Microbiology - First Aid Flashcards
Bacterial Appendages:
- made of proteins
- motility
Flagellum
Bacterial Appendages:
- made of glycoproteins
- mediate adherence of bacteria to cell surface
- sex pilus forms during conjugation
Pilus/Fimbria
Bacterial Structures:
- has a keratin-like coat
- made of dipicolinic acid, peptidoglycan and DNA
- gram ⊕ only
- resists dehydration, heat, and chemicals
Spore
Bacterial Cell Envelope:
- has an organized, discrete polysaccharide layer (except poly-d-glutamate on B anthracis)
- protects against phagocytosis
Capsule
Bacterial Cell Envelope:
- loose network of polysaccharides
- mediates adherence to surfaces, especially foreign surfaces (eg. indwelling catheters)
Glycocalyx
Bacterial Cell Envelope:
- Outer Leaflet: contains endotoxin (LPS/LOS)
- Embedded Proteins: porins and other outer membrane proteins (OMPs)
- Inner Leaflet: phospholipids
- gram ⊝ only
- Endotoxin: lipid A induces TNF and IL-1, antigenic O polysaccharide component
- most OMPs are antigenic
- Porins: transport across outer membrane
Outer Membrane
Bacterial Cell Envelope:
- space between cytoplasmic membrane and outer membrane in gram ⊝ bacteria (peptidoglycan in middle)
- accumulates components exiting gram ⊝ cells, including hydrolytic enzymes (eg. β-lactamases)
Periplasm
Bacterial Cell Envelope:
- peptidoglycan is a sugar backbone with peptide side chains cross-linked by transpeptidase
- net-like structure gives rigid support
- protects against osmotic pressure damage
Cell Wall
Bacterial Cell Envelope:
- phospholipid bilayer sac with embedded proteins (eg. penicillin-binding proteins [PBPs]) and other enzymes
- lipoteichoic acids (gram ⊕ only) extend from membrane to exterior
- site of oxidative and transport enzymes
- PBPs involved in cell wall synthesis
- lipoteichoic acids induce TNF-α and IL-1
Cytoplasmic Membrane
Bacterial Cell Envelope
Bacterial Taxonomy:
spherical
Coccus
Bacterial Taxonomy:
rod
Bacillus
Bacterial Taxonomy:
no cell wall
Pleomorphic
Bacterial Taxonomy:
spiral
Spirochete
Bacterial Taxonomy:
Gram ⊕ Cocci
- Staphylococcus (clusters)
- Streptococcus (chains or pairs)
- Enterococcus (pairs or short chains)
Bacterial Taxonomy:
Gram ⊝ Cocci
- Moraxella catarrhalis
- Neisseria
Bacterial Taxonomy:
Gram ⊕ Bacilli
- Bacillus
- Clostridium
- Corynebacterium
- Gardnerella (gram variable)
- Lactobacillus
- Listeria
- Mycobacterium (acid fast)
- Cutibacterium (formerly Propionibacterium)
Bacterial Taxonomy:
Enteric Gram ⊝ Bacilli
- Bacteroides
- Campylobacter
- E. coli
- Enterobacter
- Fusobacterium
- Helicobacter
- Klebsiella
- Proteus
- Pseudomonas
- Salmonella
- Serratia
- Shigella
- Vibrio
- Yersinia
Bacterial Taxonomy:
Respiratory Gram ⊝ Bacilli
- Acinetobacter baumannii
- Bordetella
- Burkholderia cepacia
- Haemophilus (pleomorphic)
- Legionella (silver stain)
Bacterial Taxonomy:
Zoonotic Gram ⊝ Bacilli
- Bartonella
- Brucella
- Francisella
- Pasteurella
Bacterial Taxonomy:
Branching Filamentous Gram ⊕ Bacteria
- Actinomyces
- Nocardia (weakly acid fast)
Bacterial Taxonomy:
Pleomorphic Gram ⊝ Bacteria
- Anaplasma
- Ehrlichia
- Chlamydiae (Giemsa)
- Rickettsiae (Giemsa)
- Mycoplasma (contains sterols, which do no Gram stain)
- Ureaplasma
Bacterial Taxonomy:
Gram ⊝ Spirochetes
- Borrelia (Giemsa)
- Leptospira
- Treponema
Bacterial Taxonomy:
Staphylococcus
Gram ⊕ Cocci in clusters
Bacterial Taxonomy:
Streptococcus
Gram ⊕ Cocci in chains or pairs
Bacterial Taxonomy:
Enterococcus
Gram ⊕ Cocci in pairs or short chains
Bacterial Taxonomy:
Moraxella catarrhalis
Gram ⊝ Cocci
Bacterial Taxonomy:
Neisseria
Gram ⊝ Cocci
Bacterial Taxonomy:
Bacillus
Gram ⊕ Bacilli
Bacterial Taxonomy:
Clostridium
Gram ⊕ Bacilli
Bacterial Taxonomy:
Corynebacterium
Gram ⊕ Bacilli
Bacterial Taxonomy:
Gardnerella
Gram ⊕ Bacilli
*gram variable
Bacterial Taxonomy:
Lactobacillus
Gram ⊕ Bacilli
Bacterial Taxonomy:
Listeria
Gram ⊕ Bacilli
Bacterial Taxonomy:
Mycobacterium
Acid Fast Gram ⊕ Bacilli
Bacterial Taxonomy:
Cutibacterium (formerly Propionibacterium)
Gram ⊕ Bacilli
Bacterial Taxonomy:
Bacteroides
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Campylobacter
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
E. coli
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Enterobacter
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Fusobacterium
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Helicobacter
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Klebsiella
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Proteus
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Pseudomonas
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Salmonella
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Serratia
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Shigella
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Vibrio
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Yersinia
Enteric Gram ⊝ Bacilli
Bacterial Taxonomy:
Acinetobacter baumannii
Respiratory Gram ⊝ Bacilli
Bacterial Taxonomy:
Bordetella
Respiratory Gram ⊝ Bacilli
Bacterial Taxonomy:
Burkholderia cepacia
Respiratory Gram ⊝ Bacilli
Bacterial Taxonomy:
Haemophilus
Pleomorphic Respiratory Gram ⊝ Bacilli
Bacterial Taxonomy:
Legionella
Respiratory Gram ⊝ Bacilli
*silver stain
Bacterial Taxonomy:
Bartonella
Zoonotic Gram ⊝ Bacilli
Bacterial Taxonomy:
Brucella
Zoonotic Gram ⊝ Bacilli
Bacterial Taxonomy:
Francisella
Zoonotic Gram ⊝ Bacilli
Bacterial Taxonomy:
Pasteurella
Zoonotic Gram ⊝ Bacilli
Bacterial Taxonomy:
Actinomyces
Branching Filamentous Gram ⊕ Bacteria
Bacterial Taxonomy:
Nocardia
Branching Filamentous Gram ⊕ Bacteria
*weakly acid fast
Bacterial Taxonomy:
Anaplasma
Pleomorphic Gram ⊝ Bacteria
Bacterial Taxonomy:
Ehrlichia
Pleomorphic Gram ⊝ Bacteria
Bacterial Taxonomy:
Chlamydiae
Pleomorphic Gram ⊝ Bacteria
*Giemsa
Bacterial Taxonomy:
Rickettsiae
Pleomorphic Gram ⊝ Bacteria
*Giemsa
Bacterial Taxonomy:
Mycoplasma
Pleomorphic Gram ⊝ Bacteria
*contains sterols, which do not Gram stain
Bacterial Taxonomy:
Ureaplasma
Pleomorphic Gram ⊝ Bacteria
Bacterial Taxonomy:
Borrelia
Gram ⊝ Spirochetes
*Giemsa
Bacterial Taxonomy:
Leptospira
Gram ⊝ Spirochetes
Bacterial Taxonomy:
Treponema
Gram ⊝ Spirochetes
Stains:
first-line lab test in bacterial identification
Gram Stain
- Gram ⊕—thick peptidoglycan layer retains crystal violet dye
- Gram ⊝—thin peptidoglycan layer turns red or pink with counterstain
_____ do not Gram stain well.
These Little Microbes May Unfortunately Lack Real Color But Are Everywhere
- Treponema—too thin
- Leptospira—too thin
- Mycobacteria—cell wall has high lipid content
- Mycoplasma—no cell wall
- Ureaplasma—no cell wall
- Legionella—intracellular
- Rickettsia—intracellular
- Chlamydia—intracellular, lacks classic peptidoglycan because of ↓ muramic acid
- Bartonella—intracellular
- Anaplasma—intracellular
- Ehrlichia—intracellular
_____ are seen through Giemsa stain.
Ricky got Chlamydia as he Tried to Please the Bored “Geisha.”
