How Viruses Enter Cells

Viruses have specific proteins on their surface that bind to cell surface proteins, allowing them to enter the cell and release their genomic material. Sometimes, the viral genomic material is injected through a protein channel, while the capsid remains outside the cell. In other cases, the entire virus enters the cell. Viruses only cause membrane lysis when they have multiplied inside cells and kill them to release viral particles.

The viral envelope is formed when virus particles bud off from cells, taking some membrane with them. While it can play a role in permitting viral entry, a protein-protein interaction must still occur for the capsid and genome to enter. Viruses are too large to pass through cell membrane pores.

Malaria Transmission and Life Cycle

Malaria is a disease caused by a protozoan called Plasmodium falciparum. The most likely diagnosis for someone who has recently travelled to a high-risk malaria region and has not been taking any antimalarial prophylaxis is malaria. However, leishmaniasis should also be considered if blood tests are negative for malaria.

Mosquitoes are the carriers of malaria. They inject the disease in the form of schizonts from their salivary glands into the human bloodstream. These schizonts then migrate to the liver where they invade hepatocytes and multiply as merozoites. After a while, the hepatocytes rupture and the merozoites invade red blood cells in the bloodstream. In these cells, they undergo replication as trophozoites.

At this stage, gametocytes can also be produced, which are taken up by feeding mosquitoes. In the mosquito midgut, gametocytes fuse to form an oocyst. Schizonts bud off from the oocyst to reside in the mosquito salivary glands. This completes the life cycle of malaria.

Systemic Inflammatory Response Syndrome

Systemic inflammatory response syndrome (SIRS) is a condition that is diagnosed when a combination of abnormal parameters are detected. These parameters can be deranged for various reasons, including both infective and non-infective causes. Some examples of infective causes include Staph. aureus toxic shock syndrome, while acute pancreatitis is an example of a non-infective cause. The diagnosis of SIRS is based on the presence of a constellation of abnormal parameters, which include a temperature below 36°C or above 38.3°C, a heart rate exceeding 90 beats per minute, a respiratory rate exceeding 20 breaths per minute, and a white blood cell count below 4 or above 12 ×109/L.

It is important to note that the systolic blood pressure is not included in the definition of SIRS. However, if the systolic pressure remains below 90 mmHg after a fluid bolus, this would be considered a result of septic shock. the criteria for SIRS is crucial for healthcare professionals to identify and manage patients with this condition promptly.

Treatment of Tuberculosis with Antibiotics

Tuberculosis is a bacterial infection that is treated with a combination of antibiotics. The initial treatment typically involves four antibiotics: ethambutol, isoniazid, rifampicin, and pyrazinamide. Rifampicin works by blocking mRNA synthesis at mRNA polymerase, which inhibits protein synthesis. However, it is known to induce CYP450 enzymes and can cause hepatotoxicity as a side-effect. Isoniazid inhibits the production of mycolic acids, which are essential components of the bacterial cell wall. Its side-effects include neuropathy, which can be reduced by taking pyridoxine, and hepatotoxicity. Ethambutol is bacteriocidal and acts against cell wall formation. However, it has a particular side-effect of retinopathy. Pyrazinamide is predominantly bacteriostatic and was thought to act by inhibiting fatty acid synthase, although there is debate over the exact mechanism. Streptomycin is often used as a second line therapy and works by blocking the 30s subunit, which inhibits protein synthesis.

Overall, the combination of these antibiotics is effective in treating tuberculosis, although they can have side-effects that need to be monitored. It is important to follow the prescribed treatment regimen and complete the full course of antibiotics to ensure that the infection is fully treated and to prevent the development of antibiotic resistance.

Differences in Cell Wall Composition between Fungi and Bacteria

Fungi and bacteria both have cell walls, but the composition of their cell walls differs. While bacterial cell walls contain lipopolysaccharide in Gram negative bacteria and lipoteichoic acid in Gram positive bacteria, fungal cell walls contain chitin and glucans. These polysaccharides are not found in bacterial cell walls, which do not contain cellulose like plant cell walls do.

Peptidoglycan is a major structural component of Gram positive cell walls and a minor component of Gram negative cell walls. This compound is responsible for the ability of Gram positive cells to stain dark purple and Gram negative cells to stain pink. Peptidoglycan binds crystal violet, which is used in the Gram staining process. Overall, the differences in cell wall composition between fungi and bacteria contribute to their distinct characteristics and functions.

