Microbiology ( Bacteriology) sheet # 7 Revision of last lecture : Each type of antimicrobial drug normally targets a specific structure or component of the bacterial cell eg:( cell wall, cell membrane, protein synthesis, DNA formation and replication ). In relation to Cell Wall, Drugs used : Penicillin, Cephalosporin, Glycoproteins Penicillin and Cephalosporin are very similar, with only a slight difference in chemical structure ( 5 and 6 rings ) while the B lactam ring is the same. Any additive structure related to B lactam ring, in the form of an amino, carboxyl or acetate group, might modify not only the action against gram ve and +ve bacteria but also may be associated with certain changes in pharmaceutical kinetics ( the drug s absorption, distribution, excretion.. etc ). This group of drugs, known as B Lactam drugs includes at least 50 types of penicillin and Cephalosporin. According to the chemical structure of these drugs, we can classify these drugs in relation to one specific enzyme B lactamase. If gram +ve /-ve bacteria manage to produce B lactamase, break down B lactam ring and prevent the development of a complex structure between the specific protein at the cell wall (called penicillin binding protein ), then this means the clone of bacteria is resistant, either to penicillin G simple, or to ampicillin, amoxicillin, and to some extent to Cephalosporin drug.
Therefore we have : Penicillinase-susceptible penicillin drugs Eg : Penicillin G /V amoxicillin/ ampicillin (without clavulinic acid ) Penicillinase-resistant penicillin drugs * prevent the development of the penicillinase action *manage to treat infection by gram +ve bacteria which produce penicillinase. Eg: Oxacillin Methicillin Note: Ampicillin and amoxicillin are usually associated with a specific chemical known as Clavulinic acid, which has the anti penicillinase activity but without any antibacterial effect. Due to the development of resistance against penicillin, first among gram +ve bacteria, and second among gram ve bacteria, scientists have developed more specific types of antimicrobial drugs (by further modification of penicillin drug ), and so they have produced what is called Monobactam drug in 1950. Monobactam drug is similar to penicillin, except that it contains more chemical side chains/ chemical compounds attached to the B lactam ring. These side chains allow Monobactam to produce wider activity, mainly against gram ve bacteria, which are present in the intestinal tract and associated with serious infection, eg : Enteric bacteria, E.coli. But still, both gram ve and +ve bacteria manage to develop resistance against penicillinase. Therefore the pharmaceutical industry tried once again to introduce other penicillin drugs, taking into consideration the need for high resistance to penicillinase. As a result they came up with a group of drugs known as Carbepenem / imipenem and meropenem.. which are currently the best
available drugs to treat gram ve penicillinase producing bacteria. ( expensive drugs compared to amoxicillin and ampicillin ) However, gram ve bacteria can still develop resistance to Carbepenem drug, by producing Carbepenemase enzyme, reducing its effectiveness. This situation can be found in certain clones eg: pseudomonas aeruginosa, Acinetobacter. Seven years ago in America, they discovered KPC ( klebsiella pneumonia carbanemase).. this type of organism consider multi resistance to all currently available antimicrobial drugs, including penicillin cephalosporin, etc... Mortility rate of KPC = ( 50-80 ) % due to Carbapenemase. Carbenicillin, Piperacillin, and ticracillin Concerning certain gram ve bacteria that develop in hospitalized patients ( usually associated with wound infection ), Carbenicillin, Piperacillin, and ticracillin have been developed to deal with such types of bacteria. The distinctive feature of such drugs is that they are taken through parenteral routes ( IV / IM ). (There are no oral forms ) BUT recently, they have developed oral Carbenicillin, which is restricted to pseudomonas group only. * These drugs known as an Antipseudomonas drugs.
Cephalosporins Cephalosporins are similar to penicillin as it is also developed from a type of fungus called Cephalosporin, which is usually found in solution. This fungus and its excretion ( Cephalosporin drug) were discovered in Italy in 1950 s, and later they discovered the first generation of Cephalosporin. the terms 1 st generation, 2 nd generation and so on.. can help to understand the history of development of these drugs. 1 st generation * related to drugs that can be given orally, and cover to some extent some +ve and ve bacteria * Similar to penicillin 2 nd generation * similar to Carbenecillin * Cover gram +ve bacteria, making it a broad spectrum drug. * first forms were IV ( injectble forms but nowadays scientists have developed oral forms of these drugs, which are used mainly in urinary tract / respiratory tract infection in pregnant women. 3 rd generation Belong to types of Cephalosporin drug which mainly affect gram ve bacteria more than gram +ve bacteria. They are used exactly like Monobactam drug in treatment of serious infection ( affecting blood stream and internal organs in the form of pneumonia/ meningitis..etc ). A serious infection causes a high mortality rate and requires an efficient drug to reduce its severity and cure the infection.