- Rickettsia
- Chlamydia
- Trypanosomes
- Plasmodium
- Borrelia
Stains:
- stains glycogen and mucopolysaccharides
- used to diagnose Whipple disease (Tropheryma whipplei)
Periodic Acid–Schiff Stain
PASs the sugar.
Stains:
- acid-fast bacteria (eg. Mycobacteria, Nocardia; stains mycolic acid in cell wall)
- protozoa (eg. Cryptosporidium oocysts)
Ziehl-Neelsen Stain
*Auramine-Rhodamine Stain is more often used for screening (inexpensive, more sensitive).
(Carbol Fuchsin)
Stains:
- seen through India ink stain
- Mucicarmine can also be used to stain thick polysaccharide capsule red
Cryptococcus neoformans
Stains:
- fungi (eg. Coccidioides, Pneumocystis jirovecii)
- Legionella
- Helicobacter pylori
Silver Stain
Stains:
- used to identify many bacteria and viruses
- FTA-ABS for syphilis
Fluorescent Antibody Stain
Properties of Growth Media:
- favors the growth of particular organism while preventing growth of other organisms
- eg. Thayer-Martin agar contains antibiotics that allow the selective growth of Neisseria by inhibiting the growth of other sensitive organisms
Selective Media
Properties of Growth Media:
- yields a color change in response to the metabolism of certain organisms
- contains a pH indicator
- a lactose fermenter like E. coli will convert lactose to acidic metabolites → color change
- eg. MacConkey agar
Indicator (Differential) Media
Special Culture Requirements:
H. influenzae
Chocolate agar
- Factor V (NAD+)
- Factor X (hematin)
Special Culture Requirements:
N. gonorrhoeae, N. meningitidis
Thayer-Martin agar
- selectively favors growth of Neisseria by inhibiting growth of gram ⊕ organisms with Vancomycin, gram ⊝ organisms except Neisseria with Trimethoprim and Colistin, and fungi with Nystatin
Very Typically Cultures Neisseria
Special Culture Requirements:
B. pertussis
- Bordet-Gengou agar (Bordet for Bordetella)
- potato extract
- Regan-Lowe medium
- charcoal
- blood
- antibiotic
Special Culture Requirements:
C. diphtheriae
- Tellurite agar
- Löffler medium
Special Culture Requirements:
M. tuberculosis
Löwenstein-Jensen agar
Special Culture Requirements:
M. pneumoniae
Eaton agar
- requires cholesterol
Special Culture Requirements:
Lactose-Fermenting Enterics
MacConkey agar
- fermentation produces acid causing colonies to turn pink
Special Culture Requirements:
E. coli
Eosin–Methylene Blue (EMB) agar
- colonies with green metallic sheen
Special Culture Requirements:
Legionella
Charcoal Yeast Extract agar
- buffered with cysteine and iron
_____ use an O2-dependent system to generate ATP.
Aerobes
Aerobes
Nagging Pests Must Breathe.
- Nocardia
- Pseudomonas aeruginosa
- MycoBacterium tuberculosis
Reactivation of M .tuberculosis (eg. after immunocompromise or TNF-α inhibitor use) has a predilection for the _____.
apices of the lung
____ lack catalase and/or superoxide dismutase and are thus susceptible to oxidative damage. Generally foul smelling (short-chain fatty acids), are difficult to culture, and produce gas in tissue (CO2 and H2).
Anaerobes
Anaerobes
Anaerobes Can’t Breathe Fresh Air.
- Clostridium
- Bacteroides
- Fusobacterium
- Actinomyces israelii
Anaerobes are normal flora in the _____, typically pathogenic elsewhere.
GI tract
_____ are ineffective against anaerobes becaus these antibiotics require O2 to enter into bacterial cell.
Aminoglycosides
AminO2glycosides
_____ may use O2 as a terminal electron acceptor to generate ATP, but can also use fermentation and other O2-independent pathways.
Facultative Anaerobes
Facultative Anaerobes
- Streptococci
- Staphylococci
- Enteric Gram ⊝ Bacteria
Obligate Intracellular Bacteria
Stay inside (cells) when it is Really CHilly and COld.
- Rickettsia
- CHlamydia
- COxiella
*rely on host ATP
Facultative Intracellular Bacteria
Some Nasty Bugs May Live FacultativeLY.
- Salmonella
- Neisseria
- Brucella
- Mycobacterium
- Listeria
- Francisella
- Legionella
- Yersinia pestis
The capsules of _____ serve as an antiphagocytic virulence factor. They are opsonized, and then cleared by spleen. Capsular polysaccharide + protein conjugate serves as an antigen in vaccines.
Encapsulated Bacteria
Encapsulated Bacteria
Please SHiNE my SKiS.
- Pseudomonas aeruginosa
- Streptococcus pneumoniae
- Haemophilus influenzae type b
- Neisseria meningitidis
- Escherichia coli
- Salmonella
- Klebsiella pneumoniae
- Group B Strep.
Asplenics have ↓ opsonizing ability and thus ↓ risk for severe infections; need vaccines to protect against _____.
No Spleen Here
- N. meningitidis
- S. pneumoniae
- H. influenzae
_____ containing polysaccharide capsule antigens are conjugated to a carrier protein, enhancing immunogenicity by promoting T-cell activation and subsequent class switching. A polysaccharide antigen alone cannot be presented to T cells.
Encapsulated Bacteria Vaccines
Encapsulated Bacteria Vaccines
- Pneumococcal vaccines:
- PCV13 (pneumococcal conjugate vaccine)
- PPSV23 (pneumococcal polysaccharide vaccine with no conjugated protein)
- H. influenzae type b (conjugate vaccine)
- Meningococcal vaccine (conjugate vaccine)
Urease-Positive Organisms
Pee CHUNKSS
- Proteus
- Cryptococcus
- H. pylori
- Ureaplasma
- Nocardia
- Klebsiella
- S. epidermidis
- S. saprophyticus
*predisposes to struvite (ammonium magnesium phosphate) stones, particularly Proteus
_____ hydrolyzes urea to release ammonia and CO2 → ↑ pH.
Urease
_____ degrades H2O2 into H2O and bubbles of O2 before it can be converted to microbicidal products by the enzyme myeloperoxidase.
Catalase
People with _____ (NADPH oxidase deficiency) have recurrent infections with certain catalase ⊕ organisms.
Chronic Granulomatous Disease
Catalase-Positive Organisms
Cats Need PLACESS to Belch their Hairballs.
- Nocardia
- Pseudomonas
- Listeria
- Aspergillus
- Candida
- E. coli
- Staphylococci
- Serratia
- B. cepacia
- H. pylori
Pigment-Producing Bacteria:
yellow “sulfur” granules—composed of filaments of bacteria
Actinomyces israelii
Israel has yellow sand.
