دکتر فرينبز راشذ مرنذی متخصص آسيب شنبسی تشريحی و ببلينی عضو هيئت علمی آزمبيشگبه مرجع سالمت • Antibiotical grouping • Mechanisms of action Bacteriostatic Bacteriocidal Site of action

Antibiotics

Antibiotics and vaccines are among the biggest medical advances since 1000. (Culver Pictures)

For lecture only BC Yang Thanks to work by Alexander Fleming (1881- 1955), Howard Florey ( 1898-1968) and Ernst Chain (1906-1979), penicillin was first produced on a large scale for human use in 1943. At this time, the development of a pill that could reliably kill bacteria was a remarkable development and many lives were saved during World War II because this medication was available.

A. Fleming E. Chain H. Florey

For lecture only BC Yang Penicillin: an extensively studied example

For lecture only BC Yang

A tale by A. Fleming • He took a sample of the mold from the contaminated plate. He found that it was from the penicillium family, later specified as Penicillium notatum. Fleming presented his findings in 1929, but they raised little interest. He published a report on penicillin and its potential uses in the British Journal of Experimental Pathology.

For lecture only BC Yang Antibiotic Grouping 1. ß-lactamase (penicillin,cephem,penem,monobactam, ß- lactam- ß-lactamase inhibitor 2. Aminoglycosides 3. Glycopeptides 4. Macrolides 5. Tetracyclines 6. Quinolones 7. Folate pathway inhibitors 8. Lipopeptides 9. Single drug class Mechanism of Action

• Antibiotic action can be split into 2 mechanisms:

Bacteriostatic

Bacteriocidal

Bacteriostatic

• Bacteriostatic antibiotics inhibit growth and reproduction of bacteria without killing them. • Bacteriostatic agents must work with the immune system to remove the microorganisms from the body. • Bacteriostatic antibiotics hamper the growth of bacteria by interfering with bacterial: Protein production DNA replication Cellular metabolism

Bacteriostatic Antibiotics

• tetracyclines • sulphonamides • spectinomycin • trimethoprim • chloramphenicol • macrolides • lincosamides

Bacteriocidal

• A bacteriocide is a substance that kills the bacteria of choice and, preferably, nothing else. • Microbe death is usually achieved by disruption of the bacterial cell membrane leading to lysis. Bactericidal antibiotics

• Bactericidal antibiotics • Bactericidal antibiotics kill bacteria; bacteriostatic antibiotics only slow their growth or reproduction. • Penicillin is a bactericide, as are cephalosporins, all belonging to the group of β-lactam antibiotics. They act in a bactericidal manner (by disrupting cell wall precursor leading to lysis). • Aminoglycosidic antibiotics are usually considered bactericidal, although they may be bacteriostatic with some organisms. They act by binding irreversibly to 30s ribosomal subunit, reducing translation fidelity leading to inaccurate protein synthesis). The other effect is the inhibition of protein synthesis due to premature separation of the complex between mRNA and ribosomal proteins. The final result is bacterial cell death. • Other bactericidal antibiotics include the fluoroquinolones, nitrofurans, vancomycin, monobactams, co-trimoxazole, and metronidazole.

Antibiotic Grouping 1. ß-lactamase (penicillin,cephem,penem,monobactam, ß- lactam- ß-lactamase inhibitor 2. Aminoglycosides 3. Glycopeptides 4. Macrolides 5. Tetracyclines 6. Quinolones 7. Folate pathway inhibitors 8. Lipopeptides 9. Single drug class β-Lactams

β-lactam antimicrobial agents all share the common, central, four-member β-lactam ring and the principal mode of action of inhibition of cell wall synthesis. Additional ring structures or substituent groups added to the β-lactam ring determine whether the agent is classified as a penicillin, cephem, carbapenem, or monobactam. β-Lactam/β-Lactamase Inhibitor Combinations

These antimicrobial agents are combinations that include a penicillin class antimicrobial agent and a second agent that has minimal antibacterial activity, but functions as an inhibitor of some lactamases.Currently, three β-lactamase inhibitors are in use: clavulanic acid, sulbactam, and tazobactam. The results of tests of only the penicillin portion of the combination against β-lactamase-producing organisms are often not predictive of susceptibility to the two- drug combination.

