Clinical Microbiology

Clinical Specimens

Taken near infection site using swabs, needles, sputum

Bacteremia

Bacteria in blood

Bacteriruia

Bacteria in urine

Growth-Dependent Method Purpose

Identify pathogens and determine antibiotic treatment

Growth-Dependent Method Types

Selective and differential

MIC

Tube dilution showing the lowest concentration stopping growth

E-Test

Gradient of antibiotic on strip giving zone of inhibition and MIC

Growth Independent Method Types

Antibody-antigen reactions and DNA detection (PCR)

Serology

Using antigen-antibody reactions to detect antigens and antibodies

Epitope

Antibody binding site

What does direct ELISA find

A current infection

Direct ELISA Function

Uses immobilized antibody to detect antigen

What does indirect ELISA find?

Past infection

Indirect ELISA function

Uses immobilized antigen to detect antibody

Antibody Titer

Amount of antibody in serum showing the lowest concentration to give a reaction

Antibody Titer Infection Timeline (graph)

Early —> bacteria present, no antibodies

Mid —> antibodies increase

Late —> bacteria gone, antibodies decrease

What does PCR ask?

Is pathogen DNA present?

PCR Steps

Adds specific primers

If DNA matches —> PCR product forms

If not —> no product

qPCR

Uses fluorescence and more fluorescence = more pathogen

Serotypes (Strain Differences)

Based on surface antigens

E. Coli Serotype

O (LPS) + H (flagella) —> O157:H7

Influenza Serotype

H (hemagglutinin) + N (neuraminidase) —> H1N1

Why Strains Differ

Genome rearrangements, plasmids, phages, pathogenicity islands leading to increased virulence and increased antibiotic resistance

Virulent

Extremely harmful in its effects