Transcript GRAM NEGATIVE BACILLI - University of the Witwatersrand

THE BASICS OF CLINICAL
RELEVANCE
Feb 2007
Dr W Lowman
Objectives
•
1. Correlate the physicochemical properties of the
gram-negative cell wall, with the clinically relevant
pathogenetic and virulence factors of gram-negative
bacteria.
1. 2. List the key differences between the gram-positive
and gram-negative cell wall.
3a. Understand the complexity of the
interaction between the cell wall and antimicrobials.
3b. Relate this interaction to the clinical phenomenon
of antibiotic resistance.
Feb 2007
Dr W Lowman
G- cell wall
Cytoplasmic membrane
Periplasmic space
Peptidoglycan
Outer membrane
-LPS
Feb 2007
Dr W Lowman
Feb 2007
Dr W Lowman
Nomenclature
• Family- Enterobacteriaceae
• Genus- Escherichia; Escherichia
• Species- coli; coli
Pseudomonas aeruginosa
Klebsiella pneumoniae
Feb 2007
Dr W Lowman
ID principles
• Based on phenotypic criteria in routine clinical
laboratory.
- growth characteristics; cell morphology & staining;
biochemical reactions; serological reactions
• Molecular methods more precise but primarily
used for taxonomic purposes.
- G+C% content; DNA-DNA hybridization; 16S
rRna
Feb 2007
Dr W Lowman
Bacteria & oxygen (O2)
SPECTRUM
Obligate
AnO2
Strict
Aerotolerant
Microaerophile
Moderate
Faculatative
Anaerobe
ABILITY TO TOLERATE & GROW IN PRESENCE OF OXYGEN
(ENERGY- OXYGEN USED AS TERMINAL ELECTRON ACCEPTOR)
Feb 2007
Dr W Lowman
Obligate
Aerobe
Feb 2007
Dr W Lowman
Clinical spectrum
Infections
• Community-acquired
• Nosocomial-acquired
Not always clear-cut.
Term ONSET may be more appropriate
“Healthcare-associated infection”
Feb 2007
Dr W Lowman
Community-acquired
• GIT infections- diarrhoeal illness
- Salmonella, Shigella, E.coli,
Yersinia
- Outbreaks NB!
Feb 2007
Dr W Lowman
Community-acquired
•
•
•
Urinary tract infections
E.coli
Proteus spp.
Lower respiratory tract infections
Wound/ SSTI
Feb 2007
Dr W Lowman
Nosocomial infections
• ANYTHING
• NB! in terms of antibiotic resistance.
• Most resistant organisms typically found in
this group.
• Empiric treatment becomes an important
challenge and requires informed
guesswork.
Antibiotic
susceptibilities
Pathogen(s)
Feb 2007
Dr W Lowman
Antibiotic resistance
Penetration
Enzymes
Binding
Feb 2007
Dr W Lowman
ANTIBIOTICS
ARE NOT THE
ANSWER!
Feb 2007
Dr W Lowman
Feb 2007
Dr W Lowman