3. 3
(Adapted from Levin BR, Clin Infect Dis 2001)
Antibiotics Kill Bacteria
Viruses
Bacteria
No effect
Antibiotics
X
Break down cell walls
Stop replication
4. 4
(Adapted from Levin BR, Clin Infect Dis 2001)
Antibiotics Need Time
to Work
Antibiotics p
rescribed
Day 5
X X
X
X
Medication taken for full
course of treatment
X
X
X
X
X X
X
Infection
cured!
Day 1
Day 10
5. 5
When we take antibiotics t
o treat colds and the flu, th
ey lose their effectiveness a
gainst bacteria.
This phenomenon is known a
s antibiotic resistance.
Overusing Antibiotics Makes them
Ineffective Against Bacteria
6. 6
Antibiotic Resistance
Over time, bacteria develop the ability to survive treatment
with drugs that used to kill them.
Causes of resistance:
– Unnecessary use for viral infections
– Quitting treatment too soon
– Unnecessary use of broad-spectrum medicatio
ns
8. 8
The resistant survivors
multiply. R
R
R
R
R
R
R
R
R
R
R
Treatment with penicillin
has no effect. X
Resistant Bacteria Can M
ultiply and Spread
Jane is now a carrier of
penicillin-resistant bacteria.
9. 9
(Adapted from Levin BR, Clin Infect Dis 2001)
Incomplete Treatment Ca
uses Resistance
X
X
X
X
X Day 3
Symptoms improved,
treatment stopped
Day 0
Antibiotics
prescribed
Day 10
Resistant
infection
Meanwhile, the surviv
ors multiply.
10. 10
Resistant Infections Requi
re Special Treatment
Longer tre
atment
Higher
dosage
More expe
nsive medi
cation
Intravenous (IV) m
edication,
hospitalization
11. 11
Resistant Infections are Dangerous
•Medication toxicity (side effects)
•Contagious
•Can pass resistance to other organisms
Worst Case Scenario: The infection may become
resistant to all medications (untreatable).
12. 12
Why We Overuse Antibiotics
Patients:
• Think green nasal discharge = ba
cterial infection
• Need to return to work/school
• Expect antibiotics if they’ve been
given them before
Physicians
• Think patients expect antibiotics
• Concerned about patient
satisfaction
• Diagnosis is difficult
• Time pressure
(Clin Pediatr. 199
8;37:665-672)
Antibiotic Prescription
13. 13
What is antibiotic resistance?
• Antibiotic resistance occurs when an antibiotic has lost its ability to ef
fectively control or kill bacterial growth; in other words, the bacteria
are "resistant" and continue to multiply in the presence of therapeuti
c levels of an antibiotic.
14. 14
Why do bacteria become resistant to antibiotic
s?
• When antibiotics are used to kill the bacterial microorganisms, a few
microorganisms are able to still survive, because microbes are always
mutating, eventually leading to a mutation protecting itself against th
e antibiotic
15. 15
• Antibiotics that are used correctly overwhelm the harmful b
acteria
• Overuse of antibiotics or unnecessary use creates a selective
environment
• Resistant bacteria has better fitness in this context
• Resistant strains survive and multiply.
• After reproducing, the resistant bacteria move to another ho
st.
16. 16
Resistance
• It took less than 20 years for, bacteria to show signs of resistance
• Staphylococcus aureus, which causes blood poisoning and pneumoni
a, started to show resistance in the 1950s
• Today there are different strains of S. aureus resistant to every form o
f antibiotic in use
17. 17
Multiple resistance
• It seems that some resistance was already naturally present in bacterial
populations
• The presence of antibiotics in their environment in higher concentration
s increased the pressure by natural selection
• Resistant bacteria that survived, rapidly multiplied
• They passed their resistant genes on to other bacteria (both disease cau
sing pathogens and non-pathogens)
18. 18
Transposons & Integrons
• Resistance genes are often associated with transposons, genes that easil
y move from one bacterium to another
• Many bacteria also possess integrons, pieces of DNA that accumulate ne
w genes
• Gradually a strain of a bacterium can build up a whole range of resistanc
e genes
• This is multiple resistance
• These may then be passed on in a group to other strains or other species
19. 19
Antibiotics promote resistance
• If a patient taking a course of antibiotic treatment does not co
mplete it
• Or forgets to take the doses regularly,
• Then resistant strains get a chance to build up
• The antibiotics also kill innocent bystanders bacteria which are
non-pathogens
• This reduces the competition for the resistant pathogens
• The use of antibiotics also promotes antibiotic resistance in non
-pathogens too
• These non-pathogens may later pass their resistance genes on t
o pathogens
20. 20
How humans have created the upsurge of bacteri
al diseases:
• International travel
• Inadequate sanitation
• “antibiotic paradox”
21. 21
How do bacteria become resistant?
