The document discusses antibiotic resistance, its definition, factors affecting it, and mechanisms through which bacteria develop resistance. It also highlights the importance of antibiotic susceptibility testing methods, such as the tube dilution method and disk diffusion method, to ensure effective treatment of bacterial infections. Preventive measures against antibiotic resistance include judicious use of antibiotics and following vaccination programs.

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2. ANTIBIOTIC RESISTANCE & SUSCEPTIBILITY
DEPARTMENT OF BIOLOGY,
LAHORE GARRISON UNIVERSITY
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Mariam Shafique

3. LEARNING OBJECTIVES/ OUTLINES:
At the end of this presentation the students will be able to;
Define Antibiotics, Antibiotics Resistance.
Factors Affecting Antibiotics Resistance.
Mechanism of resistance.
Prevention of antibiotic resistance
What is antibiotic susceptibility
Test for antibiotic susceptibility
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4. ANTIBIOTICS
Any of various chemical substances, produced by various microorganisms, esp. fungi, or made synthetically
and capable of destroying or inhibiting the growth of microorganism.
People may exhibit allergic reactions to antibiotics, but they are not resistant to them. It is the bacteria
themselves, not the infected host, which become resistant.
Alexander Fleming discovered penicillin, the first natural antibiotic, in 1928.
Antibiotics cannot treat viral infections, such as cold, flu, and most coughs.
Side effects can include diarrhea, an upset stomach, and nausea.
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5. ANTIBIOTICS RESISTANCE
a. The ability of bacteria and other microorganisms to with stand an antibiotics to which they were once sensitive.
b. Tolerance of microorganisms to inhibitory action of antibiotics.
c. Resistance to antibiotics is a biological phenomenon that can be accelerated by a variety of factors, including
human practices.
d. Resistance can be; drug tolerance, drug destruction, drug impermeability, cross resistance.
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7. FACTORS AFFECTING ANTIBIOTICS RESISTANCE
Patient’s incompliance to recommended treatment:
•Forget to take medication.
•May be unable to afford full course.
•Interrupt their treatment when they begin to fell better.
Irrational use of antibiotics in humans:
•Self medication (unnecessary, inadequate dose).
•Misuse (easy availability in pharmacies without prescription).
Hospitals:
•Nosocomial infection with highly resistant bacterial pathogens.
•Mainly due to poor infection control practices the handwashing changing gloves. Etc.
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8. FACTORS AFFECTING ANTIBIOTICS RESISTANCE
Physicians:
•Over prescribing of broad spectrum drugs when narrow spectrum are appropriate.
•Wrong prescription and guidelines from unskilled practitioners.
•Unnecessary prescription common in private practitioners.
Poor quality of Antibiotics:
•Expired and counterfeit antibiotics.
•Due to lack of quality compliance and monitoring.
Irrational use of Antibiotics in Animals:
•Used for growth and dieases control in poultry, cattle, pigs etc.
•We re indirectly taking taking these antibiotics when we eating these animals.
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9. FACTORS AFFECTING ANTIBIOTICS RESISTANCE
Inadequate surveillance & Susceptibility Testing:
•Unknown susceptibility pattern of bacterial isolates encourages empirical selection of broad spectrum
antibiotics.
•Due to lack of equipment and personal.
Crowding/ Travel of people & Unhygienic condition:
•Residents of developing countries often carry antibiotics-resistant fecal commensal organisms. Visitors to
developing countries passively acquire antibiotics-resistant E.coli; even if they are not taking prophylactic
antibiotics, which suggests that they encounter a reservoir of antibiotics-resistant strains during travel.
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10. MECHANISM OF DRUG RESISTANCE
There are four drug resistance strategies;
1. Impermeability
2. Pumping out
3. Inactivation
4. Modification/Alteration

11. IMPERMEABILITY
Pathogens often become resistant simply by preventing
entrance of the drug. This is done by modifying the
proteins in the cell wall.
•Many gram-negative bacteria are unaffected by penicillin
G because it cannot penetrate the envelope’s outer
membrane.
•A decrease in permeability can lead to sulfonamide
resistance. Mycobacteria resist many drugs because of
the high content of mycolic acids in a complex lipid layer
outside their peptidoglycan. This layer is impermeable to
most water soluble drugs.

12. PUMPING OUT
•A second resistance strategy is to pump the drug
out of the cell after it has entered.
•Some pathogens have plasma membrane
translocases, often called efflux pumps, that expel
drugs.
•They are relatively nonspecific and can pump
many different drugs, these transport proteins
often are called multidrug resistance pumps.
• Such systems are present in E. coli, P. aeruginosa,
and S. aureus to name a few.

13. INACTIVATION
Many bacterial pathogens resist attack by inactivating drugs through
chemical modification.
•The best-known example is the hydrolysis of the β-lactam ring of
penicillin by the enzyme penicillinase. Β-lactam antibiotics β-
lactamase.
Drugs also are inactivated by the addition of chemical groups.
•For example, bacterial resistance to aminoglycosides
aminoglycosides modifying enzymes.
It reduces the binding ability.
•Enterococci become resistant to vancomycin by changing the
terminal D-alanine-D-alanine in their peptidoglycan to a D-alanine-D-
lactate. This drastically reduces antibiotic binding.

