Comprehensive study notes on bacterial and viral pathogens affecting skin, respiratory, and urogenital systems

Comprehensive notes on bacterial and viral pathogens affecting skin, respiratory, and urogenital systems

Bacillus anthracis

Bacillus anthracis is a bacterium in the genus Bacillus and is an endospore former
Endospores are highly resistant to heat, chemicals, and drying
Most common form of anthrax is cutaneous, but can also be inhaled (pulmonary) or ingested (gastrointestinal) via respiratory or digestive systems
Endospores can be aerosolized or powdered, enabling potential use as a biological weapon
Transmission pathways:
- Contact with infected animals or soil contaminated with animal feces
Vaccination:
- High-risk individuals can receive a vaccine, but it is not routine in the United States
Pulmonary (inhalational) anthrax mortality if untreated is extremely high; even with treatment, mortality remains significant: 85\% untreated and 45\% with treatment

Clostridium perfringens

Endospore-forming, anaerobic bacterium
Causes gas gangrene by invading necrotic tissue and releasing gas and tissue-destroying enzymes in low-oxygen environments
Also implicated in foodborne illnesses discussed later in the material
Transmission often linked to poor hand hygiene or contaminated wounds

Propionibacterium acnes (Propionibacterium acnes; normal skin microbiota)

Part of normal skin microbiota
Grows on the skin; sebaceous glands produce sebum that supports growth
Causes inflammation leading to acne, especially during puberty when oil glands are more active
Not transmissible between people
Management approaches to control inflammation include reducing oil production with medications, birth control pills, or UV light exposure; as oil gland activity decreases, acne typically improves

Staphylococcus aureus

Significant healthcare-associated pathogen; part of normal skin microbiota
Provides some protective effects as part of the microbiota but can become an opportunistic pathogen when it gains access to deeper tissues
Common reservoir includes the nasal cavity
Localized skin infections: skin lesions, wound infections from trauma or surgery, cellulitis, impetigo, and scalded skin syndrome
Can disseminate to cause more serious infections: pneumonia, endocarditis, toxic shock syndrome, septicemia
MRSA: methicillin-resistant Staphylococcus aureus, a healthcare-associated resistant strain; transmission often via direct contact due to inadequate hand hygiene

Streptococcus pyogenes

Also known as Group A Streptococcus; not typically part of normal microbiota, though carrier states exist (asymptomatic carriage)
Common disease: strep throat
Skin infections: impetigo, erysipelas, cellulitis; can cause necrotizing fasciitis
Severe sequelae if untreated: rheumatic fever, glomerulonephritis, toxic shock syndrome
Generally antibiotic-sensitive in many settings (no widespread resistance highlighted in the transcript)

Escherichia coli

Normal inhabitant of the large intestine
When introduced into the urinary tract, can ascend to cause cystitis (bladder infection)
Can also cause pyelonephritis or glomerulonephritis if it ascends to kidneys
Typically spread via self-inoculation; not usually transmitted person-to-person in the same way as some other pathogens

Chlamydia trachomatis

Common sexually transmitted disease (STD); can be asymptomatic or mild
Major cause of non-gonococcal urethritis; can be associated with neonatal conjunctivitis if an infected mother passes through the birth canal
Eye infections in newborns can occur; can cause conjunctivitis and trachoma (leading cause of blindness worldwide, though rare in the United States)
Trachoma involves inward-turning eyelashes that scratch the cornea, potentially causing ulcers

Moraxella catarrhalis

Considered part of the normal microbiota of the upper respiratory tract, especially in children
Can contribute to middle ear infections (otitis media) in the context of upper respiratory infections

Bordetella pertussis

Causative agent of whooping cough
Vaccination via DTaP (or Tdap for older individuals) has reduced incidence in many settings
Highly concerning in unvaccinated or incompletely vaccinated infants, where airway obstruction and respiratory distress can be life-threatening
Transmission via droplets (coughing, sneezing, or respiratory secretions)

Corynebacterium diphtheriae

Toxin-forming and non-toxin-forming variants
Causes diphtheria; historically significant but now rare in The United States due to vaccination
Infection can cover the back of the throat with toxin, causing airway obstruction, particularly in very young children
Vaccination is provided by DPT or DTaP

Haemophilus influenzae

Common pathogen in children; Hib vaccine (conjugate) reduces disease
Can cause pneumonia, meningitis, otitis media, sinusitis, and epiglottitis
Most severe disease typically occurs in children under five years old; vaccination reduces incidence with age

