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51 Cards in this Set

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How does the skin act as a defence against microbes?

-Physical barrier


-Low pH


-Low moisture content


-Sebaceous fluid and fatty acids


-Lysozymes

Give examples of normal skin flora

Gram positive:


Staphlococcus epidermis


Staphlococcus aureus


Micrococcus luteus


Corynebacterium species


Propionibacterium (eg. P.acnes


Gram negative - usually unable to suffer harsh environment - but some transient

Differentiate between endogenous and exogenous bacteria

Endogenous = normal flora


Exogenous = from external sources eg. dirt, water, hospital equipment

Describe general characteristics of Staphlococci associated with bacterial skin infections, and list them

-Gram positive cocci - grape-like when stained


-Catalase positive


-Non-motile, non-spore formers


-Facultative anaerobes


-Enriched growth media


eg. S. aureus (most virulent, coagulase +ve)


S.epidermis, S. haemolyticus, S. lugdunensis, S. saprophyticus,

List examples of virulence factors of S. aureus

Capsule -> invasion of host cells


Protein A -> binds to antibodies


Enterotoxins -> ingestion causes food poisoning


Exfoliative toxins -> degrade superficial skin layer

Describe general characteristics of Streptococci associated with bacterial skin infections, and list them

-Gram +ve cocci - form pairs/chains on staining


-Catalase negative


-non-motile, non-spore forming


- Facultative anaerobes


-Complex media (eg blood)


Eg. S. pyogenes (group A beta haemalytic), S. agalactiae (group B beta haemalyic)

Describe the division of Streptococci species

Action on blood agar:


-Alpha - agar green - Hb partially broken down


-Beta - agar yellow - Hb broken down completely


-Gamma - agar unchanged




Beta further divided into group A - W based on carbohydrate in cell walls



Describe examples of Virulence Factors of S. pyogenes

-M protein -> adherence/invasion of host cells


-Streptokinase - dissolves fibrin clots, help spread infection


-Streptolysin S & O - lyse RBC, damage membranes


-C5a peptidase - inactives complement product



What is this condition

What is this condition? Explain clinical manifestations and what causes it.

Folliculitis.


Pustular inflammation of hair follicle and surroundings. Superficial infection of hair follicle. Bacteria usually gain entry through abrasions. Single/multiple red lesions eg. along shaving lines. Typically S. aureus, but also propionibacterium acnes (acne) or yeast/fungi.

What is this condition? Explain clinical manifestations and what causes it. 

What is this condition? Explain clinical manifestations and what causes it.

Hot-tub folliculitis - contaminated water enters hair follicles.




Pseudomonas aeruginosa

What is this condition? Explain clinical manifestations and what causes it. 

What is this condition? Explain clinical manifestations and what causes it.

Faruncles (boils).


Deep infection of hair follicle. Large (1-2cm) pus-filled, moveable nodule. Rupture -> yellow (pus) discharge.


Usually face, neck, axilla, buttocks.


Usully S. aureus, sometimes S. pyogenes



What is this condition? Explain clinical manifestations and what causes it. 

What is this condition? Explain clinical manifestations and what causes it.

Carbuncle. When multiple boils come together to form one/multiple abcesses.


Associated with malaise and fever.


S. aureus, occasionally S. pyogenes



What is this condition? Explain clinical manifestations and what causes it. 

What is this condition? Explain clinical manifestations and what causes it.

Impetigo


Highly contagious, pus-forming infection. Penetrate health skin, or through abrasion.


Crusted (non-bullous) - 'school sores' - yellow, crusted, ulcerative erosions - itchy but not painful. S. aureus or S. pyogenes.


Bullous - large blisters, initially with clear fluid, and then yellow. Rupture easily -> brown crusts. S. aureus usually.

What is this condition? Explain clinical manifestations and what causes it. 

What is this condition? Explain clinical manifestations and what causes it.

Erysipelas


Limited to dermis usually. Rapidly spreading, bright red, raised, swollen, firm lesion with sharp demarcated borders.


