-Thin, slightly curved or straight rods

-Slow growing (2-60 days)

-Acid fast cell wall = N-glycolmuramic acid

2

Non-tubercle Mycobacterium Runyon groups

Group I: Photochromogen
Group II: Scotochromogen
Group III: Non-photochromogen
Group IV: Rapid Growers

3

Group I: Photochromogens

Colonies become pigmented when exposed to light

- M. kansasii

-M. asiaticum

-M. branderi

- M. marinum

-M. intermedium

-M. nebraskense

4

M. kansasii

Growth temp = 35C

Nitrate = positive

68C catalase = positive

SQ catalase = positive

Arylsulfatase 14d = negative

5

M. kansasii microscopic

Long, slender, acid fast bacilli with distinctive beaded and banded appearance.

6

M. marinum

Growth temp = 30C

Nitrate = negative

68C catalase = negative

SQ catalase = negative

Arylsulfatase 14d = positive

7

M. marinum macroscopic

14 day growth of smooth to rough raised colonies on 7H11 agar

8

M. marinum microscopic

Long, thin, red staining (positive) with slight cross-banding

9

Group II: Scotochromogens

Colonies become pigmented when exposed to light and dark

-M. szulgai

-M. scrofulaceum

-M. gordonae

-M. europeaeum

-M. cookii

-M. hiberniae

-M. interjectum

-M. heckeshornense

-M. lentiflavum

-M. mantenii

-M. palustre

-M. parmense

-M. tusciae

-M. kubicae

10

M. szulgai

Tellurite = positive

Nitrate = positive

Urease = positive

Tween = negative

Arylsulfatase 14d = positive

11

M. scrofulaceum

Tellurite = negative

Nitrate = negative

Urease = variable

Tween = negative

Arylsulfatase 14d = negative

12

M. scrofulaceum macroscopic

Moderately large colonies with smooth grooved surface and deep golden yellow pigmentation

13

M. gordonae

Tellurite = positive

Nitrate = negative

Urease = variable

Tween = positive

Arylsulfatase 14d = negative

14

M. gordonae macroscopic

Smooth to shiny colonies on 7H11 agar with distinctive golden yellow pigmentation

15

Group III: Non-photochromogens

Produces no pigment, regardless if it is light or dark

M. avium complex (MAC)

M. celatum

M. xenopi

M. ulcerans

M. lactus

M. malmoense

M. genavense

M. haemophilum

M. heidelbergense

M. shimoidei

M. simiae

M. terrae Complex

16

Mycobacterium avium complex (MAC)

Growth temp: 35-37C

SQ catalase = positive

68C catalase = positive

Tellurite = positive

17

M. avium complex (MAC) macroscopic

Left: Smooth, transparent, flat colony type

Right: flat, rough, yellow-pigmented colony type,

recovered from patients with AIDS

18

M. avium complex (MAC) microscopic

Short bacilli staining purple/pink

19

M. haemophilum

Growth temp: 30C

SQ catalase = negative

68C catalase = negative

Tellurite = negative

20

M. ulcerans

Growth temp: 30C

SQ catalase = negative

68C catalase = positive

Tellurite = negative

21

M. xenopi

Growth temp: 42C

SQ catalase = negative

68C catalase = positive

Tellurite = negative

22

Group IV: Rapid growers

-Appear on solid media within 7 days

-can grow on routine media

-appear weakly gram positive on Gram stain

-most common infection = post-traumatic wound infections

23

M. fortuitum

-Nitrate = Positive

-5% NaCl = Positive

-Arylsulfatase 3d = Positive

24

M. fortuitum macroscopic/microscopic

Left: Young culture of small yellow-pigmented colonies Right: Microscopic colony consisting of loose, delicate, branching filaments.

