Flashcards in LOs: 36-38 Deck (21)
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36 Epidemiology of HIV:
HIV-1 vs. HIV-2
HIV-2 endemic area
Prevalence in the US
- 50% are...
- 14% constitute...
HIV-2 is a milder form and progresses slower than HIV-1
West Africa
0.5%
- men who have sex w/ men
- African-Americans
2
36 HIV Transmission:
Common modes (4)
Uncommon modes (3)
C
- sexual intercourse
- injection drug use
- vertical transmission (ART given during pregnancy)
- breastfeeding postpartum
U
- transfusion of contaminated blood
- transplantation of infected organs
- accidental inoculations of health workers with needles contaminated by infected persons
3
36 HIV Structure & Life Cycle:
Structure
- DNA/RNA enclosed in...
- Envelope consists of...
- Contents of envelope
Life Cycle
- Binding (2)
- Entry
- Viral genome
- Transcription
- Integration
- Production
- Release
S
- 2 RNA enclosed in a cone-shaped p24 capsid protein
- lipid bilayer membrane containing viral glycoproteins
- trimerix complex: transmembrane gp41 & external gp120 subunuts
L
- viral glycoprotein binds to CD4 on T helper cells, macropahges, & dendritic cells
- CD4 binds to gp120 to bind chemokine coreceptors CCR5 or CXCR4
- fusion of viral & host membranes & viral entry
- viral genome is released in the cytoplasm
- reverse transcriptase transcribes HIV RNA to dsDNA
- integrase integrates viral & host DNA
- transcription of viral DNA produces viral proteins
- protease cleaves viral polypeptide so components assemble in cytoplasm & release from cell
4
36 Natural History of Untreated HIV-1:
Primary Infection
- Lasts...
Clinical Latency
- Lasts...
- Duration
- Children
Symptoms
- Occur...
- Caused by...
- Death
P
- lasts 2-6 weeks
C
- follows w/ no symptoms for ~8-10 years (variable)
- duration related to level of viremia (higher level = shorter interval)
- shorter for children
S
- when CD4+ T-cell count < 200 cells/uL
- caused by increasing viremia or opportunistic disease
- death on average 18 months after AIDS diagnosis
5
36 HIV Pathogenesis:
1. Infection
2. CD+4 T cells...
3. Virus production
4. Host response
5. Generation of viral variants
6. Viral variants...
7. Chronic HIV infection
8. T-cell regeneration
9. Organ dysfunction
1. HIV-1 infects mainly CD4+ helper T-cells and macrophages / microglia
2. CD4+T-cells are killed
3. Virus production & CD4+T-cell destruction is massive and rapid
4. The host response (antibodies and cell-mediated immunity) is partially effective
5. High viral turnover and the error prone reverse transcriptase (RT) generates viral variants
6. These variants escape the host’s immune responses & ART therapies and cause CD4+T-cell destruction and disease progression
7. Chronic HIV infection is associated with persistent immune activation and increased levels of systemic inflammation which promotes viral replication and increased apoptosis
8. T-cell regeneration fails to keep pace with destruction, leading to progressive CD4+T-cell depletion, immunodeficiency, and death
9. Organ dysfunction can result from:
a. Direct effects of HIV
b. Immune reaction to the virus
c. Secondary infection by opportunistic pathogens
d. Increased systemic inflammation and persistent immune activation
6
36 Diagnosis of HIV-1 Infection (4)
Screening test: ELISA
Newer generation tests
Confirmatory test: HIV-1/HIV-2 antibody differentiation (Multispot) assay or Western Blot
ELISA for neonatal infection: maternal antibodies produce false positives
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36 Acute HIV-1 Infection and AIDS:
Associated with...
Occurs...
