Skin and Mucosa Infections Flashcards
Gram +. Helminths, Parasites
Normal Flora of the Skin
Staphylococcus (S. epidermidis, S. aureus)
Streptococcus (S. pyogenes: group A strept.)
Diphtheroids, (both aerobic and anaerobic; these include
Corynebacterium spp, and Propionibacterium)
Mycobacterium spp
Proteus & Pseudomonas spp
Fungi (C. albicans, various dermatophytes)
Various Viruses
Impetigo:
oozing, vesicular lesions
Normal Flora of the URT
Staph. aureus: oropharynx, nasopharynx and tonsils
Coagulase negative Staphylococci: mouth
S. pyogenes: found in nasopharynx & tonsils
Viridans streptococci: mouth
Strept. pneumoniae: found in the throat.
Anaerobic cocci, Enterococci, Bacteroides, Fusobacterium spp
Neisseria meningitidis: found in the nasopharynx.
Corynebacteria, Actinomyces spp, Moraxella, Klebsiella and
Enterobacter group, Haemophilus, Mycoplasma, Candida spp.
Staph. bacteria
Gram stain: appear as purple round bodies (cocci), mostly in clumps. Gram Positive
major players are staph aureus, epidermidis, saprophyticus (less so haemolyticus and lugdunensis)
Catalase positive, Facultative anaerobe, beta-hemolytic
virulence factors - Capsule, peptidoglycan, lipid protein A, teichoic acid
Key - many have penicillinase
grows on blood agar and most basic agars, will not grow on MacConkey agar
Staph Aureus
gram positive cocci that grows in clusters
penicillinase, capsule, lipid A, PGN, teichoic acid, forms a biofilm/slime later,
Toxins - toxic shock syndrome toxin, cytolytic, exfoliative, enterotoxin
catalase (2 H2O2 > 2 H2O + O2) and coagulase positive
Diseases caused by S. aureus
Main:
Scalded Skin Syndrome
Skin infections - boils, carbuncles, impetigo
Wound Infections
Toxic Shock Syndrome
Others - Food poisoning/enterocolitis, bacteremia, acute endocarditis, pneumonia, empyema, osteomyelities, septic arthritis
Note - elderly and pts with abnormal heart valves are predisposed for acute endocarditis, pneumonia typically follows the flu
Scalded Skin Syndrome
caused by infection with Staph aureus
begins as local redness and inflammation and spreads, forms blisters and the squamous layer of epithelium begin to peeps off and does not recover (Nikolsky’s sign)
Occurs primarily in very young children (infants/toddlers)
Toxic Shock Syndrome
caused by Staph. aureus
superantigen disease that overly stimulates the proliferation of T cells and the release of cytokines - leads to leakage and destruction of endothelial cells and systemic problems which include organs.
associated with tampon use
Dx - high temp for 14+ days, diffuse macular erythroderma, convalescent desqumamation, hypotension, mucous membrane hyperemia, cardiopulmonary and hematologic manifestation (these last three are minor criteria)
Name some exclusion criteria needed for diagnosis of TSS?
Negative blood cultures for potential / suspect pathogens - other than s. aureus
viral cultures and PCR negative
serologic titers for group A strept
absence of other possible non-infectious causes - drug reactions; autoimmune/hematologic disorders
Staph. epidermidis
Gram Positive, Normal skin flora, forms non-hemolytic colonies on blood agar
catalase-positive, coagulase-negative and onvobiocin-sensitive
slime layer
opportunistic pathogen - surgical wound infections, catheter-related UTIs and bacteremia
Staph. saprophyticus
Gram Positive
Catalase-positive, coagulase-negative, novobiocin-resistant
associated with UTIs (cyctitis) - especially in young sexually active women
Strept. bacteria
Gram Positive Cocci - grows in short or long chains, Non-motile
Facultative Anaerobes - strict anaerobes to capnophilic
Catalase-negative
Capsulated, M Protein (superantigen), F Protein, Lipoteichoic Acid, T Protein
pyrogenic exotoxin, streptolysin O/S, streptokinase, DNAase, C5a peptidase
Species are grouped (Group A, B, D) with some ungrouped
Different species have different effects on blood agar - gamma (no hemolysis), alpha (incomplete) and beta (complete)
Streptococcal Diseases
Pharyngitis - mostly Group A
Toxic Shock Syndrome
Scarlet Fever - bacteriophage strept
skin lesions - erysipelas, cellulitis, pyoderma, impetigo
necrotizing fascitis - serious, life-threatening, disseminated skin disorder
Rheumatic fever
Acute Glomerulonephritis - occurs after a Strept. throat or skin infection
Meningitis
Streptococcus pyogenes (aka Group A Strept.)
