Skin and Mucosa Infections

Question 1

Normal Flora of the Skin

Answer 1

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

Question 2

Impetigo:

Answer 2

oozing, vesicular lesions

Question 3

Normal Flora of the URT

Answer 3

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.

Question 4

Staph. bacteria

Answer 4

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

Question 5

Staph Aureus

Answer 5

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

Question 6

Diseases caused by S. aureus

Answer 6

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

Question 7

Scalded Skin Syndrome

Answer 7

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)

Question 8

Toxic Shock Syndrome

Answer 8

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)

Question 9

Name some exclusion criteria needed for diagnosis of TSS?

Answer 9

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

Question 10

Staph. epidermidis

Answer 10

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

Question 11

Staph. saprophyticus

Answer 11

Gram Positive

Catalase-positive, coagulase-negative, novobiocin-resistant

associated with UTIs (cyctitis) - especially in young sexually active women

Question 12

Strept. bacteria

Answer 12

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)

Question 13

Streptococcal Diseases

Answer 13

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

Question 14

Streptococcus pyogenes (aka Group A Strept.)

Answer 14

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)

Question 15

Diagnosis of suspected streptococcal pharyngitis

Answer 15

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)

Question 16

Toxic Shock Syndrome caused by Group A Strept

Answer 16

hypotension, renal impairment, coagulapathy, liver involvment, adult respiratory distress syndrome and more

Question 17

Diseases of Strept. agalactiae

Answer 17

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

Question 18

Viridans Streptococci

Answer 18

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

Question 19

Diseases of S. pneumoniae

Answer 19

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

Question 20

Pseudomonas aeruginosa

Answer 20

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

Question 21

Propionibacterium acnes

Answer 21

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

Question 22

Actinomyces (A. israelii)

Answer 22

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

Question 23

Buruli ulcer

Answer 23

Mycobacterium ulcerans, acid-fast bacillus

tropical areas of Africa and Asia, associated with aquatic environments

usually appears as a large ulcerative & erythematous lesion

Question 24

Parvovirus B19

Answer 24

Fifth disease, very small, naked icosahedral, ssDNA virus

infects erythrocyte precursors

rash - erythema infectiosum, (slap cheek rash)

innocuous, childhood disease

Question 25

Syphilis:

Answer 25

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

Question 26

Primary syphilis

Answer 26

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

Question 27

Secondary syphilis

Answer 27

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

Question 28

Tertiary syphilis

Answer 28

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

Question 29

Chancroid

Answer 29

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

Question 30

Granuloma Inguinale

Answer 30

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

Question 31

Lymphogranuloma venereum

Answer 31

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

Question 32

Human Papilloma Virus (HPV)

Answer 32

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

Question 33

Trichomoniasis

Answer 33

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”

Question 34

“Whiff Test”

Answer 34

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

Question 35

Bacterial vaginosis

Answer 35

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

Question 36

Genital Herpes

Answer 36

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

Question 37

G o n orrhea

Answer 37

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