micro sheet # 10

Antimicrobial agents:
Last lecture we take about beta lactam antimicrobial agents and they all share the same mechanism of action which is the binding of antimicrobial to penicillin binding protein which presents at the cell wall and binding of antimicrobial agents to these protein inhibit them from cell wall synthesis.
Actually this is not the exact mechanism, the binding of antimicrobial agents to these protein remove the inhibition from Autolysis.
Autolysis is normal enzymes present in the cell wall and their function is to facilitate division of bacteria (replication) by digestion of the cell wall. These enzymes are active during replication to form new cells (with new cell wall), but these enzymes are normally inhibited in periods other than replication and the removal of this inhibition will result in lysis of bacteria and that’s because cell wall is lysis and the cell membrane is not strong enough to maintain the integrity of the cell, unless these bacteria are placed in hypertonic environment because ……………., this can be achieved in vivo where L-forms are produced as a result of suboptimal treatment of penicillin in organisms that exist in certain places like joints where they can survive and live longer and this result in failure the treatment. Or they can be created in the lab by putting the organisms in hypertonic environment and there are protoplast(resulting from gram+ bacteria) and spheroblast(resulting from gram- bacteria), so these are forms that can survive if put in suitable environment .
Beta lactam antimicrobial agent:
*Penicillin
_the most important antimicrobial agent
_it was utilized by shwan and flory at forties and at that time most of the infections are susceptible to penicillin however penicillin resistance emerged rapidly because the ability of the organisms to produce different mechanisms deactivate or exclude the drug.
_highly effective with an extremely low toxicity, they are the best agents to achieve selective toxicity (affects cell wall which is not presents in eukaryotic cells), however they can cause fetal side effects. They has nothing to do with toxicity, they can be given in doses up to 20grams/day (therapeutic dose at infection= 2grams/day) because they are extremely safely (wide therapeutic index) however they may cause allergy in certain patients.
_there are derivatives of penicillin which have wide or narrow spectrum according to the change in the side chains, playing with the structure specially near the beta lactam ring may increase the resistance of the antimicrobial agent to beta lactamase. They all susceptible to beta lactamase, they differ in range of spectrum, enzyme stability and acid stability(taking them orally or injection).
So playing with the side chains may lead to newer derivative with deferent pharmacological and antimicrobial activity.
_Penicillin includes: Penicillin G, Penicillin V, methicillin, oxacillin, ampicillin, carbenicillin, ticarcillin, piperacillin
_penicillin classes :
I_Natural Penicillins: originally produced by fungi
_They are include: Pen G, Pen V, they are present(especially penicillin G) in either short acting(Procaine penicillin: act with 6hours so the half life is short then the dose should be repeated) or long acting(Benzathine :activity duration for a month. People who are used to be infected regularly like tonsillitis or pharyngitis are given long acting penicillins to cover them for the hole month against these infections, and this is a preventive method against Rheumatic fever (affects children 4-15 years old)this fever caused by streptococci .
_Pen G : is acid labile (destroyed by acids ) and that’s why it is injectable form, it not going to be effective in oral form
_Pen V : is acid stable, so it can be given orally
_they are used for :
_streptococcal infection, streptococci : are universally susceptible for penicillin. We don’t have resistance forms of them. However recently they describe that known as tolerant forms(they are tolerant to high doses) and that tolerance could be due to co infection with organisms that produce beta lactamase and protect streptococci( they destroy the drug ), streptococci don’t produce beta lactamase (group A streptococci). Streptococci is not resistant it tolerant due to the presence of a co infection (co pathogen) that produces beta lactamase which destroys the drug and they continue cause infection.
_syphilis and spirochete
II_Amino penicillin :In the 60s they use amination for modifying penicillin with resultant drugs: Ampicillin, amoxicillin
_they affect gram-ve bacteria
_highly susceptible to beta lactamase
