ANTIMICROBIAL RESISTANCE

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ANTIMICROBIAL RESISTANCE

• Prof. Khalifa Sifaw Ghenghesh

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• Each class of antimicrobial agent has a unique
  mode of action.
• Some antibiotics differ in their action on
  Gramve 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 gtgt Broad spectrum antibiotics.

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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

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• Antimicrobial agents can be classified to
• Bacteriostatic
• Inhibits growth and multiplication of bacteria.
• Bactericidal
• Kills bacteria.

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Bacterial Mechanisms of Antibiotic Resistance
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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 b-lactamases 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
  b-lactam drugs are inactivated outside the cell.

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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.

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3. Alteration of the target site by mutation

• PBP alteration through mutation in Gve bacteria.
• The b-lactam can no longer bind to it and the
  cell becomes resistant to the drug.
• Also occurs in G ve bacteria.

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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.

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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.

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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.

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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-resistan
  t cell survives.
• This resistant cell now multiplies and a
  streptomycin-resistant population arises.

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• 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 hosts chromosome
  by recombination.

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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
  b-lactamases, increases resistance to other
  b-lactams occurs.

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Extended Spectrum Beta-Lactamases (ESBLs)

• Mutations of the genes encoding TEM-1, TEM-2 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).

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• 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.

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Methicillin-resistance (MRSA) among Staphylcoccus
aureus isolated from different cities in Libya

• City Source No MRSA
• tested
• --------------------------------------------------
  -----------------------------
• Tripoli and Clinical samples 218 25
• Misulata
• Benghazi Nares 238 24
• (HCW, Pts, GP)
• Misurata Nares 601 26
• (HCW, Pts, GP)
• --------------------------------------------------
  -----------------------------
• Daw et al. 1996 El-Gadi 2000 Ghenghesh and
  Sanalla (2001)

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Resistance of Shigella isolated from children
with and without diarrhea in Tripoli to
antibiotics (1992-1993).

• Antibiotic resistant
• (n11)
• --------------------------------------------------
  -----------------------------------
• Ampicillin 36
• Ceftriaxone 0.0
• Chloramphenicol 27
• Ciprofloxacin 0.0
• Gentamicin 0.0
• Kanamycin 9
• Nalidixic acid 0.0
• Norfloxacin 0.0
• Streptomycin 91
• Trimethoprim-
• sulphamethoxazole 64
• --------------------------------------------------
  ---------------------------------Ghenghesh et al
  1997.

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Resistance of enterobacteria isolated from
different sources in Tripoli to antibiotics
(1991-1993)

• Antibiotic resistant
• (n215)
• --------------------------------------------------
  ----------------
• Ampicillin 58
• Chloramphenicol 26
• Gentamicin 06
• Kanamycin 29
• Tetracycline 66
• Trimethoprim- 28
• sulphamethoxazole
• --------------------------------------------------
  ----------------
• Ghenghesh et al. 1994.

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Resistance of Escherichia coli isolated from
urinary tract infections in Benghazi to
antibiotics (1996)

• Antibiotic Hospital acquired Community
  acquired (n62) (n148)
• --------------------------------------------------
  -----------------------------------Ampicillin 5
  2(84) 111(75)Carbenicillin 53(85) 117(79)C
  ephaloridine 22(35) 53(36)Chloramphenicol 3
  7(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

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Resistance of Salmonella species isolated from
children with diarrhoea in Zliten (2001) to
antibiotics.

• Antibiotic No. () resistant
• (n23)
• --------------------------------------------------
  -----------------------------------
• Ampicillin 23 (100)
• Amoxicillincalvulanic 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

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Resistance of different bacterial pathogens
isolated from ice cream in Tripoli

• resistant
• Antibiotic Gram-negative Gram-positive
• (n48) (n67)
• --------------------------------------------------
  -----------------------------------
• Ampicillin 83 90
• Amoxicillin- 40 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 NTnot tested

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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.

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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.

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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.

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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