Corynebacterium diphtheriae (Diphtheria)
Carib bacterium diphtheriae or just C diphtheriae takes its name from the Greek Carinae that means club and diphtheriae, which means leather.
So to sum this up, C diphtheriae is a club looking bacteria that causes diphtheria. An infection with a characteristic tough leathery membrane that forms in the pharynx.
Sea diphtheria has four main subspecies. C diphtheria mitis sea diphtheria, intermedius, sea diphtheriae, gravis and C diphtheria belfanti.
All right. Now, C diphtheria has a thick peptidoglycan cell wall that takes in purple dye when gram stained.
So it's a gram positive bacteria. It's aerobic which means that it requires oxygen to grow and it does not form spores.
Now, when stained with Albert stain, these bacteria demonstrate some unique features. They look like green club shaped bacteria with metachromatic Granules which are these dark blue dots made of phosphate located at the bacterial poles.
When there are a lot of them clustered together, these bacteria seem to be arranged in a characteristic pattern that resembles Chinese letters.
Finally, c diphtheria is a fastidious bacteria. This means that it can only grow on special nutrients, enriched media.
The medium commonly used to grow this bug is cystine tellurite blood auger on which seed diphtheriae grow into black colonies.
All right. Any of the c diphtheria subspecies can be either toxigenic or not, depending on whether or not they produce the diphtheria toxin or DT.
For short, DT is a cytotoxic protein or cytotoxic means it causes damage to host cells. In fact, all the c diphtheria subspecies start out as nontoxigenic but they become toxigenic after they're infected by a beta bacteriophage.
This is a kind of virus that attaches the bacteria and emerges into its own genome with the bacterias. The beta bacteria phase genome contains tox genes which codes for diphtheria toxin production.
Following this C diphtheria can make DT and in turn cause diphtheria. Now DT has two main subunits A and B joined by the disulfide bond with each of the subunits playing a specific role in the invasion and destruction to the host cells.
The B subunit, which is the bigger portion of DT complex helps binding to the host cell membrane. After attaching to the host cells, the whole DT complex gets slowly engulfed by the cell membrane which invaginate to form a sac on its inner side.
The sac then separates from the actual cell membrane forming a vesicle called an endosome within the host cell. Cytoplasm.
The medium inside the endosome becomes more acidic. And as a consequence, the disulfide bond holding the two subunits together becomes weak and eventually breaks separating the subunits.
The A subunit then diffuses through the endosome membrane into the cytoplasm where it goes straight to the ribosomes. Here it interferes with cell protein synthesis.
This happens because the A subunit has an ADP ribose group which attaches to the elongation factor. Ef two, an important ribosomal protein that joins amino acids together during protein synthesis.
This process is called ef two ADP ribosylation and it results in complete deactivation of the EF two which stops protein synthesis and leads to cell death.
All right. Now, c diphtheria mainly causes diphtheria in unvaccinated or immunocompromised.
People. Most often, the bacteria can be transmitted from one person to another, mainly by respiratory droplets following coughing or sneezing.
In which case, it causes pharyngeal diphtheria. But they can also enter the body through open lesions on the skin causing cutaneous diphtheria following inhalation of infected respiratory droplets.
C diphtheria attaches to the pharyngeal epithelial cells where they release DT toxin. This causes local inflammation that leads to necrosis of pharyngeal tissue and neck swelling.
In some cases, a portion of the pseudomembrane can detach and get lodged into the trachea or bronchi. And when it's big enough, it can block the airways completely causing death by asphyxiation.
If left untreated, the bacteria gradually invades deeper into the pharyngeal wall until it reaches the bloodstream from where it can move to distant organs like the heart causing myocarditis or inflammation of the heart muscle or the kidneys causing acute tubular necrosis or destruction to the renal tubules.
See, diphtheriae can also travel to the nerves causing nerve demyelination, meaning they destroy the myelin sheath covering the nerve axons, which leads to polyneuropathy, diphtheria, polyneuropathy usually affects the oculomotor nerve causing oculomotor palsy, meaning the muscles that move the eyes are impaired.
It can also affect the phrenic nerve which innervates the diaphragm. And in this case, it might cause trouble breathing regardless of the affected system.
People with diphtheria infection present with symptoms of low grade fever, general malaise and weakness in pharyngeal diphtheria.
People present with sore throat, a swollen neck that people commonly call bull neck in the pharyngeal pseudomembrane formation that usually can cause difficulty breathing associated with respiratory wheezes or stridor.
In cutaneous diphtheria, there are typically chronic skin ulcers which are shallow with myocarditis. There might be signs of cardiac dysfunction like arrhythmias or even heart failure, which is when the heart can't pump enough blood to meet the body's demands.
With acute tubular necrosis. There might be oliguria which is decreased urine production with oculomotor palsy.
There might be diplopia which means double vision or the person might not be able to move their eyes up down or to the side.
Diagnosing. Diphtheria is mainly done by cultures of swabbed from the pharynx or the suspected skin lesion to isolate c diphtheriae.
When the culture gets positive. Next, you want to figure out the C diphtheria strain in question is toxigenic.
This is done by elix test in which C diphtheria is grown on an auger plate that's embedded with an anti toxin impregnated filter paper.
If the strain makes DT the toxin reacts with the anti toxin resulting in bands of visible precipitations. Another method consists of detecting the bacteria's toxigenicity in its DNA using polymerase chain reaction or PCR.
The treatment for diphtheria starts right upon clinical suspicion. Even before diagnostic confirmation, it starts with isolating the patient to prevent further spread.
And then penicillin G is given or Erythromycin in case of allergy. Then if the infected bacteria is proven to be toxigenic with elix test.
Diphtheria endotoxin is given to counter the effects of the bacterial toxin. Luckily, there's a vaccine to prevent diphtheria.
This vaccine consists of a toxoid which is a modified DT with the ability to activate the immune system and make it ready to tackle a real infection without causing damage to tissues.
C Diphtheria toxoid is usually combined with other vaccines against Clostridium Tetani which causes tetanus and Bordetella pertussis which causes whooping cough.
And together they're called the DTAP vaccine given to Children between two months and six years of age. All right, as a quick recap carnibacterium diphtheriae is a gram positive club shaped bacteria that causes diphtheria infection.
It's non modal aerobic nonsporeforming and has metachromatic Granules when stained with Albert stain when infected by a beta bacteriophage C diphtheria becomes toxigenic.
So it starts to produce diphtheria toxin which causes tissue destruction and inflammation. Diphtheria can present as pharyngeal or cutaneous diphtheria.
With pharyngeal diphtheria, a pseudomembrane forms over the pharynx and larynx and it might detach and cause airway obstruction.
Sometimes the bacteria can spread to other places like the heart, resulting in diphtheria myocarditis, the kidneys resulting in acute tubular necrosis or even the nerves resulting in diphtheria polyneuropathy with cutaneous diphtheria.
There are chronic shallow skin ulcers. The diagnosis depends on cultures but treatment with penicillin, G or Erythromycin can be initiated upon clinical suspicion.
Diphtheria antitoxin is also given for toxigenic strains.
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