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PBBSC FY MICROBIOLOGY UNIT 5

  • Disease producing micro-organisms:

Disease-Producing Microorganisms

Disease-producing microorganisms, or pathogens, are microbes capable of causing infections in humans, animals, or plants. These pathogens include bacteria, viruses, fungi, protozoa, helminths, and prions. Understanding their characteristics and mechanisms is essential for diagnosis, prevention, and treatment of infectious diseases.

Categories of Disease-Producing Microorganisms

1. Bacteria

  • Description: Unicellular, prokaryotic organisms.
  • Mechanism:
    • Invade host tissues.
    • Produce toxins (endotoxins or exotoxins).
  • Examples:
    1. Escherichia coli: Causes urinary tract infections, diarrhea.
    2. Staphylococcus aureus: Causes skin infections, pneumonia, sepsis.
    3. Mycobacterium tuberculosis: Causes tuberculosis.
    4. Clostridium tetani: Causes tetanus via neurotoxins.

2. Viruses

  • Description: Acellular entities that require a host cell to replicate.
  • Mechanism:
    • Infect host cells, hijack their machinery to produce viral particles.
    • Cause cell lysis or immune-mediated damage.
  • Examples:
    1. Influenza virus: Causes seasonal flu.
    2. Hepatitis B virus (HBV): Causes liver infection.
    3. HIV (Human Immunodeficiency Virus): Causes AIDS.
    4. SARS-CoV-2: Causes COVID-19.

3. Fungi

  • Description: Eukaryotic organisms, can be unicellular (yeasts) or multicellular (molds).
  • Mechanism:
    • Cause superficial or systemic infections.
    • Opportunistic in immunocompromised hosts.
  • Examples:
    1. Candida albicans: Causes oral thrush, vaginal yeast infections.
    2. Aspergillus fumigatus: Causes aspergillosis in lungs.
    3. Cryptococcus neoformans: Causes meningitis.

4. Protozoa

  • Description: Unicellular, eukaryotic organisms.
  • Mechanism:
    • Infect through contaminated food, water, or vectors.
    • Damage host tissues directly or via toxins.
  • Examples:
    1. Plasmodium falciparum: Causes malaria.
    2. Entamoeba histolytica: Causes amoebiasis (dysentery).
    3. Giardia lamblia: Causes giardiasis (intestinal infection).

5. Helminths

  • Description: Multicellular parasitic worms.
  • Mechanism:
    • Damage tissues by feeding on host nutrients or causing mechanical obstruction.
  • Examples:
    1. Ascaris lumbricoides: Causes ascariasis.
    2. Taenia solium: Causes taeniasis (tapeworm infection).
    3. Schistosoma: Causes schistosomiasis.

6. Prions

  • Description: Misfolded proteins that cause neurodegenerative diseases.
  • Mechanism:
    • Induce misfolding of normal proteins in the brain.
  • Examples:
    1. Creutzfeldt-Jakob Disease (CJD).
    2. Bovine Spongiform Encephalopathy (BSE or Mad Cow Disease).

Mechanisms of Disease Production

1. Invasion:

  • Pathogens enter the host body through various routes (e.g., respiratory, gastrointestinal, skin).

2. Toxin Production:

  • Exotoxins:
    • Secreted proteins; highly toxic.
    • Example: Botulinum toxin by Clostridium botulinum.
  • Endotoxins:
    • Released upon bacterial cell lysis; cause systemic inflammation.
    • Example: Lipopolysaccharides (LPS) from Gram-negative bacteria.

3. Immune Evasion:

  • Mechanisms include capsule formation, antigenic variation, and intracellular survival.
  • Example: Mycobacterium tuberculosis survives inside macrophages.

4. Host Immune Response:

  • Some symptoms are caused by an overactive immune response rather than the pathogen itself (e.g., sepsis, cytokine storms).

Common Modes of Transmission

  1. Direct Contact:
    • Skin-to-skin contact, sexual contact.
    • Example: Treponema pallidum (syphilis).
  2. Indirect Contact:
    • Fomites (contaminated objects).
    • Example: Staphylococcus aureus.
  3. Airborne:
    • Pathogens in droplets or aerosols.
    • Example: Mycobacterium tuberculosis.
  4. Vector-Borne:
    • Carried by vectors like mosquitoes, ticks.
    • Example: Plasmodium (malaria).
  5. Waterborne:
    • Contaminated water.
    • Example: Vibrio cholerae.
  6. Foodborne:
    • Contaminated food.
    • Example: Salmonella.

