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Flashcards in Intro to infectious disease Deck (47):
1

Gram positive (structure)

cell wall Rigid, thick
Made up of mostly of peptidoglycan (50-60%)
A series of cross-linking (transpeptidases) help to create the building blocks of the cell wall.

2

Gram negative (structure)

multiple layered structure
Cell Wall Thin layer-one or two glycan chains
Cell wall protected by lipoprotein outer layer-which functions as penetration barrier.
lipopolysaccharide (LPS)
Matrix protein (porin)-important for regulating influx of molecules
phospholipids

3

Walls of mycobacteria (acid fast bacteria)

Contains peptidoglycan w/polysaccharide and glycolipids
Associated w/staining characteristics

4

Cytoplasmic membrane

Osmotic barrier
Energy production (electron transport-energy gradient-ATPases)
Biosynthesis transport (nutrient uptake, enzyme secretion)
Protein and lipid—lacks sterols

5

Minimum Inhibitory Concentration (MIC)

lowest concentration of antibiotic that inhibits visible growth of the bacteria. value used to indicate susceptible, intermediate and resistant

6

List of Gram Positive Cocci (Aerobic)

Staphylococcus aureus (coag+): Methicillin-sensitive (MSSA), Hospital or Community aquired MRSA
Staphylococcus epidemidis (coag -)
Staphylococcus saprophyticus (coag -)
Enterococcus faecalis
Enterococcus faecium
Enterococcus durans
β hemolytic: Streptococcus pyogenes (Grp A), Streptococcus agalactiae (Grp B,) Streptococcus bovis (nonenterococci, Grp D)
Viridans streptococci – α hemolytic: Streptococcus sangius, Streptococcus salivarius, Streptococcus mitis, Streptococcus mutans
Streptococcus pneumoniae (pneumococcus)

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Staphylococci: colonization and infections caused

Colonization: Skin, Nose
Infections Caused: Cellulitis, wounds, trauma
Bacteremia/Endocarditis, Pneumonia,Osteomyelitis
UTI
Major players in post-surgical infections
Adhere to foreign material and catheters

8

Staphylococcal resistance

Penicillin Resistance: Beta-lactamase production, > 90% of all staphylococcus are resistant to penicillin
Methicillin Resistance: MecA gene codes for novel PBP2a, ~50% of S. aureus are resistant, ~70% of CoNS are resistant
Methicillin-susceptible isolates are also susceptible to cephalosporins and carbapenems

9

Streptococcus: Colonization

Skin: Group A- S. pyogenes
Mouth: Viridans Streptococcus, Anaerobes (e.g., peptostreptococcus)
Nasopharynx: Group A- S. pyogenes
Lower GI: Group D- S. bovis, Viridans, Streptococcus, Anaerobes
Female Genital Tract: Group B- S. agalactiae

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Streptococcus: infections caused

Cellulitis: Group A- S. pyogenes, may result in Nec fasciitis
Dental carries: Viridans Streptococcus
Pharyngitis (Strep throat): Group A- S. pyogenes
Bacteremia/Endocarditis: Viridans Streptococcus
Neonatal meningitis: Group B- S. agalactiae

11

When establishing MIC, what is the difference between susceptible, intermediate, or resistant?

Susceptible- isolates may be appropriately treated with the recommended doses
Intermediate- isolates may be appropriately treated in body sites where the drug is physiologically concentrated or when a high dosage of drug can be used
Resistant- isolates are not inhibited by the achievable concentrations of a normal dose

12

WBC with differential: parameters

Neutrophils 50-70%
Lymphocytes 25-35%
Monocytes 2-6%
Eosinophils 0-6%
Basophils0-3%

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granulocytes (B.E.N)

neutrophils, eosinophils, basophils

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Neutrophils

Prevent microorganism invasion, kill invading organisms
Attracted to site of infection by chemotactic factors
Phagocytize microorganisms- eat up invading organism
Release toxic substances from granules within cell into vacuole containing organism

15

Absolute Neutrophil Count (ANC)

WBC # x (% segs (mature neutrophils)+ %bands (immature neutrophils)
The lower ANC= the higher risk for infection
Neutropenia defined based on ANC-
Mild = ANC 1000-1500/mm3
Moderate= ANC 500-1000/mm3
Severe= ANC < 500/mm3

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Lymphocytes

Effector cells of immune system, recognize invaders, tag them for removal and kill them.
Make antibodies
T cells- 80%
B cells- 20%

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Monocytes

precursors to macrophages
Serve to replenish tissues with macrophages prior to and during immune response

18

Eosinophils

Responsible for immune processes against helminths and parasites (also involved in allergic reaction)

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Basophils

Mediate inflammatory response

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Gram+: Cocci (list)- Chains

CHAINS
Streptococcus pyrogens
Viridans Streptococcus

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Gram+: Cocci (list)-Pairs

PAIRS
Streptococcus pneumoniae
Enterococcus spp.

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Gram+: Cocci (list)-clusters

CLUSTERS
Coagulase-Positive Staphylococcus (S. aureus)
Coagulase-Negative Staphylococcus (S. epidermis)

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Gram+: Bacilli

Listeria
Lactobacillus

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Gram -: Cocci

COCCI
Neisseria menigitidis
Neisseria gonorrhoeae

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Gram -: Bacilli

Escherichia coli
Klebsiella spp.
Enterobacter spp.
Proteus spp.
Serratia marcescens
Pseudomonas spp.