Pigment-Producing Bacteria:
yellow pigment
S. aureus
Aureus (Latin) = gold
Pigment-Producing Bacteria:
blue-green pigment (pyocyanin and pyoverdin)
P. aeruginosa
Aerugula is green.
Pigment-Producing Bacteria:
red pigment
Serratia marcescens
red Sriracha hot sauce
In Vivo Biofilm Producing Bacteria:
catheter and prosthetic device infections
S. epidermidis
In Vivo Biofilm Producing Bacteria:
- dental plaques
- infective endocarditis
Viridans streptococci
- S. mutans
- S. sanguinis
In Vivo Biofilm Producing Bacteria:
- respiratory tree colonization in patients with cystic fibrosis
- ventilator-associated pneumonia
- contact lens–associated keratitis
P. aeruginosa
In Vivo Biofilm Producing Bacteria:
otitis media
Nontypeable (Unencapsulated) H. influenzae
_____ promote evasion of host immune response.
Bacterial Virulence Factors
Bacterial Virulence Factors:
- binds Fc region of IgG
- prevents opsonization and phagocytosis
- expressed by S. aureus
Protein A
Bacterial Virulence Factors:
- enzyme that cleaves IgA, allowing bacteria to adhere to and colonize mucous membranes
- secreted by S. pneumoniae, H. influenzae type b, and Neisseria
IgA protease
SHiN
- S. pneumoniae
- H. influenzae type b
- Neisseria
Bacterial Virulence Factors:
- helps prevent phagocytosis
- expressed by group A streptococci
- shares similar epitopes to human cellular proteins (molecular mimicry)
- possibly underlies the autoimmune response seen in acute rheumatic fever
M protein
_____ is also known as “injectisome.” It’s a needle-like protein appendage facilitating direct delivery of toxins from certain gram ⊝ bacteria (eg. Pseudomonas, Salmonella, Shigella, E. coli) to eukaryotic host cell.
Type III Secretion System
Bacterial Genetics:
- competent bacteria can bind and import short pieces of environmental naked bacterial chromosomal DNA (from bacterial cell lysis)
- transfer and expression of newly transferred genes
- a feature of many bacteria, especially S. pneumoniae, H. influenzae type b, and Neisseria
- adding deoxyribonuclease degrades naked DNA, preventing _____
Transformation
Bacterial Genetics:
Conjugation (F+ × F–)
- F+ plasmid contains genes required for sex pilus and conjugation
- bacteria without this plasmid are termed F–
- sex pilus on F+ bacterium contacts F− bacterium
- a single strand of plasmid DNA is transferred across the conjugal bridge (“mating bridge”)
- no transfer of chromosomal DNA
Bacterial Genetics:
Conjugation (Hfr × F–)
- F+ plasmid can become incorporated into bacterial chromosomal DNA, termed High-frequency recombination (Hfr) cell
- transfer of leading part of plasmid and a few flanking chromosomal genes
- High-frequency recombination may integrate some of those bacterial genes
- recipient cell remains F– but now may have new bacterial genes
Bacterial Genetics:
- a packaging “error”
- lytic phage infects bacterium, leading to cleavage of bacterial DNA
- parts of bacterial chromosomal DNA may become packaged in phage capsid
- phage infects another bacterium, transferring these genes
Generalized Transduction
Bacterial Genetics:
- an “excision” event
- lysogenic phage infects bacterium
- viral DNA incorporates into bacterial chromosome
- when phage DNA is excised, flanking bacterial genes may be excised with it
- DNA is packaged into phage capsid and can infect another bacterium
Specialized Transduction
*Genes for the following 5 bacterial toxins are encoded in a lysogenic phage (ABCD’S):
- Group A strep erythrogenic toxin
- Botulinum toxin
- Cholera toxin
- Diphtheria toxin
- Shiga toxin
Bacterial Genetics:
- segment of DNA (eg. transposon) that can “jump” (copy/excise and reinsert) from one location to another, can transfer genes from plasmid to chromosome and vice versa
- this is a critical process in creating plasmids with multiple antibiotic resistance which can be transferred across species lines (eg. Tn1546 carrying vanA gene from vancomycin-resistant Enterococcus to S. aureus)
Transposition
Bacterial Genetics:
- formed by some bacteria when nutrients are limited
- lack metabolic activity
- highly resistant to heat and chemicals
- core contains dipicolinic acid
- must autoclave to kill by steaming at 121°C for 15 minutes
Spores
Spore-Forming Bacteria
- Bacillus anthracis—anthrax
- Bacillus cereus—food poisoning
- Clostridium botulinum—botulism
- Clostridium difficile—pseudomembranous colitis
- Clostridium perfringens—gas gangrene
- Clostridium tetani—tetanus
Exotoxins:
Source
certain species of gram ⊕ and gram ⊝ bacteria
Exotoxins:
Cell Secretion
yes
Exotoxins:
Chemical Composition
Polypeptide
Exotoxins:
Location of Genes
- Plasmid
- Bacteriophage
Exotoxins:
Adverse Effects
High
*fatal dose on the order of 1 μg
Exotoxins:
Clinical Effects
Varied
Exotoxins:
Mode of Action
Varied
Exotoxins:
Antigenicity
induces high-titer antibodies called antitoxins
Exotoxins:
Vaccines
Toxoids
Exotoxins:
Heat Stability
destroyed rapidly at 60°C (except staphylococcal enterotoxin and E. coli heatstable toxin)
Exotoxins:
Typical Diseases
- Tetanus
- Botulism
- Diphtheria
Endotoxins:
Source
outer cell membrane of most gram ⊝ bacteria
Endotoxins:
Cell Secretion
No
Endotoxins:
Chemical Composition
Lipid A component of LPS (structural part of bacteria; released when lysed)
Endotoxins:
Location of Genes
Bacterial Chromosome
Endotoxins:
Adverse Effects
Low
*fatal dose on the order of hundreds of micrograms
Endotoxins:
Clinical Effects
- fever
- shock (hypotension)
- DIC
Endotoxins:
Mode of Action
induces TNF, IL-1, and IL-6
Endotoxins:
Antigenicity
poorly antigenic
Endotoxins:
Vaccines
- no toxoids formed
- no vaccine available
Endotoxins:
Heat Stability
stable at 100°C for 1 hr
Endotoxins:
Typical Diseases
- Meningococcemia
- Sepsis by gram ⊝ rods
Exotoxins:
- two-component toxin (or three for anthrax) with B enabling binding and triggering uptake (endocytosis) of the active A component
- the A components are usually ADP ribosyltransferases; others have enzymatic activities
AB toxin
Exotoxins:
inhibit protein synthesis
- Corynebacterium diphtheriae—Diphtheria toxin
- Pseudomonas aeruginosa—Exotoxin A
- Shigella spp.—Shiga toxin (ST)
- Enterohemorrhagic E. coli—Shiga-like toxin (SLT)
Exotoxins:
- AB toxin
- inactivate elongation factor (EF-2)
- pharyngitis with pseudomembranes in throat and severe lymphadenopathy (bull neck)
Corynebacterium diphtheriae—Diphtheria toxin
Exotoxins:
- AB toxin
- inactivate elongation factor (EF-2)
- host cell death
Pseudomonas aeruginosa—Exotoxin A
Exotoxins:
- AB toxin
- inactivate 60S ribosome by removing adenine from rRNA
- GI mucosal damage → dysentery
- enhances cytokine release, causing hemolyticuremic syndrome (HUS)
Shigella spp.—Shiga toxin (ST)
Exotoxins:
- AB toxin
- inactivate 60S ribosome by removing adenine from rRNA
- enhances cytokine release, causing HUS (prototypically in EHEC serotype O157:H7).