Prevention and Control

  1. Hygiene:
    • Handwashing, sterilization, and disinfection.
  2. Vaccination:
    • Immunization against diseases (e.g., polio, hepatitis).
  3. Antimicrobial Therapy:
    • Antibiotics for bacteria, antivirals for viruses.
  4. Vector Control:
    • Insecticide-treated nets, environmental sanitation.
  5. Isolation and Quarantine:
    • Containing infectious individuals.
  6. Education and Awareness:
    • Promoting preventive measures.

Significance in Microbiology

  • Disease Understanding:
    • Identifying causative agents aids in diagnosis and treatment.
  • Public Health:
    • Surveillance of pathogens prevents outbreaks.
  • Research:
    • Development of vaccines and therapies.
  • Gram positive bacilli

Gram-Positive Bacilli

Gram-positive bacilli are a group of bacteria that are rod-shaped and retain the crystal violet stain during Gram staining due to their thick peptidoglycan layer in the cell wall. They are diverse and include both harmless commensals and significant pathogens.

Classification of Gram-Positive Bacilli

1. Based on Spore Formation

  • Spore-Forming:
    • Examples: Bacillus species, Clostridium species.
  • Non-Spore-Forming:
    • Examples: Corynebacterium, Listeria, Lactobacillus.

2. Based on Oxygen Requirement

  • Aerobic/Facultative Anaerobic:
    • Examples: Bacillus, Listeria.
  • Anaerobic:
    • Examples: Clostridium.

Key Genera and Their Characteristics

1. Bacillus

  • Characteristics:
    • Spore-forming, aerobic or facultative anaerobic.
    • Found in soil and water.
  • Pathogenic Species:
    • Bacillus anthracis:
      • Causes anthrax.
      • Produces anthrax toxin.
    • Bacillus cereus:
      • Causes food poisoning (diarrheal and emetic forms).
  • Clinical Significance:
    • B. anthracis: Bioterrorism agent.
    • B. cereus: Common in reheated rice and contaminated foods.

2. Clostridium

  • Characteristics:
    • Spore-forming, obligate anaerobes.
    • Produce potent exotoxins.
  • Pathogenic Species:
    • Clostridium tetani:
      • Causes tetanus.
      • Produces tetanospasmin (neurotoxin).
    • Clostridium botulinum:
      • Causes botulism.
      • Produces botulinum toxin.
    • Clostridium perfringens:
      • Causes gas gangrene and food poisoning.
    • Clostridioides difficile:
      • Causes antibiotic-associated colitis.
  • Clinical Significance:
    • Common in anaerobic infections.

3. Corynebacterium

  • Characteristics:
    • Non-spore-forming, aerobic.
    • Club-shaped rods.
  • Pathogenic Species:
    • Corynebacterium diphtheriae:
      • Causes diphtheria.
      • Produces diphtheria toxin.
  • Clinical Significance:
    • Vaccine-preventable disease.

4. Listeria

  • Characteristics:
    • Non-spore-forming, facultative intracellular.
    • Grows at low temperatures (4°C).
  • Pathogenic Species:
    • Listeria monocytogenes:
      • Causes listeriosis.
      • Symptoms: Meningitis, septicemia, miscarriage in pregnant women.
  • Clinical Significance:
    • Found in contaminated food (e.g., soft cheeses, unpasteurized milk).

5. Lactobacillus

  • Characteristics:
    • Non-spore-forming, facultative anaerobic.
    • Part of normal flora in the gastrointestinal and genitourinary tracts.
  • Clinical Significance:
    • Generally non-pathogenic.
    • Used in probiotics and food fermentation (e.g., yogurt, sauerkraut).

Pathogenic Mechanisms

  1. Toxins:
    • Clostridium species produce potent exotoxins (e.g., tetanospasmin, botulinum toxin).
    • Corynebacterium diphtheriae produces diphtheria toxin.
  2. Invasion:
    • Listeria monocytogenes invades host cells, evading the immune system.
  3. Spore Formation:
    • Bacillus and Clostridium form spores, enhancing survival in harsh conditions.

Laboratory Diagnosis

1. Microscopy

  • Gram staining shows purple rod-shaped bacteria.

2. Culture

  • Bacillus: Grows aerobically on nutrient agar; forms large colonies.
  • Clostridium: Grows anaerobically on blood agar; may show double hemolysis (C. perfringens).
  • Corynebacterium: Grows on Loeffler’s medium or tellurite agar; appears as “Chinese letter” arrangements.
  • Listeria: Cold enrichment; forms tumbling motility at room temperature.

3. Biochemical Tests

  • Catalase test: Positive for Bacillus and Listeria; negative for Clostridium.
  • Toxin assays: Detect toxins (e.g., diphtheria toxin, botulinum toxin).

4. Molecular Methods

  • PCR to detect specific genes for toxins or species identification.

