practical medical microbiology pht382 by dr. mohamed al-agamy assistant professor of microbiology...
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Practical Medical MicrobiologyPractical Medical MicrobiologyPHT382PHT382
ByBy
Dr. Mohamed Al-AgamyDr. Mohamed Al-AgamyAssistant Professor of MicrobiologyAssistant Professor of Microbiology
Department of Pharmaceutics & MicrobiologyDepartment of Pharmaceutics & Microbiology
College of PharmacyCollege of Pharmacy
King Saud UniversityKing Saud University
Medical MicrobiologyMedical Microbiology
Infectious Microorganisms
Bacteria"Bacteriology"
Fungi"Mycology"
Virus"Virology"
Medical BacteriologyMedical Bacteriology
Bacteria
I- Gram positive
II- Gram negative III- Acid fast
MycoplasmaChalamydiaRickettsia
Spirochetes
Classification of BacteriaClassification of Bacteria
Bacteria
Gram-Positive Gram-negative
Gram-Positive BacteriaGram-Positive Bacteria
I- Gram Positive bacteria
A- Gram positive cocci B- Gram positive rods
Spore-formingNon spore-formingCorynebacterium
AerobicBacillus anthracis
AnaerobicClostridium
Gram-Positive CocciGram-Positive Cocci
A- Gram-positive cocci
I- staphylococci II- streptococci
Species of Species of SatphylococciSatphylococci
Three species of staphyloccoci have medical Three species of staphyloccoci have medical importance:importance:– S. aureusS. aureus:: P Pathogenicathogenic & commensally found in & commensally found in
nose (nares)nose (nares) S. epidermidisS. epidermidis:: non pathogenicnon pathogenic & common & common
commensals in nares & skincommensals in nares & skin S. saprophyticus:S. saprophyticus: Cause UTI in female & Cause UTI in female &
occasionally occasionally commensallycommensally found skin found skin
StaphylococciStaphylococci
General characters:General characters:– Gram Positive CocciGram Positive Cocci– Grape-likeGrape-like– Non MotileNon Motile– Non Spore FormingNon Spore Forming– Non CapsulatedNon Capsulated– Non FastidiousNon Fastidious– Facultative AnaerobesFacultative Anaerobes– FermentativeFermentative– Catalase positiveCatalase positive
Characters of Characters of S. aureusS. aureus– Production of coagulaseProduction of coagulase– Production of phosphataseProduction of phosphatase– Production of DNaseProduction of DNase– Ferment MannitolFerment Mannitol– Gelatin liquefiedGelatin liquefied– ΒΒ-hemolysis on blood agar-hemolysis on blood agar– Acidification & clotting of Acidification & clotting of
litmus milklitmus milk
Gram stain of StaphylococcusGram stain of Staphylococcus
Virulence factors of Virulence factors of S. aureusS. aureus
Coagulase: Coagulase: – Converting fibrinogen into fibrinConverting fibrinogen into fibrin
Exofoliative toxin:Exofoliative toxin:– Desquamation of skin in case of exofoliative dermatitis in SSSSDesquamation of skin in case of exofoliative dermatitis in SSSS
TSST:TSST:– Fever, hypotension, & skin rash followed by desquamation of skinFever, hypotension, & skin rash followed by desquamation of skin
LeucocytesLeucocytes– Kills WBCsKills WBCs
Polysaccharide A and Protein APolysaccharide A and Protein A– Antiphagocytic and AdhesionAntiphagocytic and Adhesion
Enterotoxins (A,B,C,D, & E)Enterotoxins (A,B,C,D, & E)– Food poisoning (Diarrhea, and Vomiting)Food poisoning (Diarrhea, and Vomiting)
HyaluronidaseHyaluronidase– Destroy hyaluronic acid (constituent of connective tissues)Destroy hyaluronic acid (constituent of connective tissues)
,,,, and and Toxins Toxins– Destroy variety of cells (Polymorph)Destroy variety of cells (Polymorph)
Disease caused by Disease caused by S. aureusS. aureus
