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Introduction to diagnostic microbiology
08 كانون الأول، 18 Dr.Ayham Abu Laila
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Diagnosis of Bacterial Infection
Non-microbiological investigations Patient Clinical diagnosis Radiology Haematology Biochemistry Sample Take the correct specimen Take the specimen correctly Label & package the specimen up correctly Appropriate transport & storage of specimen 08 كانون الأول، 18 Dr.Ayham Abu Laila
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A proper clinical assessment is essential for optimal use of laboratory services!
08 كانون الأول، 18 Dr.Ayham Abu Laila
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08 كانون الأول، 18 Dr.Ayham Abu Laila
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Getting the specimen to the lab
Problems in delay or inappropriate storage• delay in diagnosis & treatment pathogens die contaminants overgrow Blood cultures directly into incubator not refigerator! CSF straight to lab Don't put an entire surgical specimen into formalin! Send a portion to microbiology in a sterile container 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Collecting the specimen correctly
Take an mid-stream urine avoids contamination with perineal flora CSF Avoid contamination Avoid bloody tap Throat swab Make the patient gag! Blood cultures Avoid contamination with skin organisms 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Specimens & Infection Control
Please be considerate to lab staff!! Label hazardous specimens Don't send specimens to the lab without proper packing Leaking or blood-stained specimens are not acceptable!!! 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Factors limiting usefulness of bacteriological investigations
wrong sample e.g. saliva instead of sputum delay in transport / inappropriate storage e.g. CSF overgrowth by contaminants e.g. blood cultures insufficient sample / sampling error e.g.in mycobacterial disease patient has received antibiotics 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Diagnosis of Bacterial Infection
microscopy unstained or stained with e.g. Gram stain Stain Decolorise Counterstain culture identification by biochemical or serological tests on pure growth from single colony on plates or in broth sensitivities by disc diffusion methods, breakpoints or MICs Serodiagnosis DNA technologies 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Microscopy Unstained preparations
“Wet prep” Dark-ground illumination for syphilis 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Microscopy Stained preparations
Gram-stain Acid-fast stain Ziehl-Neelsen Fluorescence Direct, e.g. auramine Immunofluorescence 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Culture of Bacteria Solid media Agar plates For Identification
For Enumeration Slopes For safe long-term culture, e.g. Lowenstein-Jensen media for TB Liquid media (broth) For enrichment or maximum sensitivity 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Advantages of Solid Media
isolation of single clonal colonies get bacterium in pure culture identify by colonial morphology quantification by colony-forming units 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Identification of Bacteria
Morphology Growth requirements Biochemistry Enzymes Antigens 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Non-cultural diagnostic methods
Antigen detection e.g. latex agglutination Antibody detection e. g. agglutination tests, complement fixation tests, indirect immunofluorescence Molecular methods Polymerase Chain Reaction 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Sensitivity tests on solid media in liquid media Breakpoint methods
disc diffusion technique in liquid media minimum inhibitory concentration (MIC) test Breakpoint methods E-test 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Diagnosis of Viral Infection
Electron microscopy Antigen detection Antibody detection Virus culture Detect cytopathic effect or antigen Molecular methods Polymerase Chain Reaction Sequencing (e.g. for sensitivities) 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Microbes and humans Very few microbes are always pathogenic
Many microbes are potentially pathogenic Most microbes are never pathogenic 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Microbes and humans Disease can come about in several overlapping ways
1. Some bacteria are entirely adapted to the pathogenic way of life in humans. They are never part of the normal flora but may cause subclinical infection, e.g. M . tuberculosis 2. Some bacteria which are part of the normal flora acquire extra virulence factors making them pathogenic, e.g. E. coli 3. Some bacteria which are part of the normal flora can cause disease if they gain access to deep tissues by trauma, surgery, lines, e.g. S. epidermidis 4. In immunocompromised patients many free-living bacteria and components of the normal flora can cause disease, especially if introduced into deep tissues, e.g. Acinetobacter 08 كانون الأول، 18 Dr.Ayham Abu Laila
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How do we know that a given pathogen causes a specific disease?
