Test 1 – Microbiology Test Answers – Flashcards

1.  Linear polymers of NAG and NAM linked with beta 1,4 bond; teichoic acid and lipoteichoic acid (major role as anchoring sites to cytoplasmic membrane)

2.  Teichoic acid- only found in G + cell walls- major antigens

Envelope- external layer outer membrane- bilayer structure composed of phospholipid, proteins, and LPS

-Most abundant protein of outer membrane: porin- subunits form channel that allows passage of small molecules. 

LPS= endotoxin; only in gram neg bacteria; Composed of Lipid A, core polysaccharide, and O-specific polysaccharide antigen

Cause shock and fever

-Periplasmic gel= between inner surface of outer membrane and outer surface of inner plasma membrane- contains hydrolytic enzymes and binding proteins involved in transport and chemotactic receptor activities.

-Both G+ and G- take up CV and Iodine

- Thin peptidoglycan and outer membrane layers of G-s does not stick to dye.

-Counterstain: safranin

G+=> purple

G-=> pink/red

• Intracellular component in cytosol

• invagination of cytoplasmic membrane
• attached to nucleoid

• Associated with division septa

Presence of:

• Specific cell wall LPS ( O antigen)

• Flagella (H antigen)

• capsular (K antigen)

ID of particular pathogen which occurs in low concentration

• Determine taxonomy of bacteria residing in oral cavity or Rapid ID of bacteria in STDs

• Portion of Single stranded DNA from specific gene attacted to each square chip
• Each square represents different gene on bacterial chromosome
• Used to determine if gene is being expressed and define quorum sensing
• If gene is expressed, RNA copies will be present in cell; mRNA is extracted, labeled and added to chip
• Homologous nucleic acids will hybridize

Average time needed to double bacterial population. 

Determined during log phase growth

• Grows only under conditions of high reducing intensity
• Lacks metabolic enzyme for using oxygen
• Lacks enzyme for processing toxic oxygen products (catalase)
• Metabolism involves anaerobic respiration

• common for oral cavity
• will grow in presence of O2 but does not use it as an electron acceptor

Capable of growing under both aerobic and anaerobic conditions

• Will employ aerobic respiration when O2 is present
• Metabolism includes fermentation, aerobic, and anaerobic respiration
• Can process oxygen products

Require oxygen for growth

• metabolism is aerobic respiration
• Can process toxic oxygen products

• grows best at low O2 levels

biochemical test

• oxidase enzyme- catalyzes oxidation or reduced cytochrome by molecular oxygen
• oxidase test reagents= artifical electron acceptors --> Kovac's reagent

• NO3, SO4, or CO2 can serve as terminal electron acceptors.;
• Large group of facultative anaerobes are nitrate reducers: predominantly hetertrophys

• E. Coli and Staphylococcus Aureus

• Nitrate reduction test: determines ability of organism to reduce nitrate to nitrites or free nitrogen gas

-NO respiratory chain or cytochromes

• requires organic compound as terminal electron acceptor
• Obligate, aerotolerant, and facultative anaerobes
• incomplete oxidation of carbs is common
• fermentative end products: lactic acid, ethanol, acetic acid, butyric acid, butanol, propionic acid or acetone.;

• naked DNA derived from one cell or virus is taken up by another cell and recombines with genome
• Competency: ability to incorporate DNA
• short period during log phase growth
• Membranes aren't fully fused in log phase

• DNA of one cell is introduced into another cell by viral infection
• In process of replication, cellular DNA may "accidentally" be incorporated into new infectious viruses.
• Generalized transduction: any region of host genome can be transduced; only chromosomal DNA
• Specialized transduction:only specific regions of chromosome are transduced, particles carry both chromosomal DNA and phage DNA.

   

• transfer DNA by direct contact between cells
• Sex pilus: sex factor F= extrachromosomal, autonomously replicating DNA molecule (plasmid)
• F promotes conjugation and gene exchange
• Male: F+; Female: F-
• F+ conjugation: F contains fertility information plus limited number of genes- promotes formation of sex pilus; F- receives single stranded copy of F which becomes double-stranded and circular, converting F- to F+

• segments of double-stranded DNA that can move from place to place within a genome or between genomes or plasmids or phages genomes
• Can cause mutations
• can carry genes; do not carry genes controlling own replication, but possess insertion sequence elements responsible for transposability

Small (1000 BP) segments of double-stranded DNA that code for site specific recombination

• When these sequences integrate into a gene, function or activity is altered. 