Treatment

  1. Antibiotics:
    • Penicillin: Effective for Bacillus anthracis, Corynebacterium diphtheriae.
    • Metronidazole: Used for anaerobic infections (Clostridium species).
    • Ampicillin: Effective for Listeria monocytogenes.
  2. Antitoxins:
    • For toxin-mediated diseases like diphtheria and tetanus.
  3. Supportive Therapy:
    • For severe infections (e.g., mechanical ventilation in botulism).

Prevention

  1. Vaccination:
    • DTP (Diphtheria-Tetanus-Pertussis) vaccine prevents diphtheria and tetanus.
  2. Food Safety:
    • Avoid consumption of contaminated foods to prevent listeriosis.
  3. Hygiene and Sterilization:
    • Proper wound care to prevent tetanus.
    • Sterilization of medical equipment to avoid Clostridium difficile infections.
  • Tuberculosis and Leprosy

Tuberculosis and Leprosy

Tuberculosis (TB) and Leprosy are chronic infectious diseases caused by species of the genus Mycobacterium. While TB primarily affects the lungs, it can spread to other organs, whereas leprosy primarily involves the skin, peripheral nerves, and mucous membranes. Below is a detailed overview of both diseases.

Tuberculosis (TB)

Causative Agent

  • Mycobacterium tuberculosis (primary cause).
  • Other species: Mycobacterium bovis, Mycobacterium africanum.

Epidemiology

  • Global Burden:
    • Approximately 10 million new cases annually.
    • Leading cause of death from a single infectious agent.
  • Transmission:
    • Airborne droplets from infected individuals.
    • Factors increasing risk: Crowding, malnutrition, HIV infection.

Pathogenesis

  1. Inhalation:
    • M. tuberculosis enters the alveoli via respiratory droplets.
  2. Immune Response:
    • Alveolar macrophages phagocytose bacteria but fail to destroy them due to the bacteria’s lipid-rich cell wall.
  3. Granuloma Formation:
    • Immune cells form granulomas to contain the bacteria.
    • Latent TB: Bacteria remain dormant in granulomas.
  4. Active Disease:
    • Reactivation occurs under immunosuppression, leading to tissue destruction and symptoms.

Clinical Manifestations

  1. Pulmonary TB (most common):
    • Persistent cough (≥2 weeks), hemoptysis, chest pain.
    • Fever, night sweats, weight loss.
  2. Extrapulmonary TB:
    • Affects lymph nodes, bones (Pott’s disease), meninges, genitourinary tract.

Diagnosis

  1. Microscopy:
    • Ziehl-Neelsen stain for acid-fast bacilli.
  2. Culture:
    • Lowenstein-Jensen medium (takes 4–8 weeks).
  3. Molecular Tests:
    • GeneXpert MTB/RIF (rapid detection, rifampin resistance testing).
  4. Tuberculin Skin Test (TST):
    • Positive in latent or active TB.
  5. Imaging:
    • Chest X-ray shows cavities, consolidation, or miliary patterns.

Treatment

  1. First-Line Drugs (RIPE regimen):
    • Rifampin (R), Isoniazid (I), Pyrazinamide (P), Ethambutol (E).
  2. Duration:
    • 6 months for drug-sensitive TB.
  3. Drug-Resistant TB:
    • Multidrug-resistant TB (MDR-TB): Requires second-line drugs like fluoroquinolones.
    • Extensively drug-resistant TB (XDR-TB): Limited treatment options.

Prevention

  1. BCG Vaccine:
    • Prevents severe forms of TB in children.
  2. Infection Control:
    • Isolation of infectious patients, use of N95 masks.
  3. Public Health Measures:
    • Screening of high-risk groups, DOTS (Directly Observed Treatment Short-course).

Leprosy (Hansen’s Disease)

Causative Agent

  • Mycobacterium leprae (primary cause).
  • Mycobacterium lepromatosis (rare).

Epidemiology

  • Global Burden:
    • ~200,000 new cases annually, mostly in tropical and subtropical regions.
  • Transmission:
    • Prolonged contact with respiratory droplets of untreated cases.
    • Susceptibility is influenced by genetic and immune factors.

Pathogenesis

  1. Entry:
    • Bacteria enter through the skin or respiratory mucosa.
  2. Target Tissues:
    • M. leprae preferentially infects cooler areas of the body, including skin, peripheral nerves, and mucous membranes.
  3. Immune Response:
    • Tuberculoid Leprosy (TT): Strong cell-mediated immunity; fewer bacteria.
    • Lepromatous Leprosy (LL): Poor immunity; high bacterial load.