Glossary I (Part 1). β-lactams: Class and Subclass Designation and Generic Name Agents Included; Generic Names Antimicrobial Subclass Antimicrobial Class penicillin penicillina penicillins amoxicillin aminopenicillina ampicillin azlocillin ureidopencillina mezlocillin piperacillin carbenicillin carboxypenicillina ticarcillin cloxacillin penicillinase-stable dicloxacillin penicillinsb methicillin nafcillin oxacillin mecillinam amidinopenicillin amoxicillin-clavulanic acid β-lactam/β-lactamase ampicillin-sulbactam inhibitor combinations piperacillin-tazobactam ticarcillin-clavulanic acid cefazolin cephalosporin Ic,e cephems (parenteral) cephalothin cephapirin cephradine cefamandole cephalosporin IIc,e cefonicid cefuroxime (sodium) cefoperazone cephalosporin IIIc,e cefotaxime ceftazidime ceftizoxime ceftriaxone cefepime cephalosporin IVc,e cefmetazole cephamycind cefotetan cefoxitin moxalactam oxacephem cefaclor cephalosporine cephems (oral) cefadroxil cefdinir cefditoren cefetamet cefixime cefpodoxime cefprozil ceftibuten cefuroxime (axetil) cephalexin cephradine loracarbef carbacephem aztreonam monobactams doripenem carbapenem penems ertapenem imipenem meropenem faropenem penem a Penicillinase-labile; hydrolyzed by staphylococcal penicillinase. b Not hydrolyzed by staphylococcal penicillinase. c Cephalosporin I, II, III, and IV are sometimes referred to as 1st-, 2nd-, 3rd-, and 4th-generation cephalosporins, respectively. Cephalosporin III and IV are also referred to as “extended-spectrum cephalosporins.” This does not imply activity against ESBL-producing gram- negative bacteria. d Although often referred to as a 2nd-generation cephalosporin, cephamycins are not included with the other cephalosporins with regard to reporting of ESBL- producing strains. e For all confirmed ESBL-producing strains, the test interpretation should be reported as resistant for this antimicrobial class or subclass.

Penicillin

Penicillin is one of the earliest discovered and widely used antibiotic agents, derived from the Penicillium mold.

In 1928, Sir Alexander Fleming observed that colonies of the bacterium Staphylococcus aureus could be destroyed by the mold Penicillium notatum, proving that there was an antibacterial agent present. Penicillins These penicillins are penicillinase-labile;hydrolyzed by staphylococcal penicillinase penicillin penicillin Penicillins

amoxicillin aminopenicillin

azlocillin ureidopencillin mezlolin piperacillin

carbenicillin carboxypenicillin ticarcillin

Penicillinase-stable penicillin

Penicillinase-stable penicillin Cloxacillin Dicloxacillin Meticillin Nafcillin oxacillin

ß- lactam /ß- lactamase inhibitor combinations

ß- lactam /ß- lactamase inhibitor amoxicillin-clavulanic acid combinations ampicillin-sulbactam piperacillin- tazobactam ticarcillin-clavulanic acid Antibacterial Effect & Mechanism of action

Antibiotic class Bacteria Mechanism

β lactams Inhibition of cell wall synthesis penicillins beta-Lactamase G+ Some non producing fastidious aerobic G- some anaerobic bacteria

β lactams- β lactamase producing β lactamase bacteria inhibitors

Sites of action

For lecture only BC Yang cephems

• The cephalosporins are a class of β-lactam antibiotics. Together with cephamycins (cephmetazole,cefotetan,cefoxitin) they constitute a subgroup of β-lactam antibiotics called cephems.

Cephems cefazolin cephalosporin Ic,e cephems (parenteral) cephalothin cephapirin cephradine cefamandole cephalosporin IIc,e cefonicid cefuroxime (sodium) cefoperazone cephalosporin IIIc,e cefotaxime ceftazidime ceftizoxime ceftriaxone cefepime cephalosporin IVc,e cefmetazole cephamycind cefotetan cefoxitin moxalactam oxacephem cefaclor cephalosporine cephems (oral) cefadroxil cefdinir cefditoren cefetamet cefixime cefpodoxime cefprozil ceftibuten cefuroxime (axetil) cephalexin cephradine

III and IV are also referred to as “extended-spectrum cephalosporins.” This does not imply activity against ESBL-producing gram-negative bacteria.

Cephems (Including Cephalosporins)

Different cephem antimicrobial agents exhibit somewhat different spectrums of activity against aerobic and anaerobic gram-positive and gram-negative bacteria. The cephem antimicrobial class classical cephalosporins, as well as the agents in subclasses cephamycin, oxacephem, and carbacephems Cephalosporins are often referred to as “first-,” “second-,” “third-,” or “fourth- generation” cephalosporins, based on the extent of their activity against the more antimicrobial agent-resistant, gram-negative aerobic bacteria. Not all representatives of a specific group or generation necessarily have the same spectrum of activity. Because of these differences in activities, representatives of each group may be selected for routine testing.

