Hello everyone, today is Monday and it is the beginning of the working days of the week, I hope you enjoy your week. We will be beginning a Microbiology series, and I will be explaining a few micro-organisms in this series, In today's post, I will be discussing Staphylococcus aureus and I am sure that this a lot of people might be familiar with this microorganism. Without any more ado, let's begin. Quickly, Microbes can be Bacteria, fungi, Viruses, and Parasites and Microbiology is the science that studies bacteriology, Virology, Mycology, and parasitology. This is just a simple introduction.
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Staphylococcus aureus is a gram-positive, catalase-positive, coagulase-positive, beta-hemolytic bacteria, that occurs in clusters. Let me quickly explain the terms which I used to qualify Staph. aureus. Gram-positive bacteria are a group of microorganisms that possesses a thick peptidoglycan layer in their cell walls. The peptidoglycan layer is responsible for the purple color characteristics when Gram is stained. Coagulase is an enzyme that is produced by certain types of bacteria, causing the clotting of plasma. Coagulase-positive bacteria are able to produce this coagulase when performing a coagulase test. Beta-hemolytic bacteria are bacteria that produce the enzymes beta-hemolysins, which cause the destruction (lysis) of the red blood cells (erythrocytes) and the formation of a "beta-hemolytic" zone on a blood agar plate.Cocci is used to describe bacteria that are spherical or oval in shape. These bacteria can exist in a single form known as Cocci, in pairs known as diplococci, in clusters known as staphylococci, or in chains known as streptococci.
Staphylococcus aureus possesses some virulent factors which include Protein A which is the protein that binds to the Fc fragment of immunoglobulin G (FC-IgG) preventing compliment activation and thereby preventing the organism from phagocytosing the bacteria. Protein A will anchor itself to Fc-IgG, preventing phagocytosis of the bacteria, and thereby preventing the bacteria from being eliminated. Staph. aureus also possesses penicillin-binding proteins which are a group of enzymes found in the cell walls of certain bacteria, especially bacteria responsible for causing infections in humans. These enzymes are important in the synthesis and maintenance of the bacterial cell wall. Staphylococcus aureus is resistant to methicilin and nafcillin. Superantigen TSST-1 (Toxic shock syndrome toxin-1) is another virulence factor for S.aureus. It is a superantigen produced by bacteria, which is a common cause of skin and soft tissue infections in humans, as well as infections such as pneumonia, sepsis, and endocarditis. It binds to MHC class 2 and T-cell Receptors and releases cytokines. S.aureus also processes enterotoxin B, which is a heat-stable toxin, which means it can survive the heat and remain active even after the bacteria has been killed. Enterotoxin B works by binding to specific receptors on the intestinal epithelial cells, leading to the activation of adenylate cyclase. This causes an increase in the levels of cyclic AMP (cAMP) in the cells, causing the secretion of water and electrolytes into the intestinal lumen. This leads to food poisoning and enterotoxemia, a condition characterized by severe diarrhea and vomiting. Finally, Staphylococcus possesses exfoliative toxin which causes staphylococcal scalded skin syndrome as well as other infections such as pneumonia, sepsis, and endocarditis. The Exfoliative toxins work by binding to the desmoglein 1 and 3 which help to hold the cells of the epidermis together. The binding causes the cleaving of the intraepidermal cell attachments, which leads to the detachment of the top layer of the skin.
Let me state clearly that diseases can be caused by either the bacteria or the toxins produced by the bacteria. When a bacteria attacks the tissue and destroy it, it can cause disease, it can also produce toxins that will indirectly cause disease. When Bactria is found in the blood, it is known as bacteremia, and when the toxins are found in the blood, it is known as Toxemia. In the case of Bacteremia, treating it has to do with using antibiotics, but in the case of toxins, antibiotics cannot be used because antibiotics target a part of the organism. In some cases, it would target the cell wall of the bacteria or other parts of the bacteria such as the protein synthesis capabilities but antibiotics will not target the toxins produced by the bacteria. Bacteria can cause diseases that include skin infection diseases (folliculitis, abscess, furuncle, carbuncle, and impetigo), it can cause Osteomyelitis, Septic arthritis, Pneumonia, Endocarditis, empyema, and brain abscess in severecases. The Staphylococcus aureus toxins can cause infection or symptoms such as the Staphylococcus Scalded sskin syndrome, Toxin shock syndrome,and food Poisoning. In this case, the toxin should be targetted and not the bacteria bacause in the case where the bacteria has been killed through heating but the toxins are still active, treating the bacteria would be a waste of time.
Remember that Staphylococcus contains coagulase which converts fibrinogen to fibrin, and that is why its lesions on the skins are always confined or localized in the area of the skin it affects. In the case of Impetigo, it can be caused by both Staphylococcus and Streptococcus but when it has blisters, it is staphylococcus. treatment for Methicillin-Susceptible Staphylococcus Aureus would br Oxycillin, Dycloxicillin, and Nafcillin. Bacteria in the blood can cause septic embolus which lead to Pyemia. These can be as a result of an abscess in the skin, lug, brain, causing septic embolus in the blood. When it reaches its target organ, it can cause other diseases. In the case where its target organ is the heart, it can cause Acute bacteria encocarditis (which afects the inner lining of the heart (the endocardium)), if the location of the septic embolus is the lungs, it can cause lung abscess, or empyema, if the septic embolus goes to the brain, it would lead to cerebral abscesses. Staphylococcus aureus is pyogenic as they trigger neutrophils and since neutrophils are the cells of acute inflammation, then they allow patients to have redness, welling, pain, hotness, and loss of fundtion in the area where it is localized.
Also let's remember that before we mention Staphylococcus Endocarditis, we have Bacteria endocarditis which is the inflammation of the heart endocardium or valve, causing fever and murmur in the heart. It can exist as Acute bacteria Endocarditis where there is an active bacteria destroying the healthy valve of the heart in cases like Staphylococcus Aureus Endocarditis, or Sub-acute bacteria endocarditis where fastidious weak bacteria are able to attack and destroy weak valves in the heart. Examples of bacteria that causes subacute endocarditis are Haemophilus species, Aggregatibacter species, and other member of the HACEK group of bacteria.
Treatment of Bacteria is usually with Penicillin, 1st and 2nd generation cephalosporins, and Beta Lactamase inhibitor but then in cases of MRSA, using 3rd order antibiotics like vancomycin or Linezoid would do justice to the bacteria infection. Beta-lactam antibiotics have a beta-lactam ring. They include penicillin and Cephalosporins but they can be succeptible to beta-lactamases as they cleave the beta-lactam. That is why it is important to give the antibiotics with beta-lactamase inhibitors such as Clavulanate and Sulbactam.