Clinical Manifestations

  1. Tuberculoid Leprosy (TT):
    • Hypopigmented or erythematous skin lesions with loss of sensation.
    • Thickened peripheral nerves.
    • Positive lepromin test.
  2. Lepromatous Leprosy (LL):
    • Widespread skin nodules, plaques, thickened skin.
    • Loss of eyebrows (madarosis), nasal deformities.
    • Negative lepromin test.

Diagnosis

  1. Skin Smears:
    • Acid-fast bacilli detected in slit-skin smears.
  2. Biopsy:
    • Granulomas in TT, foamy macrophages in LL.
  3. Molecular Tests:
    • PCR for M. leprae DNA.
  4. Clinical Features:
    • Nerve involvement, sensory loss.

Treatment

  1. Multidrug Therapy (MDT):
    • For TT: Dapsone + Rifampin for 6 months.
    • For LL: Dapsone + Rifampin + Clofazimine for 12 months or longer.
  2. Supportive Care:
    • Management of nerve damage, deformities, and secondary infections.

Prevention

  1. Early Diagnosis and Treatment:
    • Reduces transmission.
  2. Vaccination:
    • BCG vaccine offers partial protection.
  3. Surveillance:
    • Contact tracing and community health programs.

Comparison of Tuberculosis and Leprosy

AspectTuberculosisLeprosy
Causative AgentMycobacterium tuberculosisMycobacterium leprae
TransmissionAirborne dropletsProlonged contact
Primary Organs AffectedLungs, other organs (extrapulmonary TB)Skin, peripheral nerves
Immune ResponseGranuloma formationCell-mediated (TT) or poor (LL)
DiagnosisSputum smear, GeneXpert, cultureSkin smears, biopsy
Treatment Duration6–24 months (depending on drug resistance)6–12 months (longer for LL)
VaccineBCG (effective in children)BCG (partial protection)

Public Health Importance

  • Tuberculosis:
    • Leading infectious cause of death worldwide.
    • Associated with poverty, overcrowding, and immunosuppression (e.g., HIV).
  • Leprosy:
    • A neglected tropical disease causing disability and social stigma.
  • Anaerobes

Anaerobes in Microbiology

Anaerobes are microorganisms that thrive in environments devoid of oxygen. These organisms vary in their sensitivity to oxygen and can range from obligate anaerobes, which cannot tolerate oxygen, to facultative anaerobes, which can grow with or without oxygen.

Classification of Anaerobes

1. Based on Oxygen Tolerance

  1. Obligate Anaerobes:
    • Cannot survive in the presence of oxygen.
    • Lack enzymes such as superoxide dismutase (SOD) and catalase to detoxify reactive oxygen species (ROS).
    • Example: Clostridium botulinum.
  2. Aerotolerant Anaerobes:
    • Do not use oxygen but can tolerate it.
    • Example: Lactobacillus species.
  3. Facultative Anaerobes:
    • Can grow in both the presence and absence of oxygen.
    • Prefer aerobic conditions for faster growth.
    • Example: Escherichia coli.
  4. Microaerophiles:
    • Require oxygen but at lower levels than atmospheric concentrations.
    • Example: Helicobacter pylori.

Examples of Anaerobes

1. Gram-Positive Anaerobes

  • Clostridium botulinum: Causes botulism.
  • Clostridium tetani: Causes tetanus.
  • Clostridioides difficile: Causes antibiotic-associated colitis.
  • Actinomyces israelii: Causes actinomycosis.
  • Peptostreptococcus: Part of normal flora; can cause infections in immunocompromised hosts.

2. Gram-Negative Anaerobes

  • Bacteroides fragilis: Associated with intra-abdominal infections.
  • Fusobacterium nucleatum: Associated with periodontal disease.
  • Prevotella species: Cause dental and soft tissue infections.

3. Anaerobic Spirochetes

  • Treponema pallidum: Causes syphilis.
  • Borrelia burgdorferi: Causes Lyme disease.

Anaerobic Infections

Common Sites

Anaerobic infections are typically polymicrobial and occur in environments where oxygen is limited:

  1. Oral Cavity:
    • Dental abscesses, periodontitis.
  2. Gastrointestinal Tract:
    • Peritonitis, appendicitis.
  3. Female Genital Tract:
    • Pelvic inflammatory disease, bacterial vaginosis.
  4. Skin and Soft Tissue:
    • Gas gangrene, necrotizing fasciitis.
  5. Central Nervous System:
    • Brain abscesses.

Symptoms

  • Foul-smelling discharge (due to sulfur compounds).
  • Tissue necrosis.
  • Abscess formation.
  • Gas production in tissues (e.g., Clostridium perfringens).