_ acid stable so they can given orally. Their absorption and distribution in plasma is excellent.
_the only problem with these drugs is the odd use (not sure??) and this result in spread of resistance, these drugs given for no reason as a result almost all organisms are resistance to these drugs.
III_ Antistaphelococci penicillin
_ staphylococci forms resistance against penicillin mainly by production of beta lactamase
_modification of penicillin G resulted in Methicillin, oxacillin, dicloxacillin and these are stable to beta lactamase (huge change near the beta lactam ring)
_these drugs only active against staphylococci and they lack activity against gram- ve and streptococci
_in 1960 Methicillin resistance among staphylococci(staphylococcus aureus and staphylococcus epidermidis) emerged rabidly( it was produced in 1959), and now Methicillin resistance is very common in hospital, about 60% or more of staphylococcus are resistance.
_staphylococcci are classified according their ability to produce coagulase :
Coagulase +ve which is Staphylococci aureus
Coagulase -ve which is more than one species
_Methicillin resistance staphylococci are treated by glycopeptides antibiotic (Vancomycin, Teicoplanine, Bacitracin)
_we can't give Methicillin without doing sensitivity because the majority of isolates are resistant.
_ Methicillin resistance major cause of hospital acquired infection as well as community acquired infection, some of which infection are lethal.
IV_antipseudomonal penicillin
_active against Pseudomonas auruginosa ,also it is wide spread among hospitalized patients.
_it includes: Carbenicillin, Ticarcilline, Piperacillin
_they are high susceptible to beta lactamase so activity against gram-ve bacteria is lost.
Beta lactam and beta lactamase inhibitor combinations
Beta lactamase inhibitor has no activity against bacteria but they can inhibit the action of beta lactamase because they have more affinity to the enzyme than the penicillin and that’s why when they are combined together so beta lactamase inhibitor inhibit the enzyme while beta lactam kills the cell. That preserves the drug from the action of beta lactamase.
_we have three combinations:
I_Amoxicillin + clavulanate (famous name Augmentin or Amoclan)
_active against most respiratory tract, and some GI tract gram negative organisms(E.colli, streptococci….)
II_Ampicillin + sulbactam (Unasyn)
_Sulbactam is beta lactamase inhibitor
_Very good activity against GI and respiratory tract gram negatives
III_Piperacillin + tazobactam (Zosyn)
_Piperacillin is the antipseudomonal agent
Cephalosporins
_generally they are more stable to beta lactamase hydrolysis than penicillin and they have a wider antibacterial spectrum.
_some of them are acid stable and some are not so mostly they are available as injection form especially 2nd and 3rd generation.
_represents chronological classification
_1st generation cephalosporin: active against E.coli, Klebsiella, gram positives
Penicillins are active against gram positive only.
_exp: Cephalexin, Cefadroxil, Cefazolin they are good against gram +ve with limited activity against gram-ve
_most of them are available in oral forms
_2nd generation cephalosporin: active against E.coli, Klebsiella, gram-positives and also H-influenza, Enterobacter, Serratia, Citrobacter, and some anaerobes (Bacteriodes fragilis).
Exp: Cefaclor, cefuroxime, Cefoxitin, cefotetan
_Cefuroxime is the only one which is available in oral forms (acid stable)
_3rd generation cephalosporin: active against most enterobacteriacae and P. aeruginosa, they are less active against gram+ve but they are very active against gram-ve bacteria includes P.aeruginosa
_Only Ceftriaxone has usable activity against Staph. aureus
_exp: Ceftriaxone, cefotaxime, ceftazidime, cefoperazone,cefexine
_ cefexine the only one available in oral forms
_they are active against pseudomonas (ceftazidime, cefoperazone)
_they are not active against gram+ve
_4th generation cephalosporin: active against enterobacter and citrobacter because they produce extended beta lactamase.
_presented by: cefepime
_Very good activity against gram postives, including S. aureus
_Very good activity against gram negatives, including P.aeruginosa
Semisynthetic Penicillins
Their structure can be with ……… and they are produced by fungi but they can be modified in the lab.
_ they are Penicilinase-resistant penicillins like Carbapenems which has broad spectrum of activity( like emipenin or ertapenin) and monobactam (like astrenan ) which are active against gram-ve bacteria
_they are resistance to penicilinase so they are called Extended-spectrum penicillins (like penicillin with beta lactamase inhibitor are also extended spectrum)



