Microbiology: Bacteria Classification Flashcards Preview

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Flashcards in Microbiology: Bacteria Classification Deck (14):

Contents of gram positive cell wall

-Thick peptidoglycan (chains of GlcNAc and MurNAc cross-linked by peptide bridge, can be degraded by lysozyme)
-Teichoic acid (virulence factor, defines serotype, needed to survive, good Ag)
-Lipoteichoic acid (lipid linked teichoic acid)
-Cell membrane (contains nzs for ETC, transport)


Contents of gram negative cell wall

-Outer membrane (w/ porin complexes)
-LPS (lipopolysaccharide virulence factor)
-Outer membrane held together by divalent cation (Mg, Ca) bonds btwn LPS and proteins (cation bonds susceptible to antibios and chelating)
-Periplasmic space (contains nzs for transport, degradation, synthesis)
-Thin peptidoglycan
-Inner membrane


Structure of LPS

-Virulence factor made of lipid A base, polysaccharide core, O Ag repeats
-Lipid A responsible for endotoxin activity of LPS
-O Ag distinguishes serotype of species


Criteria for bacteria

-No nucleus (haploid w/ plasmids and single large chromosome)
-No organelles, 70S ribosomes, cell wall, binary fission reproduction
-Cellular respiration through PM


Phenotypic characterization

-Morphological (visible characteristics)
-Biotyping (tests for nzs)
-Serotyping (test for Ags)
-Antibiogram (test for antibio resistance)
-Phage typing (bacteriophge susceptibility)


Analytic characterization

-Cell wall FA
-Whole cell lipids
-Whole cell proteins
-Whole cell nzs


Genotypic characterization

-Mostly PCR


7 different shapes

-Coccus (sphere)
-Bacillus (rod)
-Coccobacillus (oval)
-Fusiform (thin rod)
-Vibrio (boomerang)
-Spirillum (thick short spiral)
-Spirochete (thin long spiral)


Capsule (glycocalyx)

-Loose polysaccharides and polypeptides (virulence factor, antiphagocytic)
-Only found in some bacteria, are not antigenic
-Can be slime layer when loose and nonuniform
-Biofilms can be laid down to protect colonies from antibios and host defenses
-Not necessary for growth, but important for survival w/in host


Other bacterial structures

-Pilli (for adhesion, mating)
-Flagellum (for motility)
-Antibio sensitivity (peptidoglycan synthetic nzs)
-Antibio resistance (outer membrane and nzs in it and periplasmic space)


Synthesis of peptidoglycan

-Cross link of D-ala on one chain w/ lys on other chain
-Synthesized in 3 steps starting w/ UTP
-First step units are made within cell
-Second step units are assembled at the membrane (undecaprenol phosphate conveyor belt)
-Third step unit is translocated outside the cell where it is cross linked


Inhibition of peptidoglycan synthesis by antibios

-Pre-cross linked peptidoglycan contains pentapeptide w/ terminal D-ala-D-ala unit
-B-lactam prevents linkage of D-ala w/ lys on another chain during transpeptidation rxns
-Nzs that catalyze this are penicillin binding proteins (PBPs)
-These only kill replicating bacteria



-Only GP bacteria, during harsh conditions
-Enters dormant state under a multi shelled coating
-Contains a complete copy of the chromosome, bare essential proteins
-High concentration of Ca bound to dipicolonic acid (may protect against heat/radiation)



-DNA is copied, cell wall folds around the copy and spore is ejected
-Requires potent agents to decontaminate (peroxides, chlorine dioxide, bleach + sodium hypochloride, ethylene oxide, sandia foam)