Hello everyone, I hope you are having a blissful week. Anyways, my week is still going, and it is a stressful one. You can also tell me how your week is going in the comment section. In my last post, I talked about Staphylococcus aureus, and today, I will be diving more into the microbial world and will still be writing on Staphylococcus. You can read my previous post if you haven't but I will do my best to explain Staphylococcus Aureus, Staphylococcus Epidermidis, and Staphylococcus Saprophytical in this post. This said, let's begin.
Structure and Characteristics of Staphylococcus Species
Let me quickly explain what Staphylococcus means. Staphs are bacteria in clusters, and cocci mean spherical, round, or berry-like. So Staphylococcus bacteria can be said to be bacteria that are clusters of spheres in shape. All Staphylococcus bacteria are gram-positive bacteria, with thick peptidoglycan layer which allows them to retain the crystal-violet stain. Staphylococci bacteria are non-motile bacteria as they cannot move since they do not possess flagella and they are catalase-positive bacteria. Being Catalase positive means that they contain the enzyme catalase which bubbles in Hydrogen peroxide, as a result of converting hydrogen peroxide to water and oxygen. They are facultative anaerobes which means they can usually survive in oxygen-filled environments but can also thrive where there is no oxygen. Staphylococcus species are of three types which are the Staphylococcus Aureus, which is a colonizer of the skin. It is part of the normal microbial skin flora found in different areas of the skin including the nares/nostrils. Staphylococcus Epidermidis is another staphylococcus specie that is also part of the normal microbial skin flora. Staphylococcus saprophyticus are bacteria that thrive in organically decaying environments. It can be found in organic decaying matter and the perineum and possibly in the urogenital tract.
Image credit
Coagulase is a prothrombin molecule and it is used to identify staphylococcus via the coagulase test which has to do with converting fibrinogen to fibrin. While all staphylococcus species are catalase-positive, only staphylococcus aureus is coagulase positive which converts fibrinogen to fibrin causing clumping. When Staphylococcus aureus is cultured in mannitol salt agar, it ferments to form a golding yellow colony. Staphylococcus Epidermidis and Saprophyticus are both coagulase negative, but when put into a Urea Broth which contains a phenol red indicator, they turn in into a pink solution (ammonia) due to the enzyme Urease which they both possess. Both Staphylococcus saprophyticus and Epidermidis are urease positive. When Staphylococcus Epidermiids and Saprophyticus are placed on novobiocin, Staphylococcus Epidermidis are sensitive to the drug, while Staphylococcus saprophyticus is resistant to novobiocin.
Pathophysiology and Diseases of Staphylococcus Species
When these species get into the body, how do they cause infection/disease?
- Staphylococcus Aureus
As I said in my previous post that Staphylococcus aureus can be pathogenic in two ways, Biofilms or exotoxins. Staphylococcus aureus can create Biofilm or exopolysaccharide layers. If staphylococcus gets into the bloodstream, it starts to secrete polysaccharide layers around itself which helps it to interact with one another in the bloodstream and prevent the immune system from breaking through the layer. One infection that can be caused as a result of the biofilm is catheter-associated infection. Staphylococcus aureus can also produce exotoxins such as the toxic shock syndrome toxin type 1 (TSST-1) which binds to Superantigens (SAgs) and leads to bridging between the T-cells and the antigen-presenting cell, then stimulates the immune response leading to the release of cytokines (IL-1, IL-2, TNF alpha, and IFN gamma) which causes inflammation leading to rash, vasodilation of blood vessels leading to hypotension (low blood pressure), and they can lead to fever, which are symptoms of the toxic-shock syndrome. Staphylococcus aureus can produce another toxin known as Palin Valentine leukocidin protein (Leukocidin toxin) which creates pus in leukocytes causing the death of the white blood cells causing inflammation which would damage some parenchyma tissues of the lungs causing the lung to get damaged gradually leading to necrotizing pneumonia. Staph aureus also produces an Exfoliative toxin that causes staphylococcus scalded skin syndrome. The toxin targets keratinocytes desmoglein - 1, the protein that holds keratinocytes together which causes blisters on the skin causing loss of skin. Staph aureus also releases Beta-hemolysin which lyses the red blood cell destroying the red blood cell. It also releases enterotoxin which targets enterocytes in the epithelial layer of the GI tract. Causing electrolytes to move in the GI tract, leading to inflammation of the GI tract causing gastroenteritis and diarrhea.
Staphylococcus Aureus can cause Impetigo, Cellulitis, and abscess, and can lead to Furuncle which would lead to Carbuncle. When in the muscle, they can cause inflammation of the muscles causing Pyomyositis, and in the bone can lead to osteomyelitis and septic Arthritis (in joints). When the bacteria get into the blood, they can invade the tissues causing septicemia, then spread to organs such as the meninges causing meningitis, brain abscess, Pneumonia in the lungs, and cause infective endocarditis in the heart as they affect the valve of the heart.
- Staphylococcus Epidermidis
Similar to Staphylococcus aureus, epidermidis releases biofilms exopolysaccharides which allows it to invade the immune system, but they do not produce toxins. The biofilms are usually formed on catheters such as the Vascular catheter, Urinary Catheter, Prosthetic valves, and joints which enable them to get into the body and cause diseases. This can lead to catheter-associated infections, such as Catheter-associated Urinary Tract Infections, and prosthetic valve infections.
- Staphylococcus Saprophyticus
Similar to aureus and epidermidis, Staphylococcus saprophyticus also produce biofilms in the body, as well as produces a Urease enzyme that causes diseases. It can penetrate the body through catheters, and when inside the urine, the Urease in the Staphylococcus saprophyticus breaks down Urea into carbon dioxide and ammonia. Thereby increasing the PH of the urine and encouraging the growth of bacteria. Also, compounds such as magnesium and sulfate present in the urine can combine with ammonia forming struvite crystals in the urethra causing obstruction in the urethra. It can also lead to urinary tract infections.
Reference
- https://www.ncbi.nlm.nih.gov/books/NBK482367/
- https://www.ncbi.nlm.nih.gov/books/NBK441868/
- https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4451395/
- https://www.ncbi.nlm.nih.gov/books/NBK563240/
- https://www.sciencedirect.com/topics/medicine-and-dentistry/staphylococcus-epidermidis
- https://www.ncbi.nlm.nih.gov/books/NBK8448/