Bacteria can gain resistance over time through:
•Acquired resistance
•Vertical gene transfer
•Horizontal gene transfer
22. 22
Genetic Basis of Resistance
• Spontaneous mutations in endogenous genes
• Structural genes: expanded spectrum of enzymatic activity, target-sit
e modification, transport defect
• Regulatory genes: increased expression
• Acquisition of exogenous genes
• Usually genes that encode inactivating enzymes or modified targets, r
egulatory genes
• Mechanisms of DNA transfer: conjugation (cell–cell contact); transfor
mation (uptake of DNA in solution); transduction (transfer of
DNA in bacteriophages)
• Expression of resistance genes
• Reversible induction/repression systems can affect
resistance phenotypes
24. 24
Major Classes of Antibiotics
Antibiotic Mechanism of action
Major resistance mechanism
s
β-Lactams Inactivate PBPs (peptidogly
can synthesis)
• β-lactamases
• Low affinity PBPs
• Efflux pumps
Glycopeptides Bind to precursor of peptid
oglycan
• Modification of precursor
Aminoglycosides Inhibit protein synthesis (bi
nd to 30S subunit)
• Modifying enzymes (add a
denyl or Phosphate)
Macrolides Inhibit protein synthesis (bi
nd to 50S subunit)
• Methylation of rRNA
• Efflux pumps
(Fluoro)Quinolones Inhibit topoisomerases (DN
A synthesis)
• Altered target enzyme
• Efflux pumps
28. 28
Mechanism of Action of b-Lactams (2)
• Penicillin-binding proteins (PBPs)
• Membrane-bound enzymes
• Catalyse final steps of peptidoglycan synthesis (transglycosylation and transp
eptidation)
• b-lactams
• Act on PBPs, inhibit transpeptidation
• Substrate analogues of D-Ala-D-Ala
29. 29
Resistance to b-Lactams
• Gram-negative b-lactamases
• Major resistance mechanism in nosocomial GNB pathogens
• >470 b-lactamases known to date
• Classified into 4 groups based on sequence similarity
• Ambler Class A (TEM, SHV, CTX), C and D (OXA) are
serine b-lactamases
• Ambler Class B are metallo-b-lactamases
• Their spread has been greatly exacerbated by their integration within
mobile genetic elements
• Integron-borne b-lactamase genes are part of multi drug resistance g
ene cassettes
Multidrug-resistant nosocomial pathogens
with complex resistance patterns
Selection of potent b-lactamases
through use of non-b-lactam agents
30. 30
Ambler Classification of β-Lactamases
Active site
Nucleotide seq
uence
Four evolutionarily distinct molecular classes
A C D
Serine-enzymes
B
Zinc-enzymes
β-lactamases
31. 31
Resistance to b-Lactams
• Chromosomal AmpC b-lactamases
• Several Enterobacteriaceae, including Enterobacter, Citrobacter, and
Serratia contain an inducible, chromosomal gene coding for a b-lacta
mase
• Resistant to cephalosporins and monobactams; not inhibited by clavu
lanate; Class C b-lactamases
• Plasmid-mediated AmpC b-lactamases
• Arose through transfer of AmpC chromosomal genes into plasmids
• Not inducible, with substrate profile (usually) same as parental enzy
me
• Highly prevalent in the naturally AmpC-deficient K. pneumoniae
• Emergence predominantly in community-acquired infections
(Salmonella spp., E. coli)
• Co-resistance to aminoglycosides, SXT, quinolones
• Wide dissemination worldwide (SE Asia, N Africa, South Europe, USA)
32. 32
Resistance to b-Lactams
Extended-spectrum b-lactamases (ESBL)
No consensus of the precise definition of ESBLs
In general: β-lactamases conferring resistance to the penicillins, 1st , 2nd, 3
rd, and even 4th generation cephalosporins, and monobactams, not to car
bapenems and cephamycins
Inhibited by b-lactamase inhibitor clavulanic acid
Derived from Class A b-lactamases (exceptions are Class D, OXA): TEM, SHV
, CTX-M, OXA, VEB, PER,...
Differ from their progenitors by 1–5 amino acids
Marked and unexplained predilection for Klebsiella pneumoniae
Therapeutic options: carbapenems
33. 33
Resistance to b-Lactams
• Carbapenemases
• Defined as b-lactamases, hydrolyzing at least imipenem or/and meropenem
or/and ertapenem
• Belong to Ambler Class A, B, and D, of which Class B are the most clinically sig
nificant:
• Class A: KPC, SME & NMC/IMI
• Class B: IMP, VIM & SPM metallo b-lactamases
• Class D: OXA-23, -40 & -58 related
34. 34
Class B (Metallo)-Carbapenemases
• Hydrolyzing virtually all b-lactams
• Mediate broad spectrum b-lactam resistance
• No clinical inhibitor available
• Present on large plasmids and integrons
• Genes are continuously spreading
• Associated (80%) with aminoglycoside resistance
35. 35
ORF1 aacC4 aacC1
blaIMP
blaVIM
Class I integron
5'cs 3'cs
Mobile Carbapenamases
Nosocomial outbreak of carbapenem-resistant P.aerugin
osa and A. baumanii reported in Canada and France, res
pectively
Cross-resistance to other beta-lactams and to other AB c
lasses
Link with aminoglycoside use, not necessarily carbapene
ms!
36. 36
Class D Oxacillinase — Carbapenemases
Class D enzymes
OXA-23, -24, -25, -26, -27, -28, -40, -49, -58, ….
Highly mobile (integron, plasmid)
Found in South America, South-East Asia, Europe (Greece, Spain, P
ortugal, France, Belgium)
Multi-drug resistance (penicillins and 3rd & 4th generation cephalo
sporins, BL/BL-inhibitors, aminoglycosides, SXT,…)
Variable resistance levels to imipenem and meropenem (4–>256 m
g/mL)
37. 37
Rapidly Increasing Antibiotic Resist
ance Constitutes One of the Most I
mportant Clinical, Epidemiological a
nd Microbiological Problems of Tod
ay