25

M. chelonae

-Nitrate = Negative

-5% NaCl = Negative

-Arylsulfatase 3d = Negative

26

M. chelonae macroscopic

Rapid growth (3 - 5 days) colonies

are small, spherical, smooth to

waxy, and non-chromogenic

27

M. chelonae microscopic

Short acid fast bacilli observed in acid-fast stain of microscopic section of biopsy of skin lesion

28

M. abscessus

-Nitrate = Negative

-5% NaCl = Positive

-Arylsulfatase 3d = Negative

29

M. leprae

-Causes Leprosy (Hansen disease)

-Nonculturable In vitro

-Identified through PCR: Digital PCR

30

BSL-2

•Restricted access while work is being conducted
•Appropriate PPE - lab coat and gloves, eye protection and face shields
•Work under Biological safety cabinet (BSC)
•Self-closing doors
•Sink and eyewash available
•Disinfection of work area
•Towels soaked with disinfectant ready
•Disinfectant must kill mycobacterium

31

BSL-3

•BSL-2 considerations plus:

•Laboratory professionals are under medical surveillance and may be vaccinated for the microbes they work with

•Restricted and controlled at all times

•Appropriate PPE – all mentioned in BSL-2 plus respirators in certain situations

•All work under BSC

Hands-free sink and eyewash

Negative pressurized room = Exhaust air cannot recirculate

•Entrance to the lab is through two sets of self-closing and locking doors

32

acid fast staining

Cells with high lipid content (rich in mycolic acid)

2 primary methods of staining + 1 fluorescent method of staining

Positive= deep pink, negative= dark blue

33

-Ziehl Neelsen

uses heat

34

Kinyoun

does not use heat

35

Primary stain

carbol fuschin

36

Decolorizer

acid-alcohol (3%)

37

Counter stain

methylene blue

38

auramine-rhodamine

fluorescent acid fast staining method

39

Primary stains

advantages

-more specific

-stains all mycobacteria

disadvantages

-longer examination time = must read at 100x

-less sensitive

40

Fluorescent stains

advantages

-more sensitive

-shorter examination time = can be read at 40x

disadvantages

-rapid growers do not stain well

-less specific

41

Egg-based (solid)

18-24 days

-Lowenstein Jensen (LJ)

-Petragnani = malachite green double strength

42

Agar-based (solid)

10-12 days

-Middlebrook 7H10 and 7H11

-can be created as a selective agar with antibiotics added

43

Liquid

<10 days

-Middlebrook 7H9

-Septi-check AFB (biphasic)

Can be read on Bactec or Versa-Trek

44

25-35C, dark, humidity >70%, 5-10% CO2, held up to eight weeks on solid media

optimal environment for growth of Mycobacteria

45

Solid media

advantages

-good at identifying characteristic colony morphology

-small inoculate needed

-low contamination rate

disadvantages

-long incubation times = examined weekly for growth for up to 8 weeks

46

Liquid media

advantages

-shorter incubation times

-can be monitored using conventional instrumentation

47

Mycobacterium tuberculosis complex basic characteristics

-Causes most cases of human tuberculosis
-Bacillus, curved
-Non-motile
-Aerobic
-Resistant to usual dyes (gram stain)
-stained with acid fast (see image)

48

Mycobacterium tuberculosis complex macroscopic findings

Middlebrook:

-dry, crystalline colonies (bottom image in photo)

-can also be pigmented (upper left image)

-cording pattern (macroscopic/microscopic pattern) (upper right image)

49

Mycobacterium tuberculosis complex disease

Only 15-20% of individuals who become infected develop disease

Factors that contribute to disease:

-age, malnutrition, surgery

-diabetes, hormones

-immunosuppression either naturally or through therapy

Active infection: patients are infectious

-Aerosolized droplets are inhaled by patient --> enter lungs and travel to alveoli --> multiply in alveoli --> enter bloodstream and spread to other parts of the body -->

Latent infection: patients are not infectious

-immune system cells (macrophages) ingest and surround the tubercle bacilli and form a granuloma --> bacilli destroy macrophages --> bacilli are released and other macrophages ingest them --> macrophages recruit other cells by releasing cytokines and chemokines --> granulomas form

50

General characteristics of Bordetella spp.