we can t control the development of resistance to these drugs as B lactamase and cephalosporinase can develop ( which in turn inactivate the drug ), just like penicillinase development. What is the importance of using Cephalosporin instead of penicillin? 1) Penicillin usage is often associated with the development of allergy / hypersensitivity ( anaphylactic shock, which might result in death ), WHILE Cephalosporin is less associated with allergic reactions, even though around 5-10% of those who suffer from allergy when using penicillin are also allergic to Cephalosporin. 2) Cephalosporin cover a wider range of +ve and ve infection. 3) penetration and concentration in certain tissues ( respiratory / urinary tract ) is more effective when using Cephalosporin The last Cephalosporin was developed 20 years ago, known as Cepherin, but this drug did not replace Carbapenem, as it is not so resistant to penicillinase and cephalosporinase, the reason why it is not widely used. Nowadays there are around 20 30 types of Cephalosporins in the market, but these drugs are about to vanish in 10 years or so. In General, all cephalosporins and penicillins, whether they were made in the sixties or in the 20 th century, are classified according to two main characteristics : 1) Action Spectrum : whether they work against Gram +ve or Gram ve bacteria, mainly if they affect Gram ve Enteric bacteria. 2) Resistance : whether they resist the action of penicillinases or not.
Extended Spectrum B-Lactamases : Usually it is much more complicated when dealing with Gram ve bacteria due to the fact that once a type of penicillinase develop in a bacteria against a certain type of penicillin like Amoxicillin, over a short period of time, it will also develop resistance against other types of penicillins like Monobactam for example. This property is due to what is called an Extended Spectrum B-Lactamases. An organism with this property means that it can inactivate the majority of available penicillins. In clinical medicine, it is noticed that such organisms are in fact increasing. Usually these Extended Spectrum B-Lactamases develop in hospitalized patients during treatment with B-Lactam antibiotics for a long time, due to accumulation of resistance genes in the intestinal flora there will be a selection and increase in the number of genes in other type of bacteria as well, thus resistance will be transferred to new bacteria. Take in consideration that there are more than 60 types of penicillinases each with different type of resistance gene cassette. Side Effects Related to Penicillins and Cephalosporins All Penicillin and Cephalosporin drugs might be associated with certain side effects. One of these side effects might be Hypersensitivity Reaction ( Allergic Reaction) that s why patients should be tested before administering I.V penicillin into their blood. However, if they developed such allergy they might suffer from Serum Sickness, Nephritis, Anaphylactic Shock, or even Death. Anaphylactic shocks are usually associated with organ failure that s why they are considered the most severe side effect. As a consequence testing a patient for allergies before giving him penicillin drug, specially the injectable form like I.V, is very crucial and could be life saving.
Glycopeptides : Usually made from of amino acids, 12 to 14, associated with glucose molecules, forming a large complex structure. It is found in two very famous drugs called Vancomycin and Teicoplanin. Both have the same action against Gram +ve bacteria cell wall. Their mechanism is similar to that of penicillin, both involves forming complex structures within the cell wall of bacteria and prevent the formation of the pentapeptides cross links, thus affecting the peptidoglycan layers. These two drugs are very useful against the Staph bacteria that is resistant to penicillin, which is known as Methicillin Resistant Staph Aureus ( MRSA). These MRSA are very common and important causative agents of many diseases such as Blood Sepsis, wound infection, and any infected part of the body. Its estimated that 25-30 % of infections are associated with staphylococci which include the MRSA. In addition Vancomycin is useful for the treatment of bacteria called Enterococci, specially Enterococcus Fecalis. Enterococcus Fecalis, which ia a gram +ve bacteria found in the intestines, were rarely associated with any type of infection before the use of the cephalosporins ; however, after cephalosporins were introduced specially the 2 nd and 3 rd generation- these bacteria increased in incidents causing various clinical infections. To understand the reason behind this sudden increase it is important to first know that these bacteria are naturally resistant to cephalosporins and can survive during the treatment of the intestines with such drugs. So during the treatment while other bacteria decrease in number Enterococcus Fecalis increase in number at their expense. Originally this bacteria was transferred from the animal intestines to the humans. So when treating a patient with cephalosporins you have to be aware that you are also selectively increasing Enterococcus Fecalis bacteria in number, and thus Vancomycin should be given as well during the treatment, as no other drugs can affect them. When compared to penicillins and cephalosporins vancomycin is considered to be more toxic, specially to the kidneys. Therefore patients should be evaluated before giving Vancomycin as it could lead to kidney failure.
