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
*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
gram positive cell wall
*THICK peptidoglycan layer above cytoplasmic membrane
-traps and binds gram stain (stain PURPLE)
-small molecules can diffuse
*rich in techoic and lipotechoic acid, vital to cell survival
techoic acid & lipotechoic acid
unique to gram POSITIVE cell wall
-help to anchor the cell wall
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
*acid-fast organisms (mycobacterium) have lipid-rich membrane containing mycolic acid
*organisms that lack a cell wall
*some spirochetes are too small
*intracellular pathogens
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
dispose hydrogen peroxide to water
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 MADE BY GRAM POS
-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
*ONLY GRAM +
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
-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 to prevent opsonization
virulence factor: IgA protease
-cleaves IgA and allows pathogen to enter respiratory tract
-protein enzyme
virulence factor: M protein
-resembles human cellular protein (mimicry) to prevent phagocytosis
-expressed by Strep known to cause 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