14. ALTERATION
•Resistant bacteria may either use an alternate pathway to
bypass the sequence inhibited by the agent.
•Or increase the production of the target metabolite.
•For example, some bacteria are resistant to sulfonamides
simply because they use preformed folic acid from their
surroundings rather than synthesize it themselves. Other
strains increase their rate of folic acid production and thus
counteract sulfonamide inhibition.

16. ORIGIN AND TRANSMISSION OF DRUG
RESISTANCE
Microbes that carry resistance gene survives to replicate themselves. The progeny of these
microbes will eventually become the dominant type.
Genes for drug resistance may be present on bacterial;
• chromosomes
• Plasmid (resistance genes often code for enzymes that destroy or modify drugs)
• transposons(mobile genetic elements .i.e., can easily transfer from one bacterium to another.)
•Integrons (pieces of DNA can accumulate new genes)

17. ORIGIN AND TRANSMISSION OF DRUG
RESISTANCE
When microbes replicates themselves
genetic mutations can occur, and can led to
genes which aid in surviving exposure to
antimicrobial agents.
Microbes can also acquire genes from other
microbes. These genes can be easily
transferred by horizontal gene transfer .i.e.,
Transduction, Transformation and
conjugation.
Antibiotic Resistance Mechanisms. Bacteria can resist the action of antibiotics
by (1) preventing access to (or altering) the target of the antibiotic, (2)
degrading the antibiotic, (3) altering the antibiotic, and/or (4) rapid extrusion
of the antibiotic

18. PREVENTION OF DRUG RESISTANCE
•Antibiotics should only be used when absolutely necessary.
•Use an antibiotic that is only effective against the specific type of bacteria you are infected with.
•Follow your doctor’s advice and recommendations, and complete the antibiotic treatment
exactly as prescribed.
•Never give or share your antibiotics with others.
•Never demand antibiotics for a sore throat, a cold or the flu. Antibiotics have no effect on these
conditions.
•The more antibiotic treatments you have, the greater the risk of developing resistant bacteria.

19. PREVENTION OF DRUG RESISTANCE
•It is very important to prevent infection.
• Ensure proper hygiene.
•Antibiotic resistance can be prevented
through immunization.
•It is important for both you and others that
you follow the vaccination programmes.

20. ANTIBIOTIC SUSEPITIBILITY
•Antibiotic susceptibility is the
state or fact of being likely or
liable to be influenced or harmed
by particular thing .
•Bacterial pathogen is specific to
antibiotic
TWO GENERAL METHODS
The tube dilution method
E-test
Disk dilution method

21. METHODS OF ANTIBIOTIC
SUSCEPTIBILITY
Quantitative method;
•For the testings of isolates of the healthy patients with intact immune defenses.
•For less serious infections, for example uncomplicated urinary tract infections.
Qualitative method;
•In the treatment of serious infections such as, endocarditis or osteomyelitis.
•For infections in high-risk patient groups such as immunocompromised patients (transplant
patients)
•Those who are critically ill.

22. THE DILUTION METHOD TEST
•The dilution method test determine the lowest concentration of zantibiotic that will prevent
growth of pathogens . This is known as MINIMUM INHIBITORY CONCENTRATION (MIC).
•To determine the test biologist prepare set of tube different concentration .
•Each tube is inoculated with identical number of cells inoculation and examined growth of
bacterial cell .
•The extent of growth diminished as the concentration of antibiotic increases eventually
antibiotic concentration observed at which no longer growth .this is MIC.

23. ANTIBIOTIC SUSCEPTIBILITY TEST
The second method is antibiotic susceptibility test which operate on the principal that an
antibiotic will diffuse from paper strip or disk into agar medium containing test organism .
i. ONE VERSION TEST (E-TEST)
ii. OTHER VERSION (DISK DIFFUSION METHOD)

24. E-TEST
•In one version test called E-TEST a paper strip impregnated with a marked gradient of antibiotic
is placed on the plate
•As the drug diffuses into the agar culture ,the higher drug concentration will inhibit growth of
susceptible bacterium .
•The inhibition of growth is observed as a clear oval halo on the plate .
•By reading the number on the strip (antibiotic concentratrion) where growth itersects the strip
the MIC can be determined.

26. DISK DIFFUSION METHOD
•In another version of test called DISK DIFFUSION METHOD inhibition of bacterial cell growth is
again observed as failure of a susceptible bacterium to grow leaving a clear halo around the
paper disk.
•A common application of the agar disk diffusion method is the KIRBY-BAUER TEST named after
W. M. Kirby and A.W. Bauer who developed it in 1960.
•This procedure determines the susceptibility of a microorganism to a series of antibiotics and is
performed according to standards established by FDA.

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