PATHOGENS TO KNOW

Mycobacterium tuberculosis

Acid-fast rod (special stain, not classic Gram, but technically weakly Gram-positive).

Type: Bacteria;

Disease: Tuberculosis (TB) — usually in lungs, can spread elsewhere;

Diagnosis: Chronic cough (sometimes with blood), chest X-ray, TB skin test, lab tests on sputum

Treatment/Prevention: Long course of antibiotics (isoniazid + rifampin, etc.); BCG vaccine used in some countries;

Spread/Unique: Airborne droplets; waxy cell wall makes it very tough and able to stay dormant (latent TB).

Bacillus anthracis

Purple rods (Gram-positive bacillus, often in long chains).

Type: Bacteria;

Disease: Anthrax (skin sores, lung infection, or GI infection);

Diagnosis: Lab culture, PCR, chest X-ray (for inhaled anthrax);

Treatment/Prevention: vaccine

Spread/Unique: Spore-forming (can survive decades in soil); found in livestock; potential bioterror agent.

Yersinia pestis

Pink rods (Gram-negative bacillus, often safety-pin appearance).

Type: Bacteria;

Disease: Plague (bubonic, septicemic, pneumonic);

Diagnosis: Swollen lymph nodes (buboes), fever, blood/sputum culture, rapid test; Treatment/Prevention: Streptomycin, doxycycline; isolate pneumonic cases; flea control;

Spread/Unique: Rodents are reservoir; fleas spread it; respiratory droplets for pneumonic plague.

Treponema pallidum

Spirochete, Gram stain doesn’t show well (seen by dark-field microscopy). should be colorless its consider gram neg so could be pink

Type: Bacteria (spirochete = spiral-shaped); Disease: Syphilis (stages: sores → rash → hidden → damage to heart/brain);

Diagnosis: Microscopy of sores, blood tests (VDRL, RPR);

Treatment/Prevention: Penicillin G; safe sex; prenatal screening;

Spread/Unique: Human-only; sexually transmitted or through pregnancy; no vaccine.

Rickettsia rickettsii

Tiny pink rods (Gram-negative coccobacilli, hard to see with Gram stain).

Type: Bacteria (lives inside cells); Disease: Rocky Mountain Spotted Fever (RMSF); Diagnosis: Fever, rash (starts on wrists/ankles), blood tests (PCR, serology); Treatment/Prevention: Doxycycline; tick avoidance; Spread/Unique: Spread by ticks; damages blood vessels → rash + organ damage.

Plasmodium falciparum

NOT bacteria; Protozoan parasite in red blood cells; seen by Giemsa stain, not Gram.

Type: Protozoan parasite;

Disease: Malaria (most deadly type);

Diagnosis: Blood smear (look for parasite in red blood cells), rapid tests;

Treatment/Prevention: Artemisinin-based drugs; mosquito nets; vaccine exists but limited;

Spread/Unique: Carried by Anopheles mosquitoes; high resistance to drugs.

Clostridium botulinum

Purple rods (Gram-positive bacillus, spore-forming).

Type: Bacteria (anaerobic, spore-forming);

Disease: Botulism (flaccid paralysis → can't move muscles);

Diagnosis: Symptoms (blurred vision, weakness), toxin tests;

Treatment/Prevention: Antitoxin + supportive care; avoid giving honey to infants; proper food canning;

Spread/Unique: Produces botulinum toxin, the most powerful natural toxin — blocks nerve signals.

Clostridium difficile

Purple rods (Gram-positive bacillus, spore-forming).

Type: Bacteria (spore-forming);

Disease: Antibiotic-associated diarrhea / pseudomembranous colitis;

Diagnosis: Stool toxin tests, PCR, colonoscopy (shows pseudomembranes);

Treatment/Prevention: Oral vancomycin; fecal transplant for repeat cases; careful antibiotic use;

Spread/Unique: Hospital-acquired; spores survive on surfaces; linked to long antibiotic use.

Legionella pneumophila

Pink rods (Gram-negative bacillus (round), stains faintly).

Type: Bacteria; Disease: Legionnaires' disease (severe pneumonia) or Pontiac fever (milder);

Diagnosis: Urine antigen test, special culture (BCYE agar), chest X-ray;

Treatment/Prevention: Macrolides or fluoroquinolones; disinfect water systems;

Spread/Unique: Lives in warm water (AC, fountains); spread by inhaling mist (not person-to-person).

Vibrio cholerae

Pink curved rods (Gram-negative comma-shaped bacilli).

Type: Bacteria;

Disease: Cholera (severe watery diarrhea, "rice water stools");

Diagnosis: Stool culture, rapid test, symptoms of dehydration;

Treatment/Prevention: Oral rehydration, IV fluids, doxycycline; vaccines available;

Spread/Unique: Contaminated water/food; produces cholera toxin → massive water loss from intestines.

Salmonella enterica

Pink rods (Gram-negative bacillus).

Type: Bacteria;

Disease: Food poisoning (gastroenteritis);

Diagnosis: Stool culture, PCR;

Treatment/Prevention: Usually self-limiting; fluids/electrolytes; antibiotics only in severe cases; Spread/Unique: From poultry, eggs, reptiles; fecal-oral spread.

Salmonella typhi

Pink rods (Gram-negative bacillus).

Type: Bacteria (S. enterica serovar Typhi);

Disease: Typhoid fever;

Diagnosis: Blood culture early, stool/urine later; Widal test;

Treatment/Prevention: Fluoroquinolones, ceftriaxone; vaccines; sanitation;

Spread/Unique: Human-only; spreads through contaminated food/water; can hide in gallbladder (carriers).

Neisseria gonorrhoeae

Pink diplococci (Gram-negative bacteria pairs of round cells).

It causes gonorrhea, a sexually transmitted infection.

Diagnosis is made through clinical symptoms such as genital discharge and dysuria, along with laboratory tests like NAATs or Gram stain.

Treatment is usually with ceftriaxone, and condoms help prevent infection.

It is unique because it only infects humans, shows high antigenic variation, and is becoming resistant to antibiotics.

Borrelia burgdorferi

is a spirochete bacterium that causes Lyme disease.

Spirochete, Gram stain not reliable (seen by dark-field or Giemsa).

It is identified through symptoms such as the bull's-eye rash, joint pain, and fatigue, confirmed by ELISA and Western blot testing.

Early disease is treated with doxycycline or amoxicillin, and severe cases may need intravenous ceftriaxone.

The infection is transmitted by Ixodes ticks, with mice as reservoirs and deer as tick hosts, and it adapts by changing its surface proteins.

Mycobacterium leprae

is an acid-fast rod-shaped bacterium that causes leprosy, also known as Hansen's disease.

Acid-fast rod, shows red with Ziehl–Neelsen stain (not clear purple/pink with Gram).

Diagnosis is based on skin lesions with sensory loss, nerve thickening, and confirmation by acid-fast staining or biopsy.

Treatment requires multidrug therapy with dapsone, rifampicin, and clofazimine for many months.

This pathogen is unusual because it cannot be cultured on artificial media, has a very long incubation period, and spreads mainly through prolonged respiratory contact.