Microbiology - Basic bacteriology

omranalzobaidi's version from 2015-11-28 14:22

Bacterial structure

Question Answer
Cell wall/cell membrane (gram positives)Peptidoglycan for support. Lipoteichoic acid induces TNF and IL- l .
Outer membrane (gram negatives)Lipid A induces TNF and IL-l; 0 polysaccharide is the antigen.
Outer membrane (gram negatives)Site ofendotoxin (lipopolysaccharide [LPS]);
PeriplasmSpace between the cytoplasmic membrane and outer membrane in gram-negative bacteria.
PeriplasmContains many hydrolytic enzymes, including b-lactamases.
Polysacharride capsuleProtects against phagocytosis.
D-glutamateBacillus anthracis protection against phagocytosis
Pilus/ fimbria - GlycoproteinMediate adherence ofbacteria to cell surface; sex pilus forms attachment between 2 bacteria during conjugation.
SporeResistant to dehydration, heat, and chemicals.
SporeKeratin-like coat; dipicolinic acid; peptidoglycan
GlycocalyxMediates adherence to surfaces, especially foreign surfaces (e.g., indwelling catheters)
PlasmidDNA. Contains a variety ofgenes for antibiotic resistance, enzymes, and toxins.
Unique to gram-positive organismlipotechoic acid (combination of lipid and tecichoic acids)
Unique to gram-negative organismLPS/endotoxin (outer membrane)
pleomorphic2 or more distinct forms in life cycle
Branching filamentous bacteriaActinomyces, Nocardia
PleomorphicRickettsia and Chlamydiae (Giemsa stain) - H.inlfuenza
No cell wallmycoplasma (does not gram stain)
Why mycoplasma does not gram stain well?contain sterols, and have no cell wall
Why mycobacteria does not gram stain well?contain mycolic acid. High lipid content

Bacterial stain and culture

Question Answer
Bugs that do not Gram stain wellTreponema, Rickettsia, Mycobacteria, Mycoplasma, Legionella pneumophilia, Chlamydia
Bugs with Giemsa stainChlamydia, Borrelia, Ricketsiae, Trypanosome, Plasmodium
Stain glycogen, mucopolysaccharidesPAS
Stain used to Dx Whipple's diseasePAS
Ziehl-Neelsen (carbofuchsin)Acid fast-organism (Nocardia, Mycobacterium)
Acid fast organismNorcadia (branching filamentous), Mycobacterium (gram positive rod)
India InkCryptococcus neoformans (mucicarmine can also be used to stain thick polysaccharide capsule red).
Silver stainFungi (e.g., Pneumocystis), Legionella, Helicobacter pylori.
￼Chocolate agar with factors V (NAD+) and X (hematin)H. influenzae
N. gonorrhoeae, N. meningitidisThayer-Martin (or VPN) media
Thayer-Martin (or VPN) mediaVancomycin (inhibits gram-positive organisms), Polymyxin (inhibits gram-negative organisms except Neisseria), and Nystatin (inhibits fungi); "to connect to Neisseria, please use your VPN client"
B. pertussisBordet-Gengou (potato) agar (Bordet for Bordetella)
C. diphtheriaeTellurite plate, Loffler's media
M. tuberculosisLowenstein-Jensen agar
M. pneumoniaeEaton's agar
Lactose-fermenting entericsPink colonies on MacConkey's agar
E. colieosin-methylene blue (EMB) agar
LegionellaCharcoal yeast extract agar buffered with cysteine and iron
FungiSabouraud's agar.