Symptoms
Laboratory findings
Diagnosis
HIV-1 seroconversion
2-4 weeks from transmission: Acute Retroviral Syndrome (mimics mononucleosis)
Fever, lethargy, malaise, myalgia, headaches, sore throat, rash, oral ulcers, neck stiffness, and lymphadenopathy
Clinical suspicion & positive PCR for HIV-1 RNA
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36 Chronic HIV-1 Infection and AIDS:
- Disease
- Description
- Treatment
Oral Manifestations (1)
Cutaneous Manifestations (2)
Gastrointestinal Manifestations (1)
Pulmonary Infections (2)
Central Nervous System and Ocular Infections (3)
HIV-Related Malignancies (2)
O
(1) Oral Candidiasis (Thrush)
- Topical (clotrimazole) & fluconazole
C
(1) HSV-1 or HSV-2
- Painful ulcers with raised margins; oral and perianal locations
- Oral (val)acyclovir
(2) Varicella Zoster Virus (Shingles)
- Usually one dermatome, may be multidermatomal/disseminated
- Oral (val)acyclovir
G
(1) Mycobacterium avium Complex (MAC)
- Disseminated, hepatomegaly, decreased blood counts, elevated liver enzymes
- Azithromycin, rifabutin, ethambutol, and amikacin
P
(1) Pneumocystis jiroveci Pneumonia (PJP or PCP)
- Fever, dyspnea, nonproductive cough, & bilateral interstitial infiltrates on chest x-ray
- TMP/SMX (therapy & prevention)
(2) Mycobacterium tuberculosis (Mtb)
- Risk of reactivating latent Mtb
- Rifampin/Rifabutin, Isoniazid, Pyrazinamide, Ethambutol
C
(1 )Progressive Multifocal Leukoencephalopathy (PML)
- Demyelinating disease of cerebral white matter, caused by JC virus, change in mental status, confusion, hemiparesis, ataxia
- ART therapy
(2) Cryptococcal Meningitis
- Persistent, dull headache, malaise, fever, night sweats
- Amphotericin B w/ flucytosine, then fluconazole
(3) Toxoplasmosis
- Reactivation from latent cysts, change in mental status, headaches, multiple ring-enhancing lesions on CT
- Sulfadiazine/pyrimethamine
H
(1) Kaposi’s Sarcoma (KS)
- Focal, vascular nodules in skin or other organs, caused by HHV-8 or KSHV
- ART, systemic interferon, radiation, or chemotherapy
(2) Non-Hodgkin’s Lymphoma
- In pts w/ CD4 counts
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36 Prevention of HIV Infection:
Important obstacles (4)
Approaches to HIV prevention (10)
Outcome of preventative measures greatly depends on...
Barriers to HIV eradication (3)
I
- Silent infection during which transmission can occur
- Human libido
- No effective vaccine
- Social stigma
A
- Education
- Behavioral modification
- Barrier protection
- HIV testing
- Treatment as prevention
- Circumcision
- Pre-exposure prophylaxis
- Post-exposure prophylaxis
- Prevention of maternal to child transmission (PMTCT)
- Substitute for breastfeeding
O
- Risk compensation: assuming that you use protection so you’re safe
- Uptake of intervention: actually using protection given to them (e.g. condoms)
- Access to target population
B
- Long-lived latently infected cells
- Residual viral replication
- Anatomical reservoirs that have limited penetration of ART
10
37 Role of Mobile Genetic Elements in Bacterial Virulence:
Repertoire of virulence genes dictates...
Differences in virulence gene repertoires results from...
Advantages of having virulence genes on mobile genetic elements (2)
Disadvantages of having virulence genes on mobile genetic elements (2)
Solutions to those problems (2)
What type of disease develops
Presence of many virulence genes on mobile genetic elements, including plasmids, phages, and transposons
(1) A single pathogen can cause different diseases
(2) New virulence genes can be rapidly transferred within a bacterial population
(1) Extrachromosomal mobile genetic elements tend to be unstable & can be lost
(2) It might be necessary for a single bacterial cell to acquire and maintain many mobile genetic elements
(1) Some mobile genetic elements can stably integrate onto the chromosome (phages & transposons for lysogenY)
(2) Many mobile genetic elements have acquired multiple (complementary)
virulence gene
11
37 Lytic vs. Lysogenic Bacterial Phage Infections:
Lytic Infection
Lysogenic Infection
Progeny virus is produced, but this infection is lethal for bacterial host cell
No progeny virus is produced and the infection is nonlethal for the bacterial host, but allows phage genes to be stably maintained in the lysogenized bacterium
12
37 Connection between lysogeny/phages and diphtheria:
Symptoms caused by...
Gene encoding diphtheria toxin
Regulation of diphtheria toxin expression
- Only occurs...
- Involves...