Laboratory Diagnosis

1. Sample Collection

  • Use anaerobic transport media to prevent oxygen exposure.
  • Common samples: Pus, tissue biopsies, aspirates.

2. Culture

  • Media:
    • Anaerobic blood agar.
    • Bacteroides bile esculin (BBE) agar for Bacteroides species.
  • Conditions:
    • Incubate in anaerobic chambers or jars with gas-pak systems to maintain an oxygen-free environment.

3. Microscopy

  • Gram staining reveals bacterial morphology.
  • Special stains for spore detection (e.g., Clostridium).

4. Biochemical Tests

  • Enzyme activity tests (e.g., lecithinase for Clostridium perfringens).

5. Molecular Methods

  • PCR for rapid identification of specific anaerobes (e.g., C. difficile toxin genes).

Treatment of Anaerobic Infections

1. Antibiotics

  • Effective Agents:
    • Metronidazole: Effective against most anaerobes.
    • Clindamycin: Effective for oral and respiratory anaerobic infections.
    • Carbapenems (e.g., imipenem): Broad-spectrum coverage.
    • Beta-lactam/beta-lactamase inhibitors (e.g., piperacillin-tazobactam): Effective for polymicrobial infections.
  • Ineffective Agents:
    • Aminoglycosides: Ineffective due to poor penetration in anaerobic conditions.

2. Surgical Intervention

  • Drainage of abscesses.
  • Debridement of necrotic tissue.

3. Hyperbaric Oxygen Therapy

  • Effective for conditions like gas gangrene by increasing oxygen levels in tissues and killing obligate anaerobes.

Role of Anaerobes in Normal Flora

Anaerobes are an integral part of the human microbiome, contributing to:

  1. Digestion:
    • Breakdown of dietary fibers by Bacteroides in the gut.
  2. Immune Modulation:
    • Interaction with the host immune system to maintain balance.
  3. Competition with Pathogens:
    • Preventing colonization by harmful microbes.

Prevention of Anaerobic Infections

  1. Aseptic Techniques:
    • During surgeries and invasive procedures.
  2. Timely Wound Care:
    • Cleaning and dressing wounds to prevent anaerobic growth.
  3. Antibiotic Stewardship:
    • Rational use of antibiotics to avoid dysbiosis.
  4. Vaccination:
    • Tetanus toxoid vaccine for preventing C. tetani infections.

Significance in Microbiology

  • Clinical:
    • Anaerobes are major contributors to serious infections, particularly abscesses and post-surgical complications.
  • Industrial:
    • Some anaerobes are used in biotechnology and bioremediation (e.g., methane production by methanogens).
  • Research:
    • Studies on the human microbiome highlight the role of anaerobes in health and disease.
  • Cocci

Cocci in Microbiology

Cocci are spherical or oval-shaped bacteria. They can exist as single cells or in various arrangements depending on their pattern of division. Cocci include both Gram-positive and Gram-negative bacteria, many of which are significant in human health and disease.

Classification of Cocci

1. Based on Gram Staining

  1. Gram-Positive Cocci:
    • Retain the crystal violet stain and appear purple under a microscope.
    • Examples: Staphylococcus, Streptococcus, Enterococcus.
  2. Gram-Negative Cocci:
    • Do not retain the crystal violet stain and appear pink after counterstaining.
    • Examples: Neisseria, Moraxella.

2. Based on Arrangement

  1. Diplococci:
    • Cocci arranged in pairs.
    • Examples:
      • Streptococcus pneumoniae (Gram-positive).
      • Neisseria gonorrhoeae (Gram-negative).
  2. Streptococci:
    • Cocci arranged in chains.
    • Example: Streptococcus pyogenes.
  3. Staphylococci:
    • Cocci arranged in clusters (grape-like).
    • Example: Staphylococcus aureus.
  4. Tetrads:
    • Cocci arranged in groups of four.
    • Example: Micrococcus.
  5. Sarcinae:
    • Cocci arranged in cuboidal packets of eight.
    • Example: Sarcina.

Examples of Cocci

Gram-Positive Cocci

  1. Staphylococcus:
    • Staphylococcus aureus:
      • Causes skin infections, abscesses, pneumonia, and sepsis.
      • Produces toxins causing toxic shock syndrome and food poisoning.
    • Staphylococcus epidermidis:
      • Part of normal skin flora; associated with prosthetic device infections.
  2. Streptococcus:
    • Streptococcus pyogenes (Group A Streptococcus):
      • Causes pharyngitis, scarlet fever, rheumatic fever.
    • Streptococcus agalactiae (Group B Streptococcus):
      • Causes neonatal infections, meningitis.
    • Streptococcus pneumoniae:
      • Causes pneumonia, meningitis, otitis media.
  3. Enterococcus:
    • Enterococcus faecalis, Enterococcus faecium:
      • Part of the gastrointestinal flora.
      • Cause urinary tract infections (UTIs), endocarditis.

