Basic Microbiology

BASIC MICROBIOLOGICAL
CONCEPTS
ANTIBIOTIC KILLING CURVES
AND
ANTIMICROBIAL SUSCEPTIBILITY
TESTINGS
Zakia Al-Hareth
Microbiology Lab. - AUHD
Microbiology is not a new field of study. In 1674 Anton
van Leeuwenhoek used simple,
selfmade microscopes to examine stagnant H2O,
where he observed "wee animalcules" - microscopic
organisms.
Microbiology is the study of microscopic organisms which
include many life-forms:
-Bacteria: simple, single cell
-Fungi: single & multi cell forms - yeast, filamentous
molds, complex fungi
-Protists: single cells, some multicellular algae, protozoans, slime molds
-Viruses: a cellular, protein-based lifeforms, typically
intracellular parasites
Bacteria have been grouped and named primarly on
their :
Morphological differences.
Biochemical/Metabiolic differences.
Gram stain separates organisms into 2 groups: gram
positive and gram negative bugs, also determine
whether the organism is round or rod-shaped.
Techniques used to Classify Bacteria
-Cell morphology :size and shape (rods, spheres, spiral)
-Colony shape (on petri plates)
-Stain uptake (use of characterizing stains- i.e. Gram
stains)
-Motility (mobile / immobile)
-Energy sources (autotrophs, heterotroph, etc.)
-Growth requirements (pH, salinity , oxygen, nitrogen)
COLONY MORPHOLOGY
COLONY MORPHOLOGY
-Colony diameter in millimeters.
-Pigmentation (pigmented colonies or secreting diffusible
pigments).
-Form, elevation, and margin.
-Smooth (shiny glistening surface), rough (dull, bumpy,
granular, or matte surface), or mucoid (slimy or gummy
appearance).
-Opacity: transparent, translucent, or opaque
-Texture when tested with a needle: butyrous (buttery
texture), viscous (gummy), or dry (brittle or powdery).
KELLIBSEILLA
BLOOD AGAR AND HEMOLYSIS
Tryptic Soy Agar with and without sheep
blood
‫‪HEMOLYSIS TYPE‬‬
‫حالة للدم بشكل كامل‬
‫حالة للدم بشكل جزئي‬
‫غير حالة للدم‬
STREPTOCOCCUS PYOGENES
BETA HEMOLYSIS (Β)
“VIRIDANS GROUP” STREPTOCOCCI
ALPHA HEMOLYSIS: Α
ENTEROCOCCUS FAECALIS
GAMMA HEMOLYSIS
STAINING
TYPES OF STAINING TECHNIQUES
Simple staining 
Differential staining
(use of two contrasting stains
(use of a single stain) 
e.g. methylene blue, crystal violet, separated by a decolorizing agent)
safranin
Identification
For visualization of
morphological
shape & arrangement.
Gram
stain
Visualization
of structure
Acid fast
stain Spore
stain
Capsule
stain
SIMPLE STAINING
Name of dye:- Methylene blue
Shape of cells:- bacilli
Gram +ve
S.aureus
Gram –ve
E.coli
Step 1: Crystal Violet
Step 2: Gram’s Iodine
Step 3: Decolorization
(Aceton-Alcohol)
Step 4: Safranin Red
19
Gram-positive vs.
Gram-negative bacteria
CELLULAR MORPHOLOGY AND
ARRANGEMENT
CELLULAR MORPHOLOGY
Coccus: circular:
ARRANGEMENTS
Cocci
Irregular Clusters
Staphylococci
Tetrads
Chains or Pairs
Micrococci
Streptococci
CELLULAR ARRANGEMENT
Streptococcus:chains
CELLULAR ARRANGEMENT
clumped
CELLULAR MORPHOLOGY
Spirillium
CELLULAR MORPHOLOGY (CONTINUED)
Vibrio
CELLULAR MORPHOLOGY (CONTINUED)
Rods/bacilli
CELLULAR MORPHOLOGY (CONTINUED)
coccobacilli
Section
Aerobic gram-negative
rods
Irregular gram-positive
rods
Actinomycetes
Regular gram-positive
rods
Facultatively anaerobic
gram-negative rods
Microaerophillic gramnegative curved rods
Spirochaetes
Example of genus
Pseudomonas
Corynebaterium
Streptomyces
Lactobacillus
Salmonella
Spirillium
treponema
ANTIBIOTIC KILLING CURVES
ANTIBIOTIC KILLING CURVES
CONCENTRATION-DEPENDENT KILLING
¼ TO 64 * MIC
ANTIBIOTIC SUSCEPTIBILITY
TESTING
ANTIMICROBIAL SUSCEPTIBILITY
TESTING
Minimum Inhibitory Concentration (MIC)
Lowest concentration of a given antimicrobial that will inhibit
(visual) the patient’s organism from growing after 18-24 h
incubation
Minimum Bactericidal Concentration (MBC)
Lowest concentration of a given antimicrobial that will
kill(99.9%) of the patient’s organism after 18-24 h
incubation
BROTH DILUTION
MIC/MBC
DISK DIFFUSION (KIRBY-BAUER TEST)
DISK DIFFUSION (KIRBY-BAUER TEST)
MIC on a strip
abbiodisk.com
MIC ON A STRIP
E-TEST
Basic concepts (some)
Carrier state: Certain individuals may continue to harbor a
pathogen after clinical recovery from an infectious
disease and may serve as carriers of infection
Colonization: Microorganisms which do not belong to the
normal flora of the host but do not cause local damage to
the host
Commensal: The organisms of the normal flora
Infection: A process in which an organism enters,
establishes itself, and multiplies in the host (not in
others) ; usually accompanied by a host response.
-Opportunist or opportunistic: Pathogen not able to
cause disease in healthy hosts but only in those with
impaired defense mechanisms.
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