Transcript Document 7125556

ANTIMICROBIAL RESISTANCE
Prof. Khalifa Sifaw Ghenghesh
 Each
class of antimicrobial agent
has a unique mode of action.
 Some
antibiotics differ in their
action on Gram+ve and Gram-ve
bacteria due to the difference in
the cell wall structure of such
bacteria.
 Other
antibiotics are active on
both types of bacteria >> Broad
spectrum antibiotics.
Site of action of some antimicrobial agents
Agent
Site of action
------------------------------------------------------------------Penicillins
Cell wall
Cephalosporins
Cell wall
Glycopeptides
Cell wall
Tetracyclines
Ribosome
Aminogylcosides
Ribosome
Macrolides
Ribosome
Rifamycins
RNA synthesis
Sulphonamides
Folate metabolism
Quinolones
DNA synthesis

Antimicrobial agents can be classified
to:
– Bacteriostatic:

Inhibits growth and multiplication of bacteria.
– Bactericidal:

Kills bacteria.
Bacterial Mechanisms of Antibiotic
Resistance
1. Production of enzymes that destroy the
antibiotic before it reaches its target.

b-lactamases:
– In G -ve:


b-lactam drug enters the cell through the
porin channels where it encounters the blactamases in the periplasmic space.
b-lactamases destroy the b-lactam molecules
before they reach their PBP targets.
– In G +ve:

b-lactamases excreted extracellularly. Thus blactam drugs are inactivated outside the cell.
2. The cell wall becomes impermeable
to antibiotics.

G –ve bacteria may become resistant to
b-lactam drugs by developing
permeability barriers.

This caused by altered porin channels
that no longer allow the entrance and
passage of drug molecules into the cell.
3. Alteration of the target site by
mutation
PBP alteration through mutation in
G+ve bacteria.
 The b-lactam can no longer bind to it
and the cell becomes resistant to the
drug.
 Also occurs in G –ve bacteria.

4. Possession of an efflux pump

Efflux pump is a channel in the cell
that actively exports tetracycline
molecules and other drugs out of the
cell as fast as they are transported or
diffuse into the cell.

The antibiotic can not reach its target.
5. Alteration of specific metabolic
pathways

By mutation or acquisition of genes
encoding an alternative metabolic
pathway so that the drug can not
exert an effect.
Intrinsic Resistance

Escherichia coli intrinsically
resistant to vancomycin because
vancomycin is too large to pass
through porin channels.

Gram +ve bacteria have no porins
and thus are not intrinsically
resistant to vancomycin.
Acquired Resistance
Susceptible bacteria can acquire
resistance to antibiotics by:
1. Genetic mutation:

 During multiplication of G -ve bacteria
one cell undergoes a mutation to
streptomycin for example.
 When the population of cells is exposed
to streptomycin only the mutant
streptomycin-resistant cell survives.
 This resistant cell now multiplies and a
streptomycin-resistant population arises.
2. Acquisition of resistance:
 By Conjugation:


When two bacterial cells are in close proximity
a bridge-like structure (Pilus) forms between
them.
If one of the cell carries a plasmid encoding
ampicillin resistance gene this plasmid can be
transferred to the other cell.
 By Transformation:



Gram-ve bacteria encounter a fragment of DNA
contains a gentamicin-resistance gene. This
gene has been released from a Gr +ve bacteria
during cell lysis.
The DNA fragment is taken into the cell during
transformation.
The gene is incorporated into host’s
chromosome by recombination.
Some examples of b-lactamases in
Enterobacteriaceae

Plasmid mediated TEM-1, TEM-2 and SHV-1.
– Confer resistance to ampicillin and other
penicllins.
– Inhibited by calvulanic acid.
– As level of expression of broad spectrum blactamases, increases resistance to other blactams occurs.
Extended Spectrum BetaLactamases (ESBLs)



Mutations of the genes encoding TEM-1, TEM2 and SHV-1 b-lactamases results in the
production of b-lactamases known as ESBLs.
Found in E. coli, Klebsiella pneumoniae and
other G –ve bacilli.
Hydrolyse:
– All penicillins
– All cephalosporins (except cephramycin)
and aztreonam.
– Inhibited by b-lactamase inhibitors (e.g
clavulanic acid).

Resistance to antimicrobial drugs is
a major problem that inflicts the
whole world.

