Bacteria

Enterobacteriaceae

Gram-negative rods (bacilli)

Live in the gut but can cause disease

Shigella

Can cause HUS a serious kidney condition

caused by bacterial infection, often associated with diarrhea.

can produce shiga toxin

E. coli virulence factors (UTI)

• Fimbriae (P fimbriae)

• Hemolysin

• Biofilm formation

Fimbriae (P fimbriae)

Helps it stick to urinary tract lining like velcro

Hemolysin

Damages host cells

Biofilm formation

A process where bacteria adhere to surfaces and form protective layers, enhancing survival and resistance to antibiotics.

Vibrio species

• Gram negative curved rods (comma-shaped)

• Grow on TCBS agar (green or yellow)

• Require salt- like seawater

• Cause cholera, gastroenteritis, or wound infections

Listeria Monocytogenes

• Gram positive rod

• Can grow in cold (refrigerated food)

• Spreads to cell-to-cell without leaving the host cell, helping it evade immune system

• Differentiate from S.agalactiae ( group B strep) using motility (Listeria is motile) and CAMP test

Corynebacterium diptheriae

• Club shaped gram positive rod

• Causes diptheria: sore throat, bull neck, thick gray pseudomembrane in the throat, and tachycardia

• Toxin blocks protein synthesis by inactivating EF-2 —> cell death.

Streptococci

• Gram + cocci, from chains

• Catalase-negative (unlike Staph)

• Fermentative metabolism producing lactic acid

• Can cause various infections like strep throat and pneumonia.

Hemolysis on blood agar

• Alpha (greenish, partial) e.g. S. pneumoniae

• Beta (clear, complete) e,g. S. pyogenes

• Gamma (none) e,g, Entercoccus

Bacitracin sensitivity

S. pyogenes is sensitive ( used to differentiate from others)

Staphylocci

• Gram + cocci, typically found in clusters. They can be catalase-positive (bubbles with hydrogen peroxide) and are known for causing skin infections, food poisoning, and more.

Tests for differentation

Blood agar: shows hemolysis

Baird- Parker agar: black colonies with halos = S. aureus

Mannitol salt sugar: S. aureus turns yellow (ferments mannitol), others stay pink

Coagulase Test

• A test used to differentiate between Staphylococcus aureus, which is coagulase-positive (forms clots), and other staphylococci, which are coagulase-negative.

Mycobacterium

• Acid-fast staining (due to mycolic acid in wall)

• Slow growers

• Causes granulomas: immune system tries to wall them off in the lungs like a biological prison

Latent TB

bacteria present but inactive; no symptoms; not contagious. Can reactivate later.

Primary TB

Active, contagious lung infection caused by Mycobacterium tuberculosis.

Secondary TB

A reactivation of latent tuberculosis, leading to active disease often in individuals with weakened immunity.

Miliary TB

Mycobacterium tuberculosis spreads through the bloodstream, affecting multiple organs and often presenting with systemic symptoms.

TST (Tuberculin Skin Test) or QuantiFERON Gold

Positive in infection, but may be false-negative in HIV patients due to low immune response

MAC (Mycobacterium avium complex)

a group of bacteria that can cause pulmonary disease, particularly in individuals with weakened immune systems, often associated with HIV/AIDS.

Histoplasma capsulatum

• Mimics TB in clinical signs (fever, cough, weight loss)

• Negative TST/QuantiFERON

  • Spread by spores in bird/bat droppings (Ohio/MS River Valleys)

Plasmodium spp. (malaria)

• Causes fevers, chills

• Transmitted by female anopheles mosquitoes

• blood smear shows ring stage trophozoites

Leishmania spp.

• Causes cutaneous ulcers with raised edges- “volcano sign.”

• Transmitted by sand fly

Borrelia burgdorferi (lyme disease)

• bullseye rash (erytheme migrans)

• Spread by ticks

• Causes fever, joint pain, and can affect the heart or nerves if untreated.

Clostridia

• Gram +, anaerobic rods

  • Form spores- super resistant

C. tetani

• tetanus, causes spastic paralysis (muscles locked)

• Transmitted through wounds, leading to muscle stiffness and spasms.

C. botulinum

• botulism, flaccid paralysis (floppy muscles)

• caused by a neurotoxin produced by the bacterium, often found in improperly preserved foods.

C. difficile

• causes antibiotic-associated diarrhea and colitis. It produces toxins that disrupt intestinal function, often after antibiotic treatment.

• TcdA & TcdB

C, perfringens

• causes gas gangrene and food poisoning, producing toxins that can damage tissues. Often associated with contaminated wounds or improperly cooked meats.

Atypical Pneumonia

• Caused by Mycoplasma pneumoniae and Chlamydophila pnemoniae

• “walking pneumonia” - milder, slow-onset symptoms: dry cough, fever, fatigue often affecting younger populations and those with weakened immune systems.

Gram- positive

• These bacteria have a thick wall made of petidoglycan that retains the violet stain used in the Gram staining procedure, appearing purple under a microscope.

Examples: Staphylococcus and Streptococcus.