Klebsiella pneumoniae

Encapsulated bacterium; capsule is a major virulence factor
Common nosocomial cause of pneumonia; also associated with urinary tract infections and skin infections
Notable for high levels of antibiotic resistance; underscores the importance of stringent hand hygiene in healthcare settings

Legionella pneumophila

Not transmitted person-to-person; acquired via inhalation of contaminated aerosols
Causes Legionnaires' disease (more severe) and Pontiac fever (milder)
Often associated with water systems (air conditioning, hot water systems); risk increases with poor maintenance and exposure to aerosolized water
Classified as an opportunistic pathogen; higher risk in smokers or those with respiratory problems

Mycobacterium tuberculosis

Acid-fast bacterium with a waxy cell wall that resists phagocytic clearance
TB infection diagnosed with a TB skin test (PPD) and chest imaging to assess pulmonary involvement
Strong association with AIDS; endemic in various world regions; a vaccine exists outside The United States, but not routinely used domestically in the U.S.
Tuberculosis is increasingly drug-resistant, making treatment more challenging and contributing to ongoing interest in TB as a pathogen of concern

Mycoplasma pneumoniae

Lacks a cell wall, so typical antibiotics targeting peptidoglycan are ineffective
Causes atypical or “walking” pneumonia, often milder but can spread in crowded environments (nursing homes, college dorms)
Treatment may require antibiotics that target other aspects of bacterial physiology; some patients may recover without antibiotics, particularly younger individuals

Pseudomonas aeruginosa

Opportunistic pathogen and common nosocomial (hospital-acquired) infection
Can infect lungs (pneumonia), skin, and external ear; often associated with patients in hospitals, ventilated, or with tubes (e.g., tracheostomy)
Forms biofilms and can be highly resistant to antibiotics; treatment can be difficult
Hand hygiene is critical to prevent spread in healthcare settings

Streptococcus pneumoniae

Encapsulated bacterium; major cause of community-acquired pneumonia
Capsule provides resistance to phagocytosis; increases virulence
Can spread to cause meningitis if bacteremia occurs
Vaccines exist: a pneumococcal subunit vaccine and a conjugate vaccine

Enterococcus faecalis

Normal microbiota of the large intestine
Can cause bladder infections and ascend the urinary tract to cause pyelonephritis
Like E. coli, prevention relies on proper hand hygiene and self-care to prevent infection

Neisseria gonorrhoeae

Causative agent of gonorrhea; differences in presentation between men and women (men: dysuria; women: pelvic pain and risk of PID)
Most common cause of gonococcal urethritis
Treatment with antibiotics but escalating antibiotic resistance via antigenic variation complicates management

Treponema pallidum

Causative agent of syphilis
Three stages: primary (painless chancre), secondary (rash on skin/mucous membranes), and tertiary (heart and CNS damage)
Very treatable with antibiotics; regular screening is key to early detection

Parvoviruses (Parvovirus B19)

Causes fifth disease (fifth's disease) with slapped-cheek rash in children; adults may have joint pain or anemia
Contagious via droplets; many infections are asymptomatic
No specific antiviral treatment; management is supportive care

Herpesviruses

Herpes simplex virus 1 (HSV-1): oral herpes, fever blisters; can cause herpes keratitis (eye infection); latent infection with possible reactivation
- Acyclovir can shorten duration but is not a cure for oral herpes
Herpes simplex virus 2 (HSV-2): genital herpes; can be transmitted via birth canal; virus can be shed even without active lesions
- Acyclovir used to treat outbreaks and reduce duration; no cure

Human papillomavirus (HPV)

>200 strains; about 14 high-risk strains
High-risk strains 16 and 18 are responsible for a majority of HPV-associated cancers
Diseases include genital warts and cancers (cervical, oropharyngeal, anal, vaginal, vulvar, penile)
Transmission through direct contact; wart removal does not cure the infection, but clears visible lesions; infection may resolve spontaneously in some cases

Human herpesvirus 6 (HHV-6)

Causes roseola (also called exanthem subitum)
Common in children; fever with a body-wide rash that spreads from trunk to face and extremities
Transmission via respiratory secretions; treatment is supportive care

Viral conjunctivitis

Caused by various viruses (adenoviruses, rhinoviruses, coronaviruses, and others)
Presents as pink eye with watery discharge (vs. bacterial conjunctivitis, which may have more purulent discharge)
No specific antiviral treatment; prevention and hand hygiene are key

