Unit 06: antibacterial drug therapy and beta lactams

Question 1

explain the gram reaction

Answer 1

gram positive stain purple

gram negative counterstained red

• fix cells, add crystal violet, idoine treatment which bidns to crystal violet and traps in cells, add alcohol then counterstain with safranin

Question 2

describe the gram negative bacteria

Answer 2

have an outer membrane, asymmetirc bilayer in which the outer leadlet is comprised of lipopolysaccharide

• structurally unusual membrane forms a permeability barrier that excludes wide bariety of mol and limits penetraiton of gram stain
• the murein layer is thinner and is surrounded by a second, outer lipid bilayer membrane.

Hydrophilic molecules cross this outer membrane through channels, which are formed by a cylindrical arrangement of pore proteins (porins).

have lipopolysaccharide (LPS) in the outer membrane- major antigen for the immune response to Gram-negative organisms.

Question 3

describe gram positive bacteria

Answer 3

• have a thick peptidoglycan (murein) layer whereas gram negative only have a thin layer
• thick later allows nutrients, waste producst and antibiotics to difuse
• lipoteichoic acids in outer leaflet of membrane intercalate through the cell wall to the outer surface - inolved in cell adherance, feeding and envasion of host immune system
• peptidoglycan consists of sugars (polysaccharides) and amino acids (polypeptide) that are cross linked to form the outside of the PM
• since gram stain binds to peptidoglycan- thck layer makes it stain purple

Question 5

what are the steps in anybacterial drug susceptibility testing

Answer 5

1. determine the MIC - lowest conc of drug that inhibits vidible growth
2. determine the MBC- minimum bactericidal conc, lowest conc reuqired to kill a particular bacterium

*determine by taking dilutions of the MIC and sub-culturing onto ati-bacterial free media, then test tubes for growth.

*even though may not be growth bacteria may still be alive

Question 6

MIC/MBC testing is $$$ what is usually done instead

Answer 6

• Kirby-Bauer disk diffusion test
• paper disks are impregnated with drug and palced on a plate with uniform “lawn” of bacteria
• drug idffuses into the agar and the zone of inhibition around each disk is measured after a specific time
• zone diameter is copmared to a standard regression curve that correlates this with MIC (Ug/mL) - bacterial isolate is reported as sensitive, intermediate or resistant to drug

Question 7

is bacterial resistant all or none?

Answer 7

• resistance to any drug is not an all or none charcateristic
• each infection contains a mix of bacteria of different sensitivities and therapy may leave the most resistant strains to grow
• different strains of the same abcterium from different patients may also difer in sensitivity even in same geographic area

Question 8

what are the 5 steps to selecting and administering antimicrobial drugs?

Answer 8

1. if possible identify the organism
2. initiate treatment immediately

. select a drug

4. determine dosage
5. assess drug safety

Question 9

describe step 1 of selecting/administering antimicrobial drugs - identiy the organism

Answer 9

• accomplished through Gram or other stains, using the literature or previous experience with a similar organism.
• Culture and sensitivity testing should also be performed for most life threatening infections or when a non-critical infection is resistant to empirical therapy.

Question 10

describe step 2 of selecting/administering antimicrobial drugs - initiate treatment

Answer 10

• want to do immediately
• delay may lead to other infections like meningitis or septic arthritis (v dangerous)
• treatment can begin while you are wating on results of the culture and sensitivity teating

*at this point treatment is essentially an educated guess

Question 11

describe step 3 of selecting/administering antimicrobial drugs - select a drug

Answer 11

• based on bacterial sensitivity and preferable you should use narrow spectrum drugs to avoid killing comensal bacteria
• need to determine if ebst to prescribe a bacteriostatic (stops bacteria from reproducing) or bactericidal (kills the bacteria)
• bactericidal drugs are often used if the immune system is compromised or infection is life threatening
• also consider safety, adverse effects, drug dsitribution (CNS and prostate are difficult tissues for drug to enter) and the cost to patient

Question 12

describe step 4 of selecting/administering antimicrobial drugs - determine dosage

Answer 12

• usualy done by commerical government labs
• label recommendations or consultation with a reference text is advised
• dose can be adjusted according to patients needs

