Microbiology Exam 5: Lesson 17-19

What is the outermost layer of the skin called?

Stratum corneum (keratinized outer layer)

How does the skin physically defend against pathogens and the ways pathogens can invade it?

Constant shedding of dead cells removes microbes; keratin provides a tough barrier.

Pathogens can invade through cuts, hair follicles, sweat glands, or breaks in the skin.

What are the main chemical defenses of the skin?

Antimicrobial peptides, sebum (low pH make skin inhospitable, toxic byproducts of fatty acid metabolism inhibit the growth of microorganisms ), sweat (acidic, salty), and lysozyme (breaks down peptidoglycan found in bacterial cell walls).

Also the skin’s natural microbial community that inhibits colonization by pathogens through competition.

Define Exanthem.

A skin rash arising from another focus of infection.

Define Enanthem.

A mucous membrane rash arising from another focus of infection.

Types of skin lesions

Crust (dried exudate)

Cyst (enclosed sac)

Macule (flat discoloration)

Papule (raised bump)

Pustule (pus-filled lesion)

Ulcer (open sore)

Vesicle (fluid-filled blister)

Wheal (raised area from edema)

Bulla (large blister >1cm)

What are the main structures of the eye?

Sclera, cornea, iris, pupil, eyelid, conjunctiva, lacrimal apparatus.

What are the eye’s main defense mechanisms?

Tears (contain lysozyme), blinking, and constant flushing action.

Define Conjunctivitis.

Inflammation of the conjunctiva (“pink eye”).

Define Keratitis.

Inflammation of the cornea.; may lead to blindless

Define Blepharitis.

Inflammation of the eyelid.

ACNE

• Acne is the most common skin disease in the world

• Chronic inflammatory condition involving

• Propionibacterium acnes

Staphylococcus vs Streptococcus

• Staphylococcus: Clusters, catalase-positive.

• Streptococcus: Chains, catalase-negative.

What diagnostic tests are used to differentiate Staphylococcus vs Streptococcus

• Catalase test: Staph = +, Strep = –.

• Coagulase test: S. aureus = +, S. epidermidis = –.

• Mannitol salt agar: S. aureus ferments mannitol (turns yellow). and no color change with S. epidermidis

• Blood agar hemolysis: Alpha ( bacteria partially lyse red blood cells, Released hemoglobin converted to methemoglobin, Greenish-brown zone), Beta ( completely lyse red blood cells, released hemoglobin is destroyed, clear zone around the bacterial colonies), Gamma (No hemolysis, No visible change in the blood agar around the bacterial colonies) for Streptococci.

STAPHYLOCOCCI

Gram positive cocci

Staphylococcus epidermidis

• Commonly found on the skin, mucous membranes, and respiratory tract.

• can cause infections in immunocompromised individuals or when introduced into the body through medical devices

Staphylococcus aureus

• Can be found in the nasal passages, skin, and gastrointestinal tract.

• A more virulent pathogen that can cause a wide range of infections, including skin infections, pneumonia, sepsis, and food poisoning.

What is Folliculitis and a Sty?

Staphylococcus aureus infections

Folliculitis = infection of hair follicles. A sty is folliculitis of an eyelash.

What is a Furuncle and Carbuncle?

Staphylococcus aureus infections

Furuncle- A boil — a deep abscess filled with pus.

Carbuncle- A group of connected furuncles causing deeper inflammation.

Describe Impetigo (staphylococcal form).

Staphylococcus aureus infection

Bullous impetigo; Impetigo is a superficial bacterial infection that causes the skin to flake or peel large; a fluid-filled blisters caused by exfoliative toxin A. Common in newborns.

Describe Scalded Skin Syndrome

Staphylococcus aureus infection

Caused by exfoliative toxins A and B; skin peels off in sheets, mainly in newborns and infants.

Describe Toxic Shock Syndrome (TSS).

Staphylococcus aureus infection

Caused by toxic shock syndrome toxin-1 TSST-1 (superantigen); results in high fever, rash, low BP, multi-organ failure.

it is associated with tampon use surgical wounds and skin infections.

What is MRSA, and why is it clinically significant?

Methicillin-Resistant Staphylococcus aureus; resistant to β-lactam antibiotics, common in hospitals, causes hard-to-treat infections.