Gram-Negative Cocci

  1. Neisseria:
    • Neisseria gonorrhoeae:
      • Causes gonorrhea.
    • Neisseria meningitidis:
      • Causes meningitis and septicemia.
  2. Moraxella:
    • Moraxella catarrhalis:
      • Causes respiratory tract infections such as bronchitis and sinusitis.

Pathogenic Mechanisms of Cocci

  1. Adhesion:
    • Adhesion molecules allow cocci to attach to host tissues (e.g., S. aureus binds to fibrinogen).
  2. Invasion:
    • Enzymes such as hyaluronidase break down host barriers (S. pyogenes).
  3. Toxin Production:
    • S. aureus: Produces enterotoxins, exfoliative toxins.
    • S. pyogenes: Produces streptolysins causing cell lysis.
  4. Immune Evasion:
    • Capsules prevent phagocytosis (S. pneumoniae, N. meningitidis).
    • Protein A binds immunoglobulins (S. aureus).

Laboratory Identification of Cocci

1. Microscopy

  • Gram Staining:
    • Differentiates between Gram-positive and Gram-negative cocci.
  • Morphology:
    • Observe arrangements (clusters, chains, pairs).

2. Culture

  • Media:
    • Blood Agar: For Streptococcus and Staphylococcus.
    • Chocolate Agar: For Neisseria.
    • MacConkey Agar: For Gram-negative cocci.
  • Colony Characteristics:
    • Hemolysis on blood agar:
      • Beta-hemolysis (S. pyogenes).
      • Alpha-hemolysis (S. pneumoniae).

3. Biochemical Tests

  • Catalase Test:
    • Differentiates Staphylococcus (positive) from Streptococcus (negative).
  • Coagulase Test:
    • Differentiates S. aureus (positive) from other staphylococci.
  • Oxidase Test:
    • Identifies Neisseria (positive).

4. Molecular Methods

  • PCR for specific genes (e.g., mecA gene for MRSA).

Treatment of Coccal Infections

Gram-Positive Cocci

  1. Staphylococcus aureus:
    • Methicillin-sensitive (MSSA): Nafcillin or oxacillin.
    • Methicillin-resistant (MRSA): Vancomycin, linezolid.
  2. Streptococcus:
    • S. pyogenes: Penicillin.
    • S. pneumoniae: Penicillin or ceftriaxone.
  3. Enterococcus:
    • Ampicillin or vancomycin (depending on sensitivity).

Gram-Negative Cocci

  1. Neisseria gonorrhoeae:
    • Ceftriaxone with azithromycin or doxycycline.
  2. Neisseria meningitidis:
    • Penicillin or ceftriaxone.
  3. Moraxella catarrhalis:
    • Amoxicillin-clavulanate or a respiratory fluoroquinolone.

Prevention

  1. Vaccination:
    • S. pneumoniae: Pneumococcal vaccine.
    • N. meningitidis: Meningococcal vaccine.
  2. Hygiene:
    • Handwashing, proper wound care.
  3. Antibiotic Stewardship:
    • Rational use of antibiotics to prevent resistance.

Significance of Cocci

  • In Healthcare:
    • Major causes of hospital-acquired and community-acquired infections (e.g., MRSA).
  • In Public Health:
    • Outbreaks of meningitis caused by N. meningitidis.
  • In Research:
    • Understanding biofilm formation and antimicrobial resistance.
  • Spirochaete

Spirochaetes in Microbiology

Spirochaetes are a group of unique, slender, and spiral-shaped bacteria that are motile and Gram-negative. They are characterized by their helical shape and specialized motility due to periplasmic flagella. Spirochaetes are associated with a range of diseases in humans and animals.

Characteristics of Spirochaetes

  1. Morphology:
    • Slender, spiral-shaped bacteria.
    • Size: 6–20 µm in length, 0.1–0.5 µm in width.
    • Flexible cell wall.
  2. Motility:
    • Use endoflagella (periplasmic flagella) located between the cell wall and the outer membrane.
    • Corkscrew-like movement helps them penetrate viscous environments like mucus.
  3. Gram-Negative:
    • Outer membrane contains lipoproteins and lipopolysaccharides.
    • Do not stain well with Gram stain; often visualized using dark-field microscopy.
  4. Growth Conditions:
    • Fastidious; require specific conditions for growth.
    • Many are obligate parasites.

Examples of Spirochaetes

1. Treponema

  • Treponema pallidum: Causes syphilis.
  • Treponema pertenue: Causes yaws.
  • Treponema carateum: Causes pinta.

