Exam 3 Microbiology

4 skin diseases caused by bacterial agents

Staphylococcus aureus, Streptococcus pyogenes, Clostridium perfringens, Bacillus anthracis

Staphylococcus aureus

Gram positive, withstands extreme conditions, colonize skin and mucosal surfaces, is catalase and coagulase positive

Catalase

A common antioxidant enzyme, is present in living tissues and is a key clinical enzyme involved in the breakdown of hydrogen peroxide to water and oxygen

Coagulase

An enzyme which causes the clotting of blood plasma

Virulence factors in S. aureus

Cell wall, capsule, protein A

Capsule in S. Aureus

Antiphagocytic, disrupt chemotaxis and mononuclear cell proliferation

Protein A in S. Aureus

Binds to Fc fragment of an antibody, blocks complement activation and inhibits phagocytosis

Enzymes in S. Aureus

Hyaluronidase, coagulase, staphylokinase, lipase

Cytotoxins in S aureus

Cytolysins and leukocidins

TSST

Toxic shock syndrome, a superantigen that disrupts cell signaling pathway, the massive proliferation of peripheral T cells

Staphylococcal Scalded Skin Syndrome (SSSS)

Exfoliatin A and B toxins cleave desmosomes holding epidermal cells together causing blisters

Skin infections by S aureus

Folliculitis (pimple); furuncle (boils); carbuncle; impetigo (dermis layer); cellulitis

Soft tissue MRSA skin infection

Common cause of skin lesions in non-hospitalized people; hospital acquired MRSA often leads to systemic infection

MSSA treatment

Oral therapy includes doxycycline, minocycline, trimethoprim-sulfamethoxazole

MRSA treatment

Vancomycin

Streptococcus pyogenes

Group A strep (GAS), 20% of school aged children are carriers; NOT generally considered normal microbiota

PYR test

A positive test allows for the presumptive identification of group a streptococci and group D enterococci

S pyogenes M protein virulence factor

Destroys complement components- anti phagocytic

Scarlet fever

Cause from S pyogenes; delayed type hypersensitivity reaction to S pyogenes; sandpaper skin and strawberry tounge

Clostridium perfringens

Causative agent of gas gangrene: anaerobic gram positive rods, club shaped and spore-forming

Gas gangrene (Myonecrosis)

Signs: massive tissue destruction and blackening of skin

Bacillus anthracis

Gram negative; zoonotic (infects cows and sheep); can cause cutaneous anthrax

Skin diseases caused by viral agents

Chickenpox, roseola, measles, Rubella, Parvoviris, HFMD

Varicella Zoster Virus (VZV)

Can cause chickenpox (varicella) which is primary and shingles (zoster) which is latent infection

Shingles stage

Reactivation and rashes on limited areas

Roseola (6TH disease)

Causes: HHV-6 most common, HHV-7, herpes virus

The selected agents causing skin infections

Bacterial agents, viral agents, parasitic agent, and fungal agents

Leishmaniasis

Zoonosis transmitted by female sand flies

Leishmaniasis common disease types

Cutaneous leishmaniasis (L. Tropica) and Mucocutaneous leishmaniasis (L. braziliensis)

Ringworm (cutaneous mycoses) causative agents

Dermatophytes, about 39 species in the genera Trichophyton, Microsporum and epidermophyton

Ringworm of the scalp

Tinea capitis

Ringworm of the beard

Tinea barbae

Ringworm of the body

Tinea corporis

Ringworm of the groin

Tinea cruris

Ringworm of the foot

Tinea pedis

Ringworm of the nail

Tinea unguium

Conjunctivitis bacterial cause signs

Milky discharge, common in children

Conjunctivitis viral cause signs

Burning, clear exudate, common in kids

Ocular Trachoma (neonatal) causative agents

Chlamydia trachomatis serovars A-C (A,B,Bb,C) vs (not the same as STD; D-K)

Ocular Trachoma pathogenesis

Chronic inflammation of conjunctiva that leads to scarring of inner eyelid and even blindness

Acanthamoeba keratitis

Infection in those who wear contact lenses and do not have good hygiene

Keratitis caused by herpes simplex virus HSV-1

Due to misdirected activation of oral herpes

Keratitis caused by herpes simplex virus HSV-2

Due to virus exposure during sexual activity

River blindness causative agents

Onchocerca volvulus (parasite) and Wolbachia (bacterium)

River Blindness transmission

Black fly vector

Host defense

Anatomy structure, blood-brain barrier (BBB), cerebrospinal fluid (CSF)

CSF specimen

Required through spinal tap, report to lab ASAP, STAT

Meningitis

Inflammation of the meninges, from bacteria, virus or fungi

Encephalitis

Inflammation of the brain, mostly viruses

Meningoencephalitis

Inflammation of both the meninges and the brain, various microorganisms

Streptococcus agalactiae major virulence factor

Capsule

S. Agalactiae lab tests

CAMP test: positive (CAMP toxin + beta hemolysin from S. Aureus)

