Intro to Bacteria Part 1 Flashcards
Prokaryote vs. Eukaryote (generally)
eukaryotes contain membrane bound nuclei, while prokaryotes do not
Archaeon
microorganisms found in extreme environments; possibly the earliest forms of cellular life on earth
Gram positive stain color
Blue
Gram negative stain color
Red
Gram positive cell wall
very thick cell wall with extensive amino acid cross-linking; made of peptidoglycan, teichoic acid, polysaccharides and other proteins
Gram negative cell wall
simple cross linking pattern; cytoplasmic membrane, peptidoglycan layer, THIN peptidoglycan layer (no teichoic acid), LPS layer, porins in outer membrane
LPS constituents
O-specific side chain/O-antigen, core polysaccharide, Lipid A
Gram negative endotoxin
Lipid A; causes fever, diarrhea, endotoxic shock
What can pass through a G+ cell wall?
antibiotics, dyes, detergents
What substances cannot pass through G- cell wall?
negatively charged, antibiotics that attack peptidoglycan
Key differences between G+ and G- cell wall?
G+: 2 layers, low lipid content, no endotoxin, no porin, vulnerable to lysozyme and penicillin
G-: 3 layers, high lipid content, Lipid A toxin, porin channels, resistant to lysozyme and penicillin
6 Classic most medically relevant G+ pathogens
Streptococcus, Staphylcoccus, Bacillus and Clostridium (spores), and Corynebacterium and Listeria (non spores)
G- cocci
Neisseria, Moraxella
G- spiral shaped
Spirochetes (Treponema pallidum)
Mycobacteria unique features
weakly G+ but stain better with acid-fast stain
Spirochetes unique features
G- wall but must be seen with dark field microscope (size); contain additional outer membrane with very few proteins and periplasmic flagella
Mycoplasma unique features
no cell wall, not G+ or G-
G+ obligate aerobes
Nocardia, Bacillus cereus
G+ Facultative anaerobes
Staphylococcus, Bacillus anthracis, Cornyebacterium, Listeria, Actinomyces
G+ Microaerophilic
Enterococcus, Sterptococcus
G+ Obligate anaerobes
Clostridium
G- obligate aerobes
Neisseria, Pseudomonas, Bordetella, Legionella, Brucella
G- facultative anaerobes
most G- rods
G- Microaerophilic
Spirochetes (Treponema, Borrelia, Leptospira), Campylobacter
G- Obligate anaerobes
Bacteroides
Acid-fast obligate aerobes
Mycobacterium, Nocardia
Oxygen spectrum of Mycoplasma
Facultative anaerobe
Obligate aerobes
glycolysis, Krebs, and ETC
Facultative anaerobes
aerobic bacteria that contain catalase and superoxide dismutase; CAN grow in absence of oxygen
Microaerophilic bacteria
no electron transport system, tolerate low amounts of oxygen and have superoxide dismutase
Obligate anaerobes
No enzymes to defend against oxygen, does not like oxygen
Virulence definition
degree of organism pathogenicity
pili
straight filaments arising from bacterial cell wall, serve as adherence factors
organisms with pili and cells they attach to
N. gonorrhea: cervical and bucal cells
E. coli and C. jejuni: intestinal epithelium
B. pertussis: ciliated respiratory cells
Capsules
Protective walls around cell membranes of bacteria composed of simple sugars
Capsule of Bacillus anthracis
capsule made up of amino acid residues
Why do capsules contribute to the virulence of an organism?
Neutrophils and macrophages are unable to phagocytize encapsulated bacteria
Stains that enable doctors to visualize capsules
India Ink stain, Quellung reaction
India ink stain
stain not taken up by capsule, appears as a transparent halo around cell; Cryptococcus
Quellung reaction
bacteria mixed with abs, capsule can swell with water
Endospores
formed by G+ bacillus and clostridium; metabolically dormant forms resistant to heat, cold, drying and chemical agents
Endospore protective coat consists of
cell membrane, peptiodglycan, cell membrane, keratin-like protein, exosporium
When do spores form?
