Medical Microbiology: Bacteriology I

Macroscopic (classification)

colony morphology, color, smell

Microscopic (classification)

shapes, Gram +, Gram -, Endospores, capsule, flagellum, staining

Phenotypic (classification)

aerobic vs anaerobic, biochemical characteristics, selective growth conditions (temperate, growth media)

Antigenic (classification)

Direct detection, indirect detection, immunofluorescence, enzyme-linked immunosorbent assay (ELISA), Wester Blot

Molecular (classification)

polymerase chain reaction (PCR)

Gram +

thick layer of peptidoglycan

Gram -

thin layer of peptidoglycan, outermembrane

Endospores

only gram +, vegetative state, needs signaling to get out

flagellum

movement

direct detection

use conjugated anti-target antibody

indirect detection

use conjugated secondary antibody

immunoflorescence

microscopic detection of antigens

enzyme-linked immunosorbent assay (ELISA)

detect pathogen--> active infection
Capture --> detect presence of particular antigen
antibody detection --> start with antigen to detect antibody
quick test

Western Blot

each band represents a different viral protein
often used to confirm ELISA results
if you have known antibodies --> use to detect virus
look at immune responses

Polymerase chain reaction (PCR)

amplify particular sequence of DNA
mimicking primer and DNA replication
can use for detection, sequencing (mutations), and RFLP analysis

If sequence is present in PCR...

amplification

If sequence is NOT present...

no amplification

Restriction fragment length polymorphisms (RFLP)

enzymes come from bacteria and recognize and cut DNA sequences to get particular patterns
DNA only (can be PCR product DNA)
DNA digestion with restriction enzymes producing DNA patterns

Transformations (mechanism)

[Acquisition of foreign DNA]
donor cells --> cell lysis --> DNA enters the recipient cell and integrates into DNA

Transductions (mechanism)

[Acquisition of foreign DNA]
transducing phage containing donor genomic DNA --> cell lysis --> phage infects recipient cell; donor integrates into recipient DNA

Transpositions (mechanism)

[Acquisition of foreign DNA]
moving and relocating in genome
uses transposon with inverted repeats

Conjugation (mechanism)

[Acquisition of foreign DNA]
free plasmid moves from donor to recipient cell via sex (F) pilus
integrated plasmid (episome) promotes transfer of genomic DNA, which integrates into recipient DNA

Capsule

produced outside cell; slippery so things can't bind or penetrate
no opsonization, no MAC, no phagocytosis

Biofilm

grow into giant, multicellular structure that surrounds pathogen

Spores

inert object is protected from the immune system and antibiotics until signaled
almost impossible to get rid of

proteases

destroy host proteins

variable surface proteins

antigenic variation

Adhesion

bind to receptors (proteins, sugars) on the surface of target cell

Endotoxin

part of the pathogen structure
Ex: LPS on Gram -

Exotoxin

product produced and released by the pathogen
Ex: A-B

Superantigens

trigger over release of cytokines by CD4+ T cells

Intoxication

large quantity of toxin taken in; immediate effects

Infection

accumulation of toxin in infected individual; slower effects

Bacteriostatic agent

prevent growth (put in stasis)
Ex: fridge/freezer

Bactericidal agents

destroy bacteria
Ex: cleaning wipes, bleach, detergents

Step 1 of Koch's Postulate

Bacteria must be present in every case of the disease

Step 2 of Koch's Postulate

Bacteria must be isolated from host with disease and grown in pure culture

Step 3 of Koch's Postulate

specific disease must be reproduced when a pure culture of the bacteria is inoculated into a health susceptible host

Step 4 of Koch's Postulate

bacteria must be recoverable from the experimentally infected host

Antibiotics

disruption of cell wall; inhibition of protein synthesis; inhibition of nucleic acid synthesis; antimetabolite

CD8+ T cells

Capsules cannot protect bacteria from which of the following?

-CD8+ T cells
-Opsonization via antibodies
-Opsonization via complement proteins
-Destruction via the membrane attack complex

Detergents

Which of the following would not be an example of a bacterial static process?

-Freezing
-Refrigeration
-Detergents
-Using antibiotics that prevent the synthesis of new cell walls

All of the other answers can be used to protect a bacterial pathogen from

Which of the following are mechanisms by which bacteria can protect themselves from immune responses?

-Biofilm formation
-Spore formation
-Encapsulation
-All of the other answers can be used to protect a bacterial pathogen from immune responses.

Operons

Which of the following is not a mechanisms that allows bacteria to take in foreign DNA?

-Transduction
-Conjugation
-Operons
-Transformation

All of the other answers can be used to help identify a bacterial pathogen.

Which of the following observations can be used to help identify a bacterial pathogen?

-Antigenic
-Phenotypic
-Molecular
-Microscopic
-All of the other answers can be used to help identify a bacterial pathogen.