-Fastidious GNR (coccobacilli)

-Causes severe respiratory infection and possible disseminated disease

-Family: Alcaligenaceae

-Obligate aerobes

51

B. pertussis

cause of whooping cough

52

B. parapertussis

similar disease to whooping cough

53

B. bronchiseptica

pneumonia, ear infections, bronchitis (rare)

54

Whooping cough disease presentation

1. Stage 1 = Catarrhal: runny nose and mild cough

2. Stage 2 = Paroxysmal: severe and violent coughing (vomiting and "whooping" sounding cough)

3. Stage 3 = Convalescent: recovery (cough subsides)

Toxins produced:

1. Pertussis toxin -enters target cells and activates cAMP

2. Tracheal cytotoxin-destroys ciliated epithelial cells

3. Hemagglutinin-protein binds to host cell surface

55

Pertussis toxin

enters target cells and activates cAMP

56

Tracheal cytotoxin

destroys ciliated epithelial cells

57

Hemagglutinin

protein binds to host cell surface

58

Bordetella pertussis biochemical tests

-small, gram negative non-sporulating coccoid rods

-catalase positive

-oxidase positive

-urease negative

-oxidize amino acids

-no carbohydrate fermentation

-obligate aerobe

59

Bordetella pertussis macroscopic morphology

Growth in 3-7 days

Regan-Lowe media

-small round, domed and silvery colonies

-resembling mother of pearl

Bordet-Gengou media (picture)

-domed or convex

-resembling drop of mercury

-small zone of beta hemolysis

60

Bordetella parapertussis biochemical tests

-small, gram negative non-sporulating coccoid rods

-catalase positive

-oxidase negative

-urease positive

-oxidize amino acids

-no carbohydrate fermentation

-obligate aerobe

61

Bordetella parapertussis macroscopic morphology

Growth in 2-3 days

Sheep blood agar media

-small opaque colonies

Regan-Lowe media

-larger colonies, less shiny

Bordet-Gengou media (picture)

-less domed, larger colonies

-more gray

-larger zone of strong beta hemolysis

62

Bordetella bronchiseptica biochemical tests

-small, gram negative non-sporulating coccoid rods

-catalase positive

-oxidase positive

-urease positive (within 4 hours)

-oxidize amino acids

-no carbohydrate fermentation

-obligate aerobe

63

Bordetella bronchiseptica macroscopic morphology

Sheep blood agar

-Gray, white colonies

-Flat, dull

-Hazy hemolysis

Bordet-Gengou media (picture)

-less domed, larger colonies

-larger zone of strong beta hemolysis

64

Francisella, Bartonella, Brucella

-zoonotic organisms (transmitted by animal bites)

-Fastidious GNR

-Brucella and Francisella: Not handled in routine laboratory and agents of bioterrorism

65

Brucella spp. clinical disease

B. abortus = cattle

B. melitensis = goats, sheep, and camels

B. suis = pigs

B. canis = dogs

Transmission:

-Inoculation = animal bite

-Ingestion = eating undercooked meat or unpasteurized dairy

-Inhalation = inhaled infective droplets by laboratory or meat-packing workers and hunters

66

Brucella spp. laboratory findings

-GN coccobacilli

-Gamma hemolytic on SBA and Choc in CO2

-Small translucent colonies

-Catalase positive

-Urease positive

-Oxidase positive (most strains)

B. abortus and B. suis = produce H2S

67

Francisella tularensis

-causes tularemia

-reservoirs: rabbits, beavers, and muskrats (also birds and amphibians)

Transmitted by:

1. inoculation = animal bites

2. inhalation = infective aerosols

3. ingestion = contaminated water or meat

Disease:

-lesion at site of inoculation

-enlarged lymph nodes

-flu-like symptoms

68

Francisella tularensis laboratory detection

-Gram negative coccobacilli

-requires L-cysteine and iron to grow

-needs enriched media for colonies to grow

-needs CO2 atmosphere

-oxidase negative

-catalase weakly positive or negative

-urease negative

-negative satellite test

-beta lactamase positive

69

Bartonella spp.