- unlike Shigella, EHEC does not invade host cells
Enterohemorrhagic E. coli—Shiga-like toxin (SLT)
Exotoxins:
increase fluid secretion
- Enterotoxigenic E. coli
- Heat-labile toxin (LT)
- Heat-stable toxin (ST)
- Bacillus anthracis—Edema toxin
- Vibrio cholerae—Cholera toxin
Exotoxins:
- AB toxin
- overactivates adenylate cyclase (↑ cAMP) → ↑ Cl− secretion in gut and H2O efflux
- watery diarrhea
Enterotoxigenic E. coli—Heat-labile toxin (LT)
Labile in the Air (Adenylate cyclase)
Exotoxins:
- overactivates guanylate cyclase (↑ cGMP) → ↓ resorption of NaCl and H2O in gut
- watery diarrhea
Enterotoxigenic E. coli—Heat-stable toxin (ST)
Stable on the Ground (Guanylate cyclase)
Exotoxins:
- AB toxin
- mimics adenylate cyclase (↑ cAMP)
- likely responsible for characteristic edematous borders of black eschar in cutaneous anthrax
Bacillus anthracis—Edema toxin
Exotoxins:
- AB toxin
- overactivates adenylate cyclase (↑ cAMP) by permanently activating Gs → ↑ Cl− secretion in gut and H2O efflux
- voluminous “rice-water” diarrhea
Vibrio cholerae—Cholera toxin
Exotoxins:
inhibit phagocytic ability
Bordetella pertussis—Pertussis toxin
Exotoxins:
- overactivates adenylate cyclase (↑ cAMP) by disabling Gi, impairing phagocytosis to permit survival of microbe
- Whooping Cough—child coughs on expiration and “whoops” on inspiration (toxin may not actually be a cause of cough; can cause “100-day cough” in adults)
Bordetella pertussis—Pertussis toxin
Exotoxins:
inhibit release of neurotransmitter
- Clostridium tetani—Tetanospasmin
- Clostridium botulinum—Botulinum toxin
Exotoxins:
- AB toxin
- protease that cleaves SNARE (soluble NSF attachment protein receptor), a set of proteins required for neurotransmitter release via vesicular fusion
- prevents release of inhibitory (GABA and glycine) neurotransmitters from Renshaw cells in spinal cord → spastic paralysis, risus sardonicus, trismus (lockjaw)
Clostridium tetani—Tetanospasmin
Exotoxins:
- AB toxin
- protease that cleaves SNARE (soluble NSF attachment protein receptor), a set of proteins required for neurotransmitter release via vesicular fusion
- prevents release of stimulatory (ACh) signals at neuromuscular junction → flaccid paralysis (floppy baby)
Clostridium botulinum—Botulinum toxin
Exotoxins:
lyse cell membranes
- Clostridium perfringens—Alpha toxin
- Streptococcus pyogenes—Streptolysin O
Exotoxins:
- phospholipase (lecithinase) that degrades tissue and cell membranes
- degradation of phospholipids → myonecrosis (“gas gangrene”) and hemolysis (“double zone” of hemolysis on blood agar)
Clostridium perfringens—Alpha toxin
Exotoxins:
- protein that degrades cell membrane
- lyses RBCs
- contributes to β-hemolysis
- host antibodies against toxin (ASO) used to diagnose rheumatic fever
Streptococcus pyogenes—Streptolysin O
Exotoxins:
superantigens causing shock
- Staphylococcus aureus—Toxic Shock Syndrome toxin (TSST-1)
- Streptococcus pyogenes—Erythrogenic exotoxin A
Exotoxins:
- cross-links β region of TCR to MHC class II on APCs outside of the antigen binding site → overwhelming release of IL-1, IL-2, IFN-γ, and TNF-α → shock
- Toxic Shock Syndrome: fever, rash, shock
Staphylococcus aureus—Toxic Shock Syndrome toxin (TSST-1)
Exotoxins:
- cross-links β region of TCR to MHC class II on APCs outside of the antigen binding site → overwhelming release of IL-1, IL-2, IFN-γ, and TNF-α → shock
- Toxic Shock–like Syndrome: fever, rash, shock;
scarlet fever
Streptococcus pyogenes—Erythrogenic exotoxin A
Endotoxin
ENDOTOXINS:
- Edema
- Nitric oxide
- DIC/Death
- Outer membrane
- TNF-α
- O-antigen + core polysaccharide + lipid A
- eXtremely heat stable
- IL-1 and IL-6
- Neutrophil chemotaxis
- Shock
_____ are the glycolipid LPS molecules found in the outer membrane of gram ⊝ bacteria (both cocci and rods).
Endotoxins
Endotoxins are composed of _____.
- O antigen
- core polysaccharide
- lipid A—toxic component
Endotoxins are released upon _____ or by living cells by _____ (vs. exotoxin, which is actively secreted).
- cell lysis
- blebs detaching from outer surface membrane
The three main effects of endotoxins are _____.
- macrophage activation (TLR4/CD14)
- complement activation
- tissue factor activation
Gram-Positive Lab Algorithm
Gram-Positive Cocci Antibiotic Test:
Staphylococci
Novobiocin
- Saprophyticus is Resistant
- Epidermidis is Sensitive
On the office’s “staph” retreat, there was No StRESs.
Gram-Positive Cocci Antibiotic Test:
Streptococci
Optochin
- Viridans is Resistant
- Pneumoniae is Sensitive
OVRPS (overpass)
Bacitracin
- group B strep are Resistant
- group A strep are Sensitive
B-BRAS.
_____ are gram ⊕ cocci which partially reduce hemoglobin causing greenish or brownish color without clearing around growth on blood agar.
α-Hemolytic Bacteria
α-Hemolytic Bacteria
-
Streptococcus pneumoniae
- catalase ⊝
- optochin sensitive
- Viridans streptococci
- catalase ⊝
- optochin resistant
_____ are gram ⊕ cocci which cause complete lysis of RBCs → clear area surrounding colony on blood agar.
β-Hemolytic Bacteria
β-Hemolytic Bacteria
-
Staphylococcus aureus
- catalase and coagulase ⊕
-
Streptococcus pyogenes
- group A strep
- catalase ⊝ and bacitracin sensitive
-
Streptococcus agalactiae
- group B strep
- catalase ⊝ and bacitracin resistant
Bacteria:
- Gram ⊕
- β-hemolytic
- Catalase ⊕
- Coagulase ⊕
- cocci in clusters
- Protein A (virulence factor) binds Fc-IgG, inhibiting complement activation and phagocytosis
- commonly colonizes the nares, ears, axilla, and groin
Staphylococcus aureus
Bacteria:
- Inflammatory Disease—skin infections, organ abscesses, pneumonia (often after influenza virus infection), endocarditis, septic arthritis, and osteomyelitis
- Toxin-Mediated Disease—toxic shock syndrome (TSST-1), scalded skin syndrome (exfoliative toxin), rapid-onset food poisoning (enterotoxins)
Staphylococcus aureus
Bacteria:
- important cause of serious nosocomial and community-acquired infections
- resistant to methicillin and nafcillin because of altered penicillin-binding protein
MRSA (Methicillin-Resistant S. aureus)
_____ is a superantigen that binds to MHC II and T-cell receptor, resulting in polyclonal T-cell activation.
TSST-1
_____ causes fever, vomiting, rash, desquamation, shock, and end-organ failure. It results in ↑ AST, ↑ ALT, ↑ bilirubin. Associated with prolonged use of vaginal tampons or nasal packing.
