Lecture 10 Actinomycetes

Question 1

what you should know about by now

Answer 1

Question 2

Listeria monocytogenes

Answer 2

the most important for human and animal health and causes listeriosis

There are several species of listeria –
L.monocytogenes is an important cause of
Disease in man and animals.

Short, Gram positive, non-spore forming rod.
Tumbling motility at room temperature but not
at 37C distinguishes it from others
eg. Corynebacteria.
Catalase positive facultative anaerobe.

associated with food types such as unpasteurised dairy products, sandwiches and outbreaks in food production facilities

Question 3

Listeriosis two types

Answer 3

major cause of abortion in humans and animals and also neonatal deaths

early onset perinatal intrauterine infection is an infection spread from the mother to the unborn child causing sepsis and death before birth (in humans and animals)

-pregnant women are 20 times more susceptible to infection with listeria than non-pregnant women or men

late-onset perinatal infection is an infection at birth itself so is not an aborted pregnancy but can often lead to sepsis a few weeks after birth

adult infection would be in eating infected
unpasteurised food or from whatever source or in animals is can be from earing infected silage
- in humans it is a self limiting flu like infection unless you are immunocompromised

in sheep it is associated with encephalitis (inflammation around the brain)

Question 4

listeriosis Source of infection

Answer 4

listeria is quite common in the environment and is able to survive in a dry environment it is a Saprophytic bacteria, the bacteria needs to be tested in the environment consistently in food processing plants

important to know it is psychrotrophic so it can grow and replicate in low temperatures listeria can grow at temperatures as low as 4 degrees Celsius

Question 5

Listeriosis Pathogenesis

Answer 5

can replicate in certain conditions and environments due to its saprophytic nature but when it is a human or animal pathogen it is an intracellular bacteria so it able to grow inside our cells; in cells such as macrophages which would naturally phagocytose but can induce its uptake into non-phagocytic cells and when it gets into that cell it is taken up into a phagosome (phagosome is an organelle that will usually kill bacteria) but listeria produces an enzyme that can degrade the membrane of a phagosome and can get out into the cytoplasm where it can induce polymerisation of actin it which will allow it to drive through the cell wall and disseminate into other cells nearby and in the next cell it will get into double membraned vacuole and then break out of that

Question 6

Actinomycetes

Answer 6

Question 7

Streptomyces

Answer 7

does not cause any infections but is important as a source for antibiotics
- it gives soil its smell
-grow in a network of hyphae so not individual cells,
they can produce spores but different from the way clostridia and bacillus produce; an example of convergent evolution

Question 8

Antibiotic production by
Streptomyces

Answer 8

the bacteria produce antibiotics to kill other bacteria around them in order to outcompete them and take all the nutrients

Question 9

Some Streptomyces antibiotcs

Answer 9

Question 10

Corynebacterium diptheriae

Answer 10

one in paticular called Corynebacterium diptheriae
causes diptheria
has a club shape as a result of polyphosphate inclusions at one end which given them the club shape
- they tend to divide and snap instead of in a line like e coli, so they don’t don’t grow and divide in a unified formation

Question 11

Pathology of Diptheria

Answer 11

it is possible to get infection in wounds but is usually associated as being a respiratory infections

caused by the production of a toxin
the diphtheria settles out on the epithelial cells in the upper respiratory tract and here it will start replicating and producing its toxin which kills the epithelial layer at the back of the throat and induces inflammation which creates a dead necrotic layer of epithelium at the back of the throat, inflammation causes an influx of immune cells and laying down of fibrin resulting in the production of a pseudomembrane at the back of the throat
- it occludes the throat so can make it hard to breath or swallow because of the amount of swelling and the formation of the pseudomembrane

Question 12

Pathology of Diptheria

Answer 12

symptoms are conjunctivitis
pharyngeal membrane
bull neck
severe myocarditis

• every symptom is the result of the production of the toxin of Corynebacterium diptheriae
• the effect of the toxin can go system wide and affect many different tissue including the heart
  so if you have serious weakness of the heart or lesions of the kidney it can result in death

Question 13

Diphtheria toxin

Answer 13

this is a toxin produced by a bacteriophage that is infecting the Corynebacterium cell

so diphtheria is caused by a toxin encoded on a bacteriophage
- bacteriophage are viruses that infect bacteria

part of the toxin is an enzyme called an ADP-ribosyltransferase

ADP-ribosyltransferases (ARTs) are enzymes that modify proteins, nucleic acids, and metabolites by transferring ADP-ribose from nicotinamide adenine dinucleotide (NAD+) to substrates. This process is known as ADP-ribosylation,

Question 14

Action of Diptheria toxin

Answer 14

the diptheria toxin has 2 domains, domain A and domain B
so the process of translation in our cells that’s catalysed by the ribosome which uses messenger RNA and elongation factor brings tRNA, which have amino acids on them, So the elongation factor comes out to the ribosome, gives it the tRNA with their amino acid and the ribosome sticks the amino acids together to make a polypeptide chain to make a protein so that that’s translation of messenger RNA into protein.
however what dipheria toxin does is it comes into contact with the cell, domain B binds to the outside of the cell and domain A is cleaved off and is taken up by the cell and adds an ADP ribose onto the elongation factor and so the elongation factor can no longer bind amino acid charged tRNAs so when the tRNA goes to the ribosome there will be no amino acid there and so the toxin blocks protein synthesis- it is extremely potent

Question 15

Diagnosis and treatment
of diphtheria

Answer 15

the diagnosis and vaccination is based on the toxin, similar to tetanus

the Elek test is done by taking a swab and growing diphtheria and streaking it on a plate
and using a strip of filter paper that is soaked in an antitoxin, so antibodies against the diphtheria toxin will diffuse out and so will the toxin produced by the bacteria and where the antitoxin and antibodies meet you get streaks of immunoprecipitation

the vaccine is an inactive form of the diphtheria toxin, called diphtheria toxoid vaccine and is an extremely effective vaccine