The problem is still worse in
developing countries where lack of
antimicrobial-resistance surveys
and control policies are the norm.
Methicillin-resistance (MRSA) among Staphylcoccus
aureus isolated from different cities in Libya
City
No
% MRSA
tested
------------------------------------------------------------------------------Tripoli and
Clinical samples 218
25
Misulata
Benghazi
Misurata
Source
Nares
(HCW, Pts, GP)
238
24
Nares
601
26
(HCW, Pts, GP)
------------------------------------------------------------------------------Daw et al. 1996; El-Gadi 2000; Ghenghesh and Sanalla (2001)
Resistance of Shigella isolated from children with and
without diarrhea in Tripoli to antibiotics (1992-1993).
Antibiotic
% resistant
(n=11)
------------------------------------------------------------------------------------Ampicillin
36
Ceftriaxone
0.0
Chloramphenicol
27
Ciprofloxacin
0.0
Gentamicin
0.0
Kanamycin
9
Nalidixic acid
0.0
Norfloxacin
0.0
Streptomycin
91
Trimethoprimsulphamethoxazole
64
----------------------------------------------------------------------------------Ghenghesh et al 1997.
Resistance of enterobacteria isolated from
different sources in Tripoli to antibiotics
(1991-1993)
Antibiotic
% resistant
(n=215)
-----------------------------------------------------------------Ampicillin
58
Chloramphenicol
26
Gentamicin
06
Kanamycin
29
Tetracycline
66
Trimethoprim28
sulphamethoxazole
-----------------------------------------------------------------Ghenghesh et al. 1994.
Resistance of Escherichia coli isolated from
urinary tract infections in Benghazi to
antibiotics (1996)
Antibiotic
Hospital acquired Community acquired
(n=62)*
(n=148)
------------------------------------------------------------------------------------Ampicillin
52(84)*
111(75)
Carbenicillin
53(85)
117(79)
Cephaloridine
22(35)
53(36)
Chloramphenicol
37(60)
67(45)
Gentamicin
19(31)
27(18)
Nalidixic acid
3(5)
15(10)
Nitrofurantoin
4(6)
10(7)
Tetracycline
45(73)
121(82)
Trimethoprim
52(84)
120(81)
sulphamethoxazole
-----------------------------------------------------------------------------------*(%); Tobgi et al 2001
Resistance of Salmonella species isolated from
children with diarrhoea in Zliten (2001) to antibiotics.
Antibiotic
No. (%) resistant:
(n=23)
------------------------------------------------------------------------------------Ampicillin
23 (100)
Amoxicillin+calvulanic acid
22 (95.7)
Cefoxitin
20 (87)
Gentamicin
18 (78.3)
Doxycycline
21 (91.3)
Chloramphenicol
22 (95.7)
Nalidixic acid
1 (4.3)
Norfloxacin
0 (0.0)
Trimethoprim-sulphamehtoxazole
1 (4.3)
------------------------------------------------------------------------------------Ghenghesh et al. 2002
Resistance of different bacterial pathogens
isolated from ice cream in Tripoli
% resistant
Antibiotic
Gram-negative
Gram-positive
(n=48)
(n=67)
------------------------------------------------------------------------------------Ampicillin
83
90
Amoxicillin40
45
clavulanic acid
Cefuroxime
25
NT
Ciprofloxacin
0.0
6
Gentamicin
0.0
12
Tetracycline
19
24
TMP-SMZ
12.5
25
------------------------------------------------------------------------------------Ghenghesh et al. 2003; NT=not tested
ESBLs-producing Escherichia coli and Klebsiella
pneumoniae isolated from different clinical samples
in Tripoli
Organism
No
% ESBLs
tested
-------------------------------------------------------------E. coli
383
8.6
K. pneumoniae
209
15.3
-------------------------------------------------------------Total
592
9.3
-------------------------------------------------------------Gebreel and Ghenghesh 2005.
THE PROBLEM

The high prevalence of resistant bacteria in
Libya seems to be related to antibiotic
usage
– Easy availability without prescription at drug
stores,
– Injudicious use in hospitals, and
– Uncontrolled use in animal husbandry.
CONCLUSION

The problem of antibiotic resistance is
very serious in Libya, as it appears to be
on the increase, particularly with the
emergence of resistance to newer drugs
that include the fluoroquinolones (e.g.
ciprofloxacin) among the clinically
important bacterial species.
RECOMMENDATIONS

It is urgently required:
– To ban the sale of antibiotics without prescription,
– To use antibiotics more judiciously in hospitals by
intensive teaching of the principles of the use of
antibiotics, and
– To establish better control measures of nosocomial
infections.


Regulation of antimicrobials for other than human use
is also required.
These issues are not easy to address and require the
collective action of health authorities, the
pharmaceutical community, health care providers, and
consumers