Gram (+) cocci: short or long chains, sps with M protein and hyaluronic acid in capsule, Streptolysin O, β-hemolysis
Most serious cause of bacterial pharyngitis - throat/tonsillar membrane inflamed, fever, enlarged cervical nodes and painful & difficult swallowing
healthy carriers - asymtomatic
aerosol transmission
complications - acute glomerulonephritis & rheumatic fever
skin infection complication - acute glomerulonephritis (Type III HS)
untreated - (in addition to the complication above) Rheumatic fever (upon second infection), Scarlet fever (bacteriophage - lysogenic phage, Erythrogenic toxin)
Diagnosis of suspected streptococcal pharyngitis
By clinical presentation
Throat swab - antigen detection (latex agglutination), culture with beta-hemolysis, Gram (+) cocci, Catalase (-), Test for bacitracin (A disc) sensitivity
Antibody detection - Anti-streptolysin-O (ASO Antibodies)
Toxic Shock Syndrome caused by Group A Strept
hypotension, renal impairment, coagulapathy, liver involvment, adult respiratory distress syndrome and more
Diseases of Strept. agalactiae
Group B Strept
Early Onset Neonatal Disease - Bacteremia, Pneumonia and Meningitis
Late-Onset Neonatal Bacteremia with Meningitis
In men and non-gravid women - normal colonization of the urogenital tract
Post-partum sepsis - baby passing through an infected birth canal
Viridans Streptococci
Theres many many kinda, including mutans and salivarius, normal members of the oral cavity that can cause endocarditis when gaining access into the bloodstream - usually through invasive dental procedure
Diseases of S. pneumoniae
Gram Positive - diplococci
Pneumonia
Sinusitis and Otitis Media
Meningitis
Bacteremia
Septicemia
Pneumococcal pneumonia and meningitis are the most common bacterial causes of pneumonia and meningitis
Pseudomonas aeruginosa
motile, gram-negative bacillus, non-fermenting and forms colorless colonies on MacConkey agar
oxidase-positive – diagnostic aid
LPS/endotoxin in cell wall - sepsis
causes skin infections - burns, post-surgical wounds; Skin lesion - ecthyma gangrenosum
Rx - resistance through stricture of porin proteins
Associated with Cystic Fibrosis
cytotoxic enzymes - exotoxin A & exoenzyme S inhibit protein synthesis
Propionibacterium acnes
small gram-positive rod, short chains or clumps, anaerobe
skin, conjunctiva, external ear, and in the oropharynx, combines with sebum and stimulates a host inflammatory response that leads to tissue damage - acne
Actinomyces (A. israelii)
long gram positive rods [anaerobes]; filamentous,
colonize the upper respiratory tract - cause chronic granulomatous lesions that fill with pus and abscess “lumpy jaw”, also causes pelvic / intrauterine abscesses
Sulfur granules
Buruli ulcer
Mycobacterium ulcerans, acid-fast bacillus
tropical areas of Africa and Asia, associated with aquatic environments
usually appears as a large ulcerative & erythematous lesion
Parvovirus B19
Fifth disease, very small, naked icosahedral, ssDNA virus
infects erythrocyte precursors
rash - erythema infectiosum, (slap cheek rash)
innocuous, childhood disease
Syphilis:
Treponema pallidum, a bacterial spirochete
can be seen with dark feild microscopy but cannot be gram stained
Will not culture
Disease happens in stages - primary, secondary, and tertiary
Diagnosis - clincal presentation + history + serology
serology
- non-specific tests VDRL or RPR
- specific tests - FTA or MHA-TP, ELISAs
previous method was to start with RPR and due a specific test to confirm (if RPR was +)
Now - you start with a specific test and follow up with a RPR, if both are + then its active disease
Serology must be interpreted with presentation and history because antibodies are present even after a patient is treated
Primary syphilis
Painless, sore, ulcer or lesion (aka chancre) develops on genitals and lasts a few days
slow development, regional lymph node swelling