Usually legs, or in butterfly shape on face.


Lesions preceded by chills, malaise, fever. associated with regional lymphadenopathy.


Usually S. pyogenes - usually enter through lesion.


infants/children, elderly, immunocomprimised, alcoholics, diabetics

What is this condition? Explain clinical manifestations and what causes it. 

What is this condition? Explain clinical manifestations and what causes it.

Cellulitis.


Extends to dermis/subcutaneous tissue. Tender, swollen, red, warm, borders not raised and not clearly demarcated - lesion has patches of infected/non-infected skin.


Legs in adults/elderly, around eyes in children. Also fever and regional lymphodenopathy. S. pyogenes, sometimes S. aureus.


If exposed to fresh water - Aeromonas species


If exposed to salt water - vibriovulnificus.

Describe features of prokaryotic cells:

0.2-2micrometres diameter


Nucleoid - 1 single stranded copy of DNA


No membrane bound organelles (inc. nucleus)


Cell wall - peptidoglycan


70s Ribosomes


Plasma membrane, cytoplasm


Inclusion bodies - stockpiled cellular energy stores


Endospores -



Describe endospores

Formed in mother cell in response to stress - unequal cell division. Survive for long periods, impervious to dessication/chemicals. Can germinate in appropriate environment

Describe bacterial cell walls, the types, and their association with gram staining.

Provides shape, prevents osmotic lysis.


Peptidoglycan layer made up of 2 sugar derivitives.


Gram Positive - thick peptidoglycan layer, highly crosslinked. Contains teichoic acid and lipoteichoic acid. eg. S. aureus. Appear purple when gram-stained.


Gram Negative - thinner peptidoglycan layer, outer membrane. eg. E. coli. Appear pink when gram-stained.

Explain bacterial capsules/slime layer:

Polysaccharides. Extend from surface of cell. Allow bacteria to attach to surfaces and withstand harsh conditions. Protection from host defences - poorly antigenic, anti-phagocytic

List bacterial external structures and their functions:

Fimbria - short, thin, hairlike appendages. Attachment to surfaces, motility.


Sex pilus - longer than fimbria and less numerous. required for mating.


Flagellum - thin protein tube. rotate like propellar. Clockwise -> run (forward motion), Anticlockwise -> tumble (stops)

Explain the nomenclature for the different shapes/conjugations of bacteria. 

Explain the nomenclature for the different shapes/conjugations of bacteria.

From L -> R


Cocci/Round. Rod/bacilli. Spiral/Spiralli


Diplo. Strepto. Staphylo.

Describe the different types of oxygen requirements bacteria might have:

Aerobes - grow in presence of O2


Obligate aerobes - require O2 for growth


Anaerobes - can grow in absence of O2


Obligate anaerobes - killed by O2


Facultative anaerobes - grow in presence/absence of O2

Describe the varying types of growth media

General purpose - nutrient agar/broth - most organisms basic nutrient requirements met


Enriched - general purpose supplemented with defibrinated horse/sheep blood. identify organisms that kill RBC - determines if haemalytic - alpha (partial lysis - green), beta (complete lysis - yellow) or gamma (no lysis - red)?


Selective and differential - inhibits unwanted bacteria, allows desired bacteria to grow. Macconkey Agar -Gram Negative (and not gram positive). Mannitol salt agar - Gram Positive staphlycoccus species (ferment mannitol)

Describe the purpose of the catalase test

Differentiates Gram positive -


-staphlococcus (+ve)


-streptococcus (-ve).


Whether have catalase enzyme which inactivates oxygen radicals -> water and hydrogen (bubbles)

Describe the purpose of the coagulase test

Coagulase enzyme causes clot to form when bacteria mixed with plasma.


Differentiates types of staphlococci:


-S. aureus (+ve)


-Coagulase -ve staphlococci (eg. S. epidermis).





Describe the purpose of the oxidase test

Differentiates between various gram negative bacteria.


Positive - contain enzyme cytochrome C oxidase - creates dark, oxidised product.

