LECOM Microbiology Lecture 4

Epidemiology, clinical disease, and diagnosis of Sporothrix schenckii

o Dimorphic fungus- causes rose gardener disease (from thorns)

o Initial lesion- papule (flesh colored, raised wart), may ulcerate

§ Secondary chain of nodules (about 2 weeks later)

· Follows lymphatics

o Soil organism, sphagnum moss

o Diagnose by culture

§ Yeast form in tissue (cigar-shaped yeast)

§ Mycelial form in culture

Subcutaneous mycoses

§ infection of deep layers of the skin

· Cornea, muscle, connective tissue

Systemic mycoses

§ can cause infections in healthy individuals

· Opportunistic

o Affect immunocompromised patients

§ AIDS, cancer, transplant

§ T-cells essential in control of these fungal infections

· Dimorphic fungi

· Inhalation of spores

o All cause pneumonia

· Dissemination to other sites

o CNS, liver, spleen, bone marrow, etc

Epidemiology, clinical disease, and diagnosis of Pneumocystis jiroveci

§ Number 1 AIDS illness- causes pneumonia in AIDS patients

§ Has cyst form (only fungus wit cysts)

· Also is intracellular trophic form

§ Formerly Pneumocystis carinii

· Infects IC pts (predominately HIV)

o Most common opportunistic disease in AIDS pts

· Respiratory tract is main portal of entry

o Pneumonia most common presentation

· Diagnosis: microscopy

o Sputum, bronchial alveolar lavage fluid

§ Giemsa stain for trophic forms

§ Gomori methenamine silver stain for cyst wall

Epidemiology, clinical disease, and diagnosis of Aspergillus

true mold

§ Ubiquitous

· Air, soil, decaying matter

· Nosocomial: shower heads, plants

§ 3 categories of pulmonary disease

· Allergic, noninvasive, invasive

§ Diagnosis

· Microscopy/culture of sputum

· Acute (45 degree-angled) branching hyphae

· "A" = Aspergillus

· Fungus ball- results in lung cavities where fungus bunches up

· Hemoptysis- coughing up blood

Epidemiology, clinical disease, and diagnosis of mucor

§ Rhinocerebral zygomycosis

· Invasive infection of nasal cavity, paranasal sinuses, orbit

o Painless, necrotic black ulcer

o Sinusitis and cellulitis, drainage of black pus from eye

o Ketoacidotic diabetics

§ Diagnosis

· Microscopy

o Nonseptate hyphae, branching at 90°

Epidemiology, clinical disease, and diagnosis of Cryptococcus neoformans

§ Encapsulated yeast, not dimorphic

· Found in soil and bird feces (pigeons)

o Enters lungs, disseminates to CNS

§ Clinical disease

· Meningitis in AIDS pts

§ Diagnosis:

· India ink preparation of CSF

o Stains in negative contrast

· Increased protein and WBCs, low glucose in CSF

o Culture on SDA at 37-degrees-C

Coccidioidomycosis

§ Coccidiides immitis

· "Valley fever"

o Southwest U.S.

o Arid weather

· Spherules

Histoplasmosis

§ Found in Ohio and Mississippi river basins, Great Lakes

§ Found in bird and bat droppings

· Risk: spelunking (Cave exploring), building demolition, bird roosts

§ Intracellular yeast (only one)

Antifungal mechanism of action for the cell wall

Targets the inhibition of glucan synthesis (echinocandins) and chitin synthesis (Nikkomycin)

Conazoles

o stops synthesis of ergosterol.

§ Fluconazole, itracanazole

§ Mechanism of action

· Inhibit Ianosterol 14-alpha-demthylase

o Cytochrome P-450-dependent enzyme

· Involved in conversion of Ianosterol to ergosterol

o Inhibition disrupts membrane synthesis

o Results in inhibition of fungal cell growth or cell death

Polyenes

o amphotericin B, nystatin

§ Two different mechanisms of action

· Primary mechanism: binds to ergosterol

o Makes ion pores.

o Osmotic imbalance causes leakage and cell death.

o Also binds to cholesterol, low affinity.

§ Nephrotoxicity

· Additional mechanism

o Direct membrane damage

§ Oxidation of drug causes cascade of oxidative reactions.

