Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
51 Cards in this Set
- Front
- Back
|
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? 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. |
Hot-tub folliculitis - contaminated water enters hair follicles. Pseudomonas aeruginosa |
|
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. |
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. |
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. |
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. |
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. |
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 |
|
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. |
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. |
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. |
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. |
Tinea manuum/pedis - cutaneous mycoses of hands/feet Fine scaling/pustular lesions and itching eg. Trichophyton |
|
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. |
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. |
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. |
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. |
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. |
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. |
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. |
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. |
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. |
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. |
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. |
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. |
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. |