Describe Nucleic-acid based tests

Use PCR to identify presence of pathogen's DNA in specimen

Describe Immunologic detection of micro-organisms

Detect antigen or antibody in patient’sbody fluids. eg. latex agglutination test

Describe Antibiotic susceptibility testing

Cultured pathogen tested for susceptibility to various antibiotics, to determine which treatment to use. eg. disk diffusion method.

Differentiate between unicellular and multicellular fungi

<-Multicellular - mold, mushrooms. Comprised of tubular structures (hyphae). Appear fuzzy on growth media. 

<-Unicellular - yeast. round cells form smooth, flat colonies on growth media

<-Multicellular - mold, mushrooms. Comprised of tubular structures (hyphae). Appear fuzzy on growth media.




<-Unicellular - yeast. round cells form smooth, flat colonies on growth media

What skin infection is this? Describe clinical manifestations, causative organism, and diagnosis techniques. 

What skin infection is this? Describe clinical manifestations, causative organism, and diagnosis techniques.

Pityriasis (tinea) vericolour


Disease of health people. Worldwide, but esp. tropical/subtropical.


Young adults most susceptible.


Yeast = Malassezia furfur. Superficial (keratinized skin, hair, nails).


Direct/indirect contact with samples/person-person contact.


Light skin - hyper-pigmented (dark red). Dark skin - hypopigmented (light patches). Macules irregular, raised, sometimes covered in fine scales.


Often upper trunk, arms, chest, shoulders, face, neck.


Diagnosis - microscopic examination of skin scrapings (10% KOH & parker ink colution stain. Culture generally not necessary, but synthetic media, ID after 5-7 days.



Describe cutaneous mycoses, the fungi causing them, and diagnosis:

Most common fungal diseases. Caused by Dermatophytes AKA ringworms/tineas. Infection differentiated on type of causative agent and area of body affected.


3 species of fungi:


- Trichophyton


-Microsporum


-Epidermophyton


Diagnosis - Microscopic examination of skin scrapings, culture of fungi on Sabouraud agar.



Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Tinea capitis (cutaneous mycoses of scalp)


Childhood disease predominantly.


Inflammation and scaling.


Person-person/animal-human transmission


Eg. Microsporum species

Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Tinea barbae (cutaneous mycoses of the beard)


Rural men who acquire the fungi from infected animals.


Eg. Trichophyton species

Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Tinea corporis (cutaneous mycoses of body)


Red, scaly lesions and itching.


Person-person/animal-human transmission or indirectly via infected substances eg. shared towels.


eg. Trichophyton

Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Tinea manuum/pedis - cutaneous mycoses of hands/feet


Fine scaling/pustular lesions and itching


eg. Trichophyton

Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Tinea cruris - 'jock itch' - cutaneous mycoses of groin


red, scaly lesions and itching.


eg. Trichophyton/Epidermophyton species

Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Tinea unguium - cutaneous mycoses of the nails


nail plate rises and seperates from nail bed.


eg. Trichophyton species

Name this condition, describe epidemiology and transmission. 

Name this condition, describe epidemiology and transmission.

Lymphocutaneous sporotrichosis - subcutaneous mycoses


Dimorphic fungus Sporothrix schenckii - Fungus in soil/decaying vegetation.


Endemic in Japan, Mexico, North/South America.


Prevalent in forest workers, gardeners, miners (puncture wounds)


Initial site of infection - small nodule which can ulcerate. Secondary lymphatic nodules appear ~2 weeks later. Occasional pus discharge.


Diagnosis - culture from infected tissues/pus. Yeast 35 degrees, hypae 25

Describe subcutaneous skin mycoses

Caused by Saprophytic inhabitants of soil and decaying vegetation.


Introduced to skin via. puncture wound.

Describe this skin infection, clinical manifestations, the causative organism, and diagnosis. 

Describe this skin infection, clinical manifestations, the causative organism, and diagnosis.

Cryptococcosis (Cryptococcus neoformans). Systemic mycoses


Dimorphic fungus, yeast form usually encapsulated.


3 varieties - neoformans, grubii, gattii.


