Microbiology 1 2

7/29/2019 Microbiology 1 2

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Microbiology 1-2

FPGEE Preparation

Basem SayedMarch 10, 2013


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Introduction

Type of Cells

Prokaryotes : No Nucleus, No

Organelles

o Examples: Bacteria, spirochetes,

chlamydia, rickettsia

Eukaryotes : Well-defined

nucleus and membrane bound

organelles

o Examples: Animal and plant cells

Fungi, Protozoa, metazoa


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Prokaryotes Eukaryotes

Simplicity More simple cells More advanced- complicated

Example Bacteria Fungi Protozoa Plant cells

Genetic Material

Genetic material scattered Genetic material inside the

nucleus

Genetic material is circular Linear

Cell wall

Exist in all Prokaryotes, except

mycoplasms composed of

Peptido glycan (Sugar +

Protein)

Plant cell wall composed of

Pectin and Cellulose

Fungi Cell wall is composed of

Chitin

Division Binary Fission Meiosis and Mitosis

Reproduction Asexual Sexual or asexual

Ribosomes (are different

between prok and eukar)

70 S (30S-50S) 80S (40S-60S)


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Viruses

They are extremely small microbes that are essentially

fragments of nucleic acid (DNA or RNA) packaged in a

protein shell

Viruses are seen with electronic microscope only

Viruses are not living organisms. They are acellular (April

2012).


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MCQ Questions

Mycoplasms:

Smallest free living microbes

Lack bi-layered cyotplasmic membrane

They do not required host cells for replication (differentfrom viruses)

Do not have a cell wall they are just limited by lipid

membrane

They are different from all bacteria that they are obligateintracellular parasite


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Chylamedia and Rickettsiae species

They are also small prokaryotes but larger than

mycoplasmas

They have cell walls


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Classification Characteristics Important Genera

Obligate aerobes Require oxygen Have no

fermentative pathways

Generally produce

superoxide dismutase

Mycobacterium

Pseudomonas

Microaerophilic Requires low but not full

oxygen tension

Campylobacter

Helicobacter

Facultative anaerobes Will respire aerobically

until oxygen is depleted

and then ferment or

respire anaerobically

Most bacteria, e.g.,

Enterobacteriaceae

Obligate anaerobes 1. Lack superoxidedismutase

2. Generally lack catalase

3. Are fermenters

4 Cannot use 0 2 as

terminal electron acceptor

BacteroidesClostridium

Actinomyces


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Factors affect bacterial growth

Aerobic or anaerobic conditions

Temperature

Most bacteria grow at temperature between 35C 42C

pH conditions Most bacteria favor neutral pH

Most acidic food like vinegar are rarely contaminated with

bacteria

Salinity Light conditions

Availability of water and organic materials


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Bacterial Replication

Bacteria are replicated asexually and exponentially by binary

fission


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Bacterial Growth curve


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Shapes of Bacteria


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Differences between Gm+ve and GM-ve

bacteria


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Gm +ve Gm -ve

Capsule Both have polysaccharide protective capsule

except Anthrax which has polypeptide

capsule

Outer membrane

(above the cell wall)

absent Hydrophobic

membrane:

LPS = endotoxin

Lipid A= toxic moietyPS = immunogenic

portion

Cell wall Thick and contain

Teichoic acid

Thin

Periplasmic space Absent Present

Cytoplasmic

membrane

Both


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Endospores

Some bacteria tend to form spores from vegetative cells

Survival not reproductive (One bacterium gives one spore)

Spores are resistant to chemicaJs, dessiccation, radiation,

freezing, and heat.

They germinate again in favorable conditions.


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What are the differences between endotoxin

and Exotoxin

Endotoxins:

Endotoxin (Lipopolysaccharide = LPS)

LPS is part of the gram-negative outer membrane

Exotoxins

Are protein toxins, generally quite toxic and secreted bybacterial cells (some gram+, some gram-)

Can be modified by chemicals or heat to produce a toxoid

that still is immunogenic but no longer toxic so can be usedas a vaccine

Exotoxins may be subclassed as enterotoxins, neurotoxins,or cytotoxins


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MCQs

Any microorganism can become pathogenic in such

individuals.

the likelihood of a particular infectious pathogen causing

disease is a function of the following variables:

1. the level of host resistance.

2. the aggressiveness of the invading organism, which is

known as virulence. Toxins produced by the pathogens

can also increase their virulence.

3. the absolute number of the microbes in some instances

(dose) or (inoculum).


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MCQs

Reservoirs

Environments or hosts that support growth of infectiousorganisms.

Reservoirs can be water, soil, or animals.

A carrier

It is a host that has recovered from an infectious disease butcontinues to shed the pathogen.