Staphylococcal Toxic Shock Syndrome (TSS)
_____ causes a toxic shock–like syndrome associated with painful skin infection.
Streptococcus pyogenes
_____ food poisoning due to ingestion of preformed toxin → short incubation period (2–6 hr) followed by nonbloody diarrhea and emesis. Enterotoxin is heat stable → not destroyed by cooking.
S. aureus
Bad _____ make coagulase and toxins. Forms fibrin clot around self abscess.
S. aureus
Bacteria:
- Gram ⊕
- Catalase ⊕
- Coagulase ⊝
- Urease ⊕
- cocci in clusters
- Novobiocin sensitive
- does not ferment mannitol
- normal flora of skin
- contaminates blood cultures
- infects prosthetic devices (eg. hip implant, heart valve) and IV catheters by producing adherent biofilms
Staphylococcus epidermidis
Bacteria:
- Gram ⊕
- Catalase ⊕
- Coagulase ⊝
- Urease ⊕
- cocci in clusters
- Novobiocin resistant
- normal flora of female genital tract and perineum
- second most common cause of uncomplicated UTI in young women (most common is E. coli)
Staphylococcus saprophyticus
Bacteria:
- Gram ⊕
- lancet-shaped diplococci
- encapsulated
- IgA protease
- Optochin sensitive
- associated with “rusty” sputum, sepsis in patients with sickle cell disease, and asplenic patients
- no virulence without capsule
Streptococcus pneumoniae
Bacteria:
most common cause of meningitis, otitis media (in children), pneumonia, and sinusitis
Streptococcus pneumoniae
MOPS spread pneumonia.
- Meningitis
- Otitis media (in children)
- Pneumonia
- Sinusitis
Bacteria:
- Gram ⊕
- α-hemolytic cocci
- resistant to optochin
- normal flora of the oropharynx
Viridans Group Streptococci
Viridans group strep live in the mouth, because they are not afraid of-the-chin (op-to-chin resistant).
Viridans Group Streptococci:
cause dental caries
- Streptococcus mutans
- SStreptococcus mitis
Viridans Group Streptococci:
makes dextrans that bind to fibrin-platelet aggregates on damaged heart valves, causing subacute bacterial endocarditis
Streptococcus sanguinis
Sanguinis = blood.
Think, “there is lots of blood in the heart” (endocarditis).
Bacteria:
- Gram ⊕ cocci in chains
- Bacitracin sensitive
- β-hemolytic
- Pyrrolidonyl Arylamidase (PYR) ⊕
- Hyaluronic acid capsule and M protein inhibit phagocytosis
- antibodies to M protein enhance host defense but can give rise to rheumatic fever
Streptococcus pyogenes (Group A Streptococci)
Bacteria:
- Pyogenic—pharyngitis, cellulitis, impetigo (“honey-crusted” lesions), erysipelas
- Toxigenic—scarlet fever, toxic shock–like syndrome, necrotizing fasciitis
- Immunologic—rheumatic fever, glomerulonephritis
Streptococcus pyogenes (Group A Streptococci)
ASO titer or anti-DNase B antibodies indicate recent _____ infection.
Streptococcus pyogenes (Group A Streptococci)
_____ pharyngitis can result in rheumatic fever and glomerulonephritis.
Streptococcus pyogenes (Group A Streptococci)
Pharyngitis can result in rheumatic “phever” and glomerulonephritis.
_____ strains causing impetigo can induce glomerulonephritis.
Streptococcus pyogenes (Group A Streptococci)
_____ causes blanching, sandpaper-like body rash, strawberry tongue, and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin ⊕).
Scarlet Fever
Bacteria:
- Gram ⊕ cocci
- Bacitracin resistant
- β-hemolytic
- colonizes vagina
- causes pneumonia, meningitis, and sepsis, mainly in babies.
- produces CAMP factor, which enlarges the area of hemolysis formed by S. aureus. (Note: CAMP stands for the authors of the test, not cyclic AMP.)
- Hippurate test ⊕
- PYR ⊝
Streptococcus agalactiae (Group B Streptococci)
Group B is β-hemolytic for Babies.
Pregnant women should be screened for _____ at 35–37 weeks of gestation with rectal and vaginal swabs.
Streptococcus agalactiae (Group B Streptococci)
Patients with ⊕ _____ culture should receive intrapartum penicillin prophylaxis.
Streptococcus agalactiae (Group B Streptococci)
Bacteria:
- Gram ⊕ cocci
- colonizes the gut
- S. gallolyticus (_____ biotype 1) can cause bacteremia and subacute endocarditis and is associated with colon cancer
Streptococcus bovis
Bovis in the Blood = Cancer in the Colon
Bacteria:
- Gram ⊕ cocci
- Penicillin G resistant
- Catalase ⊝
- PYR ⊕
- normal colonic flora that cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures)
- VRE (vancomycin-resistant _____) are an important cause of nosocomial infection
- more resilient than streptococci, can grow in 6.5% NaCl and bile (lab test)
Enterococci
- E. faecalis
- E. faecium
Bacteria:
- Gram ⊕
- spore-forming rod
- produces anthrax toxin
- the only bacterium with a polypeptide capsule (contains d-glutamate)
- colonies show a halo of projections, sometimes referred to as “medusa head” appearance
Bacillus anthracis
_____ causes painless papule surrounded by vesicles → ulcer with black eschar ( A ) (painless, necrotic) → uncommonly progresses to bacteremia and death.
Cutaneous Anthrax
(Bacillus anthracis)
_____ is caused by inhalation of _____ spores → flu-like symptoms that rapidly progress to fever, pulmonary hemorrhage, mediastinitis, and shock. Also known as woolsorter’s disease. CXR may show widened mediastinum.
Pulmonary anthrax
(Bacillus anthracis)
Bacteria:
- Gram ⊕ rod.
- causes food poisoning
- spores survive cooking rice (also known as reheated rice syndrome)
- keeping rice warm results in germination of spores and enterotoxin formation
-
Emetic Type
- usually seen with rice and pasta
- nausea and vomiting
- onset within 1–5 hr
- caused by cereulide, a preformed toxin
-
Diarrheal Type
- watery, nonbloody diarrhea and GI pain
- onset within 8–18 hr
Bacillus cereus
Bacteria:
- Gram ⊕
- spore-forming
- obligate anaerobic rods
Clostridia (with exotoxins)
Bacteria:
- produces tetanospasmin, an exotoxin causing tetanus
- causes spastic paralysis, trismus (lockjaw), risus sardonicus (raised eyebrows and open grin), and opisthotonos (spasms of spinal extensors)
Clostridium tetani
_____ are proteases that cleave SNARE proteins for
neurotransmitters. They blocks release of inhibitory neurotransmitters, GABA and glycine, from Renshaw cells in spinal cord.
- Tetanus toxin
- Botulinum toxin
Tetanus is treated with _____.
- Antitoxin +/− Vaccine Booster
- Antibiotics
- Diazepam (for muscle spasms)
- Wound Debridement
Bacteria:
- produces a heat-labile toxin that inhibits ACh release at the neuromuscular junction, causing botulism
- in adults, disease is caused by ingestion of preformed toxin
- in babies, ingestion of spores (eg. in honey) leads to disease (floppy baby syndrome)
- local botox injections used to treat focal dystonia, achalasia, and muscle spasms
- used for cosmetic reduction of facial wrinkles
Clostridium botulinum
Botulinum is from bad bottles of food, juice, and honey (causes a descending flaccid paralysis).
The symptoms of botulism are _____.
4 D’s:
- Diplopia
- Dysarthria
- Dysphagia
- Dyspnea
Botulism is treated with _____.