Escherichia coli serotype K1

K1 strain is the second most common cause of neonatal meningitis, lactose fermenter is pink

Listeria monocytogenes main features

Tolerate cold (enrich growth), heat, salt, pH extremes, and bile; associated with contaminated foods (dairy, fish poultry, and deli)

L. Monocytogenes transmission

Ingestion of contaminated food

Neisseria meningitidis

Gram negative diplococci, meningococcus, most serious form of acute meningitis

N. Meningitidis transmission

Person to person

Streptococcus pneumoniae

Pneumococcus, Most frequent cause of community-acquired meningitis (15%)

Haemophilus influenzae epidemiology

Six serotypes a-f; “hib” due to serotype B as the most common and invasive in the past

H. Influenzae lab diagnosis

X (hemin) and V (nicotinamide adenine dinucleotide, NAD) factors requirement

Fungal meningitis causative agents

Cryptococcus neoformans, candida

Viral meningitis

The most common form of meningitis

Naegleria fowleri

Brain-eating amoeba, amoebas forced into nasal passaged

Naegleria fowleri cont.

Primary amebic meningoencephalitis (PAM)

Acanthamoeba (GAM) pace

Slow and progressive

Toxoplasma gondii transmission pathways

Ingestion of undercooked or contaminated meat; ingestion of oocysts from cat feces; transplacental, blood transfusion, organ transplant

Proteinaceous infectious particles (prions)

Only proteins, no DNA or RNA

congenital zika virus disease location

In pregnant women

Tetanus (lock jaw)

Caused by clostridium tetani

Tetanus clinical presentation

Spastic paralysis: lockjaw, stiff neck, extreme arching of back muscles

Tetanus pathogenesis

Ascending starting from foot, leg, upper limb, and body

Botulinum pathogenesis

Descending flaccid paralysis starting from cranial nerve to upper limbs and to lower limbs

Three types of bacteremia by time period

Transient, Intermittent, continuous

Transient bacteremia

Introduced into the blood stream and cleared quickly

Intermittent bacteremia

Seed the bloodstream periodically

Continuous bacteremia

Invade at a constant rate

Bloodstream infections statistics in US

1.7 M, 270K death, 1/3 killed in a hospital

Sepsis response is

Systemic response to infection

Septic shock sign

Fall in blood pressure

Specimen collection (blood culture) procedure

Requires 2 sets- one is anaerobic and aerobic bottles; the second is at different sites (before antibiotic treatment)

Why are there 2 sets in specimen collection

To increase the bacterial detection rate and to distinguish whether there is contamination and determine whether it is true bacteremia

Identification in blood cultures

Work up (biochemical identification, kit, MALDI-ToF, BioFire)

Endocarditis pathogenesis

Microbes enter the bloodstream

Risk factors for endocarditis

Damage to heart valves or prosthetic heart valves predisposes patients to endocarditis

Acute endocarditis bacterias

Staphylococcus aureus and Streptococcus pyogenes

Speticemia/ subacute endocarditis

Bacteria: plague, tularemia, anthrax; Spirochete: Lyme disease; Virus: infectious mononucleosis

Plague (black death)

Category A bioterrorism agent; cause by Yersinia pestis; Wright stain shows “safety pin”

Yersinia pestis virulence factors, epidemiology and diagnosis

Intracelluar growth and capsule; US- endemic in western and SW states; culture=definitive

Plague 3 clinical manifestations

1) pneumonic plague (most communicable); 2) Bubonic plague; 3) septicemic plague (black death)

Bubonic form transmission

Bite of a rodent flea vector

Pneumonic form tranmission

Droplet contact (respiratory droplets)

Tularemia (rabbit fever)

Category A bioterrorism agent; caused by Francisella tularensis; very infectious

Tularemia transmission

Through lawnmower

Anthrax

Caused by Bacillus anthracis, zoonotic disease; causes systemic infection

Lyme disease

Caused by Borrelia burgdorferi; cork-screw motility; vector from deer ticks; present in Northeastern states

Lyme disease signs

Stage 1 has bull’s eye rash- Erythema Migrans; stage 3 develops into crippling polyarthritis

Infectious Mononucleosis

Kissing diseases, caused by Epstein-Barr virus (EBV); most of the world’s population (>90%) has been infected with EBV

Infectious Mononucleosis pathogenesis

Primary infection- acute infectious mono, viremia; Latency phase: EBV binds to CD21 on B cells and incorporates into host cell DNA

Infectious mononucleosis transmission and signs

Saliva and blood tranfusion; fatigue is a hallmark sign

Hemorrhagic fever diseases

Yellow fever, Dengue fever, Chikungunya, Ebola and Marburg