ELISA

Antibodies can be used to help identify a bacterial pathogen in which methods?

-PCR
-ELISA
-RFLP analysis
-All of the other answers use antibodies to help identify a bacterial pathogen.

The use of DNA as the genetic material**??

Which of the following is not different between human and bacterial cells?

-The composition of the ribosomes
-The average size of a cell
-The use of a cell wall
-The use of DNA as the genetic material

All of the other answers can be used to help identify a bacterial pathogen.

Which of the following can be used to help identify a bacterial pathogen?

-All of the other answers can be used to help identify a bacterial pathogen.
-Selective growth
-Enzymatic activity
-Aerobic vs anaerobic growth

normal flora and environment

Where is Staphylococcus found?

Staphylococcus: Transmission

person to person; fomite

Often observed with Staphylococcus

disruption of normal flora (makes spaces for new things to grow)
insertion of foreign bodies
half-life: days to weeks

Staphylococcus: Immune Avoidance

capsule, biofilm, slime layer, Protein A

Staphylococcus: Virulence Factor

adhesions (slime layer)

Staphylococcus: Toxins

cytotoxins
endotoxins
superantigens

Staphylococcus: Treatment

Antibiotics --> resistance

Methicillin-resistant Staphylococcus aureus (MRSA)

What is an example of an antibiotic-resistant form of Staphylococcus?

Staphylococcus: Control

ubiquitous
clean/sterilize medical equipment
minimize exposure

Streptococcus A (S. pyogenes)

strep throat, cellulitis, scarlet fever, necrotizing fasciitis

Strep A: Transmission

person to person, fomite

Strep A: immune avoidance

capsule
M proteins: Block C3b binding
C5a peptidase (S. pyogenes): block inflammation

Strep A: M&F proteins

adhesion
cell invasion (disruption of tight junctions)

Strep A: exotoxins

enterotoxins (A-B toxins)
Superantigens [Ex: streptolysin (lyse RBS) --> hemolytic]

Strep A: Treatment

antibiotics

Streptococcus B (S. agalactiae)

neonatal infections, normal flora getting in the wrong place

Strep B: Transmission

normal flora of vaginal tract (birth)
location is the issue

Strep B: Pathogenesis

In newborns:
bacteremia (bacteria in blood)
pneumonia
meningitis (in brain)

Strep B: Treatment

antibiotics
test women for it

Strep B: Control

minimize exposure and treatment

S. pneumonia (pneumonia)

causes infection in the lungs
diplococci
Control: vaccine against capsule

normal flora of GI tract

Where is Enterococcus found?

Enterococcus: Transmission

person to person, fomite

disruption of normal flora

Enterococcus is often observed...

Enterococcus: Virulence factors

wide range of growth: aerobic and anaerobic, high salt, broad pH
biofilm
antibiotic resistance

Enterococcus: Treatment

antibiotics --> resistance

Bacillus: Epidemiology

spore forming
stable in environment
aerosol transmission (anthracis)

Anthracis (anthrax): Transmission

ingestion (livestock)
cutaneous- most common (skin)
inhalation

Anthracis (anthrax): immune avoidance

capsule

Anthracis (anthrax): toxins

Exotoxin: plasmid encoding 3 genes

edema toxin

PA + LF = ?

lethal toxin

LF + EF = ?

Anthracis (anthrax): Treatment

antibiotics --> resistance
vaccination --> toxoid (animals)

Cereus

bigger problem --> seen in humans a lot

Cereus: Transmission

ingestion (food born pathogen)

Cereus: Virulence Factors

exotoxin

Cereus: heat stable form

emeric (vomiting)

Cereus: heat liable

diarrheal

Bacillus cereus

food poisoning

Cereus: Treatment

Pepto-Bismol for symptoms
antibiotics --> resistance

Cereus: Prevention

minimize exposure: cook/store food properly

Emeric Form: Disease onset

~2 hours

Emeric Form: Disease Duration

8-10 hours

Diarrheal Form: Disease onset

~9 hours

Diarrheal Form: Disease duration

20-36 hours

Listeria: Epidemiology

grows @ 4 C, high salt concentration, and wide pH range
facultative intracellular pathogen (can exist outside of cell)
lives inside macrophage --> pt of immune response doesn't work

Listeria: Transmission

contaminated food/dairy

Listeria: Virulence factors

cell invasion
escapes lysosome

Listeria: Disease

can cause spontaneous abortions
diarrhea
meningitis (rare)

Listeria: Treatment

self-limiting
antibiotics --> resistance (for severe cases)

Listeria: Prevention

minimize exposure: cook food properly; avoid raw dairy (soft cheeses and milk), raw vegetables, undercooked meat, etc.

Corynebacterium diphtheriae

a species of bacterium that causes *diphtheria*