Antibacterial Effect & Mechanism of action

Antibiotic class Bacteria Mechanism

cephems(Cephalosporins, Aerobic & anaerobic g+ ,g- cephamycin,oxacephem, carbacephem) Penems

The penem antimicrobial class which includes two subclasses, the carbapenems and penems, differs slightly in structure from the penicillin class; agents in this class are much more resistant to β-lactamase hydrolysis, which provides them with broad-spectrum activity against many gram-positive and gram-negative bacteria.

Antibacterial Effect & Mechanism of action

Antibiotic class Bacteria Mechanism

)Carbapenem,penem) Broad spectrum activity Penems against many aerobic g+,g- Monobactams

• Monobactam antimicrobial agents are monocyclic β-lactams. At present, aztreonam (which has activity Only against aerobic gram- negative bacteria) is the only monobactam antimicrobial agent approved for use by the FDA.

Antibacterial Effect & Mechanism of action

Antibiotic class Bacteria Mechanism

monobactam Only against aerobic gram + Glycopeptides

Glycopeptide antimicrobial agents, which include vancomycin and teicoplanin, share a complex chemical structure and a principal mode of action of inhibition of cell wall synthesis at a different site than that of The β-lactams. The activity of this group is directed primarily at aerobic gram-positive bacteria. Vancomycin is an accepted agent for treatment of a gram- positive bacterial infection in the penicillin-allergic patient, and it is useful for therapy of infections due to β-lactam- resistant, gram-positive bacterial strains (e.g., methicillin- resistan Staphylococcus aureus (MRSA) and some enterococci).

Aminoglycosides

Aminoglycosides are structurally related antimicrobial agents that inhibit bacterial protein synthesis at the ribosomal level. This class includes agents variously affected by aminoglycoside-inactivating enzymes,resulting in some differences in the spectrum of activity among the agents. Aminoglycosides are used primarily to treat aerobic, gram- negative rod infections or in synergistic combinations with cell-wall- active antimicrobial agents (e.g., penicillin, ampicillin, vancomycin) against some resistant, gram-positive bacteria, such as enterococci.

Macrolides

Macrolides are structurally related antimicrobial agents that inhibit bacterial protein synthesis at the ribosomal level. Several members of this class currently in use may need to be considered for testing against fastidious, gram-negative bacterial isolates. For gram-positive organisms, only erythromycin needs to be tested routinely. The antimicrobial spectrum of macrolides is slightly wider than that of penicillin, and therefore macrolides are a common substitute for patients with a penicillin allergy.

Common antibiotic macrolides

• Azithromycin (Zithromax, Zitromax, Sumamed) - Unique, does not inhibit CYP3A4 • Clarithromycin (Biaxin) • Dirithromycin (Dynabac) • Erythromycin • Roxithromycin (Rulid, Surlid,Roxid)

Tetracyclines Tetracyclines are structurally related antimicrobial agents that inhibit protein synthesis at the ribosomal level of certain gram-positive and gram-negative bacteria. Agents in this group are closely related and, with few exceptions, only tetracycline may need to be tested routinely. Organisms that are susceptible to tetracycline are also considered susceptible to doxycycline and minocycline. However, some organisms that are intermediate or resistant to tetracycline may be susceptible to doxycycline or minocycline or both.

Tetracyclines

• Tetracyclines are a group of broad-spectrum antibiotics whose general usefulness has been reduced with the onset of bacterial resistance. Despite this, they remain the treatment of choice for some specific indications. • They are so named for their four (“tetra-”) hydrocarbon rings (“-cycl-”) derivation (“-ine”). More specifically, they are defined as "a subclass of polyketides having an octahydrotetracene-2-carboxamide skeleton".They are collectively known as "derivatives of polycyclic naphthacene carboxamide".

Tetracyclines

The 4 rings of the basic tetracycline structure Quinolones

Quinolones (quinolones and fluoroquinolones) are structurally related antimicrobial agents that function primarily by inhibiting the DNA- gyrase or topoisomerase activity of many gram-positive and gram-negative bacteria. Some differences in spectrum may require separate testing of the individual agents.

Folate Pathway Inhibitors

Sulfonamides and trimethoprim are chemotherapeutic agents with similar spectra of activity resulting from the inhibition of the bacterial folate pathway Sulfisoxazole is among the most commonly use sulfonamides in the treatment of urinary tract infections; thus, it may be the appropriate selection for in vitro testing. Sulfamethoxazole is usually tested in combination with trimethoprim, because these two antimicrobial agents inhibit sequential steps in the folate pathway of some gram-positive and gram- negative bacteria.

