problem based microbiology
DESCRIPTION
MicroTRANSCRIPT
Problem-Based Microbiology
2008
(4) DiphtheriaCorynebaterium diphtheriae
• Recent emigrant w/ unknown immunizations
• Yellowish, leathery thick membrane in pharynx
• “Bull neck” – bilateral cervical adenopathy
• Gm+ clubs, non-motile, non-hemolytic, catalase+, aerobic
• Tellurite medium• Diptheria toxin
• Diphtheria A-B exotoxin affects Elongation Factor 2 blocking protein synthesis leading to cell necrosis
• Upper respiratory droplets, direct contact
• Tx: Diptheria antitoxin
(10) Bacterial pneumoniaKlebsiella pneumoniae
• Alcoholic, homeless• Thick, blood-tinged
sputum (currant jelly)• RUL infiltrate with
cavitary lesion (abscess)
• Gm- short plump bacilli• Lactase+, Urease+,
Indole-• Capsular polysacchride
(CPS), K antigen
• Most common Gm- pneumonia, nosocomial
• CPS are antiphagocytic, molecular mimicry with C3b and prevents alternative complement pathway, inflammation
• Aspiration pneunomia
• Tx: Piperacillin
(15) Post-Primary TuberculosisMycobacterium tuberculosis
• Recent emigrant• Fever, cough, night sweats,
weight loss• Chronic cough w/ blood-
tinged sputum• RUL infiltrates
• Acid-fast, long bacilli cord• Multinucleated giant cells• Cord Factor, phenolic
glycolipids (LAM)
• Infects macrophages (recognize LAM) inhibits phagolysosome fusion, cord factor damages PMNs, form granulomas w/ large multinucleated giant cells
• Airborne transmission
• Tx: Isoniazid+Rifampin+ Pyrazinamide+Ethambutol empirically, later INH+RIF only if susceptible
(17) HistoplasmosisHistoplasma capsulatum
• 5 workers demolish building near Ohio river
• Pigeon droppings• Multiple nodular
infiltrates, cavitary lesion in RML, popcorn calcification
• Mold in soil, yeast in humans
• Giemsa, Wright stains
• Yeasts grow in inactivated macrophages (histiocyte) causing granuloma formation, disseminate via lymph, cytokines
• Ohio/Mississippi river valleys, soil with bat/bird droppings
• Tx: Itraconazole (Amphotricin B if severe)
(18) BlastomycosisBlastomyces dermatitidis
• Tennessee landscaper• Painful R arm verrucous
skin lesion, pustular• Multiple nodular
cavitating lesions in LUL• Unresponsive to
cefuroxime/erythromycin
• White fluffy mold, large budding yeast in humans
• Neutrophils recruited forming suppurative/ granulomatous inflammation, focal microabscesses in papillary dermis
• SE US, wooded areas
• Tx: Itraconazole (Amphotericin B if severe)
(19) CoccidioidomycosisCoccidioides immitis
• Recently visited Arizona• Erythema nodosum on
back• Infiltrates in both lungs,
large cavity in RUL
• Branching septate hyphae mold in soil, non-budding spherules in humans forming endospores
• Spherule in terminal bronchiole causes chronic granulomatous inflammation, can disseminate to skin
• SW US, arid soil around rodent burrows
• Tx: Itraconazole (Amphotericin B if severe)
(22) Pneumocystis PneumoniaPneumocystis jiroveci
• Has AIDS with thrush• Bilateral air-space
consolidation with interstitial/alveolar markings “ground glass”
• Fungus, 5-8 um cysts containing intracystic sporozoites
• Giemsa, Silver, DFA stain
• Adhere to Type I pneumocytes, cysts rupture and fill alveoli, decrease surfactant secretion forming foamy exudate
• Immunocompromised
• Tx: TMP-SMX
(26) Secondary SyphilisTreponema pallidum
• Multiple sexual partners• Hx of painless ulcers on
vulva• Maculopapular rash on
palms and soles, pustular lesions and condylomata lata on face
• Spirochetes, obligate human pathogens
• Lipoproteins• RPR, VDRL tests
• Chancre, indurated painless ulcer, indicated in primary syphilis.
• Spread by lymph and blood leads to a maculopapular rash in secondary syphilis.