MRSA is especially troublesome in hospitals and nursing homes, where patients with open wounds, invasive devices, and weakened immune systems

Describe Impetigo (streptococcal form).

Streptococcus pyogenes Infection

Non-bullous form with honey-colored crusting; highly contagious spreads by contact (autoinoculation) ; common in older children and adults.

What is Erysipelas?

Streptococcus pyogenes Infection

Infection of upper dermis and superficial lymphatics; causes raised, well-demarcated red, swollen, painful area

Systemic symptoms: fever, chills

What is Necrotizing Fasciitis?

Streptococcus pyogenes Infection

Rapidly spreading “flesh-eating” infection of fascia caused by exotoxin A (superantigen); medical emergency. Has high mortality rate

What is Scarlet Fever?

Streptococcus pyogenes Infection

Complication of strep throat caused by erythrogenic toxin; causes sandpaper-like rash and strawberry tongue.

treated with penicillin or cephalexin

What are the key virulence factors of S. pyogenes?

M protein (prevents phagocytic), streptokinase (dissolves blood clots, aids spread), hyaluronidase (degrades connective tissue), streptolysins O and S (destroy red and white blood cells) , and erythrogenic toxin.

MACULOPAPULAR disease

Flat to slightly raised colored bumps

(measles (rubeola), Rubella (German Measles, Fifth Disease, Roseola, Scarlet Fever)

MEASLES (RUBEOLA)- Maculopapular rash disease

caused by Measles virus

Transmitted by respiratory route (droplets)

Starts on head → spreads to body; Macular rash and Koplik’s spots in mouth; high fever.

Prevented by MMR vaccination and supportive care

Rubella (German Measles) - Maculopapular rash disease

caused by Rubella virus

transmission by respiratory droplets

Symptoms- Maculopapular rash and fever

Congenital rubella syndrome is significant in pregnancy because it causes severe fetal damage

Prevented by vaccination and supportive care

Fifth Disease (Erythema Infectiosum) - Maculopapular rash disease

Produces a Mild Rash

• caused by Parvoviridae, Parvovirus B19

• transmitted by respiratory droplets

• Symptoms include a fiery red (“slapped check”) rash on the cheeks and ears, and trunk. It disappears within a few days

• Adults can experience symptoms similar to those of rheumatoid arthritis

• treatment includes supportive care

Roseola - Maculopapular rash disease

Caused by Human herpesvirus 6 or 7.

Transmission of Roseolais most Likely respiratory route.

Symptoms of Roseola? High fever followed by rash; may resemble measles.

Treatment? Supportive care.

Scarlet Fever (rash type)- Maculopapular rash disease

caused by Streptococcus pyogenes (erythrogenic toxin).

Rash characteristics- Fine, red “sandpaper” rash and strawberry tongue.

Treatment- Penicillin or cephalexin.

Smallpox (Variola)- Vesicular Rash Disease

Variola virus (Poxvirus family).

• Transmission? Respiratory droplets or contact with lesions.

• Features of Smallpox rash include Deep, umbilicated pustules with thick yellow fluid; clustered on extremities.

• Eradicated by vaccination (1980).

Chicken Pox and Shingles- Vesicular Rash Disease

Chickenpox caused by Varicella-zoster virus (VZV/HHV-3).

• It is transmitted by respiratory droplets or direct contact. (highly contagious)

• Clinical features include Vesicular rash, mostly on trunk; itchy; mild fever.

• Prevention/Treatment- Live attenuated vaccine; antivirals if severe.

Shingles is caused by reactivation of latent VZV/ HHV-3

• Features of Shingles rash include Painful vesicular rash along nerve pathways.

• Prevention- Shingles vaccine (Shingrix) for adults 50+.