Mycobacterium tuberculosis

Salmonella Typhimurium

• spreading factor

• affects ability of pathogen to penetrate tissues of host by hydrolyzing hyaluronic acid

• extracellular enzyme

• spreading factor that breaks down connective tissue of muscle

• Causes coagulation of fibrinogen

• Fibrin coats cell walls of bacteria, protecting them against action of phagocytes (immunologically invisible)

• involved in walling off process

• Breaks down fibrin; dissolves clots from by body to isolate infection

• Allows dissemination of bacteria

• Splits urea to form ammonium hydroxide, raises pH of urine and facilitates formation of renal calculi (kidney stones)

• Promotes colonization of Helicobacter in stomach

Example: LPS in gram -

• Lipid A= active portion
• induce fever, initiate complement cascade
• activate B lymphocytes
• stimulate production of TNF, IL-1, and prostaglandins
• Effects of exposure to LPS include fever, hypotension, shock, and death

• Site of action is more localized than endotoxin

1. A-B exotoxins
2. Membrane-active exotoxins
3. super-antigens

• B subunit= binding specificity to host cell
• A subunit= determines mechanism of action

1. neurotoxins= tetanus and botulinum toxins
2. cytotoxins= diphtheria toxin inhibits protein synthesis
3. enterotoxins= cholera toxin and E. coli cause diarrhea

• act directly on cell's surface to lyse or kill

1. leukocidins= damage membranes of neutrophils and macrophages
2. lecithinase= enzyme destroys plasma membranes- especially RBCs
3. hemolysins- destroy red blood cells and other tissue cells by producing pores in membranes

• type of exotoxin
• bind to MHC class II on antigen-presenting cells and T cells
• association causes release of high levels of IL-2 which leads to release of other cytokines

• Example: Staphylococcus aureus-mediated toxic shock syndrom toxin-1 (TSST-1)

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Neisseria gonorroheae

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Treponema pallidum

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Mycobacterium tuberculosis

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Streptococcus pyogenes

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For skin: use 70% ethyl alcohol, alcohols plus aldehyes for surface use

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• Glutaraldehyde alone or in combination with others
• Commonly used in dentistry

• "Cold Sterilization"
  

• Chlorhexidine- commonly used in dentistry for surgical scrub, as an anti-plaque agent and as a denture disinfectant.
• Effectiveness: absorption on to hydroxyapatite and salivary mucus

• Hypochlorites and poviodine= oxidizing agents
• cheap, effective
• corrode metal and quickly inactivated by organic matter

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• do not irritate skin- used for gross decontamination

• not easily inactivated by organic material

• poorly virucidal and sporicidal

• used for handpieces, ultrasonic scalers, and air/water syringes

• immunologic tests- either antigen or IgG antibody is nonspecifically bound to surface of latex bead
• Addition of specific antigen or antibody visibly agglutinates milk-white suspension

ELISA

• antibody bound to solid support
• Antigen containing sample layered over sensitized solid phase
• Enzyme-labeled Ab is added to form sandwich
• Bound enzyme plus substrate results in color change indicating presence of Ag
• Direct vs. indirect test

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Highest dilution of antimicrobial agent that is able to inhibit growth of test organism; quantitative estimate of antibiotic sensitivity.

• bacterial inoculum- applied to agar plate and then paper disks to which antimicrobial agents have been added are placed on agar surface

• zones of growth inhibition around discs indicate sensitivity to the antibiotic, whereas growth of the organism up to the disc indicates resistance.

-common susceptibility test

• paper strips containing continuous gradient of antimicrobial-agent concentrations- placed on inoculated agar surface
• After incubation: elliptical zone of inhibition forms as antimicrobial agent inhibits growth
• MIC= where growth intersects Etest strip

• Affect cell wall synthesis

• b-lactam ring: 5-member thiazolidine ring joined to b-lactam ring to which is attached a side chain; side chain determines antibacterial properties.
• Mechanism of action: inhibit last step of cell wall synthesis, in which transpeptidation reaction results in cross-linking of adjacent peptidoglycan strands (polymerization)
• Penicillin-binding proteins= occur in cytoplasmic membrane; responsible for transpeptidation reaction
• B-lactam ring portion binds to protein=prevent polymerization
• when binding occurs, lysins are released which degrae formed peptidoglycan
• penicilloic acid- inactive product formed when B-lactamases cleave ring