-reservoirs: cats (major reservoir), rodents, rabbits, sheep, foxes, dogs, and humans

Organisms and disease association:

-B. henselae = cat scratch fever/disease

-B. quintana = trench fever

-B. bacilliformis = bartonellosis

70

Bartonella spp. laboratory detection

-small, gram negative, curved bacilli with twitching motion

-catalase negative

-oxidase negative

-urease negative

-Grows on:

1. Columbia agar with 10% horse, rabbit, or sheep blood

2. SBA and Choc

3. Heart infusion agar with 5% rabbit blood

-Can be seen on:

Wright or Wright-Giemsa stain B. bacilliformis

71

Streptobacillus moniliformis

-Rat bite fever: inoculation from rat bites

-Haverhill fever: ingestion of contaminated meat or unpasteurized milk or their products

Rat-bite fever:

-Specimen = wound (rat bite inoculation site)

-colonized in the upper respiratory tract of rats

Haverhill fever:

-Specimen = blood or joint fluid

72

Streptobacillus moniliformis laboratory detection

-Gram negative bacillus (GNR/GNB)

-Non-motile

-Facultative anaerobe

-Indole, catalase, oxidase, and nitrate negative

-Urea negative

-Produces H2S

73

Spirillum minus

-Rat bite fever

-Commonly found in Asia

74

Spirillum minus laboratory detection

-Specimens of choice: blood, exudate (wound), lymph node tissue

-nonculturable organism

-spirochete identified on Wright or Wright Giemsa stain

-Inject lesion material or blood into experimental white mice or guinea pigs

75

Streptobacillus moniliformis - General Characteristics

- Gram-negative bacillus
- Facultative anaerobe
- Non-motile
- Highly pleomorphic
- Causative agent of rat-bite and Haverhill fever

76

- Rat bite
- Ingestion of contaminated food (unpasteurized milk/milk products)

Streptobacillus moniliformis - Mode of Transmission

77

L-form (lacks cell wall)

Streptobacillus moniliformis can develop ____________ colonies

78

Streptobacillus moniliformis - Spectrum of Disease

- Rat-bite fever (direct contact from a rat)
- Haverhill fever (ingestion)
- Acute onset of fever, chills, headache, vomiting, and joint pains
- Rash on the palms and soles of the feet
- Complications (Endocarditis, Septic arthritis, Pneumonia, Brain abscess)

79

Streptobacillus moniliformis - Specimens

- Blood
- Aspirates of joints
- Lymph nodes
- Lesions

80

Streptobacillus moniliformis - Cultivation

- Requires blood, ascitic fluid, or serum for growth
- SBA at 37°C with 5% to 10% carbon dioxide (CO2)
after 48 hours in a moist environment
- Nonhemolytic
- Broth = "fluff balls" or "bread crumbs"
- L-phase colonies = "Fried egg" with a dark center
and a flattened lacy edge in agar

81

Streptobacillus moniliformis - Microscopic

- Pleomorphic gram-negative bacillus
- Long tangled chains with bulbar swellings,
resemble a "string of pearls"
- Giemsa stain and Acridine orange stain acceptable

82

Streptobacillus moniliformis - Key Biochemical Tests

Indole - Negative
Catalase - Negative
Oxidase - Negative
Nitrate - Negative
Motility - Negative
Urea - Negative
Decarboxylase - Negative
H2S produced using lead acetate paper

83

Gram stain and culture

Streptobacillus moniliformis - Detection Method

84

Rat-bite (Primarily Southeast Asia)

Spirillum minus - Mode of Transmission

85

Spirillum minus - Spectrum of Disease

- Sodoku (form of rat-bite fever in humans)

- Similar to S. moniliformis (arthritis rare)

- Swollen lymph nodes prominent

- Wound spontaneously heals

- Re-ulcerates in 1 to 4 weeks to a granulomatous lesion

- Incubation period significantly longer than S. moniliformis

86

- Blood
- Exudate
- Lymph node

Spirillum minus - Specimens

87

Spirillum minus - Cultivation

- Cannot be grown on synthetic media
- Injected into white mice or guinea pigs (will take 1-3 weeks to recover)

88

Spirillum minus - Microscopic

- Thick, spiral, gram-negative (spirochete)
- Giemsa or Wright's stain can be used

89

Visualizing Spirochetes

Spirillum minus - Detection Method

90

-Chlamydia trachomatis

-Chlamydia psittaci

-Chlamydia pneumoniae

-Difficult or unable to be cultured

-Obligate intracellular bacteria

91

Chlamydia trachomatis

-Sexually transmitted infection (STD/STI)

-Four types of infections:

1. Ocular trachoma

2. Lymphogranular venereum

3. Oculogenital infection

4. Perinatal infections

Laboratory detection

-Molecular probes on urine through:

