Infectious diseases Flashcards
Selective Toxicity
An Ideal antibiotic agent targets a biological mechanism specific top the pathogen.
Easier to achieve with prokaryotes and viruses.
Minimum inhibitory concentration (MIC)
The lowest concentration of a compound that inhibits growth of the microorganism in vitro.
Minimum Bactericidal Concentration (MBC)
The lowest concentration of a compound needed to kill 99.99% of microorganisms in a colony count in vitro.
Other important pharmacokinetic factors with antibiotics
Ability to reach site of infection
Difficult areas to reach include bone, CNS, adipose.
Toxicities of Antibiotics
Allergic reactions
Idiosyncratic reactions
Pharmacogenomic reaction
Normal flora changes —> can lead to C. Diff
Bactericidal
Kills the microorganisms
Bacteriostatic
halts growth of an infection, innate immune system can then remove the pathogens
Broad Spectrum
Effective against a wide range of organisms
Extended spectrum
Agents with an intermediate range of effectiveness
Narrow spectrum
Effective against only a few organisms
Antibiotics that interfere with Cell Wall synthesis
Beta Lactams
Vancomycin
Bacitracin
Polymyxins
Antibiotics that interfere with Nucleic acid synthesis
Sulfonamides
Trimethoprim
Quinolones
Rifampin
Antibiotics that interfere with Protein synthesis
Macrolides (-mycins) Linezolid Chloramphenicol Streptogramins Tetracyclines Aminoglycosides
Cell Wall synthesis inhibitors are ____
Bactericidal
Protein and Nucleic acid synthesis inhibitors are _____
Bacteriostatic
Cell wall synthesis inhibitors prevent ________
Peptidoglycan crosslinking. This requres transpeptidase to link together D-alanine residues on murein monomers
Beta-Lactam drugs work by ____
Targeting transpeptidase. The beta-lactam ring binds transpeptidase.
Examples of Beta-lactams
Penicillins- Natural effective against Gram+ Syphillis, Extended good for Gram +/-
Cephalosporins- 5 gens, each different
Carbapenems- potent, broad spectrum
Monobactams- narrow spec, Gram - only, safe for those with allergy to Beta-lactam ring.
Beta-lactamases are a ______ that work by _____
Bacterial resistance
Opening the Beta-lactam ring
Beta-lactamase can be over come with ___
Combination therapy of strong and weak Beta-lactam.
Ex. Amoxicillin/Clavulanate
Or
Modification of antibiotic so access to ring is restricted.
Ex. Methicillin.
Glycopeptides
Cell wall inhibitors that bind to D-alanine residues on monomers.
Ex. Vancomycin
Last line treatment for MRSA
Lipopeptides
Ex. Daptomycin
Cell wall inhibitors, insert into the plasma membrane to disrupt the cell wall.
Bacitracin
Cell wall inhibitor that prevents peptidoglycan subunits from being transferred to cell surface.
Only approved for external use.
Polymyxins
Cell membrane inhibitor.
Small, positively charged peptides that disrupt structure.
Gram - only
Cannot be absorbed in GI tract due to charge.
DNA/RNA inhibitors
Broad spectrum
Direct inhibitors are Bactericidal
Indirect inhibitors are Bacteriostatic
RNA polymerase inhibitor
Rifampin
Topoisomerase inhibitor
Quinolones
DNA structure stability inhibitor
Metronidazole
Inhibitors of folic acid synthesis
Sulfonamides
Trimethoprim
Used synergistically
Protein synthesis inhibitors
Generally bacteriostatic
Either inhibit 50S or 30S ribosome
50S inhibitors
Chloramphenicol
Macrolides: Erythromycin, Clindamycin, Lincomycin
Lenzolide
30S inhibitors
Tetracyclines
Aminoglycans
Additive Combination therapy
Drugs add to each other’s efficacy in a summative manner
Ex. Beta-lactamase inhibitor + beta-lactam
Synergistic combination therapy
Drugs enhance each others efficacy greater than summative effect
Ex. Sulfonamides and trimethoprim
Antagonistic COmbination therapy
One drug impairs the efficacy of the other
Ex. Tetracyclines + Penicillins
Categories of infectious agents
Bacteria Viruses Parasites Fungi Prions
Transmission routes of infectious disease
Direct contact Fluid exchange Contamination Airborne Vector
Portals of entry
Mucosal membranes
Skin
Parenteral route (puncture)
Localized infection
Localized replication and spread of pathogen
Systemic infection
Replication and spread to blood and neurons potentially
Normal Host defenses
Skin Mucous membranes Resp tract GI tract UG tract Eyes
Host factors
Influence the course of infection: Non-specific immune response Immune status Genetics Age Nutritional status Hormones Personal Habits Fever Microbiome
Anti-viral effect of IFN
Virus infects cell and produces viral DNA, induces interferon synthesis, interferon is secreted.