Gram- negative

• These have a thin peptidoglycan layer and do not retain the crystal violet stain, appearing pink/red under a microscope.

• Examples: Escherichia coli and Salmonella.

Acid Stain Fast

Used for mycobacterium species (like TB). These bacteria have waxy, lipid rich walls.

Coccus

• Round like a ball, often found in clusters or chains.

Examples: Staphylococci and streptococci.

Bacillus

• rod-shaped like a pill

Examples: Bacillus and Clostridium and E. coli

Vibrio

• comma-shaped bacteria, often found in water.

Examples: Vibrio cholera and Vibrio parahaemolyticus.

Spirochete

• spiral like a corkscrew

Examples: Treponema and Borrelia.

Pleomorphic

• shape-shifters; they can have more than one shape

Examples: Mycoplasma and Corynebacterium.

Plasma Membrane

• a selective barrier that surrounds the cell, controlling the movement of substances in and out.

Peptidoglycan layer

• a rigid layer that gives structural support to bacterial cell walls. It’s what gives bacteria their shape and strength

Periplasm

• Only in gram negative. A gel like space where enzymes and transport proteins hang out

Outer membrane

• gram negative only includes LPS (endotoxin) which can cause fever/shock and porins which are like pores/doorways

Capsule

• a protective outer layer found in many bacteria that helps to prevent phagocytosis and can assist in adherence to surfaces.

Sex pilus

A hair-like structure used by bacteria to attach to surfaces and facilitate genetic exchange through conjugation.

Flagella

Long, whip-like structures that enable bacteria to move through fluid environments.

Spores

• A resistant structure formed by some bacteria under adverse conditions, allowing for survival during unfavorable environments.

Beta- Lactams (penicillins, cephalosporins)

• Target the peptidoglycan synthesis in bacterial cell walls, disrupting their formation and leading to cell lysis.

Rifampin

• An antibiotic that inhibits RNA synthesis in bacteria by binding to RNA polymerase, effectively blocking transcription = no new proteins

Tetracyclines, Aminoglycosides, Chloramphenicol, Erythromycin

• Classes of antibiotics that inhibit bacterial protein synthesis, affecting various stages of translation in ribosomes.

Vancomycin

• A glycopeptide antibiotic that inhibits cell wall synthesis in bacteria by preventing cross-linking of peptidoglycan, particularly effective against Gram-positive bacteria.

Fluroquinolones

• A class of antibiotics that inhibit bacterial DNA gyrase and topoisomerase IV, disrupting DNA replication and repair, making them effective against a broad range of Gram-negative and Gram-positive bacteria.

Trimethoprim/Sulfa

• A combination antibiotic that inhibits bacterial folic acid synthesis by blocking different steps in the metabolic pathway, effective against various bacterial infections.

MIC

• Minimum inhibitory concentration, the lowest concentration of an antibiotic that prevents visible growth of a bacterium.

Example: It is an important measure in determining the effectiveness of an antibiotic against a specific bacteria.

Innate Immunity

• First responders, always on duty

• Not specific responds to general threats (patterns like flagella or peptiodglycan)

• Cells: Marcophages, Neutrophils, Dendritic cells

• Act fast and coordinate with adaptive immunity. It includes barriers like skin and mucous membranes.

Adaptive Immunity

• Shows up later (after innate response)

• Highly specific- targets on exact pathogen

• Memory cells give lifelong protection

• Produces antibodies (immunoglobins)

B Cells

• made in bone marrow

• differentiates into plasma and memory b cells

Plasma Cells

• Specialized B cells that produce antibodies specific to antigens. They play a crucial role in the humoral immune response and help eliminate pathogens.

Memory B cells

• Long-lived B cells that remember past infections and can quickly produce antibodies upon re-exposure to the same antigen. They are essential for long-term immunity.

IgG

a type of antibody that provides the majority of antibody-based immunity against invading pathogens.

IgA

found in mucosal areas like saliva, tears, and gut

IgM

• first responder antibody

IgE

allergy and parasites

IgD

• Not well understood, helps B cell activation

T cells

Made in bone marrows and mature in thymus

• crucial for adaptive immunity

Helper T cells (CD4+)

a type of T cell that plays a vital role in orchestrating the immune response by activating other immune cells.

Cytotoxic T cells (CD8+)

a type of T cell that directly kills virus-infected cells and cancer cells, playing a key role in the immune response.

Regulatory T cells

a type of T cell that helps maintain tolerance to self-antigens and prevents autoimmune responses, thereby modulating the immune system.

Complement Pathway

a series of proteins in the blood that enhance the ability of antibodies and phagocytic cells to clear pathogens from an organism. It plays a crucial role in the immune response.

Oponsization

the process by which pathogens are marked for destruction by antibodies or complement proteins, enhancing their recognition and uptake by phagocytic cells.

Chemotaxis

the movement of cells toward or away from chemical signals, often guiding immune cells to sites of infection or inflammation.

Lysis

the process of breaking down or destroying cells, often through the action of antibodies or complement proteins.

Agglutination

the clumping together of particles, such as bacteria or red blood cells, typically due to the binding of antibodies.