Not part of humans normal flora. Cause disease in immunocomprimised - AIDS, cancer, organ transplants, corticosteroid treatment patients.


Enter via. respiritory route, dormant in alveoli and asymptomatic. Then, exit lung, spread haematogenously to skin, bone, eye, brain (meningoencephalitis/cryptococcal meningitis).


Bird poo - environment - humans breath in spores/yeast.


Diagnosis - Indian ink stain of sample from pus, CSF, sputum, or culture on Sabouraud agar



Explain opportunistic mycoses

Normal flora pathogenic in comprimised host with lower resistance to infection - eg. due to malnutrition, alcoholism, cancer, diabetes, other infectious disease, trauma, immunosuppression (drugs, hormones, chemotherapy, elderly)

Describe what fungi this is. Describe clinical manifestations and diagnosis. 

Describe what fungi this is. Describe clinical manifestations and diagnosis.

Aspergillosis (Aspergillus fumigatus/flavus). Worldwide in nature.


Soil, household dust, building materials, foods, water, air ducts.


Clinical manifestations - pulmonary infection with fever, chest pain, dry cough, possible dissemination to brain/kidney


Diagnosis - sample from lung biopsy, lung aspiration, broncheoalveloar lavage cultured on Sabouraud Agar.

What organism caused these infections? Describe clinical manifestations, diagnosis, and transmission. 

What organism caused these infections? Describe clinical manifestations, diagnosis, and transmission.

Candidiasis (Candida albicans).


Dimorphic fungus, simple growth requirements.


Colonises GIT, oral cavity, anus, groin, skin, nails, reproductive tract.


Human-human contact transmission.


invasive pathogen in colonised comprimised individuals.


Immunodeficient patients - superfical infections (skin, nails, oral cavity (thrush)).


Systemic, disseminated infections - blood (candidaemia), heart (myocarditis), brain, liver, kidney, GIT.


Diagnosis depends on infection - swabs and culture, urine culture, blood culture, microscopy - examine for germ tube formation.

Name this skin condition, the causative organism, epidemiology, pathophysiology and diagnosis. 

Name this skin condition, the causative organism, epidemiology, pathophysiology and diagnosis.

Entamoeba histolytica (amoeba).


Worldwide distribution, common in tropics/areas of poor sanitation.


Infected individuals contagious - cyst is infectious, passed through feces (fecal-oral/oral-anal). Infections common in mental hospitals, military/refugee camps, prisons, crowded day-care centres.


Cysts ingested. Stomash acid -> pathogenic trophozoite release -> necrosis and inflammation in colon -> spread to other organs -> abcesses


Intestinal disease symptoms - after 1-4 weeks - abdo pain/cramps, tissue damage in LI with colitis, watery and bloody diarrhoea.


Systemic - Abcess formation in liver, lung, heart, brain


Cutaneous (amebiasis) symptoms - nodules at site of invasion (perianal region) - are purulent, foul-smelling, associated with swollen lymph nodes and dysentery.


Diagnosis: Intestinal - stool samples, stain and PCR. Extra-intestinal - microscopic examination of abcess, detection of antibodies.

Name this skin condition, the causative organism, epidemiology, and diagnosis. 

Name this skin condition, the causative organism, epidemiology, and diagnosis.

Leishmaniasis - flagellated protazoa. Transmitted from animal-human (cats, dogs, birds)/ human-human by sandfly bite. Infection also by direct contain with infected lesion. Three main species - Leishmania tropica (cutaneous), L.braziliensis (mucocutaneous), L.donovani (visceral).


Cutaneous - South America, Middle East, Military troups. Papule at site of bite after 2-8 weeks -> ulcerates -> crusted over, oozes serous fluid -> can spontaneously heal, leaving scar at site of infection.


Mucocutaneous - central and south america. Destruction of mucous membranes and tissues (nose, mouth, lips), lesions do not spontaneously heal, 2ndary bacterial infections common. grossly disfiguring, death rare.


Diagnosis - clinical symptoms. Amastigotes detected via smears from lesion aspirates/tissue biopsy. PCR good if available.