shortage of needed nutrition, will become active again when appropriate nutrition is available
Exotoxins
proteins released by G+ and G- bacteria that may cause disease manifestations (anthrax, botulism, tetanus, cholera)
Neurotoxin
tetanus toxin and botulinum toxin; act on nerves or motor endplates to cause paralysis
Enterotoxins
exotoxins that act on GI; inhibit NaCl resorption, activate NaCl secretion or kill epithelial cells
Two disease manifestations of enterotoxins
Infectious diarrhea (E. coli, V. cholera, C. jejuni, S. dysenteriae), Food poisoning (toxin from food, B. cereus, S. aureus)
Pyrogenic exotoxins
cause rash, fever, toxic shock; S. aureus, S. pyogenes
Tissue Invasive exotoxins
allow bacteria to destroy and tunnel through tissues
Endotoxins
Lipid A, released when bacteria undergoes lysis, but can be shed from living bacteria; normal part of membrane that sheds off
Septic shock
sepsis that results in low BP and organ dysfunction
TNF
tumor necrosis factor/cachexin; triggers release of IL-1
IL-1
triggers release of other cytokines and PGs, vasodilation, hypotension and organ system dysfunction
Methods of genetic exchange between bacteria
transformation, transduction, conjugation, transposons
Transformation
uptake of DNA fragments from one bacterium released during lysis
Transduction
bacteriophage carries piece of bacterial DNA from one bacterium to another
Virulent phage
infects, reproduces, then lyses bacteria; generalized transduction
Temperate phage
infect bacteria, but DNA will become incorporated into the bacteria DNA (time bomb); specialized transduction
Lysogenic immunity
term used to describe ability of an integrated bacteriophage to block a subsequent infection by a similar phage
Generalized transduction
bacterial DNA mispackaged into phage, which can then go and infect another bacteria without causing it’s death
Conjugation
sex pilus forms and allows for efficient exchange of plasmid/genetic material between bacteria
Transposons
pieces of DNA that insert themselves into chromosome without having homology, often responsible for drug resistance
Agents and methods used to identify pathogens?
smears, gram staining, cultures, molecular techniques, serology, survey for ab positivity
Potential pathogens
bacteria, viruses, fungi, parasites, prions, mites, etc.
Pros of bacterial cultures
high specificity, isolates can be tested for ab sensitivity, enables biochem characterization of phenotype, less expensive, does not require special workflow, does not require specialized instrumentation
Cons of bacterial cultures
low sensitivity, cannot detect nonviable bacteria, biochem phenotype may not agree with genotype, longer time to result for slow-growing bacteria, biosafety concern
Pros of NAT methods
high sensitivity, rapid turnaround time, detection of nonviable bacteria, reduced biosafety concern, detection of ab-resistant bacteria without an initial culture
Cons of NAT methods
false positives due to cross reaction, false-negatives, genotype may not agree with biochem results, requires special instrumentation and training, few tests for ab sensitivity are available
Differentiating Staph and Strep
Staph: cocci cluster together, catalase positive (Staff has a Cat)
Strep: cocci form a strip, catalase negative
Hemolytic reactions of strep
Beta-hemolytic: completely lyse RBCs on blood agar
Alpha-hemolytic: partially lyse RBC
Gamma-hemolytic: unable to hemolyze (“non-hemolytic” streptococci)
C carbohydrate
Carb found on cell wall of Strep
Group A B-hemolytic Streptococci aka
Streptococcus pyogenes
Diseases associated with S. pyogenes
strep throat, scarlet fever, rheumatic fever, post-strep glomerulonephritis
C carb Lancefield group of S. pyogenes
Lancefield group A
M protein
Major virulence factor in S. pyogenes, inhibits complement and protects from phagocytosis
Streptolysin O
enzyme in beta-hemolytic group A strep, inactivated by oxygen, destroys RBC and WBC, ANTIGENIC (may order ASO on pt)
Streptolysin S
oxygen stable enzyme beta-hemolytic group A strep, not antigenic
Pyrogenic exotoxin
exotoxin produced by only a few strains of beta hemolytic group A strep, superstimulates T cells to pour out inflammatory cytokines
streptokinase
activates proteolytic enzyme plasmin, breaks up fibrin clot
Beta-hemolytic Grp A strep causes what diseases by local invasion or exotoxin release
Strep pharyngitis, Strep skin infection, scarlet fever, Strep TSS
Beta hemolytic Grp A strep causes what diseases by delayed antibody mediated diseases
Rheumatic fever and glomerulonephritis
Sxs and tests for Strep pharyngitis
red swollen tonsils and pharynx, purulent exudate on tonsils, high temp, swollen LNs
RADT test: group A carb
Sxs of Strep skin infections
folliculitis, pyoderma, erysipelas, cellulitis, impetigo
Erysipelas
strep infection of superficial skin, raised, bright red rash with a sharp border that advances from the initial site of infection
Pyoderma
pustule on face or extremity that breaks down after 4-6 days and forms a thick crust, leaving a depigmented area
Necrotizing fascitis
certain strains of grp A b-hemolytic strep have M proteins that block phagocytosis; swelling, heat, redness at site of infection, large blisters form and skin and muscle may die
Fournier’s gangrene
form of necrotizing fascitis in male genital area and perineum
Scarlet fever
sore throat and pyrogenic or erythrogenic toxin and fever/rash; spares the face!
