Microbiology Basics: Pathogenicity and Staining

Pathogenicity and Virulence

• Pathogenicity refers to how infectious an organism is.
• Virulence describes the ability of an organism to cause disease.
• Some bacteria produce toxins that contribute to their virulence, for example, E. coli.

Gram Staining

• Gram staining is a method used to classify bacteria based on their cell wall structure.
• Gram-positive bacteria retain the stain and appear purple due to their thick cell wall.
• Gram-negative bacteria do not retain the stain and appear pink because they have a thinner cell wall.

Bacterial Shapes

• Bacilli: Rod-shaped bacteria
• Cocci: Spherical bacteria
• Spirilla: Spiral-shaped bacteria

Common Bacterial Infections

• Chlamydia Trachomatis: Causes sexually transmitted infections and conjunctivitis.
• E. coli: Can cause urinary tract infections, traveler's diarrhea, and meningitis in children.
• Mycobacterium tuberculosis: Causes tuberculosis (TB).
• Streptococcus: Can cause pharyngitis, pneumonia, skin infections, and sepsis.

Stages of Infection

• Incubation period: The time between exposure to a pathogen and the appearance of symptoms.
• Prodromal stage: The initial appearance of mild, non-specific symptoms.
• Acute stage: The period of maximum impact of the infection, characterized by severe symptoms.
• Convalescent period: The recovery phase as the body controls the infection and symptoms resolve.

Anti-Infective Drugs

• The primary goal of anti-infective drugs is to assist the body in eliminating pathogens.
• Bactericidal drugs directly kill bacteria.
• Bacteriostatic drugs inhibit bacterial growth.
• Bacterial and human cells have distinct differences that allow selective toxicity, targeting bacterial cells without harming human cells.

Acquired Resistance

• Bacteria are capable of rapidly dividing and making errors during replication, leading to the development of drug resistance.
• Overuse and inappropriate use of antibiotics contribute to the emergence of antibiotic-resistant strains.
• MRSA (Methicillin-resistant Staphylococcus aureus) and VRE (Vancomycin-resistant Enterococcus) are examples of drug-resistant bacteria.
• To reduce drug resistance, it is crucial to use the right antibiotic for the right infection, restrict antibiotic use, and complete full courses of therapy.

Culture and Sensitivity Tests

• Culture tests identify the specific pathogen causing an infection.
• Sensitivity tests determine the effectiveness of various antibiotics against the identified pathogen.
• Broad-spectrum antibiotics are typically started for severe infections, followed by narrow-spectrum antibiotics once results from culture and sensitivity tests become available.
• Superinfections (secondary infections) may occur as a complication of antibiotic therapy.

Bacterial Resistance

• Penicillins are effective against gram-positive bacteria.
• Penicillins disrupt bacterial cell wall synthesis.
• Common side effects include nausea, vomiting, diarrhea, and allergic reactions.

Cephalosporins

• A class of antibiotics that inhibit bacterial cell wall synthesis.
• Bactericidal in action.
• Five generations of cephalosporins exist, with varying levels of effectiveness against different bacteria.

Tetracyclines

• Bacteriostatic antibiotics that inhibit bacterial protein synthesis.
• Used for a wide range of infections, including Lyme disease, chlamydial infections, and peptic ulcers.
• Can cause gastrointestinal upset, photosensitivity, and teeth discoloration.
• Should not be administered to children under 8 or pregnant women.

Macrolides

• High doses may have bactericidal activity.
• Used for infections caused by Bordetella pertussis (whooping cough), Legionella pneumophila (Legionnaires' disease), and other microorganisms.
• Can cause gastrointestinal side effects, hearing loss, and cardiac toxicity.

Aminoglycosides

• Bactericidal antibiotics that inhibit bacterial protein synthesis.
• Used for serious systemic infections caused by aerobic gram-negative bacteria.
• Given parenterally (IV or IM).
• Carry a risk of permanent ototoxicity (hearing loss) and nephrotoxicity (kidney damage).

Fluoroquinolones

• Bactericidal antibiotics that inhibit bacterial DNA synthesis.
• Effective against a broad spectrum of bacteria, especially gram-negative organisms.
• Well absorbed orally.
• Can cause nausea, vomiting, diarrhea, dysrhythmias, hepatotoxicity, tendinitis, and tendon rupture.

Sulfonamides and Urinary Antiseptics

• Bacteriostatic antibiotics that inhibit folic acid synthesis.
• Widely used for urinary tract infections.
• Can cause crystalluria (formation of crystals in urine), nausea, vomiting, and blood abnormalities.

Glycopeptides

• Vancomycin is a glycopeptide antibiotic used to treat severe infections caused by gram-positive bacteria, including MRSA.
• It is highly effective against bacteria that have become resistant to other antibiotics.
• Side effects include ototoxicity, nephrotoxicity, and Red Man syndrome.

Prototype Antibiotics

• Most prototype antibiotics are processed by the liver.
• Monitoring liver function tests (LFTs) is important during therapy.
• Steven-Johnson syndrome, a serious skin reaction, can occur with some antibiotics.

Tuberculosis

• A chronic infectious disease caused by Mycobacterium tuberculosis.
• The infection can lie dormant for years and reactivate if the immune system is weakened.
• Treatment requires a multi-drug regimen, including isoniazid, rifampin, pyrazinamide, and ethambutol, for 6-12 months.

Isoniazid

• First-line drug for tuberculosis treatment.
• Can cause neurological side effects, including neuropathy, seizures, and psychosis.
• Can increase the risk of hepatotoxicity when combined with alcohol.
• Can lead to vitamin B6 deficiency.

Fungal Infections

• Fungal infections can be superficial (affecting the skin, nails, or mucous membranes) or systemic (affecting internal organs).
• Systemic fungal infections are less common but can be more severe.

Amphotericin B

• A drug used to treat systemic fungal infections.
• It has many serious side effects, including fever, chills, vomiting, headache, nephrotoxicity, hypokalemia, cardiac arrest, and dysrhythmias.

Fluconazole

• A broad-spectrum antifungal drug.
• Often used to treat fungal infections that reach the central nervous system.
• Can cause nausea, vomiting, diarrhea, and, in rare cases, Steven-Johnson syndrome.

Nystatin

• A polyene antifungal used to treat superficial fungal infections.
• Available in topical and oral formulations.
• Well tolerated but can cause minor skin irritation or gastrointestinal upset.

Protozoan Infections: Malaria

• Malaria is a parasitic disease caused by the Plasmodium parasite.
• Mosquitoes transmit the parasite to humans through their saliva during a blood meal.
• The parasite infects red blood cells and multiplies, eventually causing the cells to rupture.

Chloroquine

• An antimalarial drug that works against the erythrocytic stage of the Plasmodium parasite.
• Can reduce high fever and help prevent malaria.

This quiz covers fundamental concepts in microbiology, including pathogenicity, virulence, bacterial classification through gram staining, and common bacterial infections. Test your knowledge on bacterial shapes, their diseases, and methods of analysis.