Human Botulinum Immunoglobulin
Bacteria:
- produces α toxin (lecithinase, a phospholipase) that can cause myonecrosis (gas gangrene; presents as soft tissue crepitus) and hemolysis
- spores can survive in undercooked food
- when ingested, bacteria release heat-labile enterotoxin → food poisoning.
Clostridium perfringens
Perfringens perforates a gangrenous leg.
Bacteria:
- produces 2 toxins
-
Toxin A
- enterotoxin,
- binds to brush border of gut and alters fluid secretion
-
Toxin B
- cytotoxin
- disrupts cytoskeleton via actin depolymerization
- both toxins lead to diarrhea → pseudomembranous colitis
- often 2° to antibiotic use, especially Clindamycin or Ampicillin
- associated with PPIs
Clostridium difficile
Difficile causes diarrhea.
Clostridium difficile is diagnosed by _____.
- PCR
- antigen detection of one or both toxins in stool
Clostridium difficile is treated with _____.
- Metronidazole
- Oral Vancomycin
Recurrent Clostridium difficile is treated with _____.
- consider repeating prior regimen
- Fidaxomicin
- Fecal Microbiota Transplant
Bacteria:
- Gram ⊕ rod
- black colonies on cystine-tellurite agar
- transmitted via respiratory droplets
- causes diphtheria via exotoxin encoded by β-prophage
- potent exotoxin inhibits protein synthesis via ADP-ribosylation of EF-2
- symptoms include pseudomembranous pharyngitis (grayish-white membrane) with lymphadenopathy, myocarditis, and arrhythmias
- lab diagnosis based on gram ⊕ rods with metachromatic (blue and red) granules and ⊕ Elek test for toxin
- toxoid vaccine prevents diphtheria
Corynebacterium diphtheriae
Coryne = club shaped
ABCDEFG:
- ADP-ribosylation
- β-prophage
- Corynebacterium
- Diphtheriae
- Elongation Factor 2
- Granules
Bacteria:
- Gram ⊕
- facultative intracellular rod
- acquired by ingestion of unpasteurized dairy products and cold deli meats, via transplacental transmission, or by vaginal transmission during birth
- grows well at refrigeration temperatures (4°–10°C; “cold enrichment”)
Listeria monocytogenes
Bacteria:
- forms “rocket tails” via actin polymerization that allow intracellular movement and cell-to-cell spread across cell membranes, thereby avoiding antibody
- characteristic tumbling motility in broth
Listeria monocytogenes
Bacteria:
- amnionitis, septicemia, and spontaneous abortion in pregnant women
- granulomatosis infantiseptica
- neonatal meningitis
- meningitis in immunocompromised patients
- mild, selflimited gastroenteritis in healthy individuals
Listeria monocytogenes
Listeria monocytogenes is treated with _____.
Ampicillin
Bacteria:
- gram ⊕
- form long, branching filaments resembling fungi
- Nocardia
- Actinomyces
Bacteria:
- aerobe
- acid fast (weak)
- found in soil
- causes pulmonary infections in immunocompromised (can mimic TB but with ⊝ PPD)
- cutaneous infections after trauma in immunocompetent
- can spread to CNS
- treated with sulfonamides (TMP-SMX)
Nocardia
Bacteria:
- anaerobe
- not acid fast
- normal oral, reproductive, and GI flora
- causes oral/facial abscesses that drain through sinus tracts
- often associated with dental caries/extraction and other maxillofacial trauma
- forms yellow “sulfur granules”
- can cause PID with IUDs
- treated with Penicillin
Actinomyces
Nocardia is treated with _____ while Actinomyces is treated with _____.
SNAP:
- Sulfonamides—Nocardia
- A**ctinomyces—P**enicillin
Mycobacteria:
- causes TB
- often resistant to multiple drugs
Mycobacterium tuberculosis
Mycobacteria:
- causes disseminated, non-TB disease in AIDS
- often resistant to multiple drugs
- prophylaxis with azithromycin when CD4+ count < 50 cells/mm3
Mycobacterium avium–intracellulare
Mycobacteria:
cervical lymphadenitis in children
Mycobacterium scrofulaceum
Mycobacteria:
hand infection in aquarium handlers
Mycobacterium marinum
All mycobacteria are _____ organisms (pink rods).
acid-fast
TB symptoms include _____.
- fever
- night sweats
- weight loss
- cough (nonproductive or productive)
- hemoptysis
_____ creates a “serpentine cord” appearance in virulent M. tuberculosis strains; activates macrophages (promoting granuloma formation) and induces release of TNF-α.
Cord Factor
_____ (surface glycolipids) inhibit phagolysosomal fusion.
Sulfatides
Tuberculosis
Tuberculosis:
PPD __ if current infection or past exposure.
PPD ⊕
Tuberculosis:
PPD __ if no infection and in sarcoidosis or HIV infection (especially with low CD4+ cell count).
PPD ⊝
Tuberculosis:
has fewer false positives from BCG vaccination
Interferon-γ Release Assay (IGRA)
Characteristics of 2° Tuberculosis include _____.
- Caseating Granulomas with central necrosis
- Langhans Giant Cells
Mycobacteria:
- caused by Mycobacterium leprae, an acid-fast bacillus that likes cool temperatures (infects skin and superficial nerves—“glove and stocking” loss of sensation) and cannot be grown in vitro
- diagnosed via skin biopsy or tissue PCR
- reservoir in US: armadillos
Leprosy (Hansen disease)
Leprosy:
- presents diffusely over the skin, with leonine (lion-like) facies
- communicable (high bacterial load)
- characterized by low cell-mediated immunity with a humoral Th2 response
- can be lethal
Lepromatous
Lepromatous form can be Lethal.
Leprosy:
- limited to a few hypoesthetic, hairless skin plaques
- characterized by high cell-mediated immunity with a largely Th1-type immune response and low bacterial load
Tuberculoid
Leprosy (Hansen disease) is treated with _____.
- Tuberculoid
- Dapsone
- Rifampin
- Lepromatous
- Lofazimine
- Dapsone
- Rifampin
Gram-Negative Lab Algorithm
Bacteria:
- Gram ⊝ diplococci
- metabolizes glucose
- produces IgA proteases
- contains lipooligosaccharides (LOS) with strong endotoxin activity
Neisseria
Bacteria:
- no polysaccharide capsule
- often intracellular (within neutrophils)
- Maltose not fermented
- no vaccine due to antigenic variation of pilus proteins
- sexually or perinatally transmitted
- causes gonorrhea, septic arthritis, neonatal conjunctivitis (2–5 days after birth), pelvic inflammatory disease (PID), and Fitz-Hugh-Curtis syndrome
- condoms ↓ sexual transmission
Neisseria gonorrhoeae
Gonococci ferment Glucose.
_____ eye ointment prevents neonatal blindness from Neisseria gonorrhoeae.
Erythromycin
Neisseria gonorrhoeae is treated with _____.
Ceftriaxone (+ Azithromycin or Doxycycline, for possible chlamydial coinfection)
Bacteria:
- polysaccharide capsule
- Maltose fermentation
- vaccine (type B vaccine not widely available)
- transmitted via respiratory and oral secretions
- causes meningococcemia with petechial hemorrhages and gangrene of toes, meningitis, Waterhouse-Friderichsen syndrome (adrenal insufficiency, fever, DIC, shock)
Neisseria meningitidis
MeninGococci ferment Maltose and Glucose.
_____ are given to close contacts as prophylaxis for Neisseria meningitidis.
- Rifampin
- Ciprofloxacin
- Ceftriaxone
Neisseria meningitidis is treated with _____.