Carbapenems
the structure contains beta lactam ring and thiazolidine ring and the side chains.
They include Imipenem, Meropenem and Ertapenem as a result of modification of side chains.
_Extremely broad activity, including S.aureus and other gram positives , Pseudomonas, and anaerobic organisms.
_the toxicity are associated with hypersensitivity and sometimes cause seizures because concentration in CSF.
_they induce beta lactamase in many gram negative bacteria
Resistance to beta lactamse is the result of:
I_ Degradation by beta-lactamases
Example: nearly all Staphylococcus aureus which produces beta lactamase which destroys the beta lactam ring
II_ Decreased permeability of the drug
Example: most gram negative bacteria refractory to Penicillin G because they don’t allow the penetration of the drug.
III_ Altered Penicillin binding proteins caused by chromosomal mutations (in the gene codes for penicillin binding proteins) that resulted in decrease affinity of penicillin binding proteins to penicillin.

Examples: Methicillin resistant Staphylococcus aureus
Penicillin resistant Streptococcus pneumoniae
Penicillinase (beta Lactamase) action
They open beta lactam ring which results on 6-amino penicillioc acid which doesn’t have antibacterial activity
Extended-Spectrum b-lactamases
Their beta lactamase that specific for drugs like penicillinase (they inactivate penicillin and sephalosporelinase which act on cephalosporins, but there is extended spectrum beta lactamase that’s are active against broad spectrum of drugs
_most drugs are susceptible to them
_they are plasmid mediated where originally discovered in Klebsiella pneumoniae, Klebsiella oxytoca and E. coli but also P. aeruginosa.these organism are present in GI tract of organism and they can undergo conjugation and transfer plasmids and this result in the spread in the resistance of them due to their ability to produce beta lactamase
_ the plasmid codes for high-level resistance to ceftazidime, cefotaxime, and aztreonam , these organism must be susceptible to aminoglycoside and Imipenem to document the availability of extended spectrum bata lactamase
_ some susceptible to b -lactam/ b -lactamase inhibitors, few susceptible to Ciprofloxacin
_there is test to confirm extended_spectrum beta lactamase(ESBL) producers is by combining one of these drugs with beta lactamase inhibitor and if the enzymes inhibited that’s prove the present of ESBL
_some susceptible to b -lactam/ b -lactamase inhibitors, few susceptible to Ciprofloxacin.
_ Treatment with carbapenems recommended because they don’t affect emiffin and other carbepenems like Meropenem and Ertapenem.
Inducible chromosomal cephalosporinases:
_they are different from the expended spectrum beta lactamase which coded by plasmid while inducible chromosomal cephalosporinases coded by chromosomes.
_they have been detected in : Serretia, P. aeruginosa, Providencia, Acinetobacter, Citrobacter and Enterobacter.
_they are induced by exposure to 3rd generation cephalosporins
If we treat these organism with 3rd generation cephalosporin they produce the inducible chromosomal cephalosporinase(ICC).
_it is a single step mutation in repressor gene leads to continuous high-level resistance to all cephalosporins and beta lactam/ beta lactamase Inhibitors.
_ Carbapenem is first line treatment, but note Cefepime(4th generation cephalosporine) has low affinity for Bush group 1 b lactamases.
Glycopeptides
_also affects the cell wall of the bacteria.
_mainly vancomycin and Teicoplanin
_nyzolin is another new one that used when the organism is resistance to vancomycin
_some organisms especially enterococci have develop resistance to vancomycin and some staphylococci specially penicillin inhibitor staphylococci (about 7 isolets) are resistance to vancomycin this decreases the option of treated methicillin resistant staphylococci which used to be treated by vancomycin
_ some of these vancomycin resistant are treated by newer drugs like lymozolide and tegazidine
_ vancomycin and Teicoplanin are Complex glycopeptides that disrupt cell wall synthesis in growing gram-positive bacteria at a later stage (bridge formation stage which the last stage in cell wall synthesis)
_ vancomycin and Teicoplanin are used For methicillin resistant staphylococci (but some of them have develop resistance), C. difficile and other gram-positives resistant to beta lactam
_C. difficile (it is an anaerobic organism that doesn’t cause disease in body normally but individual who are treated with antibiotic for long period of time cause the over growth of C.difficile so they kill the normal flora of the GI tract allowing for C.difficile produce toxins that causes diarrhea, that’s why individual who treated for long time with antibiotic they may develop diarrhea and this is known as antibiotic associated dyarria and may lead to pseudomembranous colitis which may be lethal ).
So vancomycin is an antibiotic used to treat diarrhea resulting from another antibiotic mainly by clendamycin and lincomycin and others like newer cephalosporin and some anticancer agent (metophexate).
Vancomycin can used to treat organisms that resistance to beta lactam antibiotic however one should keep in mind that vancomycin resistance have emerged among staphylococci
_most organisms develop resistance whither shorty after the introduction to the antibiotic or at a longer period of time that’s why the proper use of the antibiotic is very important.
Bacitracin
_A mixture of polypeptides used in topical applications for the treatment of skin infections caused by gram-positive bacteria.
_it can’t be given systematically because of high toxicity it can be given in ointment to treat the infection of the skin and the mucus membrane locally. It can't be given orally or parentally.
_they are produced by bacillus

Isoniazid(INH), Ethionamide, Ethambutol, and cycloserine
_These agent damage the cell wall but of mycobacteria (mycobacterium tuberculosis) only.
_ used to treat mycobacterial infection
Inhibitors of Cell Membrane Function
_the cell membrane used for respiration, oxidative phosphorylation and disposal of waste or toxic material and it is selective membrane barrier. All of these functions may be lost when agent binds to its structure.
Polymyxins (B, E)
- they are Cationic branched cyclic decapeptides (8 amino acids) that destroy bacterial cell membranes.
-they are both Nephrotoxic: limited to topical use, except for polymyxin E.
_colistin is now recommended to treat gram negative bacteria that are resistanant to emipelin and other agents especially Acinetobacter a Gram-negative which is one of the major causes of nosocomial infections infection and they may be lethal among debilitated patients, patients in intensive care unit or patient suffer from blood stream infection and CNS infection and some of these strains resistant at all antibiotic. They can be used with colistin (polymexin E) which is recommended systematically although it is toxic but it is the only option available.
Imidazoles and polyenes (antifungal, no activity against bacteria)
_they act by inhibition of the cell membrane functions through binding to the steroids in it (where steroid are not available in cell.M of bacteria except for mycoplasm )
_given Orally to treat fungal infection: ketoconazole, Itraconzole, Fluconazol
_Parentelral(injectable form) : Microconazole, Clotrimazole, Econazole
_most fungi are opthorgenistic pathogenic affect patient with weak immunity
Daptomycin
_the first cyclic lipopeptide which act against cell membrane function in bacteria through binding to the cell membrane causing depolarization an rapid lysis
_ Indications for use:
Complicated skin and skin structure infections
Staphylococcus aureus bloodstream infections, including right-sided endocarditis that can develops sequence to dental procedure
NOT for pneumonia, has no activity in lung



Done by: mona yanis
Lecture 10
10-10-2010