Lecture 5

  is an important step in the process of infection

Microbe encounters a host and possesses mechanisms to survive in a particular  of
the body

Once the microbe begins successful   then it has colonized the tissues – this
process may involve invasion into tissues

In an infection the host immunity may be interacting with the microbe but  have
yet to develop

As a consequence of microbial
colonization, mechanisms are
employed to maintain
colonization or invade tissues
which   tissue/cellular
functions or triggers  
immune reactivity =  

Bacterial gain entry via   (Skin, mucus, ciliated epithelium, antibacterial
secretions)

Non specific attractive forces that encount bacterium are 1.   2.   3.  

Specific forces involve permanent formation of many specific lock and key bonds between complementary molecules on each cell surface ( ). Examples are the  /  and the   adhesions.

**TQ  and  are negatively charged and can recruit positively charged ions. It has some repelling effect on antibiotics, but mostly functions in  

  linked directly to the peptidoglycan layer

 cid possess a transmembrane domain so anchored into the
bacterial cell membrane

  are tightly associated polysacharides with the cell wall.

What is the main function of a capsule? (The one he said would be on test) Secondary important function?

What is a slime layer?
Loosely associated  ,  , and   with the cell wall.

What are the two important function of the slim layer?

It is thought that up to  of bacterial species live in
communal associations or biofilms

Biofilm
– collections of bacteria in a “multicellular” state
where survival requires   and
  between cells

Extracellular matrix forms composed of  ,  ,
 ,  ,  ,   – scaffold for biofilm
organization and signaling as well as regulate access by
environmental factors and antimicrobials

  permits bacteria cell-to-cell communication
where bacteria coordinate the expression of certain genes in
response to signaling molecules released by the matrix

During an infection pathogenic bacteria MUST
coordinate their virulence in order to be able to
establish a successful infection – controlled by
  released by the matrix

When cell density in the biofilm is high –
  interact with colony bacteria to
promote virulence gene expression (and
  resistance factors)

Colonization (  and  )

Spreading Factors (production of  

Access Nutrient Sources
(by   enzymes)

Toxins (  and  )

Hyaluronidase
• Enzyme that attacks the networks of   opening up the  
• Produced by  ,  ,  

Collagenase
• Enzyme that breaks down  , esp. in muscle tissues
• Produced by  

Streptokinase and
Staphylokinase
• Enzymes that convert inactive   into , which digests
  and prevents clotting of blood

Streptokinase and
Staphylokinase are produced by   and  

 is needed for bacterial growth for respiration (electron transport), DNA synthesis, and free radical scaveging (antioxidant rxns)

Cytotoxins demagae host cells to release  

  lyses RBC to release hemoglobin

Neutrophils release   from   granules

Transferrin is already in the  

Bacteria use  to bind to form a complex

Host   prevents siderophore from binding to its receptor

Bacteria counteracts by using   to prevent Sn from binding to siderophore

Enzymes that act in animal cell membranes:
o Direct insertion to form a pore for  
o Enzymatic attack on host cell  
(  or  ), which destabilizes
the membrane

Hemolysins
-  or  / 
-Produced by  (streptolysin) and
  (alpha toxin)

Phospholipases
-Produced by   ( )
which hydrolyzes cell membrane  

Lecithinases
- Produced by   which destroys
  (phosphotidylcholine) in membranes

 ,  ,  
Function in bacterial nutrition and metabolism (indirectly involved in invasion)

Ig   lyse unwanted antibodies so bacteria can access host cells

 and  dissolve neutrophil extracellular traps (NETs) to escape
uptake (phagocytosis) by  

• Some peptidases lyse  
• Prevents detection and/or elimination by
host response
• EX –   and  peptidases

Exotoxins
• Produced by most bacteria

Exotoxin is usually main determinant of
 for those bacteria producing them

  are not required for pathogen growth
– Genes usually found on plasmids or encoded
by phage DNA

Most exotoxins can be denatured by  ,
 , and  , have high  
and possess specificity of action

Most of these toxins are “strongly”  . Important because very stimulatory to   Good targets for  

** TQ Exotosins are ab toxins. B part delievers active   to the cell. On endoytosis,   is released into cytoplasm.

  are purposely produced to cause damage,   are NOT purposely produced to cause damage

Lipopolysaccharide (LPS) is a component of
Gram-  cell walls

Lipopolysacchardies release endotoxins on ,  , and  

Toxcity of the endotoxin lipopolysaccharide is due to  component

The toxcitity associated with lipopolysaccahrides cause 750,000 cases of   each year, 30% mortality

Heat stable (boiling 30 min has no effect) on lipopolysaccharides; must
treat with strong   agents (peroxide,
hypochlorite,…)

Lipopolysaccharides are mildly  . Antibodies recognize   regions, but not as strong as exotoxins

High levels of endotoxin =  

Gram negative bacteria release endotoxins in into the blood spream that leads to   (  damage),  (  and  ), and activated   (decrease   and impair   exchange)

While endotoxins come from gram   bacteria, exotoxins come from gram  bacteria

While endotoxins use , exotoxins are made of 

While endotoxins are part of the  , exotoxins are  

While endotoxins are  denatured by boiling, exotoxins are   denatured by by boining

While endotoxins   more toxid, extosins   toxoid

An example of a "superantugen" is  . Superantigen grabs  and   are forces them together. It causes a   activation of T-cells. It causes the release of cytokines AKA  

Porins
• Channels in outer membrane which permit
transport of small   materials into the
 

Antibiotics (Ab) can place   pressure on
the bacteria resulting in mutation of  to
exclude drug passage

Transposons (Transposable
Elements)
- Sequence of DNA encoding a 
enzyme bounded on either end by i 

  can carry genes for antibitoic resistance

Pathogenicity Islands
- Multiple genes surrounded by   elements that encode for virulence
properties

Some strains of E. coli and other bacteria
use   for colonization
• Here  are used to initially attach to the
 
• Upon attachment the genes are activated

Type III secretion systems
o A set of proteins that form a channel
from the   to the host
cell cytoplasm – easy way to transfer
bacterial proteins into the host cell

Intimin-intimin receptor
o Intimin receptor is made by the bacteria
and transferred through the  system into the host cell which
is placed in the host cell membrane
o Intimin on the bacterial surface can now
bind the   on the host cell
membrane and facilitate   of the bacteria to the host

Plasmids are small circular DNA that replicates
  of the bacterial chromosome. They can integrate into  

Conjugative Plasmids ( -plasmids)
- Encodes   enzyme and   pili
genes
-Transferable to other  bacteria

Nonconjugative Plasmids
- Lack  genes
-Transferable to other bacteria if in a cell
already containing an  

  are viruses that infect bacteria. Each “species” of phage has a  bacterial host
o Can be exploited so as to “type” or classify bacteria ( )

Bacteriophaes have DNA or RNA that is injected through a pore in the   that is  - 

  bacteriophages degrade   and when it repackages, after replicating its own DNA it may repackage some bacterial DNA. When it lyses, it can transfer some of that   and the bacteria can then incorporate it. Called  

 /  bacterioophage injects its DNA it incorporates within   and then it excises out and replates. It takes some of the bacterial DNA with it and every new phage that's made now has that gene. Called  .

  is when DNA released by dying bacteria is taken up by
viable bacteria and incorporated into the
genome

  is the ability of a bacterium to take up naked DNA

The 4 naturally competent bacteria are
1.  
2.  
3.  
4.