Antiviral state is induced by binding of interferon to receptor on cell surface.
INTERFERON INDUCTION
EIF-2alpha Protein Kinase: inhibits initiation of mRNA translation
Oligo-adenylate synthase: activates RNSase L, leading to degradation of mRNA and tRNA.
Common types of vaccines
Inactivated pathogen
Live, attenuated
Subunit, purified antigen
Toxoid
What test delineates Staph and Strep?
Catalase test
Characteristics of a Gram-positive infection
Bullous impetigo Draining sinus tracts Erythema Fever Murmur if endocarditis Petechiae is TSS present Superficial abscesses Warmth
Streptococci
Gram positive cocci
Forms chains of cocci
Catalase negative
Ex. S. Pneumoniae, pyogenes, agalactaie, viridans
Staphylococci
Gram positive cocci
Catalase positive
S. Aureus and others
S. Aureus is Coagulase positive
Staph. Aureus diseases
Wound infection food poisoning Scalded skin syndrome TSS Endocarditis, osteomyelitis, pneumonia, brain abscesses, meningitis, and bacteremia
MRSA
Methicillin resistant staph aureus
Staph aureus virulence factors
Adhesins exotoxins- enterotoxins, TSS toxin, Exfoliative toxins Superantigens Biofilms Beta-lactamase
Conjugation
One bacteria uses a sex pili to inject part of a resistance plasmid into another
Transformation
DNA from one bacteria is lysed and incorporated into the genome of another bacteria that picks it up
Transduction
Bacteria forms bacteriophage, which injects resistance genes into new bacteria cells.
Biofilms
Aggregates of bacteria
Extremely resistance to antibiotics
Resistant to phagocytosis
Gram positive bacilli
Clostridia Bacillus Listeria Erysipelothrix Corynebacterium Mycobacteria
Can be differentiated by catalase, fermentation, urease/gelatinase, and hemolysis
Spore forming Gram + Baccilli
Clostridia
Bacillus
Anaerobic Gram + baccilli
Clostridia
Can cause abscesses and life threatening infections
Ex. C. Diff, C. Perfringens (gas gangrene)
Gram negative cocci
Neisseria
Moraxella
Appropriate culture medium for GNC
Blood agar
Chocolate agar
Thayer-Martin agar(selective for neisseria)
Neisseria
Oxidase positive
Catalase positive (except, elongata)
N. Gonorrhea
N. Meningitidis
Gram negative bacilli
Haemophillus Aggregatibacter Actinobacillus Pasturella Enterobacteriaceae Pseudomonas Burkholderia Stenotrophomonas Acinetobacter
Enterobacteriaceae
Escherichia Salmonella Shigella Yersinia Klebsiella Proteus Citrobacter Enterobacter Serratia
Type of Haemophillus
Inflenzae
Aegyptius
Ducreyi
Most common Gram negative infections
E. Coli Pseudomonas aeruginosa Klebsiella Acinetobacter baumannii Enterobacteriaceae
Risk factors for Gram - infection
Hospitalization Recent surgery Urinary catheter War wounds Dialysis Mechanical ventilator Weak immune system
Gram - Spiral shaped bacteria
Campylobacteraceae
Helicobacteraceae
Other Gram - bacilli
Bordetella pertusis Brucella Francisella tularensis Legionella pneumophila Bartonella Vibrio
Moraxella catarrhalis
3rd leading cause of bacterial ear infections in children
URI in adults
Cause of COPD exacerbation
Serratia marcescens
Hospital settings/ medical exposure
Immunosuppresion, previous antibiotics, catherterization
Infecctive endocarditis in drug users
Enterobacteria family
Haemophilus influenzae
Hib is primary causative agent of acute epiglottis
Characteristics of bacteria
Prokaryotes Cell wall Nucleoids and plasmids Flagella, pili Capsules Virulence factors