1. PCR

2. Strand Displacement Amplification (SDA)

3. Transcription-mediated amplification (TMA)

92

Chlamydia psittaci

-Zoonotic disease transmitted to humans by birds

-inhalation of infected aerosols

-Pneumonia

-Spleen and liver enlargement

Laboratory detection:

-Serology: complement fixation (CF) and indirect microimmunofluorescence

-Need BSL-3 containment

93

Chlamydia pneumoniae

-Pneumonia (mild to moderate)

-Bronchitis

-URI like sinusitis

Laboratory detection:

1. Serology:

-complement fixation (CF) and indirect microimmunofluorescence

-questionable reliability

2. Nucleic acid amplification (NAAT)

-PCR and RT-PCR

-two kits commercially available through multiplex resp panels.

94

Rickettsiae

-Disease dependent on vector

1. Spotted fever = tick borne illness

2. Typhus group = lice or fleas

3. Scrub typhus group = chiggers

(Orientia tsutsugamushi)

95

Anaplasmataceae

Ehrlichiae chaffeensis

-Infect monocytes

-causes Human Monocytic Ehrlichiosis (HME)

Anaplasma phagocytophilum

-Infect BM derived cells (neutrophils)

-causes Human Granulocytic Anaplasmosis (HGA)

96

Rickettsia and Ehrlichiae

Direct detection methods
-IHC
-PCR and RT-PCR
Serodiagnosis
-IFA
-EIA
-Agglutination reactions
-Line blot
-Western blotting

97

Coxiella burnetii

-causes Q fever (lung infection)

-acquired through inhalation of infected aerosols from animals (zoonotic disease)

-requires BSL-3 safety

-identified by serologic testing and PCR

98

Tropheryma whipplei

-causes Whipple disease

-seen in middle age men

-causes diarrhea, arthralgia, and tender abdomen

-detected by PCR

-gram positive actinomycete

99

Klebsiella granulomatis

-causes granuloma inguinale (donovanosis)

-sexually transmitted

-causes enlarged painless lesions and lymph nodes in the genital and groin region

100

Mycoplasma and Ureaplasma

-highly fastidious

-slow growing

-facultative anaerobes

-no cell wall

-belong to class Mollicutes

101

Mycoplasma

-normal flora in the:

1. oropharynx

2. upper respiratory tract (URI)

3. genitourinary tract (GU)

-transmission

1. sexual contact

2. transplants

3. mother to fetus

4. respiratory secretions (M. pneumoniae)

102

M. pneumoniae

-Asymptomatic to walking pneumonia

-URI and LRI infectons

103

M. genitalium

-Nongonococcal urethritis in men

-Cervicitis and PID in women

104

U. urealyticum and M. hominis

-Systemic infections in neonates

-Invasive disease in patients who are immunosuppressed

-Urogenital tract infections

105

Ureaplasma spp.

-Has been isolated from tissue (e.g., chorioamnion) of neonates

106

Mycoplasma and Ureaplasma laboratory detection

Difficult to culture, but not impossible

-See photo for culture morphology

-agar used for growth: beef or soybean protein with serum, yeast extract, and specific GFs, including glucose, urea, and arginine

Nucleic acid detection

-PCR

-RT-PCR

-Multiplex panels

107

Gram positive, spore forming bacilli

-Obligate anaerobes

-Catalase negative

-Endospore forming

Organisms:

-Clostridium perfringens

-Clostridium botulinum

-Clostridium septicum

-Clostridium tetani

-Clostridiodes (formerly Clostridium) difficile

108

Clostridium perfringens

-Produce exotoxins that causes gas gangrene and food poisoning

-Specimen of choice: fresh stool processed within 24 hours of collection

-detected using 16s rRNA nucleic acid testing

109

Clostridium botulinum

-Produces neurotoxin that causes flaccid paralysis of respiratory and other muscle groups

-Specimen of choice: serum, feces, vomitus, or gastric contents

-detected using PCR

110

Clostridium tetani

-Produces tetanospasmin that disrupts nerve impulses to muscles that causes lockjaw, exhaustion, and respiratory failure