lesion often goes unnoticed in women
highly infectious, disease is transmissible
lesions heals with or without treatment
Secondary syphilis
Develops a few weeks after untreated primary syphilis
Flu-like symptoms caused by the dissemination of treponemes - fatigue, fever etc
characteristic maculopapular skin rashes (through out the body, in DPR on palms, in pic on ankles)
lesions resolve and ensues a long latency period
Tertiary syphilis
Usually preceded by a multi-year latency
Nodular skin lesions and gummas
Cardiovascular - aortic aneurysms
Neurosyphilis - blindness, insanity, spinal cord damage (tabes dorsalis), ataxic, shuffling gain and paresis
Gumma: A necrotic granuloma of tertiary syphilis
Chancroid
Haemophilus ducreyi, gram - bacillus
more common in tropical parts of the world
Causes soft, painful chancres on genitals plus buboes - unlike syph it’s not systemic
Dx: appearance of pink bacilli from a pt sample + culture on chocolate agar
Granuloma Inguinale
aka “Donovanosis” Caused by Klebsiella granulomatis
Encapsulated, intracellular, gram-neg. rod, lactose fermenter
common in Papua New Guinea, Caribbean, S. America, India, S. Africa, Australia and Vietnam
disease begins as subQ nodules that erode into painless granulomatous ulcerations that bleed easy
Dx - donovan bodies (the bacteria) seen in host cells - Giemsa stain; pathognomonic
Lymphogranuloma venereum
Chlamydia trachomatis
Very rare, tropical & sub-tropical
Chief complaint(s) are swollen and tender inguinal area (skin and nodes) + malaise
Like syphilis theres a primary painless ulcer/papule
Occurs mostly in men
confined to columnar epithelial cells in the genital tract and eye; infect macrophages and spread to regional lymph nodes
Human Papilloma Virus (HPV)
papovavirus family, circular double-stranded DNA
anogenital warts, cervical intraepithelial neoplasia
in malignancies the viral DNA is integrated in to host genome
cervical carcinoma associated with types 16, 18, 6 and 11. First two highest risk. (vaccine)
path findings - Koilocytic atypia w/ halo
physical finding - Condyloma accuminata
Trichomoniasis
motile, pear-shaped protozoan parasite, vaginalis
trophozoite with multiple flagella
pathogenesis - itchy, malodorous, yellow-green vaginal discharge. Cervix is highly erythematous, vaginal inflammation is possivle
asymptomatic in men
Dx - wet mount prep and loos for motile trichomonads or “whiff test”
“Whiff Test”
for diagnosing Trich
mixing a swab of vaginal fluid with a 10% potassium hydroxide solution - smelling it, strong amine odor indicates trickomoniasis or bacterial vaginosis
Bacterial vaginosis
Gardnerella vaginalis, gram-variable rod. Associated with increased numbers (further assoc with disbalance of lactobacilli)
could also be caused by Mobiluncus,
characterized - malodorous vaginal discharge and “clue cells”
clue cell - squamous epithelial cell encircled by myriad of small rod-like bacteria
Risk factors - multiple sex partners, cigarette smoking, poor nutrition, douching, using IUD, bad personal hygiene
Genital Herpes
2 serotypes of herpes simplex virus: types 1 & 2
HSV-2 – multiple vesicular/ulcerative-type lesions of the genital tract
large, enveloped virus dsDNA
painful lesion with flu-like symptoms
Dx - history and clincal presention, Tzanck smear (multinucleated giant cells), isolation of virus from patient sample and serotyping and DNA probe analysis of patient sample
G o n orrhea
Neisseria gonorrhoeae, a gram-neg, dipplococci
grows only on chocolate agar, ferments only glucose, oxidase +
antigenic variation, IgA protease
may be asymptomatic - especially in women
Causes thick, yellow-green discharge and itching or burning on urination (urethritis) > septic arthritis, PID, pustular skin lesions, and in rare cases - Fitz-Hugh-Curtis syndrome (infection of liver capsule)
neonatal conjunctivitis - baby through infected birth canal