- Ceftriaxone
- Penicillin G
Bacteria:
- small gram ⊝ (coccobacillary) rod
- aerosol transmission
- nontypeable (unencapsulated) strains are the most common cause of mucosal infections (otitis media, conjunctivitis, bronchitis) as well as invasive infections since the vaccine for capsular type b was introduced
- produces IgA protease
Haemophilus influenzae
Bacteria:
- culture on chocolate agar, which contains factors V (NAD+) and X (hematin) for growth;
- can also be grown with S. aureus, which provides factor V via RBC hemolysis
Haemophilus influenzae
Bacteria:
- epiglottitis
- “cherry red” in children
- “thumb sign” on lateral neck x-ray
- meningitis
- otitis media
- pneumonia
Haemophilus influenzae
HaEMOPhilus
- Epiglottitis
- Meningitis
- Otitis media
- Pneumonia
Haemophilus influenzae is treated with _____.
- Amoxicillin +/− Clavulanate–mucosal infections
- Ceftriaxone–meningitis
- Rifampin–prophylaxis for close contacts
Bacteria:
- vaccine contains type b capsular polysaccharide (polyribosylribitol phosphate) conjugated to diphtheria toxoid or other protein
- given between 2 and 18 months of age
Haemophilus influenzae
Bacteria:
- Gram ⊝
- aerobe
- coccobacillus
-
Virulence Factors
- Pertussis toxin (disables Gi)
- Adenylate Cyclase toxin (↑ cAMP)
- Tracheal Cytotoxin
- may be mistaken as viral infection due to lymphocytic infiltrate resulting from immune response
Bordetella pertussis
Stages of Pertussis
- Catarrhal—low-grade fevers, Coryza
- Paroxysmal—paroxysms of intense cough followed by inspiratory “whooP” (“whooping cough”), posttussive vomiting
- Convalescent—gradual recovery of chronic cough
Pertussis is prevented by _____ vaccines.
- Tdap
- DTaP
Bacteria:
- Gram ⊝ rod
- Gram stains poorly
- seen on silver stain
- grows on charcoal yeast extract medium with iron and cysteine
- detected by presence of antigen in urine
- labs may show hyponatremia
- aerosol transmission
Legionella pneumophila
Think of a French legionnaire (soldier) with his silver helmet, sitting around a campfire (charcoal) with his iron dagger—he is no sissy (cysteine).
Legionella pneumophila causes _____ which presents with severe pneumonia (often unilateral and lobar), fever, GI and CNS symptoms. Common in smokers and in chronic lung disease.
Legionnaires’ disease
_____ is mild flu-like syndrome caused by Legionella pneumophila.
Pontiac Fever
Legionella pneumophila is treated with _____.
- Macrolide
- Quinolone
Bacteria:
- Gram ⊝ rod
- aerobic
- motile
- Oxidase ⊕
- non-lactose fermenting
- found in water
- grape-like odor
Pseudomonas aeruginosa
Bacteria:
- mucoid polysaccharide capsule may contribute to chronic pneumonia in cystic fibrosis patients due to biofilm formation
- corneal ulcers/keratitis in contact lens wearers/minor eye trauma.
Pseudomonas aeruginosa
Pseudomonas aeruginosa is associated with _____.
PSEUDOMONAS:
- Pneumonia
- Sepsis
- Ecthyma gangrenosum
- UTIs
- Diabetes
- Osteomyelitis
- Mucoid polysaccharide capsule
- Otitis externa (swimmer’s ear)
- Nosocomial infections (eg. catheters, equipment)
- Addicts (drug abusers)
- Skin infections (eg. hot tub folliculitis, wound infection in burn victims).
_____ is a rapidly progressive, necrotic cutaneous lesion caused by Pseudomonas bacteremia. Typically seen in immunocompromised patients.
Ecthyma Gangrenosum
Pseudomonas aeruginosa is treated with _____.
CAMPFIRE:
- Carbapenems
- Aminoglycosides
- Monobactams
- Polymyxins (eg. polymyxin B, colistin)
- Fluoroquinolones (eg. ciprofloxacin, levofloxacin)
- ThIRd- and fourth-generation cephalosporins (eg. ceftazidime, cefepime)
- Extended-spectrum penicillins (eg. piperacillin, ticarcillin)
Bacteria:
- Gram ⊝ rod
- non-lactose fermenting
- Oxidase ⊝
- can invade the GI tract via M cells of Peyer patches
- Salmonella
- Shigella
Bacteria:
- Reservoir: humans only
- can disseminate hematogenously
- produces H2S
- has flagella
-
Virulence Factors
- Endotoxin
- Vi Capsule
-
Infectious Dose (ID50)
- High—large inoculum required
- acid-labile (inactivated by gastric acids)
Salmonella typhi
Bacteria:
- monocytic immune response
- causes constipation, followed by diarrhea
- causes typhoid fever (rose spots on abdomen, constipation, abdominal pain, fever)
- carrier state with gallbladder colonization
- antibiotics prolong duration of fecal excretion
Salmonella typhi
Salmonella typhi vaccines are _____.
- Oral vaccine—live attenuated S. typhi
- IM vaccine—Vi capsular polysaccharide
Salmonella typhi is treated with _____.
- Ceftriaxone
- Fluoroquinolone
Bacteria:
- Reservoir: humans and animals
- can disseminate hematogenously
- produces H2S
- has flagella
- Virulence Factor: Endotoxin
- Infectious Dose (ID50): High
Salmonella spp.
(except S. typhi)
Bacteria:
- PMNs in disseminated disease
- causes diarrhea (possibly bloody)
- no vaccine
- poultry, eggs, pets, and turtles are common sources
- gastroenteritis is usually caused by nontyphoidal species
- antibiotics not indicated
- antibiotics prolong duration of fecal excretion
Salmonella spp.
(except S. typhi)
Bacteria:
- Reservoir: humans only
- cell to cell spread
- does not produce H2S
- no flagella
-
Virulence Factor:
- Endotoxin
- Shiga toxin (Enterotoxin)
-
Infectious Dose (ID50):
- Low—very small inoculum required
- acid stable (resistant to gastric acids)
Shigella
Bacteria:
- PMN infiltration
- causes bloody diarrhea (bacillary dysentery)
- no vaccine
-
Species in order of decreasing severity (less toxin produced):
- S. dysenteriae
- S. flexneri
- S. boydii
- S. sonnei
- invasion of M cells is key to pathogenicity
- organisms that produce little toxin can cause disease
- antibiotics shorten duration of fecal excretion
Shigella
Four F’s:
- Fingers
- Flies
- Food
- Feces
Bacteria:
- Gram ⊝ rod
- usually transmitted from pet feces (eg. puppies), contaminated milk, or pork
- causes acute diarrhea or pseudoappendicitis (right lower abdominal pain due to mesenteric adenitis and/or terminal ileitis)
Yersinia enterocolitica
Bacteria:
- MacConkey agar—pink colonies
- EMB agar—purple/black colonies
Lactose-Fermenting Enteric Bacteria
Lactose-Fermenting Enteric Bacteria
Lactose is key. Test with MacConKEE’S agar.