-Specimen of choice: feces

-detected using PCR

111

Clostridiodes (Clostridium) difficile

-produces toxins A and B that causes pseudomembranous colitis

-Specimen of choice: freshly passed stool; must be liquid or unformed within 2 hours of collection

-detected using PCR

-Immunoassays for toxins A and B

112

Gram positive, non-spore forming bacilli

-disease location correlates to organisms

-many are normal flora (NF) in certain body sites that cause opportunistic disease

113

Actinobactum

NF in urinary tract; causes urinary tract infections

114

Actinomyces

NF in vaginal tract; causes bacterial vaginosis

115

Atobopium

NF in vaginal tract; causes bacterial vaginosis

116

Bifidobacterium

probiotics

117

Eubacterium

NF in oral mucosa; causes oral infections

118

Eggerthella

causes intra- and peri-abdominal infections

119

Anaerobic Lactobacillus

NF in oral mucosa; causes dental carries, endocarditis, and bacteremia

120

Cutibacterium

skin

121

Mobiluncus

NF in vaginal tract; causes bacterial vaginosis

122

Gram positive, non-spore forming bacilli laboratory detection

1. MALDI-TOF

2. Biochemically inert

3. Rapid tests

-15% catalase test

-indole

-nitrate reduction

-motility

123

Gram negative rods

Bacteroides fragilis group

•Non-pigmented Prevotella spp.

•Pigmented Porphyromonas and Prevotella spp.

Bacteroides ureolyticus

Fusobacterium

Leptotrichia

Sneathia

Proteobacteria

124

Bacteroides fragilis group

-oral mucosa and GI tract

-Saccharolytic

-Bile resistant

-Nonpigmented

-Growth on anaerobic blood agar

-hydrolyzes esculin on Bacteroides bile esculin agar (BBE) (Black color and growth on plate)

125

Porphyromonas spp.

•Asaccharolytic
•Pigmented
•Fluoresce brick red or brown to black pigment

126

Prevotella spp.

•Saccharolytic
•Fluoresce brick red or brown to black pigment

127

Fusobacterium spp.

•Nonmotile, pleomorphic rods
•Typically isolated from oral cavity (biofilms)
•Sensitive to kanamycin
•Fluoresce chartreuse
•Bread crumb-like colonies

128

Gram positive cocci

•Normal microbiota of the oral cavity and the upper respiratory and GI tracts:

Peptostreptococcus

Ezakiella

Finegoldia

Gallicola

Parvimonas

Peptococcus

Peptoniphilus

Murdochiella

Staphylococcus

Anaerococcus

129

Gram positive cocci laboratory detection

-sensitive to vancomycin

-resistant to colistin

-Peptostreptococcus anaerobius and Parvimonas micra

-sensitive to SPS

-MALDI-TOF

-NAAT

1. 16s rRNA sequencing

2. PCR

3. Oligonucleotide arrays

130

Gram negative cocci

•Normal microbiota of the oral cavity and the respiratory, genitourinary, and GI tracts:

Veillonella

Megasphaera

Anaeroglobus

Negativicoccus

Acidaminococcus

131

Gram negative cocci laboratory detection

-resistant to vancomycin

-MALDI-TOF

-NAAT

1. 16s rRNA sequencing

2. PCR

3. Oligonucleotide arrays

132

Antimicrobial agents

-include antibiotics

-natural and synthesized substances

-Target organisms to either inhibit or kill them

133

bacteriostatic

Antimicrobial agents that inhibit bacterial growth

134

bactericidal

Antimicrobial agents that kill the organism

135

Antibiotics

Obtained and purified from other microbial organisms

136

Pharmacodynamics

Ensuring that the right agent is administered through the best route of transmission (IV, IM, orally)

-Ensuring that the right agent is high enough in concentration to induce an inhibitory or killing organism

137

Pharmacokinetics

-Ensures anatomic approximation

-Properties

1. Adsorption - how it gets into the body

2. Distribution - where does it go in the body

3. Metabolism - what happens to the drug to make it leave the body

138

Cell wall synthesis inhibitors

1. Beta-lactam antimicrobial agents
2. Glycopeptide agents
3. Lipoglycopeptide agents

139

Beta Lactam antimicrobial agents

-four membered nitrogen containing ring

-Mechanism of Action (MOA) = binds to beta lactam inhibiting transpeptidation and inhibit cell wall synthesis