• Treatment- Acyclovir or valacyclovir to shorten duration and reduce pain

Herpes Simplex (cold sores/fever blisters)- Vesicular Rash Disease

HSV-1 (primarily oral):

• Infections: Cold sores/fever blisters (vesicles on lips), herpes gladiatorum (vesicles on skin), herpetic whitlow (fingers), herpes encephalitis

• HSV-1 can remain latent in trigeminal nerve ganglia

• Transmission: Direct contact, saliva

HSV-2 (primarily genital):

• Infections: Genital herpes

• Latency: Sacral nerve ganglia

• Complications: Neonatal herpes (transmission during birth), herpes encephalitis

• Transmission: Sexual contact, vertical transmission

Treatment: Acyclovir, valacyclovir, famciclovir (suppress replication, reduce symptoms, do not cure)

Viral latency

Latency: Virus remains dormant in host cells without active replication, but can reactivate later

Varicella-Zoster Virus (HHV-3):

• Primary infection: Chickenpox (varicella)

• Latency site: Dorsal root ganglia of spinal nerves

• Reactivation: Shingles (herpes zoster) - typically in adults, immunocompromised, or elderly

Herpes Simplex Virus-1 (HSV-1):

• Primary infection: Cold sores/fever blisters (oral herpes)

• Latency site: Trigeminal nerve ganglia

• Reactivation: Recurrent oral herpes lesions triggered by stress, UV exposure, illness

WARTS AND WART LIKE ERUPTIONS

Warts (Verrucae):

• Causative agent: Human papillomaviruses (HPV) - over 100 types

• Transmission: Direct contact, autoinoculation, indirect contact with contaminated surfaces

• Types: Common warts, plantar warts, flat warts, genital warts

Treatment:

Cryotherapy, salicylic acid, imiquimod, or may resolve spontaneously.

Describe Molluscum contagiosum.

Caused by a poxvirus; spread by direct or sexual contact; causes smooth, firm, umbilicated lesions. 

There is usually no treatment, mechanical removal can be performed (virus not eliminated)  

Dermatomycoses (Tineas/Ringworm)

Causative agents: Dermatophytes (fungi that metabolize keratin)

• Trichophyton, Microsporum, Epidermophyton species

Infect skin, hair, nails (wherever keratin is present)

Transmitted through direct contact with infected individuals, animals, or contaminated surfaces

Types by body location:

• Tinea capitis: Scalp and hair

• Tinea barbae: Beard area ("barber's itch")

• Tinea corporis: Body/trunk ("ringworm") - circular, raised, red rings

• Tinea cruris: Groin ("jock itch")

• Tinea pedis: Feet ("athlete's foot") - blisters between toes

• Tinea unguium (onychomycosis): Nails

Treatment: Topical or oral antifungals (azoles, terbinafine, griseofulvin)

CANDIDIASIS

caused by Candida albicans (yeast)

Occurs in skin and mucous membranes of genitourinary tract and mouth

Thrush: An infection of mucous membranes of mouth

Opportunistic. Predisposing factors:

• Antibiotic use (suppresses normal bacterial flora)

• Diabetes (elevated glucose)

• Immunosuppression (HIV/AIDS, chemotherapy, corticosteroids)

• Pregnancy (hormonal changes)

• Moisture and occlusion

Topical treatment with miconazole or nystatin

PITYRIASIS VERSICOLOR

Endogenous skin infection that occurs in warm, humid climates

Caused by Malassezia species (lipophilic yeast)

Hypopigmented or hyperpigmented patches

Treated with antifungal creams or shampoos (Head and Shoulders with antifungal zinc pyrithione)

SPOROTRICHOSIS

Caused by Sporothrix schenckii (dimorphic fungus)

Subcutaneous nodules along lymphatic channels

"Rose gardener's disease" - from thorn pricks

SCABIES

caused by Sarcoptes scabiei

Transmitted through direct skin contact, contaminated bedding/clothing

symptoms:

• Burrows in the skin to lay eggs

• Linear burrow pattern is pathognomonic (highly characteristic of a disease)

• Intense itching (worse at night)

Treatment with topical insecticide (permethrin, lindane)

PEDICULOSIS (LICE)

Caused by Pediculus humanus

Transmitted through direct contact, sharing of personal items

Symptoms:

• Itching, visible lice or nits (eggs) on hair shafts

Types

• P. h. capitis (head louse)

• P. h. corporis (body louse)

• P. h. pubis (“crabs”)

Treatment with topical insecticides (permethrin, malathion), nit removal

LEISHMANIASIS

caused by Leishmania species (protozoan)

Spread by the bite of infected sandfly

• Cutaneous form: skin ulcers/lesions at bite site

Treated with antimonial drugs, amphotericin B

Describe Trachoma.