• Neurosyphilis (teritiary)• Sexual, congenital spread
• Tx: Penicillin G (doxycycline if allergic)
(30) ChlamydiaChlamydia trachomatis
• Multiple sexual partners• Lower abd pain, vaginal
discharge, dysuria, cervical motion tenderness
• Pelvic Inflammatory Disease
• Gm- cell layers w/ LPS• Serotypes D-K most
common
• Most frequently reported STD in US
• Elementary bodies (EB) enter columnar epithelial cells of cervix becoming reticulate bodies (RB) which multiply and release EBs, inflammation
• Tx: Doxycycline (and cefoxitin for anerobes)
(31) TrichomoniasisTrichomonas vaginalis
• Sexually promiscuous• Yellow, foamy vaginal
discharge with foul odor• “Strawberry cervix”
• Motile, pear shaped• Human-only host• Fishy odor with KOH test• No stippled “clue cells”
• Inflammatory response (vaginitis) with PMNs present, direct damage causes microulcerations, increased vaginal pH
• Most men asymptomatic
• Tx: Metronidazole
(32) Candidiasis (Yeast Infection)Candida albicans
• Thick whitish vaginal discharge
• Vulvar itching• Denys sexual activity• Recent ATB use
• Yeast with pseudohyphae, produce chlamydospores
• Yeast cell cultivation in human serum yields distinctive germ tubes
• With disruption of normal flora, C. albicans overgrows on muco-cutaneous surfaces forming cottage cheese-like discharge
• Broad-spectrum ATB
• Tx: Topical antifungals (clotrimazole) or oral fluconazole
(33) HIV-1Human immunodeficiency virus type 1• Unprotected MSM• Diffuse maculopapular
rash on abdomen
• Retrovirus• gp120, gp41• ELISA + Western Blot
• gp120 binds to CD4 which allows it to bind to CXCR4 (T-cells) or CCR5 (T-cells/ Mφ) co-receptors.
• gp41 leads to fusion and cell entry
• Sex, IV Drug Use, Congenital spread
• Tx: Combination anti-retroviral therapy (HAART)
(35) SalmonellaSalmonella typhimurium
• Family has cramps, vomiting, diarrhea (bloody)
• Ate turkey and stuffing
• Gm- motile rods, facultative anaerobic, lactase-, oxidase-
• Stool cultures
• 2nd leading cause of food-borne disease
• Localized invasion results in influx of neutrophils, can cause bacteremia w/ LPS inducing sepsis
• Poultry, eggs, dairy
• Tx: NONE (self-limiting)
(38) E. Coli O157:H7Enterohemorrhagic Escherichia coli (EHEC)• Severe abdominal
cramps, watery turning into bloody diarrhea
• Ate pink hamburgers
• Gm- rod, Indole+, Lactase+, Sorbitol non-fermenting
• Stool cultures
• Most common cause of bloody diarrhea
• Attaches to brush border of intestinal epithelium
• Shiga-toxins cause endothelial damage leading to blood loss
• Ground beef, unpasteurized milk
• Tx: NONE (self-limiting)
(39) CholeraVibrio cholerae
• Traveled to Bangladesh• Profuse rice-water
diarrhea, vomiting, sweating, cramps
• Taking H2-blocker drug
• Gm-, comma-shaped• Motile, oxidase+,
faculatative anaerobe• Acid-sensitive• Cholera toxin (CTX)
• Pandemic due to O:1 biotype El Tor
• CTX activates adenyl cyclase cascade increasing cAMP, accumulate NaCl in lumen leading to dehydration
• Contaminated water/food
• Gulf coast US: shellfish
• Tx: Rehydration therapy (oral rehydration sol’n)
(42) C. difficile-associated diarrhea (CDAD)Clostridium difficile
• Frequent diarrhea• Erythematous, friable
colonic mucosa• Hx of broad spectrum
ATB treatment
• Gm+, spore-forming rod, strict anaerobe
• Toxin A, Toxin B• Stool sampled for toxin
(ELISA)
• Toxin B more potent, inactivate GTP-binding proteins causing break-up of actin filaments damaging cellular lining
• Exposure to broad-spectrum ATB (clindamycin, cephalo-sporin, ampicillin)
• Tx: Metronidazole
(46) Amebic DysenteryEntamoeba histolytica
• Traveled to India• Intermittent diarrhea
with blood and mucus• Multiple small
