histo lesson 5

Bacteria and Disease

  • Overview of Bacteria

    • Bacteria are ubiquitous, found in various environments including:

    • Air

    • Water

    • Food

    • Soil

    • Deep oceans

    • Volcanic environments

    • Highest mountain peaks

  • Characteristics of Bacteria

    • Bacteria are classified as prokaryotes, meaning they:

    • Lack a true nucleus

    • Lack membrane-bound organelles

Normal Bacterial Flora

  • Definition & Role

    • The human body hosts many beneficial bacteria, specifically in the:

    • Digestive (gastrointestinal) system

    • Functions of normal bacterial flora include:

    • Controlling the growth of pathogenic bacteria

    • Supporting the immune system to prevent infections

    • Producing enzymes that aid food breakdown, enhancing nutrient absorption

  • Locations of Bacteria

    • Different types of bacteria colonize various body sites including:

    • Skin

    • Mouth

    • Respiratory tract

    • Gastrointestinal tract

    • Genitourinary tract

  • Terminology

    • Bacteria that reside on or in the human body without causing disease are termed:

    • Colonizing bacteria

    • Normal bacterial flora

Opportunistic Pathogens

  • Definition

    • Microorganisms that usually do not cause disease in healthy individuals

    • Entry into the Body

      • Can enter through cuts, wounds, or injuries breaking the skin barrier

  • When Diseases Occur

    • Disease is likely when:

    • Immune system is weakened

    • Normal body barriers are compromised

  • Example

    • Staphylococcus aureus:

    • Commonly found on the skin, part of normal flora

    • Post skin barrier compromise (e.g., cut), it can cause localized infections (e.g., wound infection, abscess)

Pathogens

  • Definition

    • Microorganisms capable of causing disease in humans

    • Disease onset can occur when:

      • Immune system is weakened

      • Normal body defenses are compromised

  • Routes of Entry

    • Pathogenic bacteria can enter through:

    • Food

    • Water

    • Air

    • Saliva

    • Blood and other body fluids

  • Example of Pathogenic Bacteria

    • Salmonella:

    • Transmitted via contaminated food or water

    • Can cause gastrointestinal illness characterized by:

      • Diarrhea

      • Abdominal cramps

      • Fever

Examples of Pathogenic Bacteria Causing Disease

  • Streptococcus

    • Commonly found in the human body with both harmless and pathogenic strains

    • Pathogenic Example:

    • Streptococcus pyogenes (Group A Streptococcus)

      • Causes bacterial pharyngitis (strep throat)

      • Complications if untreated:

      • Rheumatic fever

      • Glomerulonephritis

      • Other infections:

      • Impetigo

      • Necrotizing fasciitis (flesh-eating disease)

  • Staphylococcus

    • Commonly found on skin and in the nose

    • Staphylococcus aureus:

    • Main strain causing disease

    • Infections include:

      • Boils

      • Impetigo

      • Folliculitis

      • Severe infections (e.g., pneumonia, septicemia)

      • Toxins leading to food poisoning and toxic shock syndrome

Additional Examples of Pathogenic Diseases

  • Gonorrhea

    • Caused by Neisseria gonorrhoeae (sexually transmitted)

  • Diarrhea / Enteritis

    • Inflammation of intestines leading to diarrhea and abdominal discomfort, caused by various pathogens

  • Ear Infections

    • Affect outer, middle, or inner ear caused by bacteria or viruses

  • Dysentery

    • Intestinal infection causing bloody or mucous diarrhea with symptoms of painful abdominal cramps, nausea, and vomiting

  • Septicaemia

    • Serious bloodstream infection, potentially leading to sepsis

Other Diseases Caused by Toxins

  • Toxicosis

    • Disease caused by bacterial toxins rather than bacteria itself

    • Caused by certain species including:

      • Staphylococcus

      • Clostridium botulinum

      • Other Clostridium species

  • Rocky Mountain Spotted Fever

    • A tick-borne disease caused by Rickettsia rickettsii

  • Botulism

    • Severe paralytic illness from botulinum toxin of Clostridium botulinum

  • Meningitis

    • Inflammation of meninges due to various pathogens (bacterial, viral, fungal)

  • Tetanus

    • Toxin-mediated disease by Clostridium tetani, causing muscle rigidity and spasms

Intracellular vs Extracellular Organisms

  • Intracellular Organisms

    • Live within host cells

    • Types:

      1. Obligate intracellular

      • Can only survive inside cells

      • Examples: Viruses, Intracellular bacteria (e.g., Chlamydia, Rickettsia)

      1. Facultative intracellular

      • Can live inside or outside cells

      • Can survive without host cells

  • Extracellular Organisms

    • Live outside of cells

  • Most bacteria fall into the extracellular category.