Bacterial cell wall is composed of
peptidoglycan branched together by Amino acids
Cell wall in Gram Positive bacteria
Thick peptidoglycan layer outside plasma membrane
Cell wall of Gram negative bacteria
Thin peptidoglycan layer between two lipid bilayers, outside layer contains imbedded endotoxins
Objects of Antibiotic activity
Nucleic acid synthesis RNA polymerase Ribosome protein synthesis Folate synthesis Cell membrane Cell Wall LPS and/or TLR4
Differential media
Allows closely related bacteria to grow, in a unique way that allows their differentiation when compared to each other
Ex. Blood agar
Selective media
Used to isolate a particular kind of bacteria, allowing only the selected type of bacteria to grow.
Blood Agar
Differential media, can be used to distinguish between bacterial species that are alpha hemolytic, beta hemolytic, and non-hemolytic
Chocolate Medium
Non-Selective growth medium
Thayer-Martin Medium is has been treated with antibiotics so that it IS SELECTIVE ONLY to Neisseria.
MacConkey Agar
Selective and differential medium
It is SELECTIVE for Gram (-) and Enteric bacilli because of its crystal violet and bile salts, and DIFFERENTIATES based on amount of lactose fermentation by turning pink in the presence of fermentation.
Bacterial virulence factors
Capsule
Cell surface structures
Secreted toxins and enzymes
Indirect virulence factors
Siderophores
Secretion machinery
Catalase
Regulatory factors
Mycoplasma
Simplest bacteria, no cell wall, very small genome
Complex nutritional requirements
Triple later cell membrane
Generally infects upper respiratory tract
Attached to sialoglycoproteins
Can secrete oxidants— damage tissues
Mycoplasma pneumoniae
Ureaplasma urealyticum
Spread through droplets
IgM, IgG and IgA in that order respond
Immunity is not long lasting, can relapse.
Mycoplasma pneumoniae clinical manifestations
Dry cough Wet cough after 3-4 days Tracheobronchitis Scattered rhonchi and expiratory wheeze Atypical pneumonia may develop Can exacerbate asthma
Mycoplasma pneumoniae Diagnosis
Mild leukocytosis
WBC up to 15,000 microliter
Non-viscous sputum
non-specific radiological images
Mycobacteria
Aerobic, immobile, bacilli, gram positive
Slow growing. Mycolic acid in cell wall—> only stain with Acid Fast
Some species may be pigmented yellow or orange
Lipid rich cell wall
tuberculosis, NTM, leprae
Mycobacterium tuberculosis
Can be caused by many species of Mycobacterium
One of the world’s deadliest diseases
Leading killer of HIV infected patients
Lowenstein-Jensen culture media
Infectious pulmonary TB, easy to transmit
Nontuberculosis mycobacteria (NTM)
Over 150 found in nature
M. Avium is most pathogenic
Difficult to diagnose
Mycobacterium lepra
Causes Leprosy
Slow proliferation, incubation for months to years
Only 5% of people can actually develop leprosy
Close contact transmission
Can be tuberculoid or lepromatous
Legionella
Found in freshwater and human made building water systems
Spread through droplets
Elderly/immunocompromised most at risk
Grows in Buffered charcoal yeast Extract agar
Chlamydia
Biphasic developmental cycle
Environmentally stable infectious particle (EB)
EB stain purple with Giemsa, non-infectious RBs stain blue
Elementary bodies enter host cell, form reticulate bodies which multiply and differentiate into elementary bodies. Forms inclusion in cell.