Chronic eye infection caused by Chlamydia trachomatis; transmitted by direct contact or flies; causes scarring and blindness.

Leading infectious cause of blindness worldwide.

Treatment: Azithromycin, tetracycline

What parasitic infections affect the eyes?

• Onchocerciasis (River blindness): Onchocerca volvulus (nematode/roundworm) spread via blackfly.

• Acanthamoeba keratitis: From contaminated water/contact lenses.

• Loiasis: Loa loa transmitted by deerfly; worms migrate under conjunctiva.

What is the Central Nervous System (CNS) and the three layers of the meninges that protect?

The CNS consists of the brain and spinal cord, responsible for processing and integrating information.

• Dura mater – tough outer layer

• Arachnoid mater – middle layer with CSF in subarachnoid space

• Pia mater – delicate inner layer adhering to brain tissue

What is the blood-brain barrier (BBB) and its function?

Separation of circulating blood and the brain extracellular fluid (BECF) in the central nervous system (CNS)

Function: Protects brain from pathogens and toxins in bloodstream

Structure: Tight junctions between blood vessel cells act as selective filter

Clinical Problem:

• Limits immune cell access

• Limits antibiotic penetration

• Once pathogens cross BBB → difficult to treat

How can some bacteria like Borrelia and Treponema cross the BBB?

They are spirochetes with internal flagella that allow corkscrew-like movement through the barrier.

How does meningitis differ from encephalitis?

• Meningitis: Inflammation of meninges.

• Encephalitis: Inflammation of brain tissue.

What is meningoencephalitis?

Inflammation of both the meninges and the brain.

What are the three main bacterial species that cause meningitis?

• Neisseria meningitidis (meningococcal meningitis)

• Streptococcus pneumoniae (pneumococcal meningitis)

• Haemophilus influenzae type b (Hib meningitis)

All 3 species can cross the blood-brain barrier, inflaming the meninges

All vaccine-preventable

How is bacterial meningitis transmitted and what are the characteristic symptoms?

Transmitted by droplet (respiratory secretions).

Symptoms include Fever, headache, stiff neck (classic triad)

, nausea, vomiting, altered mental state, and sometimes convulsions or coma.

What body fluid is sampled to diagnose and what diagnostic methods are used to confirm bacterial meningitis?

Cerebrospinal fluid (CSF) obtained via lumbar puncture.

to confirm CSF analysis, Gram stain, latex agglutination test, culture. (CSF appears cloudy in bacterial infections) are used.

What rash is characteristic of Neisseria meningitidis (meningococcal meningitis) infection?

Petechial rash (purple/red skin spots from blood vessel invasion)

What is the causative agent of listeriosis and how is it transmitted?

caused by Listeria monocytogenes.

Transmitted through contaminated food — cold cuts, soft cheeses, unpasteurized milk, and fecal-contaminated foods.

Why is Listeria monocytogenes associated with refrigerated foods and who are at high risk for it?

It can grow at refrigerator temperatures (~4°C), unlike most foodborne pathogens.

Pregnant women (can cross placenta), elderly, and immunocompromised individuals.

What is the causative agent of tetanus and how is it acquired?

caused by Clostridium tetani.

acquired through deep puncture wounds contaminated with soil or feces ("Rusty nail" = deep wound + soil = anaerobic environment)

Tetanospasmin released from dead cells blocks

relaxation pathway in muscles

• Muscles cannot relax, causing spastic paralysis (rigid, "lockjaw")

• Muscle spasms so severe bones can break

Prevention by vaccination with tetanus toxoid ((DTaP, Tdap) and booster (dT)

Treatment with tetanus immune globulin

What is the causative agent of botulism?

Caused by Clostridium botulinum

Intoxication comes from ingesting botulinum toxin (Home-canned vegetables, garlic in oil, fermented fish, and honey (infants).

Botulinum toxin blocks release of neurotransmitter acetylcholine

• Muscles cannot contract, causing flaccid paralysis (limp, droopy)

What are the three types of botulism?

• Food-borne – ingestion of preformed toxin

• Infant – toxin formed in intestines (floppy baby syndrome)

• Wound – infection of wounds, often in IV drug users

What preventive measures help avoid botulism?