Specific bacteriology

Question Answer
Obligate aerobesNocardia, Pseudomonas aeruginosa, Mycobacterium tuberculosis, and Bacillus.
Obligate anaerobesClostridium, Bacteroides, and Actinomyces.
Obligate intracellularRickettsia, Chlamydia.
Facultative intracellularSalmonella, Neisseria, Brucella, Mycobacterium, Listeria, Francisella, Legionella, Yersinia pestis
Encapsulated baderiaStreptococcus pneumoniae, Haemophilus infiuenzae type B, Neisseria meningitidis, Escherichia coli, Salmonella, Klebsiella pneumoniae, and group B Strep.SHiNE SKiS.
Catalase-positive organismsPseudomonas, Listeria, Aspergillus, Candida, E. coli, S. aureus, Serratia.
Urease-positive bugsCryptococcus, H. pylori, Proteus, Ureaplasma, Nocardia, Klebsiella, S. epidermidis, S. saprophyticus.
yellow pigment.S. aureus
yellow "sulfur" granules, which are composed of filaments of bacteria.Actinomyces israelii
blue-green pigment.Pseudomonas aeruginosa
red pigment.Serratia marcescens
Protein A (Binds Fc region of Ig - Prevents opsonization and phagocytosis)S. aureus.
lgA protease (help invading mucosa)S. pnewnoniae, H. influenzae type B, and Neisseria (SHiN) in order to colonize respiratory mucosa.
M protein (prevent phagocytosis) group A streptococci.
Seen in burn wounds, complications of DM, nosocomial pneumonia, pneumonias in CF patientsPseudomonas
Normal flora in GI tractanaerobes
Aminoglycoside are ineffective against these bacteriaanaerobes
Lack of catalase or superoxide dismutaseanaerobes
foul smelling, difficult to culture and produce gas in tissue (CO2 and H2)anaerobes
Can't make own ATPobligated intracellular
positive quellung reaction (capsule swell)encapsulated bacteria
opsonized and cleared by spleenencapsulated bacteria
chronic granulomatous disease are susceptible tocatalase-positive bacteria
Different bt polysaccharide vaccine with and without conjugated proteinconjugated protein bind to polysacchardie antigen to promote T cell activation and class switching -> with conjugated protein IgG, without only IgM

Bugs with exotoxins

Question Answer
Inactivated EF-2Diptheria toxin, Exotoxin A
Inactivate 60S ribosome y removing adenine from rRNAShiga toxin, Shiga-like toxin
Overactivated cAMP, Cl and water secretion in gutHeat Labile toxin
overactivated cGMP, decrease resorption of NaCl and water in gutheat stable toxin
mimics cAMP, edematous borders of black eschar in cutaneous anthraxB.anthracis (edema factor)
overactivate cAMP, activating Gs, Cl secretion in gut, "rice-water" diarrheacholera toxin
high cAMP, disabling Gi, impair phagocytosis to permit survival of microbepertussis toxin
Whooping coughpertussis toxin
cleave SNARE protein required for neurotransmitter releasetetanospasmin, botulinum toxin
muscle rigidity and lock jaw, prevent release of GABA and lycine in spinal cordclostridium tetany
flaccid paralysis, floppy baby, prevent release of ACh at neuromuscular junctionbotulinum toxin
phospholipase that degrades tissue and cell membranesAlpha toxin (C.perfringens)
protein that degrades cell membranestreptolysin O (S.pyogenes)
bring MHC II and TCR in proximity to outside of antigen binding site to cause release of IFN-g and IL-2 -> shockS.aureus (TSST-1), S.pyogenes (exotoxin A)
Toxic shock syndrome, scalded skin syndrome (exfoliated toxin), food poisoning (enterotoxin)S.aureus
Toxic schock syndromeS.aureus or S.pyogenes
beta-hemolysis, host antibody against ASO can be used to Dx rheumatic fevers.pyogene (streptolysin O)
myonecrosis (gas gangrene), hemolysis (double zone on blood agar)C.perfringens (Alpha toxin)
Cause HUSShigella (ST) or EHEC O157:H7 (SLT)
Cause HUS, enhance cytokine release but do not invade host cellsO157:H7
cause HUS, dysentery, increase cytokine release, invade host cellShigella
cause host cell deathPseudomonas aeruginosa (Endotoxin A)
pharyngitis with pseudomembrane in throat and severe lymphadenopathyC.diptheriae (diptheria toxin)
Extremely heat stableendotoxin
O-antigen, lipid Aendotoxin
fever, hypotension, edema, neutrophil chemotaxis, DICendotoxin

Bacterial genetics

Question Answer
Transformation ' competence 'take naked DNA from environment
TransformationSHiN (S.pneumo, H.influenza, Nesseria)
Conjugationtransfer of plasmid dsDNA from F+ to F-, or F+ can incorporate into DNA, termed high-frequency recombination cell.
TranspositionDNA segment that jump from one location to another, can transfer gene from plasmid to chromosome.
Generalized transductionLytic phage, cleave bacteria DNA, package, part of DNA in viral capsid -> infect another bacteria
Specialized transductionLysogenic phage, viral DNA incorporate into bacteria chromosome, bacteria gene excise with phage DNA -> infect another bacteria
Lysogeny specialized transductionShiga-like toxin, Botulinum toxin, Cholera toxin, Diptheria toxin, Erythrogenic toxin (s.pyogene)