Vectors

They do not cause infectious diseases but carry pathogens fromone host to another.

Mosquitoes are vectors for malaria, yellow fever, West Nilevirus, and Dengue fever.

Ticks are vectors for Lyme disease, Rocky Mountain spottedfever, and Q fever.

fleas are vectors for the plague.


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Classifications of diseases and infections

Infections are classified as :

Primary infections: if the initial disease is caused by the

invading organism.

Secondary infection: it generally occurs because of a

weakened immune system or because of the use of

antimicrobials.

Infectious diseases can also be referred to by their

geographic site of onset

community acquired

hospital acquired infection develop after admission to a

health care institution (nosocomial infection).


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Communicable diseases

Communicable infectious diseases refer to those that canbe transmitted from host to host.

All communicable diseases are infectious, but not allinfectious diseases are communicable;

if an infectious disease is highly communicable it is said tobe contagious.

Communicable infectious diseases can be:

endemic, which refers to a low level of disease within a

select geographic area. An epidemic refers to an explosive outbreak of a disease

within a population.

pandemic indicates a disease that is worldwide.


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Staphylococcus

Genus Features

Gram-positive cocci in

clusters

Species of medical Importance

S. aureus

S. epidermidis: normal flora

S. saprophyticus: The only

species of staph able to

cause UTI N.B. All staph species are

Catalase positive (streptococci

are catalase negative)


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Staphylococcus aureus

Distinguishing Features Small, yellow colonies on blood agar B-

hemolytic

Coagulase positive (all otherStaphylococcus species are negative)

Reservoir Normal flora : Skin

Nasal mucosa (25% of population arecarriers)

Transmission

Hands

Sneezing Surgical wounds

Contaminated food

Potato salad

Canned meats


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Pathogenesis

Toxic Shock syndrome toxin-1 (TSST-1): superantigen

Entertoxins: fast acting and heat stable

Exfolatins: skin exfoliating toxin involved in scaled skinsyndrome (SSS)

Diseases

Toxic shock syndrome: Fever, hypotension, sun burn like

rash that desquamates on palms and soles.


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Continue diseases of staph. A.

Gastroenteritis (food poisoning):

Enterotoxin is ingested with food.

2- 6 hours after ingesting toxin: nausea, abdominal pain,

vomiting, followed by diarrhea

Impetigo

Erythematous papules because of Coagulase, and

exfoliatins toxin.


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Treatment

Gastroenteritis is self-limiting.

Nafcillin/oxacillin are drugs of choice because of

widespread antibiotic resistance as staph is a huge

nosocomial infectious agents.

For methicillin-resistant Staphylococcus aureus (MRSA):

vancomycin is the drug of choice

For vancomycin-resistant Staphylococcus aureus (VRSA) or

vancomycin-intermediate S. aureus (VISA):

quinupristin/dalfopristin (Synercid)R


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GENUS: STREPTOCOCCUS

Genus Features

Gram-positive cocci in chains

Catalase negative

Species of Medical Importance S. pyogenes

S. agalactiae (group B streptococci; GBS)

S. pneumoniae

Viridans streptococci


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Streptococcus pyogenes

Reservoir

Human throat

Skin

Transmission Direct contact

Respiratory droplets


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Virulence factors

Streptokinase: breaks down fibrin dot

Exotoxins A-C (pyrogenic or erythrogenic exotoxins) Causefever and the rash of scarlet fever.

Diseases

1. Pharyngitis

Abrupt onset of sore throat, fever, malaise, and headache;tonsillar abscesses and tender anterior cervical lymph

nodes

2. Scarlet fever

blanching "sandpaper'' rash (palms and soles are usuallyspread), strawberry tongue, and nauea and vomiting


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Sequelae of Streptococcal infections

Disease Sequelae of Mechanisms/Sympt

oms

Rheumatic fever Pharengitis with Strept.Pyogenes

Antibodies to heart

tissue/

2 weeks postpharyngitis, fever, joint

inflammation.

type II hypersensitivity

Acute

glomerulonephritis

Pharyngitis or skin

infection

Immune complexes

bound to glomeruli,pulmonary edema

and hypertension,

smoky" urine (type III

hypersensitivity)


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Cont. S.Pyogenes

Treatment

Beta lactam drugs

Macrolides arc used in the case of penicillin allergy.

Prevention Prophylactic antibiotics (B-lactams and macrolides) should

be considered in patients for at least 5 year post acute

rheumatic fever.