Drug classes:

1. Penicillins

2. Cephalosporins

3. Monobactams

4. Carbapenems

140

Beta Lactamase

neutralizes the beta-lactam antibiotics

-Other methods of resistance:

1. Genetic mutations with the penicillin binding proteins (PBPs)

2. Genetic recombination

3. Overproduction of normal PBPs

141

Beta-Lactam/Beta-Lactamase Inhibitor

Combination of:

1. Beta Lactam antibiotics (Penicillins, Cephalosporins, Monobactams, or Carbapenems)

2. Beta lactamase inhibitors = Sulfbactam, Clavulanate, Tazobactam, and Avibactam

Combinations include:

1. Ampicillin/Sulfbactam

2. Amoxicillin/Clavulanate

3. Piperacillin/Tazobactam (Pip/Tazo)*

*most common combination

142

Glycopeptide agents antimicrobial agents

-Large molecules that cannot penetrate gram negative cell walls

-MOA: •Bind to the end of the peptidoglycan, interfering with transpeptidation, and inhibiting cell wall synthesis and growth

Drugs:

-Vancomycin

-Teicoplanin

Considerations:

-Drug levels must be drawn (Peak and Trough) due to risk of renal toxicity

-Administration <3 days due to renal toxicity

143

Lipoglycopeptide agents antimicrobial agents

-Semi-synthetic agents that contain hydrophobic groups

MOA: Inhibit transglycosylase (anchor) and transpeptidase which inhibit cell wall synthesis and increase cell permeability

Drugs:

-Dalbavancin

-Oritavancin

-Telavancin

144

Lipopeptides

Drugs: Daptomycin

-MOA: Creates a pore in the membrane and makes the cell more permeable to ions which cause cell death

-Effective against gram positive bacteria

Drugs: Polymyxin B and E (colistin)

-MOA: Makes the membrane more porous to external agents that normally wouldn't be allowed through

-Effective against gram negative bacteria

-Agent of last resort for Pseudomonas aeruginosa and Acinetobacter spp. infections.

145

Inhibitors of protein synthesis

MOA: Bind to either 30s or 50s ribosomal subunits

Drug classes:

-Aminoglycosides

-Macrolide-Lincosamide-Streptogramins (MLS group)

-Ketolides

-Oxazolidinones

-Chloramphenicol, Tetracyclines, glycylglycines

146

Antimicrobial agents: Aminoglycosides

MOA: Irreversibly binding to protein receptors on the organism’s 30S ribosomal subunit

-Works on both Gram positive and Gram negative organisms

Drugs:

•Tobramycin

•Amikacin

•Neomycin

•Gentamicin

•Streptomycin

•Kanamycin

147

Antimicrobial agents: Macrolides

MOA: Reversibly binds to the 23S ribosomal RNA (rRNA) on the bacterial 50S ribosomal subunit

-bacteriostatic, but can be bacteriocidal depending on organism infective dose

-Works on Gram-positives and organisms without cell walls, treponemes and rickettsiae

Drugs:

-Erythromycin

-Azithromycin

-Clarithromycin

148

Antimicrobial agents: Lincosamides

MOA: •Binds to the 50S ribosomal subunit and prevent elongation by interfering with the peptidyl transfer during protein synthesis.

Bacteriocidal or bacteriostatic: Dependent on:

-Bacterial species

-Size of inoculum

-Drug concentration

Drugs:

-Clindamycin

-Lincomycin

149

Antimicrobial agents: Streptogramins

MOA: Cyclic peptides that bind irreversibly to the 50S subunit of the bacterial ribosome.

-Effective against both Gram-positive and Gram-negative organisms

Drugs:

-Quinupristin

-Quinupristin-dalfopristin

150

Antimicrobial agents: Ketolides

MOA: Binds to the 23S rRNA of the 50S ribosomal subunit

-Effective against:

Gram-negative and Gram-positive bacteria

•Fastidious GNR = Francisella tularensis

Nonculturable organisms: Mycoplasma, Mycobacteria, Chlamydia, and Rickettsia spp.