Localized suppurartive (Pyogenic) inflammation:Localized suppurartive (Pyogenic) inflammation:– Folliculitis Infection of hair folliclesFolliculitis Infection of hair follicles– Furuncle Infection of an obstructed hair follicleFuruncle Infection of an obstructed hair follicle– Carbuncle Larger abscessCarbuncle Larger abscess– Deep Lesions (Osteomyelitis, Endocarditis & Meningitis)Deep Lesions (Osteomyelitis, Endocarditis & Meningitis)
Toxigenic infectionToxigenic infection– Scalded Skin Syndrome (SSS)Scalded Skin Syndrome (SSS)– Toxic Shock SyndromeToxic Shock Syndrome
Food poisoningFood poisoning– Nausea, Vomiting, Diarrhea without Fever within 8 h after Nausea, Vomiting, Diarrhea without Fever within 8 h after
ingestion of toxins in the contaminated foodingestion of toxins in the contaminated food
Laboratory diagnosis of Laboratory diagnosis of StaphylococcusStaphylococcus
Specimen:Specimen:– Pus, Urine, Stool, Blood, CSFPus, Urine, Stool, Blood, CSF
Gram Stain:Gram Stain:– Gram Positive Cocci, arranged in clusterGram Positive Cocci, arranged in cluster
Culture:Culture:– Blood agarBlood agar (Non-Selective Media) (Non-Selective Media)
Coagulase Positive Staphylococci are Pigmented & hemolyticCoagulase Positive Staphylococci are Pigmented & hemolytic
Coagulase Negative Staphylococci are non-pigmented & non-Coagulase Negative Staphylococci are non-pigmented & non-hemolytichemolytic
MSAMSA is selective differential medium for staphylococci is selective differential medium for staphylococci– It contains: NaCl (7.5%), Mannitol, & Phenol RedIt contains: NaCl (7.5%), Mannitol, & Phenol Red– The cause of The cause of selectivityselectivity due to presence of high salt due to presence of high salt
concentrationconcentration– The cause of The cause of differentialdifferential because contains mannitol because contains mannitol
(sugar) and phenol red (pH indicators turns yellow in (sugar) and phenol red (pH indicators turns yellow in acidic pH and turns red in alkaline pH).acidic pH and turns red in alkaline pH).
Mannitol fermentation on MSA
Mannitol fermentedYellow colonies:
S. aureus
Mannitol nonfermenterRed colonies:
S. epidermidis& S. saprophyticus
The catalase test is distinguished streptococci from The catalase test is distinguished streptococci from staphylococcistaphylococci
flood culture with drops of 3% H2O2 flood culture with drops of 3% H2O2
Catalase-positive cultures bubble at onceCatalase-positive cultures bubble at once
The test should not be done on blood agar because The test should not be done on blood agar because blood itself will produce bubbles blood itself will produce bubbles
Catalase test
PositiveMicrocococcaceae
Staphylococci
NegativeStreptococcaceae
Streptococci
H2O2 H2O + O2 (gas, ↑)Staphylococci
Catalase
Catalase test
Coagulase TestCoagulase TestPrinciple:Principle:
This test used to differentiate between S. aureus (CPS) & other Staphylococcus species (CNS)
Coagulase test
Coagulase PositiveStaphylococus aureus
Coagulase-NegativeS. epidermidis & S. saprophyticus
Fibrinogen (Plasma)
Coagulase Fibrin )Clot(
Coagulase TestCoagulase Test
The tube coagulase test The tube coagulase test (Free):(Free):
Procedure:Procedure: – Mix 0.1 ml of culture + 0.5 ml of plasmaMix 0.1 ml of culture + 0.5 ml of plasma– Incubate at 37C for 4 hIncubate at 37C for 4 h– Observing the tube for clot formationObserving the tube for clot formation– Any degree of clotting constitutes a Any degree of clotting constitutes a
positive testpositive test
AdvantageAdvantage– More accurateMore accurate
DisadvantageDisadvantage– Time consumedTime consumed
S. aureus S. epidermidis