Koch's postulates the pathogen must be present in every case of the disease the pathogen must be isolated from the diseased host & grown in pure culture the specific disease must be reproduced when a pure culture of the pathogen is inoculated into a healthy susceptible host the pathogen must be recoverable from the experimentally infected host 08 كانون الأول، 18 Dr.Ayham Abu Laila
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The iceberg concept of infectious disease
poliomyelitis in a child 0.1-1% of infections are classical clinical disease clinically apparent less severe disease rubella 50% of infections are clinically apparent Spectrum of virulence asymptomatic infection rabies 08 كانون الأول، 18 100% of infections Dr.Ayham Abu Laila are clinically apparent
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How do we know that a given pathogen causes a specific disease?
Diagnosis and effective treatment of infection depends not just on isolating an organism, but in establishing a plausible link between the laboratory findings, recognised syndromes and the patient's clinical condition Recognised syndromes e.g. septicaemia, endocarditis, osteomyelitis meningitis, UTI, pneumonia pharyngitis patient's clinical condition potential pathogen isolated from or detected in clinical samples 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Microbes and humans Evidence for a potential pathogen being clinical significant (particularly for bacteria) Isolated in abundance Isolated in pure culture Isolated on more than one occasion Isolated from deep tissues Evidence of local inflammation Evidence of immune response to pathogen Fits with clinical picture 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Normal flora All body surfaces possess a rich normal bacterial flora, especially the mouth, nose, gingival crevice, large bowel, skin This can be a nuisance in that it can contaminate specimens it can cause disease This is beneficial in that it can protect against infection by preventing pathogens colonising epithelial surfaces (colonisation resistance) removal of the normal flora with antibiotics can cause superinfection, usually with resistant microbes 08 كانون الأول، 18 Dr.Ayham Abu Laila
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How to identify pathogen
Culture characteristics Morphology and staining biochemical tests Serological characteristics Other characteristics 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Culture characteristics
Shape Margin Optical properties Elevation Texture Color Odor Animation 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Morphology and staining
Cell shape Arrangement Staining reaction Gram stain Negative stain End spore stain Acid fast stain 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Specimen processing Receiving Recording Culturing Staining Isolation
Identification Sensitivity test 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Patient details Name, Age Hospital No
Sex, For female: wither pregnant or lactating Address Suspected diagnosis Travel history immunization 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Identification of specimens
Patient details Type of specimen Collection date and time Laboratory No Test requested Name of ordering physician 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Specimen rejection criteria
Mismatch information Improper container or temperature Insufficient specimen Leaking specimen Formalin specimen Dried out swap Late specimen Physician must be informed about rejection 08 كانون الأول، 18 Dr.Ayham Abu Laila
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Report of bacteriology result
CSF, body fluid, blood, and wound: positive gram stain Culture and isolation Identification Ear: Potential pathogens; S. aureus, G –ve Eye: report identification of any organism 08 كانون الأول، 18 Dr.Ayham Abu Laila
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>Report of bacteriology result
Gastrointestinal: Routine screen for Salmonella, shigella, campylobacter, Vibrio, and E. coli O157:H7 Negative culture will be reported as “No enteric pathogens isolated” Lower respiratory and sputum: report identification of any organism 08 كانون الأول، 18 Dr.Ayham Abu Laila
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>Report of bacteriology result
Nasal / nasopharyngeal: report identification of any Gram –ve rod, S. aureus, S. pneumonia, H. influenza, N. meningitides, group A streptococci. Skin: Predominant organism Throat: group A streptococci, Sensitivity test 08 كانون الأول، 18 Dr.Ayham Abu Laila
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> Report of bacteriology result
Mouth: you must identify interest to be screened i.e. C. albicans, C. diptheriae Urine: report identification and antimicrobial sensitivity on colony count greater than CFU Plates with 3 or more will be reported Mixed flora of less than will be reported as normal skin flora 08 كانون الأول، 18 Dr.Ayham Abu Laila
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> Report of bacteriology result
Vaginal / cervical: Report predominant organisms Mixed culture of lactobacillus, diptheroids, staphylococcus, alpha streptococcus, and yeast will be reported as normal vaginal flora. 08 كانون الأول، 18 Dr.Ayham Abu Laila
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08 كانون الأول، 18 Dr.Ayham Abu Laila
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