Microbiology Flashcards
Describe the key features of Staphylococcus sp.
Gram +ve cocci in clusters. Aerobic and facultatively anaerobic. Coagulase + ve (staph aureus) or -ve (staph epidermidis, saprophyticus etc)
When would you find enterotoxin being produced?
Food poisoning
What is SSSST?
Toxin produced by staph- Staph Scalded Skin Syndrome Toxin
Describe staph epidermidis
Skin commensals. May cause infection- artificial materials (Joints, valves, IV catheters)
What can staph saprophyticus cause?
UTI in women of child bearing age
Describe streptococcus sp
Gram +ve cocci in chains. Aerobic (and facultatively anaerobic). Classified by haemolysis - Beta = complete, alpha=partial, gamma = non-haemolytic
What toxin can be produced by beta-haemolytic strep?
Haemolysin- damage tissues
What further classification beyond haemolysis can be used in strep?
Antigenic structure on surface (serological): Group A- (throat, severe skin infections), Group B- (meningitis in neonates)
What are the 2 classes of alpha- haemolytic strep?
Strep pneumonia-Pathogen, commonest cause of pneumonia. Viridans- commensals of mouth, throat, vagina
What are the non-haemolytic streptococci?
Enterococcus sp (E. faecalis, E. faecium)- commensals of bowel, common cause of UTI
Name some competitive bacterial flora
Staph epidermidid, corynebacterium sp. (diphtheroids), Proprionobacterium sp.
When might you find staph. aureus infection of the skin?
Boils, carbuncles, minor skin sepsis, cellulitis, infected eczema, impetigo, wound infection, staphylococcal scalded skin syndrome
When might you find strep. pyogenes infection of the skin?
Infected eczema, impetigo, cellulitis, erysipelas, necrotizing fasciitis (may also be caused by mixed bacterial infection).
How might you diagnose a bacterial skin infection?
Swab of lesion if surface broken
Pus or tissue if deeper lesion
+/- blood cultures, if appropriate
What is the antibiotic of choice for treating sensitive strains of Staph. aureus?
Flucloxacillin
What antibiotic is used to treat strep. pyogenes?
Penicillin (also treated by flucloxacillin)
What is the treatment for necrotizing fasciitis?
Life threatening. Requires immediate surgical debridement as well as antibiotics
What is necrotizing faciitis?
Bacterial infection spreading along fascial planes below skin surface > rapid tissue destruction. Not much on surface, severe pain
What are the 2 types of necrotizing faciitis?
I- Mixed anaerobes & coliforms,usually post abdo surgery. II- Group A strep infection
How would you treat leg ulcers?
Vascular problem, only swab if signs of cellulitis/infection. Treat strep pyogenes, staph aureus, other beta-haemolytic strep (B,C,G), anaerobes (esp diabetics)
What is dermatophyte (fungal) infection?
Ringworm
Describe the names of ringworm infections and locations
Tinea capitis-scalp, Tinea barbae-head, Tinea corporis- body, Tinea manuum- hand, Tinea unguium- nails, Tinea cruris- groin, Tinea pedis - foot (athletes foot)
What is the pathogenesis of dermatophyte infection?
Fungus enters abraded or soggy skin
Hyphae spread in stratum corneum
Infects keratinised tissues only (skin, hair, nails)
Increased epidermal turnover causes scaling
Inflammatory response provoked (dermis)
Hair follicles and shafts invaded
Lesion grows outward and heals in centre, giving a “ring” appearance
Are men or women more commonly affected by dermatophyte infection?
Men
Who does scalp ringworm mainly affect?
Children
Who does foot and groin ringworm mainly affect?
Men
What are some sources of dermatophyte infection?
Other infected humans (most likely)- anthropophilic fungi, animals (cats, dogs, cattle)- zoophilic fungi, soil (less common in UK)-geophilic fungi
What casual organisms are involved in dermatophyte infection?
Trichophyton rubrum (>70%), Trichophyton mentagraphytes (>20%): human-human. Microsporum canis - cats, dogs-humans
What is the treatment for dermatophyte infections?
Small areas of infected skin, nails Clotrimazole (Canestan) cream or similar Topical nail paint (amorolfine) Extensive skin infections Nail infections Scalp infections Terbinafine orally Itraconazole orally
Where does candida commonly cause infection?
Skin folds where area is warm and moist - candida intertrigo. Under breast, groin areas, abdo skin folds, nappy areas in babies
What is the diagnosis and treatment for candida?
Swab for culture, treat with clotrimazole cream, oral fluconazole
Describe scabies
Caused by sarcoptes scabiei. Chronic crusted form Norwegian scabies. Incubation period up to 6 wks. Itchy rash affecting finger webs, wrists, genital area
What is the treatment of scabies?
Malathion lotion, applied overnight to whole body and washed off next day. Benzyl benzoate (avoid in children)
Describe pediculosis (lice infestation)
Various types- pediculus capitis/corporis(Vagabonds disease) = head/body. Phthirus pubis -pubic louse. Associated with intense itch, treat using malathion
What virus are Chicken pox and Shingles due too? (And which is which?)
