BACTERIAL CLASSIFICATION AND DIAGNOSIS OF
BACTERIAL DISEASE
Disease causing agent
Bacterial, fungal, viral or other?
Treatment
Antibiotic sensitivity
Source of infection
Food, air or contact?
Epidemiology
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 +
Staphylococcus, Streptococcus, Clostridium,
Bacillus
Gram -
Enteric, respiratory and others
Acid-fast Bacteria
Mycobacterium
Wall-less
Mycoplasma
Unusual G+ G- AF WL IC
Obligate intracellular
Rickettsia, Chlamydia
Bacterial classification
Cell morphology
Shapes Bacteria
Rod
Cocci
Spiral G+ G- AF WL IC
Associations
Individual Rod Cocci Rod Cocci Spiral
Diplo-
Staphylo-
Strepto-
Bacterial classification
Growth characteristics Bacteria
Oxygen requirement
Aerobic
Anaerobic
G+ G- AF WL IC
Microaerophilic, aerotolerant
Facultative
Rod Cocci Rod Cocci Spiral
Spore formation
Intracellular/extracellular + spore - + +/- -O2
Fastidious/non-fastidious
Classification & Diagnosis
Type of colonies
Appearance
Color, shape, size and smoothness
On differential media
Blood, MacConkey, EMB
On selective media
MacConkey, Thayer-Martin
Classification & Diagnosis
Metabolism
Utilization of specific substrates
Lactose (Sal/Shi/Yer/)-
Citrate (E. coli-/Klebsiella+)
Production 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. epidermidis-
Oxidase---Neisseria gonorrhoea+
Urease---Proteus+, Helicobacter+
Antibiogram pattern
Phage 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 RT-PCR
Rate of increase
2n
RAPD of P. aeruginosa
Molecular diagnosis
Reduce reliance on Technically
culture demanding
Faster Relatively expensive
More sensitive Can be too sensitive
More definitive Provides no
More discriminating information if results
Techniques adaptable are negative
to all pathogens
Bioterrorism
Pathogen detection
Fastand accurate
Mobile
Inexpensive
Source investigation
Differentiating Staphylococci from Streptococci
Gram stain and morphology
Both Gram +
Staphylococci: bunched cocci
Streptococci: chained cocci (S. pneumoniae form diplococcus)
Enzyme tests
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 On blood agar Growth inhibition disc
S. pyogenes (group A) b-hemolytic Sensitive to bacitracin
S. agalactiae (group B) b-hemolytic Resistant to bacitracin
S. pneumoniae (pneumococcus) a-hemolytic Sensitive to optochin
Viridans a-hemolytic Resistant to optochin
Differentiating the Gram- bacteria
Cocci
Neisseria
Rods
Type of disease they cause
Enteric Gram- rods
API test
Curved
Vibrio, Campylobacter, Helicobacter
Spiral Gram- organisms
Spirochetes
Gram negative
Straight rods Curved rods
Lactose+ Lactose- Campy blood agar TCBS agar
42oC+ 25oC- Yellow
Oxidase+
Citrate+ Citrate- H2S+ H2S-
Campylobacter Vibrio
Klebsiella E. coli Salmonella Shigella
Bacteria
Intra Wall
Gram+ Gram- Acid Fast Cellular Less
Cocci Rod Spiral Rod Cocci M.t. Rickettsia Mycoplasma
M.l. Coxiella
N.c. Erlichia
Chlamydia
Staph. Strep. Non-spore Spore Treponema Neisseria
Borrelia Moraxella
Leptospira
Fil Rod +O2 -O2
B.a. C.b. Curve
S. a. A A.i. C.d. Straight
S. e. B L. m. B.c. C.t.
S. s. Pn C.p.
C.d. Vibrio
Vir
Campylobacter
+O2 +/-O2 -O2 Other Helicobacter
P.a. Enteric Bact.
Resp. Zoo GU
Bordetella. Yersinia H. ducreyi
H. influenzae Pasteurella Gardnerella
Legionella Brucella Calymmatobacterium
Francisella
Streptobacillus