Strep TSS
pyrogenic toxin
Erythema marginatum
nonpruritic rash typically occurring on trunk and extremities, not face; occurs in patients with rheumatic fever
Tinea corporis
rounded lesion that typically has a fine scale and may cause alopecia; central clearing and raised borders; pruritic
Erythema migrans
bull’s eye appearance, Lyme disease; central erythema and necrosis
Erythema multiforme
maculopapular rash located on palms and feet that generally spreads; can result from drug rxn or viral and bacterial infections; bull’s eye appearance, pruritic, blanches away slowly
Erythema nodosum
erythematous macules that are painful; usually occurs on shins
Rheumatic fever presentation
children 5-15 yrs of age, typically follows strep pharyngitis; fever, myocarditis, joint swelling, chorea, subcutaneous nodules, erythema marginatum
Acute post-strep glomerulonephritis
ab-mediated inflammatory disease of glomeruli; antigen-antibody complexes deposit in BM of glomeruli
Presentation of acute post-strep glomerulonephritis
child in office complaining of puffy face, dark urine; may have hypervolemia/high BP; recent history of throat or skin infection
Grp B Streptococci genus/species
Streptococcus agalactiae
Age-group most commonly affected by Grp B Strep
neonates; most common cause of neonatal meningitis, pneumonia, and sepsis
Grp B Strep presentation
fever, vomiting, poor feeding, irritability
3 most common pathogens associated with meningitis in neonates and infants <3mo?
E. coli, L. monocyotogenes, grp B Strep
Most common bacterial cause of meningitis later in life
Neisseria meningitides, Haemophilus influenzae
Viridans Grp Streptococci hemolytic rxn
alpha-hemolytic
Where are Viridans Grp Streptococci normally found?
GI tract, nasopharynx, gingiva
Associated infections of Viridans Grp Strep
dental infections, endocarditis, abscesses
Presentation of Subacute Bacterial Endocarditis
low-grade fever, fatigue, anemia, heart murmur secondary to valve destruction
Presentation of acute infective endocarditis
shaking chills, high spiking fevers, rapid valve destruction
Bacteria commonly found in brain or abd organ abscesses
Anginosus species (Strep. intermedius), microaerophilic
Grp D Strep sub groups
Enterococcus and non-enterococci
Hemolytic pattern of Grp D Strep
alpha- or gamma-hemolytic
Normal residence of enteroccoci
human intestines/normal bowel
Unique growth characteristics of enteroccus
ability to grow in 40% bile or 6.5% NaCl
Common diseases associated with Enterococcus
UTI, biliary tract infection, bacteremia, subacute bacterial endocarditis
Enterococcus in nosocomial infections
second to third most common cause of hospital acquired infections
Drug resistance of Enterococci
resistant to nost G+ bacteria; vancomycin and ampicillin, esp
Non-enterococci common genus/species
Strep bovis and equinis
Growth conditions of Strep bovis
40% bile acid (but not 6.5% salt!)
S. bovis in colon cancer
remarkable association, not sure if it’s a cause or marker?
Strep pneumoniae disease manifestations
bacterial pneumonia and meningitis in adults, otitis media in kids
Quellung reaction for Strep pneumoniae
capsule swells
Optochin sensitivity for Strep pneumoniae
growth inhibited by optochin (unlike S. viridans)
Most common cause of pneumonia in adults
S. pneumoniae
Presentation of pneumococcal pneumonia
rigors, high fevers, chest pain with respirations, SOB, yellow-green sputum
Three organisms associated with otitis media
S. pneumoniae, H. influenzae, M. catarrhalis
Who is given the pneumococcal vaccine
immunocompromised, elderly, asplenic or HIV positive individuals
Emerging abx resistance of S pneumoniae
penicillin ,erythromycin, sulfamethoxazole, chloramphenicol
