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Flashcards in Lecture 22 Deck (51):
1

What is diagnostic microbiology for, what do clinical microbiologists do?

Isolation of species, the growth depednet versus growth independent diagnostic methods
to use enrichment, selective and differential media

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What do clinical microbiologists do?

Dectect, identify and characterise the microbes that cause infectious disease from samples collected from the infected

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Direct observation

Important in infectious diseases

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Indirect observation

involving immunological or molecular procedures e.g. Ig, and Serology

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Clinical microbiology labratories

Often seen in hospitals , clinics to grow, isolate and identify bacterial and viral pathogens within 48 hours

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Aims of clinical Microbioogy labs?

Provide accurate information in presense or absense of organsim in disease. Antimicrobial testing and suseptibility

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Lab tests carried out do

Detect microorganism or products produced, and see whether evidence of paitents immune resposonse to infection has occured

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3 main aims of Laboratory test

1. Identification of micro oganism by isolation and culture
2. identification of specific microbial product (eg.g capsuale and toxins )
2. Detection of specific antibodies to a pathogen

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Specimen

Saliva , Sputum, Blood, Catheter, Clean urine, Skin swab, skin, Spinal tap, faeces

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Sterile Body Sites

Do not contain bacteria so any bacteria found there are significant. E.g. blood, bone marrow, CSF, tissues, lower respiratory tract

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non sterile body sites

Open to external environment and contain bacteria. e.g. mouth, nose, upper respiratroy trat, skin, GI, female genetalia, urethra

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Normal Microflora

Rich in microbial biodiversity and home to vast numbers of bacterial cells. 10^14 cells associated with human body, while only 10^13 are human cells

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Normal Microflora

Found on external surfaces including Respiratory, GI, and Genitourinarry tracts.

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Composition of normal flora varies from individual to individual

Some bacterial species are carreid only transiently, most are fairly permanent, difficult to alter composition of the normal flora of the gut in healthy individual.

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Opportunisitc infections

Normal flora can cause disease. Even organsims not normally considered invasive or pathogenic occurs in compromised hosts

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Microflora in Esophagus, Stomach

Lactobacilli

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Microflora in Small Bowel

Lactobacilli streptococci, enterobacteria

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Microflora in Large Bowel

Bacteroids, Fusobacterium, Ecoli, Strep faecalis, enterobacteria

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Microflora in Fecal Matter

Bacteroids spp, bifidobacteria wubacteria, coliforms strep

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Colonisation resistance

Competition for space and nutrients with pathogens

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Antibacterial Substance

Release of bacteriocin and colicins to prevent pathogen growth

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Antigenic Stimulation

Continued from commensals cross reacting protective immunity against pathogens

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Vitamin K production

Gut

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Commensal bacteria may cause disease at their site of carriage or nearby

Step. mutans in mouth and dental caries, Step pnemoniae in upper air ways may cause otitis media and sinusitis

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Microflora have the potential to contaminate diagnostic specimens

INterpretation of Gram stains on samples, and cultured results

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Perinal flora in Urine

is normal microflora, therefroe taking a mid-stream urine sample

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Aspetic procedures is ised including sterile sample containers and sampling methods to prevent contamination of specimen

Stored appropriately

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Specimen collection

Appropriate specimen supsected of causing disease, at appropriate time, before receiving antimicrobials, collecting enough and an adequate number of samples more more tests

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Specimen isolation and identification

additional information, appearance, history of oversea travel

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Microscopy

First important step in examination of all specimnen. Detect motility, dye and stains

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Gram Staining

important differential staining techniuq in bacteriology

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Direct and indirect immunoflourecnes

Direct - Fluorescently labelled antibacterial antibody
Indirect - unlabelled antibacterial antibody then fluoresenlty labeled anti rabbit antibody.

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Fluorescence microscopy

Naturally fluorescent substances e.g. HBLV treated with IgG antibodies

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Culture dependency

Bacteria and fungi can be cultured on a solid nutrient or liquid mediumgives colony appearance, and cultures can be differential, selective or non selective

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Detection of pathogen

Since there will be a collection of oragnisms from a non sterile plate, the pathogen will have to be detected .

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Media

Nutrients , agar, pH indicators, proteins, carbs,

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Culture

Propogation of microoganisms using various media

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Media types

General purpose 0 Supporing growth Nutrient and TSA
Enriches for fastigious organsmis, blood and chocolate

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Enrichment Media

Blood, wserum extract, TSA support the growth of fastidious microorganisms

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Blood Agar

Citrated Blood, variable to hemolysis

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A hemolysis

Green, brown halo around colony. Step. gordonii or S. pnemoniae

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B hemolysis

Complete lysis of blood. Staph aureus, Step pyogenes

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Non hemolytic

No change in media , Staph, epidermidis

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Chocolate Agar

Medium with brown colour from heated blood. used for isolation of N. gonorrhoease

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Selective

Favours growth of one type of microorganisms and inhibits the grwoth of other

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Differential Media

Distinguishes between different groups of bacteria - biochemical characteristics

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Selective media , e.g. MSA and MacConkey

MSA (high NaCl conc) which will inhibit growth of most microbes but will select Staphylococcus,
MacConkey agar - bile salts

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Differential media

Several types of organisms and displays differences in colony size, media colour, gass formation, precipitate

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Selective and Differential Meidum

Mannitol Salt agar -
MacConkey agar differentiates lactose fermenting bacteria (pink red) and lactose negavtie (no pink)

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Differential Medium TSIA - triple sugar ion agar

fermentable carbs, red phenol to indicate pH change, iron to indicate gas production
Slant, Butt, H2S production

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Differential Media - Chromagar Orientation

Uses colour fomration to distinguish 7 common urinary pathogens