1. Antistaphylococcal penicillins: resistant to beta-lactamase
2. Aminopenicillins: beta-lactamase sensitive
3. antipseudomonas penicillins: beta-lactamase sensitive

• Affect cell wall
• produced by Fungi
• 6-member dihydrothiazine ring joined to a beta-lactam ring; similar mode of action as penicillins
• broader spectrum than penicillins
• Basic structure allows moderate resistance to beta-lactamases but not cephalosporinases

• affect cell wall synthesis
• Beta-lactam with carbon substituted for sulfur
• Imipenem

• affect cell wall synthesis
• mode of action: similiar to beta-lactams
• Example: aztreonam

• "suicide" inhibitors of beta-lactamases
• beta-lactams that bind to and inactivate beta-lactamase enzymes
• Examples: clavulanic acid and fulvactam
• Clavulanate + amoxicillin= augmentin
• clavulanate + ticarcillin= tigmentin

• affect cell wall synthesis

• inhibit use of lipid-linked cell wall intermediates in assembly of linear peptidoglycan molecule
• Used for multi-resistant Gram + bacteria
• Not effective for Gram - because it will not pass outer membrane
• Example= Vancomycin

• Affect cell wall synthesis

1. bacitracin= topically applied; gram +;; targets a lipid carrier responsible for moving peptidoglycan precursors through cytoplasmic membrane to cell wall
2. polymixins= fatty acid portion penetrates into hydrophobic portion of outer membrane of gram - bacteria; ring portion interacts with LPS and phospholipids; can cause serious nephrotoxicity; used for external treatment of localized infections (eye and skin)

• Interfere with nucleic acid synthesis
• mechanism of action: inhibit DNA replication by inhibiting the supercoiling of DNA; binds to DNA gyrases
• Nalidixic acid, ciprofloxacin, levofloxacin, gatifloxacin, and moxifloxacin

• interfere with nucleic acid synthesis
• bind to DNA-dependent RNA polymerase and prevent RNA synthesis (transcription level)
• Rifampin= mycobacterium tuberculosis
• Rifabutin= mycobacterium avium

• interfere with nucleic acid synthesis
• reduced form acts as free radical that damages bacterial DNA
• Anaerobic bacteria produce nitroreductase that reduces compound when taken up by organisms
• no significant activity against aerobic or facultatively anaerobic bacteria

• inhibit protein synthesis
• Doxycycline= commonly used in dentistry- periochips and localized aggressive periodontitis
• Bacteriostatic
• Can cause tooth staining in developing teeth

• inhibit protein synthesis
• commonly used for anaerobic, Gram negs
• common prophylactic in dentistry (broad spectrum)

1. Sulfonamides= structural analog of PABA- interferes with microbial growth by competitively inhibiting incorporation of PABA into folic acid.
2. Trimethroprim= structural analog of dihydrofolic acid- inhibits synthesis of folic acid

Corynebacterium diphtheria and Clostridium tetani

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Both are toxoid components for children and adults

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Bordetella pertussis

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Acellular or killed whole cell components for children

All are conjugate components (capsular polysaccaride + protein)

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Haemophilus influenza type B-; kids

Streptococcus pneumonia-; kids

Neisseria meningitides A and C-; high risk groups military, college students

Streptococcus pneumonia

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Capsular polysaccharides components for high risk groups- Elderly

1. S. aureus (coagulase +)
2. S. epidermidis (coagulase -)
3. S. saprophyticus (coagulase -)

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Staphylococcus

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Staphylococcus

1. coagulase
2. hyaluronidase

1. Alpha toxins- membrane active toxin- lyse RBCs
2. enterotoxins- resistant to gastric enzymes, heating; superantigens which act on neural receptors in GI tract; food poisoning
3. exfoliative toxins- "scalded-skin syndrome"- young children; lysis of intracellular attachment at granular layer of epithelium
4. toxic shock syndrom toxin-1 (TSST-1)- pyyrogenic, lethal hypotension, rash, multiple organsystems; superantigen; direct toxic effects endothelial cells resulting in capillary leakage and hypotension

1.; skin infections- most common bacterial infections in humans- folliculitis, boils, carbuncles, and impetigo; staph scalded-skin syndrom

2. Food poisoning- severe cramping, abdominal pain, nausea, vomitting, and diarrhea

3.; Toxic shock syndrome- acute febrile illness- hypotension, vascular coagulation, renal failure, acidosis, and rash; vaginal association in females and focal staph petechial infection in males.