Microbiology - Exam 3 Material

endotoxins

• lipopolysaccharides (LPS) of gram negative bacteria

  • integral part of outer membrane

  • lipid A component extremely toxic

  • toxicity due to immune reaction

• release only by lysis

• heat stable

• can’t be “detoxified” to make a vaccine

lipid A

what part of lipopolysaccharide (LPS) is toxic?

low concentration of LPS

produce “alarm” reaction

immune response

high concentration of LPS

septic shock, severe hypotension, clotting factors released, DIC, multi-organ system failure

exotoxins

• both by gram positive and negative bacteria

• toxins released from bacteria

• can be “detoxified” by heat

• most act enzymatically

• are plasmid or phage encoded

• production often regulated by growth conditions or host signals

• some can be made into effective “toxoids”

benefits of exotoxins

killing host defense cells

obtain nutrients from host cells or tissues

help in dissemination

A part of AB toxin

“active” portion

has toxic or enzymatic activity

causes damage to the host

B part of AB toxin

“binding” portion = receptor specificity

determines host species and host cell specificity

diptheria toxin

inactivates elongation factor-2 which stops protein synthesis

only when it sense low iron

cholera toxin

cAMP accumulates which causes loss of control of ion flow

toxicity from overproduction of metabolite

massive watery diarrhea

shiga toxin

not excreted from bacteria

• released when organisms are lysed

stops host cell protein synthesis by targeting rRNA

tetanus toxin

rarely moves from site of infection

A-B toxin causes symptoms that act at a distance

blocks release of inhibitory neurotransmitters

membrane-disrupting toxins

• cytotoxins, hemolysins (rupture red blood cells)

• insert into membranes to form pores

  • low concentration = inhibit target cell function

  • higher concentration = lyse target cells by osmotic shock

• some have phospholipase activity

  • remove polar head groups

  • destabilization

• less cell type specific

proteolytic toxins

• lysis of proteins

• facilitate invasion or provide nutrients

• immunoglobulin and complement proteases

• “spreading factors” aid in tissue invasion

superantigens

• toxicity comes from a hyper inflammatory response

• bind antigen-presenting cells to T cells causing the overproduction of proinflammatory signals to the immune system

importance of media for culturing microbes

• accurate diagnostic

• must have pure culture (single bacterial species)

three general categories of media

physical, chemical, functional

liquid media

bacteria suspended throughout media

supports growth to high density

hard to obtain pure cultures

semisolid media

used to determine motility

solid media

firm surface on which cell can form discrete colonies

advantageous for microbial isolation

bacterial growth is slower and limited to surface area

chemically defined media (synthetic)

exact formula with defined molecular content

standardized

difficult to make

must know the nutritional requirements of organism

complex media (nonsynthetic)

if any component of the media is not described by an exact chemical formula

contain extracts, blood, serum, peptone

provide rich mixture of nutrients for microbes with complex needs

supports many types of organisms

composition varies from batch-to-batch

selective media

contains components that inhibit the growth of certain microbes but not all microbes

important for isolation of microorganisms

differential media

designed to show visible differences between different groups of organisms

depending on the medium, could manifest as colony size/color changes, media color changes, or formation of gas or precipitates

reducing media

reduces oxygen content to support anaerobic growth

transport media

preserves specimens between clinic and testing facility

assay media

used to test various bacertial phenotypes (drug resistance)

live media

viruses and some bacteria only grow in live tissue culture cells (intracellular) or animals

Luria Bertani broth

nonsynthetic or complex

• 10 g Tryptone

• 5 g Yeast Extract

• 10 g NaCl

• 1 L H20

agar

solidifying agent

most common

polysaccharide dervied from red seaweed

Blood agar plates (BAP)

• general purpose, enriched media used to grow fastidious organisms

• a differential media

• alpha, beta, gamma

Eosin-methylene blue (EMB) agar

• selective and differential media used to isolate gram negative bacteria

• methylene blue (inhibits growth of gram positive bacteria)

• eosin: dye that reacts with organic acids secreted by growing bacteria resulting in a color change to dark purple