Basic Bacteriology Flashcards
targets of antibiotics that prokaryotes have that eukaryotes don’t
ribosomes & cell wall
pathogen associated molecular patterns
highly conserved motifs in the cell wall of bacteria, recognized by Pathogen Recognition Receptors
*can be targeted with antibiotics
bacterial cell wall
*chemical composition: peptidoglycan is a sugar backbone with peptide side chains, cross-linked by transpeptidase
-composed largely of NAG and NAM sugars, connected by beta-glycosidic bonds
-CROSS-LINKED by amino acids (L and D symmetry) to form SHEETS of peptidoglycan layers
*function: netlike structure gives rigid support, protects against osmotic pressure damage
gram positive cell wall
* THICK peptidoglycan layer above cytoplasmic membrane
-traps and binds gram stain (PURPLE means gram positive)
-small molecules can diffuse
*rich in techoic acid and LIPOTECHOIC acid, vital to cell survival
liPOteichoic acids = gram POsitive
techoic acid & lipotechoic acid
unique to gram POSITIVE cell wall
-help to anchor the cell wall
liPOtechoic acid = gram POsitive
gram negative cell wall
*THIN
*3 layers:
1. thin outer membrane, rich in LPS and porin molecules
2. periplasmic space (a pool for enzymes such as beta-lactamases)
3. cytoplasmic membrane
periplasmic space
*unique to gram negative
*contains thin peptidoglycan and a pool for enzymes (like beta lactamases)
LPS in the gram neg outer membrane
3 covalently linked components:
1. outer carbohydrate chains of 1-50 oligosaccharide units
2. core polysaccharide that is water soluble
3. lipid A (ENDOTOXIN) - stimulates TLR4 receptors when bacteria lyse
gram staining exceptions
- Treponema, Leptospira: spirochetes, too thin to be visualized
- Mycobacteria: acid-fast organisms; cell wall has high lipid content (mycolic acid)
- Mycoplasma, Ureaplasma: no cell wall
- Legionella, Rickettsia, Chlamydia, Bartonella, Anaplasma, Ehrlichia: primarily intracellular
mnemonic: These Little Microbes May Unfortunately Lack Real Color But Are Everywhere
classification of bacteria based on shape/morphology
-coccus
-coccobacillus
-vibrio (comma-shaped)
-bacillus (rod)
-spirochetes
obligate aerobes
-need oxygen
-use glycolysis, Krebs cycle, and ETC
-have enzymes to handle ROS
facultative anaerobes
-prefer oxygen, but can use anaerobic fermentation as an alternative energy source
-have enzymes to handle ROS
obligate ANaerobes
-lack enzymes needed to handle oxygen
-use anaerobic fermentation that produces gas such as gangrene
superoxide dismutase
dispose superoxide radical to hydrogen peroxide
catalase-positive organisms
*catalase degrades hydrogen peroxide (H2O2) to water and bubbles of O2
people with CGD (NADPH oxidase deficiency) have recurrent infections with catalase-positive organisms
catalase test: strep vs. staph
*staph is catalase (+)
*strep is catalase (-)
enzyme deficiency in chronic granulomatous disease (CGD)
*lack of NADPH oxidase
*patients susceptible to catalase (+) organisms
spores
*ONLY GRAM POSITIVE bacteria
-metabolically dormant
-thick protective covering composed of multiple membranes, peptidoglycan mesh, keratin-like protein, and outer exporium
-resistant to heat, cold, drying, and chemical agents
examples of spore-forming species
Bacillus and Clostridium
recall: ONLY GRAM + microbes can form spores
- Bacillus: B anthracis (anthrax); B cereus (food poisoning)
- Clostridium: C botulinum (botulism), C difficile, C perfringes, C tetani
obligate intracellular organisms
-cannot live outside host
-steal ATP
facultative intracellular organisms
-invade host and resist lysosome when it is advantageous
-evade host defenses
-ex: listeria monocytogenes
coagulase
*converts fibrinogen to fibrin (to cause coagulation)
*bacteria use clotting to evade host immune defenses
*often used to differentiate types of Staph
*cloudy/clot at the bottom = positive
urease
*converts urea to ammonia and CO2, raising pH
*organisms grown in buffered broth with pH indicators as a test
*PINK = POSITIVE; yellow = negative
virulence factors
-molecules and structures that enhance bacterial effectiveness
-improve entry into host and formation of colonies
-aid in host immune system evasion or immunosuppression
-assist bacteria in acquiring nutrients
examples of important virulence factors
-capsule
-exotoxins
-protein A
-IgA protease
-M protein
virulence factor: capsule
*highly charged, hydrophilic structure
*acts as a barrier to phagocytosis and complement-mediated lysis
*major determinant of virulence:
-protect against phagocytosis
-polysaccharide outer layer
virulence factor: exotoxins
-disrupt cellular functions of host cell or allow tissue evasion
-usually proteins
-made and RELEASED by bacterium
virulence factor: protein A
*binds Fc region of IgG
1. prevent opsonization
2. prevent phagocytosis
*expressed by Staph aureus
virulence factor: IgA protease
*enzyme that cleaves IgA, allowing bacteria to adhere to and colonize mucous membranes
-protein enzyme
-secreted by Strep pneumoniae, H influenza type B, Neisseria
virulence factor: M protein
*helps prevent phagocytosis
*expressed by Group A Streptococci
*has sequence homology with cardiac myosin (molecular mimicry) that likely underlies the autoimmune response seen in ACUTE RHEUMATIC FEVER
selective media
has additive (e.g. antibiotics) that inhibit the growth of non-desirable bacteria, but FAVORS bacteria of interest
differential/indicator media
allows observable changes in media appearance based on bacterial growth; often pH based
-ex: MacConkey agar; citrate agar
blood agar
contain sheep or horse blood to detect bacteria’s HEMOLYTIC ABILITY (allows bacteria to obtain iron)
*cooked at a lower temperature so that RBCs remain intact
*useful for diff kinds of Strep
beta-hemolysis on blood agar
COMPLETE digestion of blood around a colony
alpha-hemolysis on blood agar
PARTIAL lysis of RBCs with greenish-brown residual membranes
gamma-hemolysis on blood agar
NO lysis of RBCs
chocolate agar (selective media)
cooked blood agar, so that the RBCs are already lysed
Kirby Bauer test
tests for antibiotic sensitivity
*larger rings of no growth mean that antibiotic is good against that bacteria