Drugs:

-Telithromycin (chem derivative of erythromycin A)

151

Antimicrobial agents: Oxazolidinones

MOA:

-Interact with the 23S rRNA in the 50S ribosomal subunit

-Inhibiting 70S initiation complex formation and blocking translation

-generally used for multi-drug resistant organisms (MDRO)

Drugs:

-Linezolid

-Tedizolid

152

Antimicrobial agents: Chloramphenicol

MOA: Reversible binding to the 50S ribosomal subunit, inhibiting transpeptidation.

-Severe BM toxicity so use is limited

-effective against Gram-positive and Gram-negative bacteria including some anaerobes and nonculturable organisms

153

Antimicrobial agents: Tetracycline

MOA: Bind reversibly to the 30S ribosomal subunit,

-interfering with the binding of the tRNA–amino acid complexes to the ribosome, preventing peptide chain elongation

-Upper GI toxicity

-Effective against Gram-negative, Gram-positive, Mycoplasma spp. and intracellular pathogens

154

Antimicrobial agents: Glycylglycines

MOA: Reversibly binds to the 30S ribosomal subunit.

-Synthetic derivative of tetracycline

-used only as a last resort medication due to increased mortality

-used for complicated intra-abdominal infections, skin infections and community-acquired pneumonia

Drugs:

-Tigecycline

155

Inhibitors of nucleic acid synthesis

Fluoroquinolones

-- Bind to and interfere with DNA gyrase enzymes.

-- Newer quinolones inhibit topoisomerase IV

Metronidazole

-- Nitro group is reduced in bacterial cytoplasm, generating cytotoxic compounds that disrupt DNA

Rifamycin (Rifampin)

-- Binds to DNA-dependent RNA polymerase and inhibits RNA synthesis

156

Metabolic inhibitors

Sulfonamides

-- Inhibits dihydropteroate synthase in the folic acid pathway

Trimethoprim

--Inhibits dihydrofolate reductase in the folic acid pathway

Nitrofurantoin

--Drug intermediates bind to bacterial ribosomal proteins and ribosomal RNA (rRNA)

157

Biologic Antibiotic resistance

reduced susceptibility of an organism to an antimicrobial agent

158

Clinical antibiotic resistance

drug is no longer effective for clinical use

159

Environmentally mediated antibiotic resistance

resulting from physical/chemical characteristics of the environment

160

Microorganism-mediated antibiotic resistance

genetically encoded traits

161

Intrinsic resistance

-Normal genetic, structural, or physiologic state of a microorganism

-Often encoded in the chromosome of the organism and not readily transferable

-Predictable

162

Acquired resistance

-Altered cellular physiology and structure caused by changes in a microorganism’s genetic makeup

-A result of genetic exchange and recombination

-Unpredictable

163

Goals of AST in the laboratory

-determine resistance mechanisms of bacterial and their response to antimicrobial agents

-measuring acquired resistance when it is unpredictable

164

Standardization of AST

Purposes:

1. Optimize bacterial growth

2. Optimize conditions for antimicrobial integrity and activity

3. Maintain reproducibility and consistency

Achieved by: 0.5 McFarland turbidity standard

165

Broth dilution test

a method of determining the minimal inhibitory concentration (MIC) by using serial dilutions of an antimicrobial drug

Interpretation:

-Susceptible (S) = inhibitory growth of organism

-Intermediate (I) = unable to determine susceptibility

-Resistant (R) = antimicrobial agent is ineffective

166

Agar dilution

MIC is determined by antimicrobial concentrations and organisms are brought together on an agar-based medium

Interpretation:

-Susceptible (S) = inhibitory growth of organism

-Intermediate (I) = unable to determine susceptibility

-Resistant (R) = antimicrobial agent is ineffective

167

Disk diffusion

Antibiotic disks of known concentrations are placed on the surface of an agar plate that has been seeded with a lawn of bacteria (0.5 McFarland turbidity standard)

After incubation, the diameter of the zone of inhibition around each disk is measured in millimeters

-Diameter of zone = breakpoints to determine S/I/R

Interpretation:

-Susceptible (S) = inhibitory growth of organism

-Intermediate (I) = unable to determine susceptibility

-Resistant (R)= antimicrobial agent is ineffective