Varicella Zoster Virus (Chickenpox is Varicella, Shingles is Zoster)
Describe Chickenpox
Primary infection typically in childhood. Generalised rash/fever. Virus establishes latency in sensory nerve roots
Describe Shingles
Reactivation later in life, typically old age. Rash is dermatomal
Describe the symptoms of Chickenpox
Macules-papules-vesicles-scabs-recovery/ Centripetal, varying density, inflammed skin, fever, itch
What complications can occur as a result of chickenpox?
Complications- secondary bacterial pneumonitis haemorrhagic scarring, absent or minor encephalitis
What are the predictors of severity of chickenpox?
Extremes of age, depressed cell mediated immunity
Describe neonatal VZV
Secondary to chickenpox in mother in late pregnancy
Higher mortality
Prevention with Varicella Zoster Immune Globulin in susceptible women in contact
Describe the symptoms of Shingles
Dermatomal distribution of rash. Tingling/pain to erythema to vesicles to crusts
What is the pain in Shingles known as, and what kind of pain is it?
Zoster associated (after wk4 Post herpetic neuralgia), neuralgia often effecting trigeminal
What should you look out for regarding the trigeminal nerve and shingles?
Shingles effecting particular divisions of the nerve, effecting the relevant part of the face
Describe Ramsay-Hunt Syndrome
Vesicles and pain in auditory canal and throat. Facial palsy (7th nerve), irritation of CNVIII-deafness, vertigo, tinnitus. Aka geniculate or otic herpes zoster
What virus causes primary gingivostomatitis, who does it commonly and symptoms?
HSV- pre school children. Causes extensive ulceration in and around mouth for ~1 wk
What can HSV cause in general?
Blistering rash at vermillion border. Can spread- to finger or eczema: herpetic whitlow, eczema herpeticum
What can HSV Type 1 cause?
Main cause of oral lesions, causes half of genital herpes, causes encephalitis
What can HSV Type 2 cause?
Rare cause of oral lesions, causes half of genital cases, encephalitis/disseminated infection (particularly neonates)
What drug can be used as an antiviral against VZV and HSV?
Aciclovir
Describe aciclovir
Analogue of guanosine. Selectively incorporated into viral DNA inhibiting replication. Early/good example of non-toxic effective anti-viral. Does not eliminate latent virus
What are some triggers of erythema multiforme?
Drug reactions, and some infections : HSV, Mycoplasma pneumoniae bacterium
Describe Molluscum contagiosum
Fleshy, firm, umbilicated, pearlescent nodules- 1-2mm in diameter. Self limiting, but can take months. Common in children, can also be sexually transmitted
What can be used to treat molluscum contagiosum?
Local application of liquid nitrogen
Describe the causes, groups effected, and treatment of warts
Caused by HPV, commonest in children. Self limiting, uncomplicated- topical salicylic acid can be used. If on feet- verrucas
Name some diseases that can be caused by HPV
HPV 1-4 warts/verrucas. Genital warts HPV 6 and 11. Cervical cancer HPV 16 and 18. Head and neck cancer.
What is Herpangina, what causes it and tests used to identify it?
Blistering raash of back of mouth. Caused by enterovirus- coxsackie virus, echovirus. Self limiting. Swab of lesion, sample of stool for enterovirus PCR
What is the cause and groups effected by Hand, Foot and Mouth disease?
Enteroviruses (esp coxsackie viruses). Typically children, family outbreaks. Not same as animal disease
Describe erythema infectiosum
Aka slapped cheek, parvovirus B19. Rash on face, fades and lacy macular rash on body appears. In adults rash may be absent, and acute polyarthritis of small joints may be prominent.
What are the complications of parvovirus B19?
spontaneous abortion fetal hydrops as precursor Aplastic crises sudden drop in haemoglobin seen in patients with short red cell life span Thalassaemia Hereditary spherocytosis Sickle cell anaemia Chronic anaemia in immunosuppressed patients
How is the presence of parvovirus b19 confirmed?
Antibody testing rather than skin swabs- parvovirus B19 IgM test
What is Orf, symptoms and diagnosis?
Virus of sheep “scabby mouth” Firm, fleshy nodule on hands of farmers Constitutional symptoms rare Self limiting Clinical diagnosis, lab confirmation not used
Describe the primary infection presentation of syphillis
Chancre formed- painless ulcers at site of entry
Describe the secondary infection presentation of syphilis
Red rash over body
Prominent on soles of feet and palms of hands
Mucous membrane “snail track” ulcers
Describe the tertiary infection presentation of syphilis
CNS, cardiovascular, gummatous etc etc
What causes syphilis, and how it is diagnosed and treated?
STI with bacterium Treponema pallidum, diagnosed by blood test or swab of chancre for PCR. Treated using penicillin injections
What is the vector, cause, presentation, lab confirmation and therapy for Lyme disease?
Vector
Ticks
Cause: bacterial
Borrelia burgdorferi
Presentation
Early: erythema migrans(diagnostic, no lab confirmation needed)
Late: heart block, nerve palsies, arthritis.
Lab confirmation: mainly for late presentations and is a blood test for antibody to organism
Therapy: doxycycline or amoxicillin