hemorrhagic areas with ulcers in sigmoid colon
• Trophozoite in host and infective cyst in feces
• Cyst transforms in small intestine and migrate to large intestine, invading colon causing cell and PMN lysis, can cause flask-shaped ulcers
• Fecal-oral transmission
• Tx: Metronidazole and Paromomycin
(47) GiardiasisGiardia lamblia
• Backpacking in Rockies• Watery diarrhea turning
greasy and foul smelling
• Trophozoite pear-shaped, face-like appearance, cysts in stool
• Stool antigen test
• Trophozoites attach to brush border causing villus atrophy resulting in diarrhea
• Beavers, dog feces contaminated water
• Tx: Metronidazole
(48) CryptosporidiosisCryptosporidium parvum
• Untreated AIDS• Chronic watery diarrhea
• Acid-fast, intracellular, extracytoplasmic coccidian oocysts
• Ziehl-Neelsen staining
• Oocysts release sporozoites infecting the jejunum between microvilli, impairing adsorption resulting in water loss
• Water-borne transmission
• Tx: IV rehydration, restore HAART
(49) AscariasisAscaris lumbricoides
• Originally from Mexico• Poor appetite, abd pain• Eosinophilia• Intestinal obstruction• Nematode eggs in stool
• Largest human roundworm
• Eggs have “bumpy coat”
• Larvae hatch, invade intestinal mucosa, travel through portal and systemic circulation to lungs and alveolar walls (Loeffler syndrome). Larvae are reswallowed.
• Tropical regions, soil, produce, children 3-8 yo
• Tx: Mebendazole
(50) StrongyloidiasisStrongyloides stercoralis
• Traveled to El Salvador• 3w worsening diarrhea,
abd pain, fevers• Eosinophilia• Maculopapular rash on
groin and buttocks
• Rhabditiform larvae with prominent genital primordium
• Filariform larvae penetrate skin and migrate to lungs where they are reswallowed into the jejunum causing GI symptoms and can reinfect peri-anally.
• Humid tropical regions, direct contact with soil (walking barefoot)
• Tx: Ivermectin
(51) Hydatid Cyst DiseaseEchinococcus granulosus
• Emigrated from Argentina raising sheepdogs
• Fever, chills, jaundice, upper abd pain
• Liver has large multi-loculated cyst with bile duct dilation
• Tapeworm, 3 proglottids• Hydatid cysts
• Oncospheres invade and develop into cysts in liver, lung, brain, etc. Can lead to biliary duct dilation and jaundice, hydatid cysts cause abd pain
• Dog feces
• Tx: Surgery, Albendazole
(52) SchistosomiasisSchistosoma mansoni
• Recent immigrant from Kenya
• Eosinophilia• Hepatosplenomegaly w/
portal HTN• Vomiting w/ blood
• Blood trematode• Egg w/ lateral spine
• Cercariae penetrate skin and migrate to veins, eggs migrate but some are trapped and die in tissue causing granulomatous rxn in liver and spleen.
• Infected snails in open water
• Tx: Praziquantel
(53) Hepatitis AHepatitis A Virus (HAV)
• Fever, jaundice, dark yellow urine, pale stools
• Sight of food triggers nausea
• High ALT and AST
• Picorna – ssRNA+ icosahedral capsid
• Hepatitis panel serology
• Replicates in liver, CTL response, viremia, and eventually cleared
• Worldwide: Poor sanitation, US: Shellfish
• Tx: NONE (self-limiting)
(58) MeningitisListeria monocytogenes
• Headache, confusion, no nuchal rigidity
• Hx: Steroid use for RA• MRI show meningeal
enhancement
• Gm+, intracellular small rods, grow at 4⁰C, β-hemolysis, tumbling motility, ferment glucose.
• Internalin, listeriolysin O, phospholipases
• Internalin induces host cells to engulf. Phospholipases allows it to escape phagosomes, spread via pseudopods. Killed by T cell-mediated activation of Mφ.
• Meningitis in newborns• Processed meat, soft
cheeses
• Tx: Ampicillin + Aminoglycoside
(67) OsteomyelitisStaphylococcus aureus
• Spreading painful, warm, tender, necrotic-appearing boils on L leg with fever.