Question 13

describe step 5 of selecting/administering antimicrobial drugs - safety

Answer 13

imp to consider when need for drug is not critical

Question 14

what disease processes require special consideration and basic principles cannot be applied

Answer 14

osteomyelitis, foreign bodies, abcesses, intracellular pathogens and immunodeficiency

Question 15

why does osteomyelitis reuqire special consideraition before antibiotic prescription

Answer 15

• type of infection and inflammation of the bone or bone marrow
• in chronic osteomyelitis patients, antibitic therapy is unually prolonged compared to toher infections -lasting 6-12 weeks

despite this recurrence of infection is common

Question 16

why do foreign bodies reuqire special consideraition before antibiotic prescription

Answer 16

• foreign bodies like quils, slivers, nails or plant awns always come with risk of subsequent bacterial infection
• the foreign material must first be removed and then prophylactic antimicrobials are administered (generally broad spectrum) before any signs of infection appear

Question 17

why do abscesses reuqire special consideraition before antibiotic prescription

Answer 17

• abcess is a collection of pus (neutrophils) that has accumulated in tissue as a response to ifnection agent
• before treatment can be administered, abscess needs to be drained
• in some cases dont need antimicrobial after

Question 18

why do intracellular pathogen reuqire special consideraition before antibiotic prescription

Answer 18

• mycobacteria, salmonella and legionells surive inside cells therefore it is necessary to use a drug that enter cells readily

Question 19

why do immunodeficiencies reuqire special consideraition before antibiotic prescription

Answer 19

• deficient host defences sucha s those that are the result of infectious disease, stres,autoimmune or inherited diseases and idopathic immunodeficiency may reuqire drug conc that are much higher than normal

Question 20

describe prophylactic treatment usign antimicrobials

Answer 20

• refers to use of pharmacologic agents fr prevention rather than treatment
• used in situations where there is high risk of serious infection following trauma like meningitis and/or when a patients condition predisposes them to more serious infection like UTI
• risk period must be known and covered in order for this treatment to be successful
• ex prophylactic therapy could be used following radiation therapy in some cases where the individuals immune system may be compromised as the benefits during period outweigh risks adn ride effects

Question 21

prophylactic treatment during surgical situations

Answer 21

• microbes could enter body during procedure
• includes the opening of any portion of GI tract or major abdominal or thoracic organ (gut resection, hysterectomy, C-section, cardiac surgery), opening a joint, major proedures of head/neck or placement of prosthesis

Question 22

appropriate antimicrobal drug selection for prophylactic sue requires knowledge on

Answer 22

General spectrum of activity

Major adverse effects

Distribution/elimination

First line, second line, or emergency classification

Cost

Possible routes of administration

Question 23

what are the 6 main categories of antimicobial drugs

Answer 23

beta-lactams, aminoglycosides, tetracyclines, sulfonamides, fluoroquinolones, and macrolides.

Question 24

what are the 5 main sites of action for antimicrobial drugs

Answer 24

Inhibition of cell wall assembly

Damage to cell membrane

Inhibition of protein synthesis

Inhibition of nucleic acid synthesis

Damage to DNA

Question 25

what are the 3 general groups of antibacterial drugs

Answer 25

those that inhibit eznymes in DNA synthesis and integrity - those targeting transcription and translation to inhibit bacterial processes that meidate RNA and protien synthesis - those that inhibit steps in bacterial cell wall synthesis

Question 26

what is a beta lactam

Answer 26

- common systemic antimicrobial agent that is very safe and effective - only works for actively growing bacteria - contain a four membered lactam (cyclic amide) which confers antibacterial activivty but sensitive to destruction by bacteria expressing beta-lactamases

Question 27

what are commonly prescribed beta lactams

Answer 27

- penicillins and cephalosporins

Question 28

how are bacteria resistant to B lactams

Answer 28

- able to cleave the B lactam bond reuqired for antibiotic action - B lactamase inhibiots like **clavulanic acid and sulbactam** act as decoys by binding to (inhibiting) B-lactamase enzymes \*structural similarity between B lactamase inhibitos and the B lactam antibioitcs

Question 29

what is clavulanic acid

Answer 29

act as decoys by binding to (and thereby inhibiting) β-lactamase enzymes.