Cell lysis spreads EBs.
Obligate parasites
Can only be cultured in Eukaryotic cell lines.
Ricketsiaceae
Obligate intracellular parasite Transmitted via arthropod Fever, rashes, vasculitis Coccobacilli Multiply in endothelial cells of small blood vessels Infected cells swell, necrose
E. Coli
Food poisoning, UTI, gastroenteritis, newborn meningitis
Pseudomonas aeruginosa
Lung and UTI
Klebsiella
Meningitis, lung, UTI and blood stream infections
Acinetobacter baumannii
Several infections in war wounds
Enterobacteriaseae
UTI, lung and bloodstream infections, food poisoning
What is a virus?
A virus is a pathogen that is not alive. The basic structure of a virus is a genome composed of RNA or DNA, a capsid, and an optional envelope.
Viral Genomes
Can be ssDNA or dsDNA, linear or circular
Can be ssRNA, plus or minus sense, or dsRNA
Genome can be complete or fragmented.
Plus sense RNA
the genome is ready to be translated into proteins
Minus sense RNA
The genome must first be transcribed to a plus sense RNA in order to be translated into protein
Naked virus
Lacks an envelope
Basic steps of viral life cycle
- Attachment to host
- Entry to host cell- Endocytosis or membrane fusion (doesn’t need step 3)
- Uncoating
- Viral gene expression
- Viral genome replication
- Assembly of capsids
- Maturation
- Egress- budding or cytolysis
Cytopathic effects of viral replication
Lytic infection
Syncytium formation
Hyperplasia
Transformation
Lytic infection
Virus can only replicate via cell lysis, so it produces characteristic lysed cells, visible on stain by the lack of cytoplasm and shriveled nucleus remaining.
Syncytia formation
Enveloped viruses can cause fusion between cell membranes of infected cells, forming giant cells. HIV does this.
Hyperplasia
Cells multiply in order to absorb stimulus. Ex. Epstein Barr Virus, Papilloma virus
Transformation
Changing of normal cell function to abnormal, usually cancerous growth. Ex. HTLV (leukemia), HPV (cervical cancer)
Common viral causes of latent infection
Measles
Herpes simplex
Herpes zoster
Immunopathological reaction example
Dengue virus causing plasma leakage in eye
Example of viral cause of altered development
Zika virus— microcephaly
Rubella virus, cytomegalovirus can also cause birth defects
Acute viral infections
Acute followed by clearing
Ex. Rhinovirus, rotavirus, Influenza virus
Chronic infection
Virus does not clear after acute infection
Ex. Hepatitis B, C
Latent infection
Reactivates at certain periods of time.
Ex. Herpes simplex and zoster
Slow virus infection
Acute infection followed by persistent infection and virus overproduction.
Ex. Measles virus SSPE, HIV
Viral factors influencing outcome of infection
Virus host range
Viral virulence
$ of viral particles present in inoculum
RNA viruses encode their own ____
RNA polymerase
Picornavirus features
Rhinoviruses and Enteroviruses
Naked
Plus-sense ssRNA, linear
Cytolytic
Enteroviruses
PH range 3-10
Small intestine major site
Prefer 37 degrees C
Rhinoviruses
pH 6-8
Primary at nasal mucosa
Prefer 33 degrees C
Picornavirus syndromes
Aseptic meningitis Encephalitis Common cold Febrile rash illnesses (HFM disease) Conjunctivitis Herpangina Myositis and myocarditis Hepatitis
Paramyxovirus Features
Negative sense ssRNA, linear
Enveloped, fusion proteins, HNs
Mumps, measles, respiratory tract infections (resp syncytial virus, parainfluenza virus, metapneumoviruses)
Budding to spread
Orthomyxovirus Features
Influenza viruses Negative sense, ssRNA, segmented Enveloped, Surface glycoproteins Hemagglutinin and Neuraminidase (HN) Very antigenically variant Transfer via budding
Orthomyxovirus antivirals
Target unique replication features, attachment and polymerase
Orthomyxovirus syndromes
Respiratory tract infections, mild to severe
Vaccination can decrease severity
Reovirus Features
8-11 segments of dsRNA
Naked
Rotavirus
Cytolytic
Rotavirus
Leading cause of severe, dehydrating gastroenteritis in children under 5. Infects enterocytes, destroying them, decreasing GI absorption, causing diarrhea
Retrovirus features
Plus sense, ssRNA with reverse transcriptase
RNA is transcribed into DNA and inserted into cellular genome
Enveloped.