Coagulase TestCoagulase TestTwo Methods:Two Methods:– The slide MethodThe slide Method– Tube MethodTube Method
The slide coagulase test The slide coagulase test – Used to detect bound coagulase or clumping factorUsed to detect bound coagulase or clumping factor– Add one drop heavy bacterial suspension and one drop of plasma on Add one drop heavy bacterial suspension and one drop of plasma on
clean slideclean slide– Mixing well and observing for clumping within 10 secondsMixing well and observing for clumping within 10 seconds
AdvantageAdvantage– Rapid diagnosisRapid diagnosis
DisadvantageDisadvantage– Less accurate Less accurate
Deoxyribonuclease (DNAase) testDeoxyribonuclease (DNAase) test
Principle:Principle:– DNA is insoluble in acidDNA is insoluble in acid– DNA is hydrolyzed into oligonucleotides by the DNA is hydrolyzed into oligonucleotides by the
action of DNaseaction of DNase– Nucleotides soluble in acidNucleotides soluble in acid
DNase test
PositiveStaphylococus aureus
NegativeS. epidermidis & S. saprophyticus
DNase TestDNase Test
Procedure & result:Procedure & result:– Inoculate DNA agar with tested organism in circular motionInoculate DNA agar with tested organism in circular motion– Incubate at 37C for 24-48hIncubate at 37C for 24-48h– Observe DNase activity by adding 1N HCl to the agar surface, a zone of clearing Observe DNase activity by adding 1N HCl to the agar surface, a zone of clearing
indicates a positive testindicates a positive test– The zone represents the absence of DNAThe zone represents the absence of DNA– The medium around colonies not producing DNase remains opaque, which is a The medium around colonies not producing DNase remains opaque, which is a
reflection of the precipitation of DNA by the added acid.reflection of the precipitation of DNA by the added acid.
Novobiocin SensitivityNovobiocin Sensitivity
A simple disk diffusion test for estimating novobiocin susceptibility A simple disk diffusion test for estimating novobiocin susceptibility used to distinguish used to distinguish S. saprophyticusS. saprophyticus from other clinically species from other clinically speciesInoculated overnight culture on Mueller-Hinton agar Inoculated overnight culture on Mueller-Hinton agar Add novobiocin disk on inoculated plateAdd novobiocin disk on inoculated plateIncubate at 370C overnightIncubate at 370C overnight Novobiocin resistance is intrinsic to Novobiocin resistance is intrinsic to S. saprophyticusS. saprophyticus but but uncommon in other clinically important species.uncommon in other clinically important species.
Novobiocin test
SensitiveS. aureus
S. epidermidis
ResistantS. saprophyticus
Preparation of Smear and StainingPreparation of Smear and Staining
Preparation of smearPreparation of smear– Solid cultureSolid culture– Liquid cultureLiquid culture– Distribute culture in slideDistribute culture in slide– Air dryAir dry– Heat fixHeat fix– Ready to stainReady to stain
Gram StainGram Stain– Primary Dye (C.V.) Primary Dye (C.V.) – Mordant (iodine)Mordant (iodine)– Decolorizer (Alcohol)Decolorizer (Alcohol)– Counterstain (Safranin)Counterstain (Safranin)– All applied for 1 minAll applied for 1 min– After each step wash with After each step wash with
waterwater– Blot dryBlot dry– Add one drop of immersion oilAdd one drop of immersion oil– Examine under oil immersion Examine under oil immersion
lenslens
Practical WorkPractical Work
Gram stainGram stain
Catalase testCatalase test
Mannitol fermentation on MSAMannitol fermentation on MSA
Coagulase Test by Tube and Slide MethodCoagulase Test by Tube and Slide Method
DNAase TestDNAase Test