Diphtheria toxin
Carried by a phage (beta-phage) which can lysogenically infect Corynebacterium diphtheriae (a gram-positive bacterium), leading to stable expression of diphtheria toxin
- Under low-iron conditions
- An iron-binding repressor called DtxR (Diphtheria Toxin Repressor) encoded by the dtxR gene present in the C. diphtheriae chromosome (not encoded on the phage)
13
37 Corynebacterium diphtheria:
Biological Characteristics
- Type
- Aerobe/Anaerobe
- Growth
- Contains...
- Resistance
Reservoir
- Pathogenic
- Nonpathogenic
Transmission (2)
Virulence Factors (2)
Pathogenesis
- Colonization
- Produces...
- Symptoms
- Formation of...
- ...which becomes...
- C. diphtheriae cells...
Diagnosis (3)
Treatment (2)
Prevention
BC
- gram+ club-shaped rod
- aerobic
- fastidious, grows on selective media containing tellurite salts
- contains polyphosphate granules
- resistant to environmental factors
R
- humans
- nontoxigenic in throats of healthy people
T
- nasopharyngeal: inhalation of aerosol droplets
- cutaneous: droplets settle on skin at site of a cut or ulcer
VF
- adhesins
- diphtheria toxin: responsible for the disease, inhibits hot cell protein synthesis by ADP-ribosylating elongation factor 2
P
- colonization of nasopharynx or skin
- produces diphtheria toxin & necrosis
- symptoms: malaise, sore throat, enlarged cervical lymph nodes
- formation of a pseudomembrane in the throat that contains bacteria, fibrin, necrotic epithelial cells, PMNs, and RBCs
- pseudomembrane becomes more adherent w/ time, enlarges, blocks respiration, & causes death
- C. diphtheriae cells remain on the mucosal epithelium (not invasive), some are absorbed & enter circulation to damage internal organs, causing death
D
- clinical grounds
- culture (tellurite agar)
- toxin testing
T
- antitoxin
- antimicrobials: erythromycin or penicillin
P
- DPT vaccine
14
37 Pathogenicity Islands:
Definition
Features (4)
Transfer and integration of virulence factors
- Can involve...
- Example pathogen
Lysogeny & Cholera (4)
Clustering of virulence genes in one specific region of a bacterial chromosome
- Transferred from other isolates
- Found in both gram+ & gram(-) bacteria
- A single bacterial cell can carry >1 pathogenicity island
- Type III secretion systems of gram(-) bacteria are on pathogenicity islands
- Lysogenic infection by a phage
- Diphtheria
- Toxigenic V. cholerae is lysogenized with a phage (the CTXf phage) that carries the genes that encode for the production of cholera toxin and other accessory enterotoxins
- Transfer of CTXf between V. cholerae isolates converts the recipient to virulence
- The receptor for CTXf phage is the TCP (toxin-coregulated pilus) adhesion
- The TCP is required for V. cholerae colonization of the small intestine
15
37 Vibrio cholera:
Biologic characteristics
- Type
- Motility
- Aerobe/Anaerobe
- Oxidase
- Growth
- Characteristic of Vibrio spp.
- Classified by...
- V. cholerae distinguished from other Vibrio spp. by...
- Serotypes associated w/ epidemic/pandemic spread
Transmission/Reservoir
Virulence Factors
- Most important
- Accessory enterotoxins (2)
- Colonization factors (4)
Regulators of VF production
- Expression
- Involves...
- Binding
Pathogenesis
- Ingestion
- Survival
- VF expression
- Regulator
- Produces...
- Severe cholera
- No...