Transfers via budding
HIV, feline leukemia virus
Parvoviridae Features
Very small
Naked
linear, ssDNA with hairpins
Only replicates in actively dividing cells
Human Parvovirus B19
Replicates in immature erythroid cells
Aplastic crisis
Fifth disease
Fetal death
Polyomaviridae
Small
Naked
heat-stable, solute resistant
Circular dsDNA
Slow replication cycle, in cell nucleus, uses cellular enzymes
JC virus, BK virus, Merkel cell virus
Usually only in immunocompromised patients
JC virus
Causes progressive multifocal leukoencephalopathy
BK virus
Associated with nephropathy in transplant recipients
Merkel cell virus
Associated with the majority of Merkel cell skin carcinomas
Papillomaviridae
Small
Circular, dsDNA
Naked
Causes warty lesions, many types, can cause genital cancers
Adenoviridae
Medium sized, naked
Capsisd contains spike-like attachment protein
Linear, dsDNA with repeats
Cytolytic
“pan-handle” replication
Causes acute respiratory disease, conjunctivitis, gastroenteritis
Hepadnaviridae
Small, enveloped
Circular, partially dsDNA
Envelope contains lipid and viral surface antigens
Hepatitis B, persistent infection associated with liver cancer
Herpesviridae
Large, enveloped with glycoprotein spikes (peplomers)
Linear, dsDNA
Can establish latent infections
Encodes its own DNA polymerase
HSV, Zoster, Epstein-Barr, HHV 6, 7, 8, Cytomegalovirus
Causes of mononucleosis
Epstein-Barr virus
Cytomegalovirus
Poxviridae
Very large virus Lipid contraining envelope. Linear, covalently closed, dsDNA genome Replicate in cell cytoplasm Small pox, vaccinina, molluscum contagiosum, monkey pox
Fungi
Yeast
Molds
Dimorphic
Opportunistic
Fungal branching
Hyphae
True pathogenic fungi
Asperillus
Candida
Histoplasma
Opportunistic fungi
Cryptococcus
Pneumocystis
Mycotoxicoses
amanitin and phalloidin- Magic mushrooms
Aflatoxin- grows on peanuts
ergotism- grows on grains
Fungal cell wall
Composed of chitin
Contains ergosterol
Ergosterol is the main target of most antifungals
Pathogenesis of Fungal infections
Granuloma formation
Acute suppuration
Medium for culturing fungal infection
Sabouraud’s agar
Types of parasites
Protozoa: amoebas, sprozoans, flagellates, cilliates
Metazoa/Helminths: Roundworms, flatworms (flukes and tapeworms)
Protozoan parasites
Entamoeba Giardia, Leishmania Trichomonads, trypanosoma Plasmodium (Malaria), Cryptosporidium Toxoplasma
Helminths
Multicellular organisms
Large parasitic worms
Flukes, Tapeworms, and round worms (nematodes)
Pathogenesis of helminths
Toxic byproducts
Mechanical tissue damage
Immunopathology
Helminth evasion of immune system
Molecule mimicry
Antigenic variation
Intracellular location
Immunosuppression
Antiparasitic drugs
Heavy metals
Quinolone derivatives
Folic acid antagonists
Prions
Infectious, misfolded proteins
Scrapies protein
Fatal neurodegenerative diseases
Prion diseases
CJD Variant CJD Gerstmann-Straussler-Scheinker Syndrom Fatal Familial insomnia Kuru Mad Cow disease (bovine) Chronic wasting disase (deer)