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BACTERIAL CLASSIFICATION AND DIAGNOSIS OF
BACTERIAL DISEASE

Disease causing agent


Treatment


Food, air or contact?
Epidemiology


Antibiotic sensitivity
Source of infection


Bacterial, fungal, viral or other?
Cholera, Diphtheria
Prevention

E. coli O157:H7 outbreak, Shigella, Listeria
Antibiotic sensitivity
Site of sampling

Sterile sites
Blood
 Cerebrospinal fluid (CSF)
 Body fluids (Peritoneal and pleural)


Non-sterile (normal flora)
Respiratory tract
 Ear, eye and mouth
 Skin (wound and abscess)
 Urine (mid-stream)
 Feces

Bacterial classification

Wall structure

Gram +


Gram 

Mycobacterium
Mycoplasma
Unusual

Bacteria
Wall-less


Enteric, respiratory and others
Acid-fast


Staphylococcus, Streptococcus, Clostridium,
Bacillus
Obligate intracellular

Rickettsia, Chlamydia
G+
G-
AF
WL
IC
Bacterial classification

Cell morphology
 Shapes



Rod
Cocci
Spiral
Bacteria
G+
G-
AF
 Associations




Individual
DiploStaphyloStrepto-
Rod Cocci
Rod Cocci Spiral
WL
IC
Bacterial classification

Growth characteristics
 Oxygen


requirement
Aerobic
Anaerobic


Bacteria
G+
Microaerophilic, aerotolerant
G-
AF
Facultative
 Spore
formation
 Intracellular/extracellular
 Fastidious/non-fastidious
Rod Cocci
+ spore -
Rod Cocci Spiral
+ +/-
-O2
WL
IC
Classification & Diagnosis

Type of colonies
 Appearance

Color, shape, size and smoothness
 On

Blood, MacConkey, EMB
 On

differential media
selective media
MacConkey, Thayer-Martin
Classification & Diagnosis

Metabolism
 Utilization


Lactose (Sal/Shi/Yer/)Citrate (E. coli-/Klebsiella+)
 Production

of specific substrates
of certain end products
Fermentation end products





Acid (acetate, propionic acid, butyric acid etc.)
Acetoin
Alcohol
Amine
H2S
Classification & Diagnosis

Specialized tests
 Immunological


O-, H- & K-Ag (serotype)
Precipitation, agglutination
 Specialized




enzymes
Catalase--- Staph+. vs. Strep-.
Coagulase---S. aureus+ vs. S. epidermidisOxidase---Neisseria gonorrhoea+
Urease---Proteus+, Helicobacter+
 Antibiogram
 Phage
pattern
typing
 Fatty acid profile
Immunological detection
Conventional diagnosis methods
Conventional method

Depend on ability to culture
 Treponema

pallidum
Slow, esp. for fastidious species
 Mycobacterium

spp.
Not always definitive
Molecular diagnosis






Ribotyping
Restriction fragment length polymorphism
(RFLP)
DNA hybridization
PCR, RT-PCR and RAPD
Nucleic acid sequence analysis
Phage-GFP (TB)
RFLP
GGATCC
CCTAGG
DNA hybridization
In situ
Hybridization
PCR
Rate of increase
2n
RT-PCR
RAPD of P. aeruginosa
Molecular diagnosis






Reduce reliance on
culture
Faster
More sensitive
More definitive
More discriminating
Techniques adaptable
to all pathogens




Technically demanding
Relatively expensive
Can be too sensitive
Provides no
information if results
are negative
Bioterrorism

Pathogen detection
 Fast
and accurate
 Mobile
 Inexpensive

Source investigation
Differentiating Staphylococci from Streptococci

Gram stain and morphology




Enzyme tests



Both Gram +
Staphylococci: bunched cocci
Streptococci: chained cocci (S. pneumoniae form diplococcus)
Staphylococci: catalase +
Streptococci: catalase -
Growth


Staph.: large colonies (non-fastidious), some hemolytic
Strep.: small colonies (fastidious), many hemolytic (a or b)
Staphylococci
 S.
aureus: coagulase +
 S. epidermidis: coagulase -
Streptococci
Streptococci
S. pyogen es (group A )
On blood aga r
b-hemolytic
Growth inhibiti on d is c
Sens iti ve to bacitr acin
S. agalactiae (group B)
b-hemolytic
Resistant to bacitr acin
S. pneumoniae (pneu mococcus)
a-hemolytic
Sens iti ve to optochin
Viri dans
a-hemolytic
Resistant to optochin
Differentiating the Gram- bacteria

Cocci


Neisseria
Rods
Type of disease they cause
 Enteric Gram- rods



Curved


API test
Vibrio, Campylobacter, Helicobacter
Spiral Gram- organisms

Spirochetes
Gram negative
Curved rods
Straight rods
Lactose+
Citrate+
Klebsiella
CitrateE. coli
Lactose-
H2S+
Salmonella
Campy blood agar
42oC+ 25oC-
TCBS agar
Yellow
Oxidase+
Campylobacter
Vibrio
H2SShigella
Bacteria
Gram+
Cocci
Staph.
S. a.
S. e.
S. s.
Gram-
Rod
Strep.
A
B
Pn
Vir
Non-spore
Spiral
Spore
Fil
Rod
+O2 -O2
A.i.
C.d.
L. m.
B.a. C.b.
B.c. C.t.
C.p.
C.d.
Acid Fast
Rod
Cocci
Treponema
Borrelia
Leptospira
+/-O2
P.a.
Enteric
-O2
Curve
Other
Vibrio
Campylobacter
Helicobacter
Bact.
Resp.
Bordetella.
H. influenzae
Legionella
Zoo
Yersinia
Pasteurella
Brucella
Francisella
Streptobacillus
Wall
Less
Rickettsia Mycoplasma
Coxiella
Erlichia
Chlamydia
Neisseria
Moraxella
Straight
+O2
M.t.
M.l.
N.c.
Intra
Cellular
GU
H. ducreyi
Gardnerella
Calymmatobacterium