Main Body Sites for Normal Bacterial Flora

  • Skins

    • Especially in moist areas like the groin and between toes

  • Eyes

  • Respiratory tract

    • Nose, mouth, and throat

  • Urinary tract

    • Upper urinary tract: kidneys and ureters

    • Lower urinary tract: bladder and urethra

  • Digestive (gastrointestinal) tract

    • Includes mouth, pharynx, esophagus, stomach, small intestine, large intestine, rectum, and anus

Normal Flora of the Digestive Tract

  • Stomach

    • Very few bacteria due to high acidity

  • Small Intestine

    • Contains limited numbers of bacteria

    • Common organisms include:

    • Streptococci

    • Lactobacilli

    • Yeasts (especially Candida albicans)

  • Large Intestine (Colon)

    • Primary site of bacteria in the body

    • High volume of normal feces comprises bacteria from the colon

    • Notable bacteria groups:

    • Bacteroides

    • Bifidobacterium

    • Eubacterium

    • Coliforms (e.g., E. coli, Proteus, Klebsiella, Enterobacter)

    • Streptococcus

    • Lactobacillus

    • Clostridium

  • The digestive tract hosts both gram-positive and gram-negative bacteria.

The Body’s Relationship with Bacteria

  • Symbiotic Relationships

    • Different types of relationships exist between normal bacterial flora and the human body.

1. Mutualism

  • Both host and microorganism benefit.

  • Example: Escherichia coli (E. coli)

    • Resides in intestines, receiving nutrients and habitat.

    • Produces Vitamin K for the host, essential for normal blood clotting (hemostasis).

2. Commensalism

  • One organism benefits while the other is neither helped nor harmed.

  • Example:

    • Staphylococcus epidermidis

    • Lives on skin, feeds on dead skin cells without causing harm

3. Parasitism

  • One organism benefits at the host’s expense.

  • Potential levels of host harm range from mild illness to severe disease.

  • Parasites can be:

    • Ectoparasites (live on host’s body)

    • Endoparasites (live inside host)

  • Examples: Ticks, Lice, Tapeworms

Pathogenic Relationships

  • Pathogenicity

    • Occurs when a microorganism causes damage to the host during infection.

    • Pathogens can cause disease in otherwise healthy individuals.

Opportunistic Pathogens

  • Cause disease when the host is immunocompromised or when barriers are breached.

  • Situational triggers include:

    • Destruction of normal flora (e.g., by antibiotics)

    • Immunosuppression from medications or illnesses

  • Example: Clostridioides difficile (C. difficile)

    • Can overgrow after antibiotic treatment, leading to severe diarrhea and colitis

Mutualist Relationship Benefits

  • Most normal flora have mutualistic relationships with the human host.

    • Bacteria benefit from a conducive environment to live and multiply.

    • Benefits to the Human Host include:

    • Improved nutrition and digestion

    • Production of vitamins (e.g., Vitamin B, Vitamin K)

    • Breakdown of indigestible food components into absorbable forms

How Normal Flora Protect the Host from Infection

  • Normal bacterial flora protect the body from pathogenic organisms in several ways:

    • Occupying Space

    • Fill available niches, making it difficult for pathogens to adhere and proliferate.

    • Competing for Nutrients

    • Utilize available nutrients, outcompeting invading pathogens and preventing their multiplication.

    • Producing Antibacterial Substances

    • Some normal flora produce chemicals inhibiting or killing harmful microorganisms.

Are Normal Flora Always Beneficial?

  • No, Not Always

    • Normal flora are beneficial when remaining in their usual body sites.

    • When they enter different sites or if the immune system is compromised, they may act as opportunistic pathogens.

    • Example: E. coli

    • Normal flora in the intestine but can cause urinary tract infections if it enters the urinary tract.

Normally Sterile Body Sites

  • Definition of Normally Sterile Sites

    • Areas of the body that should not contain microorganisms.

    • Presence of bacteria in these sites typically indicates infection.

    • Examples of Normally Sterile Sites:

    • Blood

    • Cerebrospinal fluid (CSF)

    • Pleural fluid

    • Chest fluid

    • Thoracentesis fluid

    • Peritoneal fluid

    • Ascites

    • Pericardial fluid

    • Bone and bone marrow

    • Synovial fluid (in joints)

    • Internal organs