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Today. Streptococcus pneumoniae or strep pneumoniae can be broken down into strepto. Which means chain coccus.
Which means round shape and pneumoniae. Which refers to the fact that it causes pneumonia no surprises. There so strep pneumoniae are round bacteria that tend to grow in chains.
Usually in lancet. Looking pairs called diplococci. Theyre the most common cause of community acquired pneumonia meaning pneumonia.
Acquired somewhere other than the hospital. Ok. Now.
A little bit of microbe anatomy and physiology strep. Pneumoniae has a thick peptidoglycan cell wall. Which takes in purple dye.
When gram stained. So this is a gram positive bacteria theyre non motile and dont form spores and also theyre facultative anaerobes. Meaning that they can survive in both aerobic and anaerobic environments finally theyre catalase negative.
Which means. They dont produce an enzyme called catalase. Ok.
Now when cultivated on a medium. Called. Blood.
Agar. Strep. Pneumoniae.
Colonies. Cause alpha hemolysis. Also called green hemolysis.
Because they produce hydrogen peroxide. Which partially oxidizes initially red hemoglobin in the blood agar to green methemoglobin. Other streptococcus species.
Like strep viridans. Are also alpha hemolytic. So an optochin test is done to distinguish strep pneumoniae.
Thats where a few drops of optochin are added to the culture. Strep. Pneumoniae are optochin sensitive meaning.
The bacteria dies. After adding. Optochin.
Whereas. Strep viridans. Are optochin resistant meaning.
They survive. Now. Strep.
Pneumoniae has a number of virulence factors that are like assault weaponry. That help it attack and destroy the host cells and evade the immune system. So first strep pneumoniae is encapsulated meaning.
Its covered by a polysaccharide layer called a capsule. The capsule has pili and fimbriae. Which are hair like extensions that help it attach to a host cell.
Once attached to a mucosal surface like in the nasopharynx or the middle ear strep pneumoniae can multiply and produce biofilms a biofilm is basically a layer of goop like material made of exopolysaccharides or eps. Within. Which strep pneumoniae bacteria live and reproduce comparing a biofilm to strawberry jam.
The seeds would be the bacteria and the rest of the jam would be the eps. The bacteria in the biofilm hide from the hosts immune system and antibiotics and even exchange resistance genes sneaky as if that wasnt enough strep pneumoniae also produces toxins and the most important ones are iga protease and pneumolysin iga protease destroys immunoglobulin a or iga which normally binds invading bacteria so neutrophils can destroy them thats like a computer virus first taking over the antivirus software. And then theres pneumolysin.
Which activates. The hosts complement system a set of plasma proteins involved in immunity. This results in a local inflammation which not only destroys the bacteria.
But also the host tissues like alveolar capillaries and pneumocytes and heres the most interesting part strep pneumoniae can actually peacefully colonise the nasal cavities and sinuses. Where it doesnt do any harm. So long as the immune system keeps them in check restricting their growth and preventing them from spreading somewhere else in the body problems arise in individuals with weaker immune systems like infants and the elderly other immune weakening conditions include an hiv infection diabetes malignancy or alcohol abuse additionally.
Some toxic compounds in cigarette smoke can weaken the local respiratory defense mechanisms making individuals more susceptible to strep pneumoniae infections strep pneumoniae can cause a number of infections. One example is rhinosinusitis. Which is when the mucous membrane lining the nose and the paranasal sinuses gets inflamed resulting in fever facial pain and headaches.
Sometimes when the walls of the paranasal sinuses are very thin and strep pneumoniae can get into the cranial cavity resulting in meningitis with meningitis people develop a fever neck stiffness and a headache strep pneumoniae can can also invade the eustachian tube and cause an infection of the middle ear or otitis media. Which causes pain and an earache chronic otitis media can spread to the mastoid antrum behind the ear. Where it causes mastoiditis finally from the mastoid antrum.
The infection can spread to the cranial cavity. Which is another way strep pneumoniae causes meningitis. However the most common disease caused by strep pneumoniae is pneumonia.
Strep pneumoniae sticks to the alveolar cells. The pneumocytes and releases pneumolysin. Which leads to destruction of the pneumocytes and alveolar capillaries pneumonia causes fevers and chills chest pain and cough in severe cases strep pneumoniae can cross the alveoli capillary wall and enter the blood resulting in bacteremia eventually.
Bacteremia can cause serious problems like sepsis which can lead to hypoperfusion of vital organs sepsis caused by strep pneumoniae is particularly common in people with spleen problems because the spleen plays an important role in immunity especially against encapsulated bacteria. So strep pneumoniae infections are typically worse in individuals who have undergone a splenectomy. Which is when the spleen is removed or in those with sickle cell disease.
Who have functional asplenia once in the bloodstream strep pneumoniae can also cause pneumococcal endocarditis forming clumps called vegetations that damage the valves. It can also infect the pericardium resulting in purulent pericarditis. Which is where pus collects in the pericardial.
Sac. Strep. Pneumoniae can also spread to a joint resulting in septic arthritis or it can cross the blood brain barrier and cause meningitis as a complication of bacteremia rather than invading directly as part of a primary disease once it has crossed the blood brain barrier.
It can also cause an intracranial or spinal epidural abscess. Finally strep pneumoniae can spread from the bloodstream to the peritoneum causing spontaneous bacterial peritonitis. This is more common in individuals with cirrhosis who develop ascites or too much fluid in the peritoneal cavity diagnosing.
A strep pneumoniae infection relies on cultures from biological samples. Like pus sputum. Cerebrospinal fluid or peritoneal fluid.
Alternatively. Pcr can be done to detect strep pneumoniae dna. Individuals.
At risk for a strep pneumoniae. Infection should get vaccinated. This includes young children below 2 years and old people.
Over 65 years. Other high risk groups include those with chronic diseases. Such as diabetes.
Hiv cancer. Most importantly those with sickle cell disease. And those whose with functional asplenia.
Currently vaccines against strep pneumoniae are divided into two main groups based on their mechanism of action. The first one is the pneumococcal polysaccharide vaccine also known as ppv 23. Because it contains 23 purified capsular antigens and this one is mostly recommended in adults.
Another category is the pneumococcal conjugate vaccine or pcv13. Which contains the capsular polysaccharides specific to 13 strep pneumoniae serotypes bound to a non toxic recombinant variant of the diphtheria toxin called crm197. Which serves as a carrier protein pcv13 is recommended in young children finally treatment for infections with strep pneumoniae.
Require antibiotics. And the classic first line of treatment are beta. Lactam antibiotics.
Like penicillins g and v. Or cephalosporins. However.
Strep pneumoniae has been progressively developing resistance against penicillins and its derivatives such as amoxicillin and ampicillin. So alternatives. Include fluoroquinolones.
The combination of amoxicillin and clavulanic acid third generation cephalosporins like ceftriaxone and cefotaxime ultimately. Vancomycin and linezolid can be used alright as a quick recap strep pneumoniae is a gram positive round bacterium that lives in chains they are non motile non spore forming alpha hemolytic and optochin positive these bacteria are found asymptomatically colonizing the nasal cavities and sinuses. But they can take advantage of a weakened immune system especially in very young or very old individuals or in those.
With diabetes. Hiv. Infection cancer.
Splenectomy or those with sickle cell disease. They cause diseases. Such as rhinosinusitis.
Otitis media. Pneumonia and meningitis the treatment of infection with strep pneumoniae involves the use of penicillins. But in the case of resistant strains fluoroquinolones third generation cephalosporins and vancomycin can be used .
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