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Streptococcus pneumoniae

Distinguishing Features

Lancet-shaped diplococci

Alpha hemolytic

Reservoir human upper respiratory tract

Transmission

Respiratory droplets

Virulence factors Polysaccharide capsule is the major virulence factor


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Diseases of Streptococcus pneumoniae

Most common cause of the following diseases Adult Typical pneumonia (community acquired pneumonia):

(especially in sixth decade of life)

Adult meningitis

Otitis media and sinusitis in children--most common cause

Laboratory Diagnosis Quellung reaction: positive (swelling of the capsule with the

addition of type-specific antiserum)

Treatment

Bacterial pneumonia: macrolides

Adult meningitis: Ceftriaxone or cefotaxime. Vancomycin isadded if penicillin-resistant S. pneumoniae has been reported inthe community

Otitis media and sinusitis in children: amoxicillin, erythromycin


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Prevention:

1. Antibody to the capsule

2. Vaccine

Pediatric (PCV, pneumococcal capsular vaccine)o Conjugated to diphtheria toxoid

Adult (PPV, pneumococcal polysaccharide vaccine)

Recommended for all adults 65 years of age and any at-risk

individuals


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GENUS: CLOSTRIDIUM

Genus features

Gram positive rods

Spore forming

Anaerobic

Species of Medical Importance

Clostridium tetani

Clostridium botulinum

Clostridium perfringens Clostridium difficile


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Clostridium tetani

Reservior

Soil

Transmission

Puncture wounds from rusty nails

Pathogenesis

Spores germinate .in the tissues, producing tetanus toxin

(exotoxin also called tetanospasmin).

Binds to ganglioside receptors Blocks release of inhibitory mediators (glycine and GABA)

at spinal synapses.


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Disease

Tetanus: characterized by risus sardonicus,

Opisthotonus and extreme muscle spasms.

Treatment of Actual Tetanus

Hyperimmune human globulin (TIG) to

neutralize toxin plus metronidazole or penicillin

Spasmolytic drugs (diazepam); debridement

delay closure of wound

Prevention

Toxoid is formaldehyde-inactivated toxin.

Wound care


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Clostridium botulinum

Reservoir

soil/dust

Transmission

foodborne/traumatic

Pathogenesis

Spores survive in soil and dust; germinate in moist, warm,

nutritious anaerobic conditions

Release Botulinum toxin (polypeptide neurotoxin ) Heat labile (unlike staph), 10 minutes 60.0C

Blocks release of acetylcholine at the myoneuronal

junction resulting in a reversible flaccid paralysis


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Forms of botulism

Adult botulism Infant botulism

Acquisition Preformed toxin

ingested (toxicosis)

Poorly canned alkaline

vegetables (green

beans), smoked fish

Spores ingested:

household dust, honey

Symptoms 1-2 day onset of

Symptoms: weakness,

blurred vision, flaccid

paralysis (reversible),

diarrhea

flaccid paralysis, weak

feeding/crying; may lead

to respiratory arrest

Treatment Respiratory support,

Trivalent (A-B-E)

antitoxin

Respiratory support and

hyperimmune human

serum

Prevention Proper food canning No honey first year


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Clostridium perfringens

Distinguishing Features

Large gram-positive, spore-forming

rods (spores rare in tissue),

"stormy fermentation" in milk media

Double zone of hemolysis

Reservoir

soil and human colon

Transmission traumatic implantation


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Pathogenesis

Spores germinate under anaerobic conditions in tissue.

Vegetative cells produce:

Alpha toxin (phospholipase C) is a lecithinase. It disrupts

membranes, damaging RBCs, platelets, WBCs, endothelial

cells which results in tissue destruction and myonecrosis.

Identified by Nagler reaction: egg yolk agar

Twelve other toxins damage tissues.

Enterotoxin produced in intestines in food poisoning: watery diarrhea, cramps (similar to E. coli); resolution


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Disease

Gas gangrene (myonecrosis)

Contamination of wound with soil or feces

Acute and increasing pain at wound site

Tense tissue (edema, gas) and exudate

Systemic symptoms include fever and tachycardia

Rapid, high mortality

Treatment of Gangrene

Debridement, delayed closure of wound, clindamycin andpenicillin, hyperbaric chamber


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Clostridium difficile

Reservoir

human colon/gastrointestinal tract

Transmission

Endogenous

Pathogenesis

Toxin A; enterotoxin damaging mucosa leading to fluid

increase; granulocyte attraction

Disease(s) pseudomembranous colitis (yellow plaques on colon

antibiotic-associated (clindamycin, cephalosporin,

amoxicillin, ampicillin diarrhea, colitis, or)


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Diagnosis

Culture is not diagnostic because organism is part of

normal flora

Stool exam for toxin production

Treatment

Severe disease--metronidazole (vancomycin): use only if

no other drug available.

Mild disease--discontinue other antibiotic therapy

Microbiology 1 2

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