2. Borrelia

  • Borrelia burgdorferi: Causes Lyme disease.
  • Borrelia recurrentis: Causes relapsing fever.

3. Leptospira

  • Leptospira interrogans: Causes leptospirosis.

4. Others

  • Spirochaeta: Free-living in aquatic environments.
  • Brachyspira: Causes intestinal infections in animals.

Diseases Caused by Spirochaetes

1. Syphilis (Treponema pallidum)

  • Transmission: Sexual contact, vertical transmission (congenital syphilis).
  • Stages:
    • Primary: Painless ulcer (chancre) at infection site.
    • Secondary: Rash, lymphadenopathy, mucocutaneous lesions.
    • Tertiary: Cardiovascular syphilis, neurosyphilis, gummas.
  • Diagnosis:
    • Dark-field microscopy, serology (VDRL, RPR, FTA-ABS).
  • Treatment:
    • Penicillin G.

2. Lyme Disease (Borrelia burgdorferi)

  • Transmission: Ixodes tick bite.
  • Stages:
    • Early localized: Erythema migrans (bull’s-eye rash), fever.
    • Early disseminated: Neurological and cardiac symptoms.
    • Late: Arthritis, chronic neurological symptoms.
  • Diagnosis:
    • ELISA, Western blot, PCR.
  • Treatment:
    • Doxycycline or amoxicillin.

3. Relapsing Fever (Borrelia recurrentis)

  • Transmission: Louse-borne or tick-borne.
  • Symptoms: Recurrent episodes of fever, chills, headache.
  • Diagnosis:
    • Peripheral blood smear during febrile episodes.
  • Treatment:
    • Doxycycline or erythromycin.

4. Leptospirosis (Leptospira interrogans)

  • Transmission: Contact with contaminated water or animal urine.
  • Symptoms:
    • Mild: Fever, myalgia, conjunctival suffusion.
    • Severe (Weil’s disease): Jaundice, renal failure, hemorrhage.
  • Diagnosis:
    • Microscopic agglutination test (MAT), culture, PCR.
  • Treatment:
    • Doxycycline or penicillin.

Laboratory Diagnosis of Spirochaetes

  1. Microscopy:
    • Dark-Field Microscopy:
      • Used for direct visualization (e.g., T. pallidum in syphilis).
    • Silver Stain:
      • Highlights spirochaetes in tissue sections.
  2. Culture:
    • Requires specialized media (e.g., Barbour-Stoenner-Kelly medium for Borrelia).
    • Difficult and time-consuming.
  3. Serology:
    • Used for syphilis, Lyme disease, and leptospirosis.
    • Examples:
      • VDRL and RPR for syphilis.
      • ELISA and MAT for leptospirosis.
  4. Molecular Methods:
    • PCR: Detects specific DNA sequences for accurate diagnosis.

Treatment of Spirochaetal Infections

  • Antibiotics:
    • Penicillin: First-line treatment for syphilis.
    • Doxycycline: Effective for Lyme disease, leptospirosis.
    • Ceftriaxone: Used for severe or disseminated infections.
  • Jarisch-Herxheimer Reaction:
    • Acute febrile reaction following treatment, especially in syphilis and Lyme disease.

Prevention and Control

  1. Hygiene and Sanitation:
    • Avoid exposure to contaminated water (leptospirosis).
    • Practice safe sex to prevent syphilis.
  2. Vector Control:
    • Use of insect repellents and protective clothing to prevent tick bites (Lyme disease).
  3. Vaccination:
    • Available for leptospirosis in some regions.
  4. Public Awareness:
    • Education on recognizing symptoms and seeking timely medical attention.

Significance of Spirochaetes

  1. Medical Importance:
    • Cause significant morbidity and mortality globally.
  2. Research Applications:
    • Studied for their unique motility and immune evasion strategies.
  3. Public Health:
    • Surveillance and control programs for diseases like syphilis and leptospirosis.
  • Rickettsiae

Rickettsiae in Microbiology

Rickettsiae are a group of obligate intracellular, Gram-negative bacteria that cause a variety of zoonotic diseases in humans. They are transmitted primarily by arthropod vectors like ticks, lice, fleas, and mites. Rickettsial infections are significant for their potential to cause severe systemic illnesses.

