Microbiology: Bacteria Classification

Question 1

Contents of gram positive cell wall

Answer 1

• 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)

Question 2

Contents of gram negative cell wall

Answer 2

• 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

Question 3

Structure of LPS

Answer 3

• Lipopolysaccharide
• 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

Question 4

Criteria for bacteria

Answer 4

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

Question 5

Phenotypic characterization

Answer 5

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

Question 6

Analytic characterization

Answer 6

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

Question 7

Genotypic characterization

Answer 7

-Mostly PCR

Question 8

7 different shapes

Answer 8

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

Question 9

Capsule (glycocalyx)

Answer 9

• 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

Question 10

Other bacterial structures

Answer 10

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

Question 11

Synthesis of peptidoglycan

Answer 11

• 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

Question 12

Inhibition of peptidoglycan synthesis by antibios

Answer 12

• 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

Question 13

Endospore

Answer 13

• 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)

Question 14

Sporogenesis

Answer 14

• 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)