Proper canning (121°C), nitrites in sausages, avoiding honey in infants, and not eating from swollen cans.

tetanus vs botulinum toxin on muscles.

• Tetanus toxin: Prevents relaxation → spastic paralysis.

• Botulinum toxin: Prevents contraction → flaccid paralysis.

LEPROSY (HANSEN'S DISEASE)

Caused by Mycobacterium leprae

Acid-fast rod that grows best at 30°C

• Core body temperature: 37°C (98.6°F)

• Cooler body parts are affected (Fingers, toes, nose, ears, skin surface). This is WHY extremities are damaged

Grows in peripheral nerves and skin cells

Transmission requires prolonged contact with an infected person

• Low infectivity (95% naturally immune)

• Incubation: 3-5 years

What are the two forms of leprosy?

• Tuberculoid (neural): Loss of sensation in skin areas

  • Strong immunity, few bacteria, localized lesions, nerve damage, better prognosis

• Lepromatous (progressive): Disfiguring nodules over body

  • Weak immunity, many bacteria, disfiguring nodules (“Leonine facies”), worse prognosis.

How does viral meningitis compare to bacterial meningitis?

Aseptic meningitis is Milder, self-limiting (7–10 days), no bacteria in CSF (“aseptic”), caused by enteroviruses or herpesviruses.

Treatment: Supportive care only

Can viral encephalitis result from both primary and secondary infections?

Yes. Primary = virus directly invades CNS (HSV, arboviruses, rabies).
Secondary = reactivation or complication (measles → SSPE, human coronaviruses).

ARBOVIRAL ENCEPHALITIS

Caused by arthropod-borne viruses that belong to several families

transmitted by mosquito bites; mosquitoes transmit virus from infected birds to humans.

ex: West Nile virus, Eastern/Western equine encephalitis viruses.

-Fever, headache, confusion, seizures, paralysis, or coma.

Those who recover may have paralysis and mental disorders

No treatment or vaccine but can be prevented by Mosquito control, protective clothing, repellent

Poliomyelitis (Polio)

caused by Poliovirus

transmitted through Ingestion of contaminated water or food.

Initial symptoms: Sore throat and nausea

Virus enters CNS → destroys motor neurons

• Flaccid paralysis (limbs, trunk)

• Bulbar polio: Respiratory paralysis (can be fatal)

Prevention: vaccination (enhanced-inactivated form)

Rabies

Transmitted through bites from infected animals (bats, raccoons, foxes, skunks, coyotes).

Symptoms: (once CNS affected) Agitation, depression, hydrophobia,hallucinations; once symptoms appear, nearly 100% fatal.

post-exposure vaccination for rabies is possible it needs Long incubation period (up to 1 year) allows time for immune response before virus reaches brain.

• Wound cleaning, rabies immune globulin (RIG), and 4-dose vaccine series over 14 days.

*must start before symptoms. after symptoms it is too late because the virus is in the CNS

PRION DISEASES

Misfolded proteins (no DNA or RNA). contain no nucleic acids and are resistant to normal sterilization.

EX: 

• Humans: Creutzfeldt-Jakob disease (CJD), Kuru

• Animals: Mad cow disease, sheep scrapie

Symptoms: Rapid dementia, muscle weakness, ataxia, always fatal.

Primary Amoebic Meningoencephalitis (PAM)

caused by Naegleria fowleri.

acquired by Amoeba in warm freshwater (lakes, ponds, hot springs) enters via nose and travels up olfactory nerve.

outcome: Rapidly fatal (>97% mortality); causes destruction of brain tissue; death in 7–14 days.

prevented by Avoid submerging head in warm freshwater, use nose clips, maintain proper pool chlorination.

Which diseases are transmitted by droplets?

Bacterial meningitis, viral meningitis, some encephalitis cases.

Which diseases are transmitted by food?

Listeriosis, botulism, polio.

Which disease are transmitted by animal bites?

Rabies

Which disease are transmitted by mosquitoes?

Arboviral encephalitis (West Nile, Equine).

Which are transmitted by contaminated water?

Polio, Naegleria fowleri (PAM).

Which nervous system diseases can be prevented by vaccination?

• Meningitis (Neisseria, Streptococcus pneumoniae, Hib)

• Tetanus

• Polio

• Rabies (pre/post-exposure)