Question 30

what is sulbactam

Answer 30

act as decoys by binding to (and thereby inhibiting) β-lactamase enzymes.

Question 31

what is the mechanism of action for beta lactams

Answer 31

- inhibition of cell wall synthesis - bacterial cell wall is made up of cross linked peptidogylcans - enzyme bacterial transpeptidase catalyzes the cross linking of sugars with the amino acids to form the outer layer of the cell wall \*beta lactams inhibit cell wall synthesis by inactivating bacterial transpeptidase which results in a defective cell wall and ultimately cell lysis

Question 32

how do penicillins work

Answer 32

- bind covalently to bacterial transpeptidase and result in the destruction of enzyme - inhibits cell call synthesis

Question 33

what is penicillin G

Answer 33

- narrow spectrum of activity but highly effective - penicillin G is used to treat serious infections with Gram positive bacteria (rod and cocci) as well as some anaeobes - not very stable in acidic conditions so reuqired to injection rather than oral admin

Question 34

what is penicillin V

Answer 34

Gastric acid stable counterpart Can be taken oraly but less effective

Question 35

what penicillians are resistant to penicillinase

Answer 35

- dicloxacilin, oxacilin and cloxacilin - have little activity against baceria other than gram positive bacteria - stable in acidic environments

Question 36

what is dicloxacilin used to treat

Answer 36

stubborn S. aureus infections which are resistant to most penicillins

Question 37

what is amoxicillin

Answer 37

penicillin with borad spectrum of action - target gram positive aerobes, anerobes and several important gram neg pathogens - high bioavailability comparied to other penicillins (~80%) - much more effective in combination with penicillinase inhibitors like clavulanic acid

Question 38

pharmacokinetics of beta lactams

Answer 38

- distribution involes most tissues except for the CNS and prostate (unless they are inflammed) - elimination of agent occurs via urine excretion - 10% filtered while other 90% is actively secreted into the tubules - half life of penicillines might increase as much as 20 fold in cases of renal failed

Question 39

resistnace to beta lactams

Answer 39

- poor to no penetration of beta lactam complex in gram negatie cell walls, making most penicillins ineffective against gram neg bacteria - bacteria can acquire bacterial penicillinases during growth- plasmid encoded and can be transferred to other bacteria - altered penicillin binding protein (such as those in staph infections) can reduce the binding affinity of penicillin for transpeptidase

Question 40

adverse effects of penicillins

Answer 40

- hypersensitivity reactions - mild allergy to anaphylactic rxn (rare) - various subgroups of penicillins thet are all corss sensitixing - approx 5% of all humans have reported haivng a penicillin allergy at some point - non allergic skin rashed have been reported with amoxicillin - seizures may occur following admin of b lactams bc they lower seizure threshhold - avoid high doses in patients with renal disease or epileptic episodes - certain animals can experience colitis which can cause diarrhea and be life threatening

Question 41

what are cephalosporins?

Answer 41

- v similar to penicillins in terms of mechanisms, distribution, elimination and fact they cause hypersensitivity reactions \*\*cephalosporinsa re not susceptible to penicillinases - 5-10% of humans with a penicillin allergy are also allergic to cephalosporins, and should thus these should also be avoided to be safe.

Question 42

describe spectrum of actiivty of cephalosporins

Answer 42

classified by “generations”, indicating changes and/or improvements to their structure and activity since the first cephalosporin was discovered in 1945. - first genertion v similar to amoxicillin - used to treat gram postive aerobes, anerobes and some medically ipmortnat gram neg aerobes like E.coli **cephalexin** is common ex of first gen

Question 43

Cefuroxime

Answer 43

Second gen Also used against anerobes Most second gen drugs are more effective against gram neg bacteria than first gen

Question 44

cefotaxime

Answer 44

- example of third gen - greater affinity for gram negative aerobes - can cross BBB in CNS readily so use to treat meningitis (specific to cefotaxime)

Question 45

fourth generation cephalosporins

Answer 45

reserved for life threatening infections - rapidly penetrate through the outer memrbane of gram negatie bacteria enhancing their activity - aslo active against B lactamase producing bacteria which amy inactivate third gen cephalosporins