Sulfonamides

• There are several sulfonamide-based groups of drugs. The original antibacterial sulfonamides (sometimes called simply sulfa drugs) are synthetic antimicrobial agents that contain the sulfonamide group. Some sulfonamides are also devoid of antibacterial activity, e.g., the anticonvulsant sultiame. The sulfonylureas and thiazide diuretics are newer drug groups based on the antibacterial sulfonamides. • Sulfa allergies are common, hence medications containing sulfonamides are prescribed carefully. It is important to make a distinction between sulfa drugs and other sulfur-containing drugs and additives, such as sulfates and sulfites, which are chemically unrelated to the sulfonamide group, and do not cause the same hypersensitivity reactions seen in the sulfonamide

Trimethoprim • Trimethoprim is a bacteriostatic antibiotic mainly used in the prophylaxis and treatment of urinary tract infections. Trimethoprim was commonly used in combination with sulfamethoxazole, a sulfonamide antibiotic, which inhibits an earlier step in the folate synthesis pathway (see diagram above). This combination, also known as co-trimoxazole, TMP- sulfa, or TMP-SMX, results in an in vitro synergistic antibacterial effect by inhibiting successive steps in folate synthesis. This claimed benefit was not seen in general clinical use.Its use has been declining due to reports of sulfamethoxazole bone marrow toxicity, resistance and lack greater efficacy in treating common urine and chest infections, and side effects of antibacterial sulfonamides. As a consequence, the use of co-trimoxazole was restricted in1995. Sulfonamides

The structure of the sulfonamide group Lipopeptides

Lipopeptides are a structurally related group of antimicrobial agents, whose principal target is the cell membrane. The polymyxin subclass, which includes polymyxin B and colistin, has activity against gram- negative organisms. Daptomycin is a cyclic lipopeptide with activity against gram-positive organisms. Lipopeptide activity is strongly influenced by the presence of divalent cations in the medium used to test them. The presence of excess calcium cations inhibits the activity of the polymyxins, whereas the presence of physiologic levels (50 mg/L) of calcium ions is essential for the proper activity of daptomycin.

Antibacterial Effect & Mechanism of action Antibiotic class Bacteria Mechanism

Glycopeptide(vancomycin, Primarily aerobic g+ Inhibition of cell wall teicoplanin) synthesis

Aminoglicosides Primarily g-rods,synergistic Inhibit protein synthesis at combination with cell wall ribosomal level active drugs(pen,amp,van) against resistant g+ bacteria

Macrolides fastidious g- .for G+ only Inhibit protein synthesis at erythrmycin need to be tested. ribosomal level

Tetracyclines G + , G- Inhibit protein synthesis at ribosomal level

Quinolones(quinolones,flu G + , G- Inhibiting DNA gyrase or oroquinolones) topoisomerase Antibacterial Effect & Mechanism of action

Antibiotic class Bacteria Mechanism Sulfonamide /trimetoprim G+,G- Inhibition of folate pathway Folate pathway inhibitors Lipopeptide G-(polymyxin B,colistin) Cell membrane G+ Daptomycin Single – Drug class chloramphenicol Inhibit protein synthesis clindamycin Inhibit protein synthesis Linezolid Inhibit protein synthesis streptogramins Inhibit protein synthesis telitromycin Inhibit protein synthesis tigecycline Inhibit protein synthesis rifampin RNA synthesis inhibitors nitrofurantoin Inhibit protein synthesis at ribosomal level Single-Drug Classes

The following antimicrobial agents (antimicrobial class) are currently the only members of their respective classes used in humans that are included in this document, and are appropriate for in vitro testing. These include chloramphenicol (phenicols), clindamycin (lincosamides), linezolid (oxazolidinones), quinupristin-dalfopristin (streptogramins), telithromycin (ketolides), tigecycline (glycylcyclines), all of which inhibit protein synthesis, and rifampin (ansamycins), which is an RNA synthesis inhibitor. Nitrofurantoin (nitrofurans), which is used only in the therapy of urinary tract infections, acts by inhibiting several protein synthesis-and-assembly steps at the ribosomal level. Fosfomycin (fosfomycins), also approved by the FDA for urinary tract infections, inhibits enzymes involved in cell wall synthesis. Chloramphenicol

• Chloramphenicol is a bacteriostatic antimicrobial originally derived from the bacterium Streptomyces venezuelae, isolated by David Gottlieb, and introduced into clinical practice in 1949. • It was the first antibiotic to be manufactured synthetically on a large scale. Chloramphenicol is effective against a wide variety of microorganisms; it is still very widely used in low income countries because it is exceedingly inexpensive, but has fallen out of favour in the West due to a very rare but very serious side effect: aplastic anemia. • In the West, the main use of chloramphenicol is in eye drops or ointment for bacterial conjunctivitis. • Chloramphenicol has recently been discovered to be a life saving cure for chytridiomycosis in amphibians. Chytridiomycosis is a fungal disease that has been blamed for the extinction of one-third of the 120 frog species lost since 1980.

Sites of action

For lecture only BC Yang