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Gram -: coccobacilli

Haemophilus influenzae

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Pneumococci: Colonization

Oropharynx
Nasopharnyx

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Pneumococci: infections caused

Otitis media
Sinusitis
Bronchitis
Pneumonia (CAP- community acquired pneumonia)

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How do you treat Streptococcus

Penicillin
(More resistance seen with α- hemolytic strep, specifically S. miti)

30

Concern for patients with Asplenia

Patients are at risk for fulminant sepsis syndrome
Lack filtration mechanism of spleen macrophages
Cannot clear encapsulated organisms (body requires spleen to clear the following bacteria)
S. pneumoniae
H. influenzae
N. menigitiis

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Treatment of Pneumococci

3rd generation cephalosporins (ceftriaxone)
May de-escalate with cultures and sensitivities
(Penicillin not a good choice d/t resistance)

32

Enterococci: colonization

Gastrointestinal tract
Female genital tract
Very resistant- harder to kill than staph or strep

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Enterococci: infections

Opportunistic- takes over when you lose normal flora or when immune system is compromised.
Urinary tract infection
Bacteremia/Endocarditis
Intra-abdominal infections

34

Gram negative (Aerobic) List

Rods: Enterobacteraciae: Enterobacter spp, Escherichia coli
Klebsiella pneumoniae
Proteus vulgaris, Proteus mirabilis
Serratia marcenena
Pseudomonas aeruginosa

Cocci/coccobaccilli: Haemophilis influenzae, Nisseiria meningitiis

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Enterobacteraciae (gram -)

GI tract colonization
(Also: Soil,Water, Vegetation)

Gram negative have Lipopolysaccharide (LPS), Cell wall component
Acts as an Endotoxin

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Enterobacteraciae: infections

Urinary tract infections (accounts for 70%)
Intraabdominal infections
Bacteremia
Nosocomial pneumonia (pts in hospital, not out in community)
Diabetic foot infections

37

Enterobacteraciae Resistance

Prevalent
More common in hospital-acquired infections
Treatment guided by in vitro susceptibility testing--cultures are essential

38

Pseudomonas aeruginosa: colonization

Not considered normal flora (soil, water, vegetation)
Can colonize upper respiratory tract of immunocompromised patients
Cystic fibrosis
COPD

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Pseudomonas aeruginosa: infections

Opportunist: Immunocompromised patient
If pt has been on Broad spectrum antibiotics
Ventilation equipment-psudomonas clings to equipment (thats why you see it in cystic fibrosis a lot).

Nosocomial infections
Hospital acquired pneumonia (HAP)
Febrile neutropenia
Skin and soft tissue infections (burns, trauma, post-surgical)
Urinary tract infections (nursing home or hospital most likely)

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SPACE

Remembering when to double cover—treat these with 2 antibiotics:
Serratia
Pseudomonas
Acinetobacter
Citrobacter
Enterobacter

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Gram – Coccobacilli

Haemophilus influenzae
Encapsulated
More virulent
Not regular colonizer
Causes meningititis

No capsule
Colonizes upper resp tract
Causes ottitis media, sinusitis, CA

42

Polysaccharide Capsule

Eludes immune system
Requires spleen for elimination
PS capsule is target for vaccine
Hib vaccine
Meningococcal vaccine

43

Anaerobes

Upper and lower GI tract, vaginal colonizers
Associated with intraabdominal infection, aspiration pneumonia, endometritis, PID, diabetic lower extremity infections, dental carries, head and neck
Above diaphragm
Peptostreptococcus spp. (gram + cocci)
Actinomyces spp (gram + rod)
Fusobacterium (gram – rod)

Below diaphragm
Bacteroides fragilis (gram – rod)
Lactobacillus (gram + rod)
Clostridium spp (gram + rod)

Gram-negative isolates are usually penicillinase producers

44

Atypicals

Not normal colonizers
Not able to gram stain
Multiply intracellularly
Examples:
Mycoplasma pneumonia
Legionella pneumophilia
Chlamydophila pneumoniae

Can result in CAP (community acquired pnemonia)

45

Even Some Super Killers Have Pretty Nice Capsules

Escherichia Coli
Streptococcus Pneumoniae
Salmonella
Klebsiella pneumoniae
Haemophilus influenzae
Pseudomonas aeruginosa
Neisseria meningitidis
Cryptococcus neoformans (yeast)

46

Nine Important “Classes” of Bacterial Pathogens (1-5)

Streptococci- Group A strep, viridans strep
Streptococcus Pneumoniae
Enterococcus- usually faecalis
Staphylococci- S. aureus, coagulase-negative
Atypical bacteria- Mycoplasma, Chlamydia, Legionella

47

Nine Important “Classes” of Bacterial Pathogens (6-9)

Haemophilus influenzae
Gram- negative rods- E.coli, Klebsiella, Proteus, etc.
Pseudomonas aeruginosa
Anaerobes- Bacteroides, Clostridia, Prevotella