Name this skin condition, the causative organism, epidemiology, and diagnosis. 

Name this skin condition, the causative organism, epidemiology, and diagnosis.

African trypanosomiasis (sleeping sickness)


Trypanosoma brucei gambiense (West Africa). Trypanosoma brucei rhodesiense (East Africa). Trypomastigotes are spread by the tsetsefly.


Painful, red, indurated nodule at site of bite. Initial leasion may heal spontaneously, but organism continues to proliferate and spread -> fever, lymphadenopathy, CNS involvement - begin to act sleepy, cant sleep at night, sleep in day, eventual coma.


Diagnosis - trimastigote ID in blood spears, aspirations from lymph nodes & CSF. PCR?

Name this skin condition, the causative organism, epidemiology, and diagnosis. 

Name this skin condition, the causative organism, epidemiology, and diagnosis.

American trypanosomiasis (Chagas disease). Trypanosoma cruzi – Trypomastigotes spread by bite of reduviid(triatomine) bug.


Mostly young children, bite around eye, mouth and other face. Trypomastigite present in faceces of reduviid bug (bites, poops in bite).


Acute - painful red nodule (chagoma) around eyes and face. Untreated - symptoms resolve but infection persists -> myocarditis, meningoencephalitis, enlarged spleen/liver/oesophogus, death from heart blockage/brain damage.


Chronic - infection silent for years/life, but increased risk of developing clinical disease (see above).


Diagnosis: thick and thin blood smears in acute stage, biopsy of lymph nides, spleen, liver, BM. Xenodiagnosis (exposure of infected tissue to uninfected bugs, then examine bugs for amastigote/trypomastigote stages. PCR?

Name this skin condition, the causative organism, epidemiology, and diagnosis. 

Name this skin condition, the causative organism, epidemiology, and diagnosis.

Cutaneous Larva Migrans


Hookworm (Ancylostoma braziliense, A. caninum). From cats and dogs.


Young children (contact with animal feces with worms/eggs) in soil, sandpits, on beaches. Larvae penetrate skin and remain trapped (weeks-months) -> serpentine tunnels.


Migrating larvae -> severe pruritis, scratching -> secondary bacterial skin infections.


Diagnosis = clinical appearance, travel history to endemic areas, larvae in skin biopsy.

Name this skin condition, the causative organism, epidemiology, and diagnosis. 

Name this skin condition, the causative organism, epidemiology, and diagnosis.

Filariasis - Roundworm (Wuchereria bancrofti). Larvae transmitted by mosquitoes. Larvae fro initial site of infection -> lymphatics (arms, legs, groin) -> grow into adults. 3-12 months later, males fertilise females, produce microfilariae -> bloodstream.


Endemic - Central Africa, Asia, Mediterranean coast, Haiti, Costa Rica, Brazil, Islands of Pacific.


Some people asymptomatic.


Acute - treatable. Fever, chills, lymphadenitis.


Chronic - lymph nodes enlarge in extremities (elephantitis), scrotum, testes.


Diagnosis - ID of microfilariae in blood. Clinically no need to ID species, as treatment same (except Onchocerca - River Blindness).

Name this skin condition, the causative organism, epidemiology, and diagnosis. 

Name this skin condition, the causative organism, epidemiology, and diagnosis.

Human Scabies - Sarcoptes scabeie - itch mite - arthropoda.


Mite transmission - direct contact, contact with infected clothing/bed sheets, sexual intercourse.


Endemic - daycares, nursing homes, military bases, prisons, backpackers.


adult mites enter skin, creating burrows. Females lay eggs in burrpws, larvae develop under skin. Weeks-months later - extreme pruritis (sides of fingers, buttocks, external genitalia, wrists, elbows, ankles. Intense itching and scratching -> 2ndary bacterial skin infections.


Immunodeficient - Norwegian scabies - general dermatitis, excessive scaling and crusting - highly contagious crusts.


Diagnosis - mites/eggs in skin scrapings/biopsy.