• Bone scan shows intense uptake in femur
• Gm+ cocci, clusters, catalase+, coagulase+, β-hemolytic
• Protein A, hemolysins, hyaluronidase, leukocidin
• Most common cause of skin infections
• Fibronectin-binding protein causes colonization in skin breaks that invade the mucosal barriers, makes pyogenic exudate, spreads locally or hematogenously to the bone (osteomyelitis)
• Human nasal carrier
• Tx: Nafcillin (Vancomycin if MRSA)
(68) Necrotizing FascitisStreptococcus pyogenes
• Severe pain, swelling in L thigh, purplish becoming rapidly grayish
• Gm+ cocci in chains, β-hemolysis, facultative anaerobic, catalase-, bacitracin-sensitive
• Hyaluronic acid, M-protein, LTA, hemolysin O and S, enzymes
• LTA-M protein binds to epidermis and resist phagocytosis, spread into subcutaneous tissue, dermis, and fascia via hyaluronidase prompting pyogenic inflammation.
• Direct contact, types M1 or M3 common for skin
• Tx: Surgery, Penicillin G (clindamycin if allergic)
(69) Gas GangreneClostridium perfringens
• Severe pain at colon carcinoma surgery site
• Discolored skin, hemorrhagic bullae, serosanguineous (thin brownish) discharge, extensive gas in soft tissue
• Gm+ box-shaped rods, anaerobic, catalase-, double β-hemolysis, deep tissues
• Nagler rxn (+ lecithinase)
• Bowel surgery allows anaerobes access to tissue and flourish with facultative anerobes. Α-toxin has phospholipase C activity on cell membranes, other enzymes produce gas, muscle turns black and gangrenous
• Normal human colon flora
• Tx: Surgery, Penicillin, Clindamycin
(71) Ringworm (tinea capitis)Microsporum canis
• Raised lesions with center nodules and peripherial scaling on head.
• Received dog recently
• Monomorphic fungi, spindle-shaped macro-conidia, white mold
• Wood’s light (UV) on hair• Keratinases, proteinases
• Only found in dead layer of epidermis, keratinases allow invasion of keratinized tissue, snake-like, annular, nodular, vesicular lesions.
• Found on cats and dogs
• Tx: Griseofulvin (concentrates in keratin), OTC drugs
(72) SporotrichosisSporothrix schenckii
• Multiple mildly painful erythematous lesions starting from thumb to elbow with lymphangitic streaking.
• Thumb has dry, shallow, ulcerated lesion
• Fungal dark-pigmented mold in soil, cigar-shaped yeasts in tissue, florally arranged microconidia
• Sabouraud dextrose agar
• “Rose handler’s disease”• Spores enter punctured skin
and form smooth/verru-cose painless nodules, spread via lymph forming chains of nodules or suppurating granulomas (plasma cells, neutrophils)
• Sphagnum moss, hay, thorny plants
• Tx: Itraconazole
(76) Native-Valve EndocarditisViridans streptococci
• Night sweats, “splinter hemorrhage” in fingernail, conjunctival petechiae
• Hx: Heart murmur• Hx: Wisdom tooth removal
w/ no ATB• Echo shows 8mm mobile
vegetation on bicuspid aortic valve
• Gm+ cocci in chains, α-hemolytic, optochin-resistant
• Results from transient bacteremia with preexisting valve abnormality. Minor trauma from turbulence leads to deposition of fibrin and platelets, binding bacteria forming micro-colonies leading to Janeway lesions, Osler nodes, Roth spots, splinter hemorrhages
• Normal oral/GI flora
• Tx: Bactericidal ATB (Penicillin G)
(77) PneumonitisCytomegalovirus (CMV)
• Moderate respiratory distress, bilateral interstitial infiltrates
• Received allogeneic bone marrow transplant, taking Bactrim
• Β-herpesvirus, dsDNA with capsid and env, can progress to latency
• Giant cells (cytomegalic) with intracellular inclusions (with halo “Owl’s eye”)
• Most common cause of post-transplant infection
• Multiplies in nucleus, enters latent state in leukocytes/ lymphocytes, can cause interstitial pneumonia on reactivation (spreading to pneumocytes)
• Close contact with body fluids (saliva)
• Tx: Ganciclovir (Foscarnet if resistant)
(78) Lyme Disease (LD)Borrelia burgdorferi
• Home in wooded CT• Multiple tick bites• Rash under armpit with
central clearing• Myalgia, arthralgia, fever
• Spirochete, motile• OspA, OspB• ELISA + Western Blot
• Ticks inoculate host, spread outwards and trigger inflammatory cytokines, can cause auto-immune Abs
• Black-legged deer-ticks• US: NE, MN, WI, Pacific
• Tx: Doxycycline
(79) MalariaPlasmodium falciparum
• Immigrated from W Africa• Intense periodic fevers,
drenched in sweat• Hepatosplenomegaly• Generalized seizure
• Protozoa with 4 stages: ring (around central vacuole), trophozoite (Schuffner dots), schizont (chromatin dots), gametocyte (crescent-shaped).