Coxsackievirus (hand, foot, and mouth disease)

Also called hand, foot, and mouth disease (Kosaki virus is a mis-spelling in the transcript)
Common in children; fever, sore throat, and distinctive rash on hands and feet, sometimes painful
Complications can include dehydration; treatment is supportive

Varicella-zoster virus (VZV)

Varicella (chickenpox): vesicular rash, fever, headache, malaise; transmission via respiratory secretions and contact with rash
Varicella vaccine protects children from chickenpox
Latency allows reactivation as shingles (herpes zoster) in adults; shingles vaccine protects against reactivation
No specific antiviral for chickenpox; shingles pain can be treated with neuropathic pain agents (e.g., gabapentin/Neurontin) and sometimes antidepressants

Respiratory viruses and common cold

Common cold caused by >200 viruses; major groups include adenoviruses, coronaviruses, rhinoviruses
Symptoms: mild fever, headache, aches, fatigue, nasal congestion, sneezing; typically 1–2 weeks
No targeted antiviral treatment; management is supportive care

Influenza viruses

Types A, B, and C; subtypes include N1 and H1 among others
Flu vs. cold: flu generally has higher fever, more severe headache and body aches, and greater fatigue
Transmission via respiratory droplets or contact with secretions
Vaccination available; prevention includes hand hygiene and avoiding contact with sick individuals; cover coughs/sneezes
Antiviral medications (neuraminidase inhibitors) can reduce duration if given early, ideally within the first 48 hours

Measles (Rubeola) and Rubella (German measles)

Measles (rubeola): red rash with Koplik spots (early sign inside the cheek); can cause pneumonia or encephalitis; may be fatal in rare cases; highly vaccine-preventable via MMR
Rubella: milder rash and fever; but dangerous for pregnant women because rubella can cross the placenta and cause congenital defects (congenital rubella syndrome)
Vaccination: MMR vaccine covers measles, mumps, and rubella; rubella is particularly monitored due to fetal risks

Respiratory viruses causing pneumonia

Viral pneumonias can be caused by adenoviruses, influenza viruses, parainfluenza, and respiratory syncytial virus (RSV)
Treatment is primarily supportive; no specific antivirals for many of these infections

Variola (smallpox)

Variola virus has been eradicated globally; historical significance in vaccination debates
Not a current circulating threat, but part of the historical context for vaccination and biosecurity discussions

Urogenital viruses: herpes and HPV (recap)

Herpesviruses (HSV-1 and HSV-2) share similar transmission risks (unprotected sex; birth canal exposure) and latent biology; treatment with acyclovir reduces duration but is not curative
HPV: high-risk strains 16 and 18 linked to many cancers; other strains commonly cause genital warts; transmission via direct contact; prevention primarily through vaccination and wart treatment

Practical and public health implications

Endospore-forming bacteria (e.g., Bacillus anthracis, Clostridium perfringens) pose significant bioterrorism and wound infection risks; strict infection control and vaccination strategies are crucial
Antibiotic resistance (e.g., MRSA in Staphylococcus aureus and resistant Klebsiella spp., Pseudomonas aeruginosa) highlights the importance of hygiene, stewardship, and vaccination where available
Vaccination programs (DTaP, Hib, pneumococcal vaccines, MMR, varicella, HPV, influenza) are central to reducing disease burden and preventing severe complications
Transmission pathways (droplet, contact, feco-oral, vertical from mother to child, airborne via aerosols) require targeted public health measures like hand hygiene, isolation, safe sex practices, and proper vaccine coverage
Many viruses lack specific antiviral treatments; management focuses on symptom relief and supportive care, emphasizing prevention through vaccination and hygiene

Summary of vaccination-linked diseases and vaccine targets

DTaP: protects against diphtheria, tetanus, and pertussis
Hib (Haemophilus influenzae type b) vaccine: prevents invasive disease in young children
Pneumococcal vaccines (subunit and conjugate): protect against encapsulated Streptococcus pneumoniae
MMR: measles, mumps, and rubella protection
Varicella vaccine: protects against chickenpox; shingles vaccine for adults
HPV vaccines: protect against high-risk and common HPV strains linked to warts and cancers
Influenza vaccination: annual protection against circulating influenza strains
Additional vaccines target Bordetella pertussis, Corynebacterium diphtheriae, and others as part of routine immunization schedules