Echinocandins

§ Caspofungin, micafungin

§ New, highly selective semisynthetic lipopeptides

· Inhibit synthesis of 1,3-beta-glucans

o Important constituents of fungal cell wall

o Mammalian cells do not have 1,3-beta-glucans.

§ Beta-D-glucan synthase is found in cell membrane

§ Found in cell wall.

· Selective fungal toxicity

o Glucans are also important in cell division and growth.

Mycotoxins

§ Toxins produced by filamentous fungi

· >100 toxigenic fungi, >300 mycotoxins identified

o Do not enhance ability of fungus to cause disease

§ Mycotoxins made at 20-30°C

· Ingested, inhaled, or direct contact

o Majority from eating contaminated foods

· May cause acute or chronic disease

§ Symptoms and severity depend on:

· Type of mycotoxin

· Amount and duration of exposure

· Route of exposure

· Age, sex, and health of exposed person

§ Exposure and influences: inhalation, ingestion, and direct contact

Aflatoxin

§ Aspergillus flavus toxins

· Ingested in contaminated food

o Corn, peanuts, some tree nuts

· Hepatotoxic (jaundice)

o Causes liver failure.

Ochratoxin

§ nephrotoxin

o Produced by Aspergillus and Penicillium

§ Found on cereals, coffee, bread, and pork

o Causes kidney problems

Ergot alkaloids

§ contain lysergic acid

· (LSD)

· Ingested when contaminated grain used to make bread or cereals

· 2 forms of ergotism

o Gangrenous form

§ Peripheral vasoconstriction, necrosis of distal extremities

o Convulsive form

§ Muscle spasms, seizures, hallucinations

· Salem witch trials

protozoa

o Small single-celled organisms

§ Life functions occur in single cell

§ 7 major subgroups, 4 of clinical importance

· Sarcomastigophora

o Amebae and flagellates

· Ciliophora

o ciliates

· Apicomplexa

o Sporozoa (aka coccidia)

· Microspora

o Simple nutritional requirements

§ Through pinocytosis or phagocytosis

o Protective measures

§ Cyst form: survival in harsh conditions (cyst= infectious form)

· Not as metabolically active

o Protozoa without cysts have direct transmission via arthropod vector (eg. malaria)

· Evasion of immune system via surface antigen variation

o Reproduction by binary fission

§ Some protozoa have sexual reproduction

metazoa

o All parasites that are not protozoa (multicellular)

§ Helminths: worms

· Nematodes, trematodes, cestodes

§ Arthropods: crabs, insects, ticks, etc.

o Helminths ingest host tissue and/or fluids

o Protective measures

§ Tough external layer (cuticle)

§ Immune evasion

· Antigenic variation

· Secrete enzymes that destroy host cells

Identify the mode of infection for human parasites: Protozoa

§ Acquired through pinocytosis and phagocytosis

§ Cyst- survival in harsh conditions (infectious form)

· Protozoa without cysts have direct transmission via arthropod vector (ex: malaria and mosquitos)

§ Evasion of immune system via surface antigen variation

§ Trophozoites- protozoa and diagnostic material (Entamoeba)

trophozoite

active, motile, feeding stage of protozoa

Identify the mode of infection for human parasites: metazoa

§ Helminths: worms

· Nematodes, trematodes, cestodes

· Arthropods: crabs, insects, ticks, etc.

§ Helminths ingest host tissue and/or fluids

§ Protective measures

· Tough external layer (cuticle)

· Immune evasion

o Antigenic variation

o Secrete enzymes that destroy host cells.

Amoeba (Protozoa)

· Highly invasive (find for diagnostic)

· Pseudopodia

· Entamoeba

o Bloody diarrhea

· Naegleria fowleri

o Primary amoebic meningoencephalitis

o Soil and fresh water - ponds, lakes, etc.

o Invade nasal cavity

§ Causes meningitis then coma (deadly, 4-5 d)

Flagellates (protozoa): trichomonas vaginalis

o STD: 180 million cases/yr

§ Vaginal discharge, itching, redness

Flagellates (protozoa): Giardia lamblia

o Fecal-oral transmission, contaminated water

Causes malabsorption syndrome

Flagellates (protozoa): Trypanosoma cruzi ("kissing kids)

o Causes Chagas disease

o Found in South America

o Transmitted by reduviid bug

o Causes cardiomyopathy

coccidia

· Cryptosporidium ("Crypto")