Diagnosis (3)
Prevention (2)
Treatment (3)
BC
- gram(-) comma-shaped rods
- motile
- facultative anaerobes
- oxidase+
- thiosulfate-citrate-bile salts (TCBS) agar
- halotolerant
- serotyping (O antigen)
- biochemical tests
- O1 & O139
T/R
- T: ingestion of contaminated food/water
- R: estuary waters
VF
- Cholera toxin: causes increased cAMP levels in intestines --> fluid & electrolyte loss
- Zonula occludens toxin (affects tight junctions) & accessory enterotoxin (forms ion channels)
- Toxin-coregulated pilus, biofilm production, other adhesins, & other colonization factors
R
- Coordinately expressed: controlled by the ToxR regulon
- Involves TcpP, ToxR, & ToxT
- ToxT binds to virulence gene promoters & activates their expression
P
- ingested & passed through gastric acid barrier
- survives gastric acid by biofilm
- virulence factor expression is turned on while moving through intestinal mucus via flagella
- ToxR regulon allows production of toxin coregulated pilus (TCP)
- produces cholera toxin during colonization to increase cAMP & activate ion secretion --> fluid/electrolyte loss & diarrhea
- severe cholera: diarrheal fluid has a pale yellow/brown color with flecks of small
white mucous material ("rice water stool"), poor skin turgor, sunken eyes, vomiting, dehydration, cardiac problems, shock, coma, & death
- no invasion or leucocytes
D
- clinical grounds
- stool culture
- biochemical/serologic tests
P
- good hygiene, good water, and cooked food
- oral vaccines; O1, O139, & B-subunit recombinants
T
- restore fluid/electrolyte balance
- oral rehydration solution (sodium uptake results in water uptake)
- azithromycin
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38 Regulation of Bacterial Virulence Gene Expression:
Coordinate regulation
Global regulator
Environmental changes
Signals that change virulence gene expression (4)
Sensing mechanisms (2)
Multifactorial viurlence allows expression of all necessary virulence genes to be turned on/off at the same time
Coordinate regulation is achieved with this single regulatory element
Signal the bacterium to coordinately turn on/off virulence gene expression
- Macro- & micro-environmental
- Bacterium senses when it's inside/outside a host cell (vs. another cell)
- Temperature
- pH
- Nutrient changes (e.g., iron)
- Osmolarity
- Two component regulatory systems
- Quorum sensing
17
38 Two Component Regulatory Systems:
Regulates..
Components (2)
Cross-talk
Many bacterial functions, including virulence factor expression in both gram-positive and gram- negative bacteria
(1) Sensor protein: transmembrane protein, activates the cytoplasmic histidine kinase domain
(2) Transcriptional regulator: cytoplasmic protein, activates some but represses other gene expression
- A single bacterial cell can carry more than one type of two component regulatory system
- Cross-talk can regulate gene expression
- Possible for a system to regulate another
18
38 The PhoP/PhoQ System in Salmonella:
PhoP & PhoQ
Responds to...
Activation
- Turns on...
- Turns off...
Survival (2)
Mechanisms of resistance to antimicrobial peptides (2)
Essential for virulence
- PhoP: transcriptional regulator
- PhoQ: membrane sensor
Conditions (e.g., low Mg2+ levels) found inside acidified phagosomes, becoming activated when Salmonella enter phagocytes
Increases expression of some genes (pag genes), but represses expression of other genes (prg genes)
- Turns on expression of pag genes needed for intracellular survival
- Turns off prg genes that were needed for extracellular survival/early steps in pathogenesis
- PhoP/PhoQ mutants do not survive in macrophages, so this system is important for survival inside phagocytes
- Increased expression of pag genes enables Salmonella to survive inside phagocytes by permitting resistance to antimicrobial peptides
(1) Activate expression of a second two component regulator (PrmA/PrmB) that modifies LPS so it no longer binds antimicrobial peptides
(2) Production of membrane proteins which protect the Salmonella cell from antimicrobial peptides
19
38 Quorum Sensing Systems:
What bacterial pathogens need to do before causing disease
Some pathogens use quorum sensing to...
Quorum sensing involves...
Ex. Pseudomonas aeruginosa
Reach a critical density
Sense their population density and accordingly adjust their virulence factor expression
Production/secretion of a small autoinducer
- When the bacterial population reaches proper density, the autoinducer activates transcriptional regulators
- This leads to increased expression of virulence genes
Activation of a transcriptional regulator leads to production of a new autoinducer, which activates transcription of additional virulence genes.
20
38 Cross-Talk Between Quorum-Sensing and Two-Component Regulatory
Systems:
Cross-talk
Ex. S. aureus (2)
Expression of a virulence gene is often under the control of multiple regulatory systems
(1) An autoinducer binds to and activates AgrC, the sensor protein of a two component regulatory system
(2) The autoinducer of one S. aureus strain can bind to, but not activate, the AgrC of another S. aureus strain, inhibiting toxin expression by that strain
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