Characteristics of Rickettsiae

  1. Morphology:
    • Small, pleomorphic Gram-negative coccobacilli.
    • Weakly Gram-staining; better visualized with Giemsa or Gimenez staining.
  2. Intracellular Lifestyle:
    • Obligate intracellular parasites; cannot replicate outside host cells.
    • Infect endothelial cells lining blood vessels, leading to vasculitis.
  3. Transmission:
    • Arthropod vectors (ticks, lice, fleas, mites) transmit rickettsiae to humans.
  4. Energy Dependence:
    • Lack full metabolic pathways; rely on host ATP and other metabolites.
  5. Growth Requirements:
    • Grown in cell cultures, embryonated eggs, or laboratory animals.

Classification of Rickettsiae

1. Based on Disease Groups

  1. Spotted Fever Group (SFG):
    • Causes spotted fever rickettsioses.
    • Examples:
      • Rickettsia rickettsii (Rocky Mountain spotted fever).
      • Rickettsia akari (Rickettsialpox).
  2. Typhus Group (TG):
    • Causes epidemic and endemic typhus.
    • Examples:
      • Rickettsia prowazekii (epidemic typhus).
      • Rickettsia typhi (endemic or murine typhus).
  3. Scrub Typhus Group:
    • Caused by Orientia tsutsugamushi.
    • Transmitted by chigger mites.

Diseases Caused by Rickettsiae

1. Spotted Fever Group

  • Rocky Mountain Spotted Fever (RMSF):
    • Causative Agent: Rickettsia rickettsii.
    • Vector: Ticks (Dermacentor species).
    • Symptoms:
      • Fever, headache, myalgia.
      • Rash beginning on wrists and ankles, spreading to the trunk and palms/soles.
    • Complications:
      • Vasculitis, multi-organ failure, death if untreated.
    • Treatment:
      • Doxycycline.
  • Rickettsialpox:
    • Causative Agent: Rickettsia akari.
    • Vector: Mites.
    • Symptoms:
      • Mild febrile illness with a papulovesicular rash.
    • Treatment:
      • Doxycycline.

2. Typhus Group

  • Epidemic Typhus:
    • Causative Agent: Rickettsia prowazekii.
    • Vector: Human body louse (Pediculus humanus).
    • Symptoms:
      • High fever, severe headache, rash (sparing palms and soles).
    • Complications:
      • Brill-Zinsser disease (relapsing form of typhus).
    • Treatment:
      • Doxycycline.
  • Endemic (Murine) Typhus:
    • Causative Agent: Rickettsia typhi.
    • Vector: Fleas (Xenopsylla cheopis).
    • Reservoir: Rodents.
    • Symptoms:
      • Fever, headache, rash (less severe than epidemic typhus).
    • Treatment:
      • Doxycycline.

3. Scrub Typhus

  • Causative Agent: Orientia tsutsugamushi.
  • Vector: Chigger mites.
  • Symptoms:
    • Fever, headache, lymphadenopathy.
    • Eschar at the bite site, maculopapular rash.
  • Complications:
    • Pneumonitis, myocarditis, meningoencephalitis.
  • Treatment:
    • Doxycycline or azithromycin.

Pathogenesis

  1. Invasion:
    • Rickettsiae invade endothelial cells of blood vessels.
  2. Replication:
    • Multiply within the cytoplasm or nucleus of host cells.
  3. Vascular Damage:
    • Cause vasculitis, leading to increased vascular permeability, edema, and hemorrhage.

Laboratory Diagnosis

  1. Specimen Collection:
    • Blood samples during febrile periods.
    • Biopsy of rash or eschar.
  2. Staining:
    • Giemsa or Gimenez staining to visualize rickettsiae.
  3. Serology:
    • Weil-Felix test (obsolete but still used in some regions).
    • Indirect immunofluorescence assay (IFA): Gold standard.
  4. Molecular Techniques:
    • PCR for specific rickettsial DNA.
  5. Culture:
    • Requires specialized cell culture systems.

Treatment

  1. First-Line Therapy:
    • Doxycycline is the drug of choice for all rickettsial infections.
  2. Alternatives:
    • Chloramphenicol (in specific cases such as pregnancy or allergy).
  3. Supportive Care:
    • Hydration, antipyretics, and management of complications.

Prevention and Control

  1. Vector Control:
    • Use insect repellents, tick removal, and rodent control.
  2. Personal Protection:
    • Wear protective clothing in endemic areas.
  3. Vaccination:
    • Limited to epidemic typhus in specific settings (e.g., military).
  4. Public Health Measures:
    • Surveillance and early treatment of cases to prevent outbreaks.

Significance in Microbiology

  1. Medical Importance:
    • Rickettsiae cause severe zoonotic diseases with significant morbidity and mortality.
  2. Research:
    • Study of obligate intracellular survival mechanisms.
  3. Epidemiology:
    • Monitoring outbreaks helps in public health interventions.
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Categorized as PBBSC FY MICROBIOLOGY, Uncategorised