· One of most common water-borne diseases (Giardia)

o Stable in environment (Cyst)

§ Chlorination

· Clinical: watery diarrhea, stomach cramps, vomiting

o Severe in AIDS pts

o Form cyst sand sporozoite

Malaria Sporozoite

o infectious form

Mosquito injects this into person

malaria: menzoites

§ Causes symptoms of malaria

§ Infectious form of RBC

Malaria gametocytes

§ Diagnostic form

§ Food vacuole= parasite stomach

· Malaria eats hemoglobin

§ Cyclical fever- fever and chills that just come and go

§ Tropical

Severe Malarial Anemia

§ Lots of parasites

· Anemia (Hb

diagnosis of malaria tests

Blood smears - cheap, reliable, still used

· Thick smear (look for pathogen)

o Concentration method to detect organisms

· Thin smear (count pathogen amount)

o Identify species of malaria (under high mag.)

§ P. falciparum

· Ring form within RBC

· Crescent-shaped (banana- or sausage-shaped) mature gametocyte

Babesia microti

· Causes babesiosis

o Transmitted by black-legged ticks (deer ticks, effects RBCs)

o Malaise, chills, myalgia, anemia, fever (>40oC)

§ Severe disease:

· Night sweats, weight loss, hematuria

Toxoplasmosis

· Caused by Toxoplasma gondii

· Transmitted mainly by cats

o Changing cat litter (in cat feces)

o Also in undercooked meat

· Generally asymptomatic disease

· Cross placenta, effects fetus

o Can cause hydrocephalus and eventual blindness of child

Nematodes

· Intestinal roundworms

o Most common helminths in U.S.

· Infection diagnosed by examination of eggs in stool

o Very important to recognize these

Most commonly associated with poor sanitation

pinworm

· Enterobius vermicularis: pinworm

o Fecal-oral,

§ Most common worm infection in U.S.

whipworm

Trichuris trichiura

Heavy infections = bloody diarrhea, anemia

Hookworm

o Ancylostoma duodenale

§ Old world hookworm

o Necator americanus

§ New world hookworm

Filarial worms

o Nematodes inhabit lymphatics and subcutaneous tissue

Wuchereria bancrofti

· Block lymphatics and cause edema

· Lymphatic filariasis (elephantiasis)

· Scrotal elephantiasis

Brugia malayi

· Tropical pulmonary eosinophilia

o Cough, fever, eosinophilia

Onchocerca volvulus

· African river blindness

o Transmitted by blackfly

· Microfilariae migrate to skin and eyes

· Causes blindness

Dracunculus medinesis

· Found in Asia and equatorial Africa

· Ingested in drinking water

· Female causes ulcer

o Abscess formation

Trematodes

· Flukes

o Flat, leaf-shaped worms, larger than nematodes

o Most hermaphroditic

§ Except schistosomes

o All flukes have clam or snail intermediate host

§ Intermediate host infected by free-swimming cercaria

§ Humans ingest metacercariae (fecal-oral transmission)

· Except for schistosomes

o Cercariae directly infect humans

all flukes have what?

operculated eggs (operculum)

Lung Fluke

o Paragonimus westermani

§ Found in Asia, Africa, India, Latin Am.

§ Infection from undercooked (raw) crab or crayfish

· Snail is intermediate host

§ Clinical: looks like TB

§ Diagnosis: eggs in sputum (cough up blood= cough up eggs)

Schistosoma haematobium

· Hematuria, bladder cancer

o Urine

· Diagnosis: terminal spine (terminal= tobi)

S. japonicum

Occasional bloody diarrhea

S. mansoni

· Bloody diarrhea (mesentery)

o Stool

Diagnosis: lateral spine ("middle of egg)