The Structure and Reproduction of Fungi

Fungi are composed of hyphae, which are Multinucleated cells that are only partially separated from each other by septae. These cellular structures contain multiple membrane-bound nuclei and all other organelles, including vacuoles. Hyphae grow at their tips, branch, and connect with other hyphae to form a mesh called the fungal mycelium. While some fungi reproduce only asexually, most also demonstrate a form of sexual reproduction that involves the combination of two haploid structures, such as a hyphae and a spore.

There are some fungi that exist as single cells, but they do not form a mycelium. Patients at risk of fungal infections include those on prolonged immunosuppression, prolonged steroid treatment, prolonged neutropenia, or those with congenital or acquired immunodeficiency disorders. Unlike plants, fungi do not have an organized system for transporting water. The fungal cell wall is different in composition from bacterial and plant cell walls, but it is still referred to with the same term.

Cell Surface Projections

Flagella, fimbriae, and pili are all types of cell surface projections found in bacteria. Flagella are composed of flagellin and have a motor pump at the base that propels the filamentous structure to allow bacteria to move. This movement is important for bacteria such as Helicobacter pylori to penetrate through gastric mucus. Fimbriae and pili are short projections that aid in attachment. They can be used to attach to an epithelial layer, which increases virulence, or to attach to other bacteria, which facilitates the exchange of genetic material.

In contrast, microvilli are cell surface projections found on the apical surfaces of human epithelial cells, such as enterocytes. They increase the surface area for absorption, allowing for more efficient nutrient uptake. Overall, these cell surface projections play important roles in bacterial movement, attachment, and nutrient absorption in human cells.

Bacterial Survival in the Presence of Oxygen

Bacteria can be categorized into two types: aerobic and anaerobic. Anaerobic bacteria cannot survive in the presence of oxygen due to the formation of oxygen radicals that damage intracellular structures. On the other hand, aerobic bacteria have high levels of the enzyme superoxide dismutase, which breaks down the superoxide anion and prevents oxidative damage. Additionally, aerobic bacteria have several other similar enzymes that protect against oxygen radical-induced injury.

Anaerobic bacteria generate ATP in an oxygen-independent process, such as fermentation of long-chain fatty acids. Facultative anaerobic bacteria prefer an anaerobic environment but have sufficiently high levels of anti-oxidant enzymes that they can survive in an aerobic environment.

Carbonic anhydrase is an enzyme that converts water and carbon dioxide into H+ and HCO3−. Coenzyme Q is part of the electron transport chain, while lactate dehydrogenase converts pyruvate into lactate. NADPH oxidase is used in the ‘respiratory burst’ to generate toxic oxygen radicals.

In summary, the survival of bacteria in the presence of oxygen depends on their ability to protect against oxygen radicals. Aerobic bacteria have high levels of protective enzymes, while anaerobic bacteria generate ATP in an oxygen-independent process. Facultative anaerobic bacteria can survive in both environments due to their high levels of anti-oxidant enzymes.

The causes of urinary tract infections (UTIs) are a common health problem that affects millions of people worldwide. Escherichia coli is the most common cause of UTIs, which is a type of Gram-negative rod that can survive with or without oxygen. UTIs can be classified into two categories: uncomplicated and complicated.

Uncomplicated UTIs occur in individuals with normal urinary tracts and without recent surgery or recurrent infections. On the other hand, complicated UTIs occur in patients with structural abnormalities, recent urological surgery, or other reasons for abnormal infectious organisms.

The majority of uncomplicated UTIs are caused by Escherichia coli, followed by Proteus species and other bacteria. In contrast, complicated UTIs are mostly caused by Proteus species, followed by Escherichia coli and other bacteria such as Klebsiella sp.

All of these bacteria are Gram-negative, facultative anaerobic rods that can cause a range of symptoms, including pain, burning, and frequent urination. In summary, the causes of UTIs is crucial for effective diagnosis and treatment.

While Escherichia coli is the most common cause of uncomplicated UTIs, Proteus species are more likely to cause complicated UTIs. By identifying the type of bacteria responsible for the infection, healthcare providers can prescribe the appropriate antibiotics and prevent the development of antibiotic resistance.

The obligate intracellular pathogen that can cause respiratory and genital tract infections is Chlamydia trachomatis.

Chlamydia trachomatis is a bacterium that can cause a variety of infections in humans, including respiratory infections such as pneumonia and genital tract infections such as urethritis, cervicitis, and pelvic inflammatory disease (PID). It is transmitted through sexual contact and can also be transmitted from mother to newborn during childbirth, leading to neonatal conjunctivitis and pneumonia.