• Thick/thin film blood smear
• Sporozoites infect liver cells, mature and invate RBCs (Duffy Ag) and feed on Hg leading to anemia, thrombocytopenia, hypoglycemia, lactic acidosis. Can persist in liver
• Mosquitos
• Tx: Chloroquine (Primaquine for liver infections, mefloquine if resistant, exchange transfusion if severe)
(81) LeptospirosisLeptospira interrogans
• Recently returned from boating trip in August
• High fever, myalgia, severe HA, photophobia
• Swollen conjunctiva
• Spirochetes, long, thin, motile with hooked ends
• ELISA, microagglutination test (MAT)
• Hooked ends and flagella allows burrowing into tissues leading to bacteremia followed by inflammatory and immune response which can lead to jaundice
• Rat or livestock urine
• Tx: Oral doxycycline (IV penicillin if severe)
(82) PasteurellosisPasteurella multocida
• R hand and axilla was swollen and tender
• Hx: Bitten by cat
• Gm- short rods, oxidase+, encapsulated
• Chocolate agar• Bipolar staining
• Polymicrobic, capsule and endotoxin trigger inflammation with purulent drainage
• Cats (sometimes dogs)
• Tx: Penicillin G
(84) SmallpoxVariola major
• Papulovesicular lesions on face and extremities at same stage of development, bumpy lesions filled with opaque fluid
• Already had chickenpox
• Herpes, linear dsDNA, dumbbell-shaped core
• Eradicated worldwide• After week-long
incubation, flu-like symptoms, maculo-papular rash on face, palms, soles.
• Bioterrorism agent
• Tx: NONE (self-limiting)
(85) PlagueYersinia pestis
• Lives in Arizona• Painful L groin mass, firm
and tender• Small hemorrhages on skin
of R leg
• Gm- “safety-pin” shaped, nonmotile, oxidase-, ferment glucose, reduce nitrates
• F1 glycoprotein, protease, coagulase, exotoxin
• Wright stain
• F1 avoids phagocytosis and multiplies in Mφ, spread to lymph nodes forming “buboes” and can cause bacteremia, widespread petechial lesions from vascular necrosis if systemic
• Rodents, carnivores, cats, dogs are animal reservoirs
• Flea vectors
• Tx: Streptomycin
(88) Hantavirus Pulmonary Syndrome (HPS)
Sin Nombre Virus• Fever, malaise, muscle
aches, hypotension, SOB• Camping in rural NM with
deer mice• Bilateral interstitial
infiltrates with hilar indistinctness
• Left-shift (22% bands)
• Bunyavirus, spherical, circular ssRNA-, triple-segmented
• Serology, RT-PCR
• Attach to cells at b3 integrin receptor, replicate in cytoplasm, initiate TNF, IL-2 response. Activated CD8 T-cells produce holes in infected pneumocytes leading to bilateral infiltrates, left-shift, thrombocytopenia, pulmonary edema, hemoconcentration
• Rodent urine or droppings
• Tx: Supportive care
(91) Severe Acute Respiratory Syndrome (SARS)SARS Coronavirus
• Mild SOB, hypoxia• Hx: Care of patient with
severe respiratory illness• Bilateral lower lobe
interstitial infiltrates
• Coronavirus, ssRNA+, enveloped with club-shaped peplomers, nonsegmented
• Infection leads to diffuse alveolar damage (DAD), multinucleated giant cells with no viral inclusions, squamous metaplasia, increased fibrosis
• Respiratory droplets
• Tx: Supportive Care