- Citrobacter
- Klebsiella
- E. coli
- Enterobacter
- Serratia (weak fermenter)
E. coli produces _____, which breaks down lactose into glucose and galactose.
β-galactosidase
_____ grows colonies with a green sheen.
E. coli
Bacteria:
- Gram ⊝ rod
-
Virulence Factors:
- Fimbriae—cystitis and pyelonephritis (P-pili)
- K Capsule—pneumonia, neonatal meningitis
- LPS Endotoxin—septic shock
Escherichia coli
E. coli Strains:
- microbe invades intestinal mucosa and causes necrosis and inflammation
- dysentery
- clinical manifestations similar to Shigella
Enteroinvasive E. coli (EIEC)
E. coli Strains:
- produces heat-labile and heat-stable enterotoxins
- no inflammation or invasion
- Traveler’s Diarrhea (watery)
Enterotoxigenic E. coli (ETEC)
ETEC = Traveler’s Diarrhea
E. coli Strains:
- no toxin produced
- adheres to apical surface
- flattens villi
- prevents absorption
- diarrhea, usually in children
Enteropathogenic E. coli (EPEC)
EPEC = Pediatrics
E. coli Strains:
- O157:H7 is most common serotype in US
- transmitted via undercooked meat, raw leafy vegetables
- Shiga-like toxin causes Hemolytic-Uremic
- Syndrome
- dysentery (toxin alone causes necrosis and inflammation)
- does not ferment Sorbitol (vs. other E. coli)
Enterohemorrhagic E. coli (EHEC)
EHEC = Hemorrhagic, Hamburgers, HUS
EHEC produces Shiga-like toxin which causes _____: triad of anemia, thrombocytopenia, and acute renal failure due to microthrombi forming on damaged endothelium → mechanical hemolysis (with schistocytes on peripheral blood smear), platelet consumption, and ↓ renal blood flow.
Hemolytic-Uremic Syndrome (HUS)
Bacteria:
- Gram ⊝ rod
- intestinal flora that causes lobar pneumonia in alcoholics and diabetics when aspirated
- very mucoid colonies caused by abundant polysaccharide capsules
- dark red “currant jelly” sputum (blood/mucus)
- nosocomial UTI
- associated with evolution of multidrug resistance (MDR)
Klebsiella
5 A’s of KlebsiellA:
- Aspiration pneumonia
- Abscess in lungs and liver
- Alcoholics
- DiAbetics
- “CurrAnt jelly” sputum
Bacteria:
- Gram ⊝
- comma or S shaped (with polar flagella)
- Oxidase ⊕
- grows at 42°C
- major cause of bloody diarrhea, especially in children
- fecal-oral transmission through person-to-person contact or via ingestion of undercooked contaminated poultry or meat, unpasteurized milk
- contact with infected animals (dogs, cats, pigs) is a risk factor
- common antecedent to Guillain-Barré syndrome and reactive arthritis
Campylobacter jejuni
Campylobacter likes the hot campfire.
Bacteria:
- Gram ⊝
- flagellated
- comma shaped
- Oxidase ⊕
- grows in alkaline media
- endemic to developing countries
- produces profuse rice-water diarrhea via enterotoxin that permanently activates Gs, ↑ cAMP
- sensitive to stomach acid (acid labile)
- requires large inoculum (high ID50) unless host has ↓ gastric acidity
- transmitted via ingestion of contaminated water or uncooked food (eg. raw shellfish)
- treat promptly with oral rehydration solution
Vibrio cholerae
Bacteria:
- Gram ⊝ rod
- curved
- flagellated (motile)
-
Triple ⊕:
- Catalase ⊕
- Oxidase ⊕
- Urease ⊕
- urea breath test or fecal antigen test are used for diagnosis
- Urease produces ammonia, creating an alkaline environment, which helps survival in acidic mucosa
- colonizes mainly antrum of stomach
- causes gastritis and peptic ulcers (especially duodenal)
- risk factor for pepti ulcer disease, gastric adenocarcinoma, and MALT lymphoma
Helicobacter pylori
Helicobacter pylori is treated with triple therapy which includes _____.
Antibiotics Cure Pylori.
- Amoxicillin (Metronidazole for Penicillin allergy)
- Clarithromycin
- Proton Pump Inhibitor
Bacteria:
- spiral-shaped
- axial filaments
Spirochetes
Spirochetes
BLT
- B**orrelia (big size)—B**orrelia is Big
- Leptospira
- Treponema
Among the spirochetes, only _____ can be visualized using aniline dyes (Wright or Giemsa stain) in light microscopy due to size.
Borrelia
Treponema is visualized by _____.
- Dark-Field Microscopy
- Direct Fluorescent Antibody (DFA) Microscopy
Bacteria:
- Lyme disease
- transmitted by the Ixodes deer tick (also
- vector for Anaplasma spp. and protozoa Babesia)
- natural reservoir is the mouse (and important to tick life cycle)
- common in northeastern US
Borrelia burgdorferi
Lyme Disease Symptoms
A Key Lyme pie to the FACE:
- Facial nerve palsy (typically bilateral)
- Arthritis
- Cardiac block
- Erythema migrans
Stages of Lyme Disease
- Stage 1—Early Localized: erythema migrans (typical “bulls-eye” configuration is pathognomonic but not always present), flu‑like symptoms
- Stage 2—Early Disseminated: secondary lesions, carditis, AV block, facial nerve (Bell) palsy, migratory myalgias/transient arthritis
- Stage 3—Late Disseminated: encephalopathy, chronic arthritis
Lyme disease is treated with _____.
- Doxycycline (1st line)
- Amoxicillin
- Cefuroxime (pregnant women and children)
Bacteria:
- spirochete
- hook-shaped ends
- found in water contaminated with animal urine
Leptospira interrogans
_____ presents with flu-like symptoms, myalgias (classically of calves), jaundice, photophobia with conjunctival suffusion (erythema without exudate). Prevalent among surfers and in tropics (eg. Hawaii).
Leptospirosis
_____ is the severe form of _____ with jaundice and azotemia from liver and kidney dysfunction, fever, hemorrhage and anemia.
Weil Disease
(Icterohemorrhagic Leptospirosis)
Bacteria:
- spirochete
- causes syphilis
Treponema pallidum
Syphilis:
- localized disease presenting with painless chancre
- dark-field microscopy is used to visualize treponemes in fluid from chancre
- VDRL ⊕ in ~ 80%
Primary Syphilis
Viral Structure
Influenza Viruses:
- causes pandemics
- reassortment of viral genome segments, such as when segments of human flu A virus reassort with swine flu A virus
Genetic/Antigenic Shift
Sudden shift is more deadly than gradual drift.
Influenza Viruses:
- causes epidemics
- minor changes based on random mutation in hemagglutinin or neuraminidase genes
Genetic/Antigenic Drift
Sudden shift is more deadly than gradual drift.
Hepatitis Serologic Markers
Hepatitis Serologic Markers:
best test to detect acute hepatitis A
Anti-HAV (IgM)
Hepatitis Serologic Markers:
- indicates prior HAV infection and/or prior vaccination
- protects against reinfection
Anti-HAV (IgG)
Hepatitis Serologic Markers:
- antigen found on surface of HBV
- indicates hepatitis B infection
HBsAg
Hepatitis Serologic Markers:
indicates immunity to hepatitis B due to vaccination or recovery from infection
Anti-HBs
Hepatitis Serologic Markers:
antigen associated with core of HBV
HBcAg
Hepatitis Serologic Markers:
- IgM = acute/recent infection
- IgG = prior exposure or chronic infection
- IgM may be the sole ⊕ marker of infection during window period
Anti-HBc
Hepatitis Serologic Markers:
- secreted by infected hepatocyte into circulation
- not part of mature HBV virion
- indicates active viral replication and therefore high transmissibility and poorer prognosis
HBeAg
Hepatitis Serologic Markers:
indicates low transmissibility
Anti-HBe
HIV
Time Course of Untreated HIV Infection
- Dashed lines on CD4+ count axis indicate moderate immunocompromise (< 400 CD4+ cells/mm3) and when AIDS-defining illnesses emerge (< 200 CD4+ cells/mm3).
- Most patients who do not receive treatment eventually die of complications of HIV infection.
- During clinical latency phase, the virus replicates in lymph nodes.
Four Stages of Untreated HIV:
- Flu-like (acute)
- Feeling fine (latent)
- Falling count
- Final crisis