Cestodes

tapeworms

Tapeworms

o Flat and ribbon-like

o Head (scolex) has cup-shaped suckers and hooks

o Segmented bodies

§ Proglottids

o All are hermaphroditic

o Complex life cycles

o Eggs in feces diagnostic

§ Cannot differentiate between species

All are operculated

pork tapeworm

o Taenia solium

o Undercooked pork

§ Found in Africa, SE Asia, India, Mexico, Latin Am., China, Slavic countries

o If larvae ingested in meat

§ Abdominal discomfort, diarrhea, indigestion

o Diagnosis

§ Proglottids/eggs in feces

o Cysticercosis

§ Ingestion of eggs, larvae disseminate

· Calcify in tissues

o Neurocysticercosis (number 1 cause of seizures)

§ Hydroencephalitis, meningitis, nerve damage, seizures (epilepsy), visual defects (eye)

o Diagnosis

§ Imaging studies for calcified cysticerci

· (CT, MRI)

Fungal metabolism

§ Heterotrophic

· Absorptive nutrition

o Secretes enzymes.

o Decomposition

o Absorbs products.

§ Contributions

· Decay process

· Produce antibiotics, organic acids, sterols

· Fermentation products

o Alcoholic beverages, soy sauce, cheese, breads

· Infectious agents (all fungi have pathogenic potential)

o Have high morbidity as fungi targets immunocompromised individuals.

Fungal Structure

§ They are eukaryotic and have a cell wall, nucleus, and organelles

§ Cell wall

· Made of chitin

o Beta-glucan chains (target for anti-fungal)

§ Polymer of N-acetylglucosamine

§ Not peptidoglycan

§ Cell Membrane

· Contains ergosterol (maintains fluidity of fungi)

o Major target for anti-fungal

mold: septate hyphae

contain cross-walls (septum-looking structure)

mold: aseptate hyphae

· apical extension (digs into tissue)

o Without cross-walls

o Can't see individual cells

pathogenicity of fungi

o Primarily opportunistic

o Fewer virulence factors compared to bacteria.

§ Dimorphs

· Escape phagocytosis

o Blastomyces, Coccidioides spherules

· Histoplasma is intracellular.

§ Candida has morphotypes.

§ Cryptococcus has capsule.

§ Allergies: IgE and ABPA

Sabouraud dextrose agar

· Low pH (5.0) inhibits bacterial growth

· Often supplemented with antibiotics

· If there is growth, then the unknown substance is a fungus.

potassium hydroxide (KOH) test

Identifies fungal infections, dermatophytes

Superficial mycoses

§ limited to superficial areas of skin and hair

· Caused by fungi that colonize the outer layer

o Do not elicit host immune response

o Usually non-destructive (asymptomatic)

Cutaneous mycoses

§ infection of keratinized layer of skin, nails, hair

· Dermatophytes (aka Ringworms)

o Infections- tineas

o Three genera

§ Trichophyton (most important)

§ Microsporum

§ Epidermophyton

Epidemiology, clinical disease, and diagnosis of Tinea capitis

o Caused by Microsporum

§ Fluorescence under UV light

· Wood lamp (useful in diagnosis)

Epidemiology, clinical disease, and diagnosis of Candida albicans

o Normal flora of mouth, vaginal tract, gut, skin, mucous membrane, systemic

o Infection in immunocompromised patients

o Oral thrush

o Diaper rash, vulvovaginitis, intertriginous areas

o Fungus can be wiped away, leaves behind redness.

o Diagnosis

§ Laboratory findings: growth on Sabouraud dextrose agar

§ Microscopy

· Yeast, budding hyphae, pseudohyphae

· Germ tubes for Candida albicans

· Will stain Gram-positive.

Blastomycosis

§ Blastomyces dermatitidis

· Found in Ohio and Mississippi river basins, Great Lakes

· Associated with decaying matter (inhaled)

o Soil and lead litter

· Broad-based budding yeast

Trichothecenes

o Inhibit protein synthesis in eukaryotic cells

o Contamination of food w/ Fusarium, Stachybotrys

§ GI hemorrhage/vomiting

· Pancytopenia; bleeding from nose, mouth

Cerebral Malarial

§ Low # of parasites

· Usually milder anemia

· Reversible coma

· Most common cause of death

o 15-20% mortality even with treatment

roundworm

Ascaris lumbricoides

o Dog and cat roundworms (Toxocara Canis, T. Cati)

§ Visceral larval migrans

· Worms migrating through tissue

§ Worm can curdle up and form obstructins

Schistosomes

o Caused by blood trematodes - blood flukes

§ Africa and South America