Inhibition of membrane integrity : Generally speaking these drugs either change the composition or the transport processes of the cell membrane or contribute to the efflux process of pumping drugs outside the bacteria. Such drugs are toxic and should not be used in simple clinical infection. Drugs that follow this mechanism, like Colistin, should only be given when other cephalosporins and penicillins fail to produce the desired effect like when bacteria develop extended spectrum b-lactamases. Colistin is a modified drug from polymixen. Polymixen is made of large molecules of different structures cycles and others- and considered hydrophobic thus rarely interacts with water, and finally it can even damage human s cell membranes. This complex polypeptide structure is bactericidal to both gram +ve and gram ve bacteria, however it is usually only given against gram ve bacteria e.g Enteric infections specially ones that are resistant to penicillins and cephalosporins as mentioned earlier. Colistin is also the only way to treat patients of blood sepsis with Klebsiella of multi-resistance like KPC, as well as in cases of meningitis or pneumonia, despite the fact that patients may end up with kidney failure and death. To sum up, Colistin Is only used against multi resistance organisms and in special cases. Here in Jordan it is only found in King Hussien Cancer Center. Another drug of less importance, that isn t used for systemic infections, but to superficial layers of skin infections like gland infections is Bacitracin. Bacitracin is a useful drug against gram +ve and gram ve that are resistant to many drugs, however like Colistin it is also very toxic. It should not be given in an oral or injectable form despite the fact that long time ago it was used by surgeons for 1 or 2 days- to reduce the intestinal flora before important intestinal operations. Now it is exclusively used tropically as ointments on skin.
Inhibition of protein synthesis : 1- Aminoglycosides In the beginning, it is important to know that bacteria have special kind of ribosomes called 70S ribosomes. These are made of two subunits, the 30S and the 50S depending on centrifugation and sedimentation. The S refers to Svedberg unit. Svedberg is the name of the Swedish scientist who first noticed the difference between bacterial and human ribosomes. This difference is of great importance, as it allows us to use such drugs that target the 30S or 50S subunit. If we had the same ribosomes then both the human cells and the bacterial cells will be attacked. These drugs are very useful bactericides, and were first introduced in the beginning of the fifties under the name Aminoglycosides. As the name indicates they are made of many amino groups as well as carboxyl, oxy, and alcohol groups. The first Aminoglycoside to be marketed was Streptomycin which was further modified to Kanamycin. Following the kanamycin was Neomycin then in the seventies they were followed by Gentamycin. Their importance lies in the fact that they interact with the 30S subunit resulting in the inhibition of the poplypeptide chain formation and the mrna attachment, which in turn prevent replication of bacteria indirectly. In addition to their inhibition of protein synthesis effect, they to some extent- damage the composition of the membrane, increasing the leakiness of the cell. This leakiness result in the escape of some anions and cations that disturb the cell s osmotic balance and eventually produce a killing effect. So they have two effects on the bacterial cells. Aminoglycosides are useful against gram ve facultative anaerobes and NOT AGAINST ANEROBES, they are also rarely used against gram +ve bacteria. When used in treatment whether sepsis, wound infection, or Enterococcus infection- it is used in association with drugs like penicillin or cephalosporin, where the penicillin damage the cell wall and the aminoglycosides inhibit protein synthesis, forming what is called a synergistic reaction. A synergistic reaction is an additive reaction where 2 effects act together instead of one resulting in a more bactericidal effect than when either of the drugs is working alone. it should be noted that Aminoglycosides are only given injectably and not orally as they will be inactivated by the stomach s acidity, and thus they are only given to hospitalized
patients. The dose given has to be monitored in the hospital as not to produce any side effects if the does increased. It s side effects include Ototoxicity which result in damage to the 8 th cranial nerve, Nephrotoxicity, and kidney failure. That s why dose monitoring in these drugs is more crucial that when dealing with other drugs like penicillin. For Example, increasing or decreasing the penicillin drug by 1 or 2 grams will not produce any major side effect, in contrast in aminoglycosides changing the dose by 5 or 10 milligrams could lead to serious side effects. It covers a wider gram ve spectrum than penicillin or cephalosporin. Resistance against aminoglycosides can be produced by the gram ve bacteria during the long run. This resistance is in the form of enzymes produced by the bacteria that can attack the Acetylate, Phosphorylate or adenylate groups and inactivate aminoglycosides. In our country gram ve bacteria such as E-Coli, Klebsiella, and Acinetobacter is 20% to 40% resistant to aminoglycosides. The most widely used aminoglycosides currently are Gantomycin and Amikacin, and amikacin being the most commonly used in Jordan. Neomycin and Streptomycin are rarely used, the later usually used as an anti-tuberculosis drug during which it is given in combination with other drugs. 2- Tetracyclines It is composed of four cycles associated with different functional groups like amino and oxo groups. It was used effectively against a wide variety of both gram +ve and gram-ve bacteria and even against certain anaerobes. For that reason in the fifties it was one of the most used drugs against all types of infections specially here In Jordan. Tetracyclins is considered to be more bacteriostatic than bactericidal. This means that using it as recommended by the manufacturerusually 2 to 4 g- will produce a bacteriostatic effect; however, increasing the does will produce a bactericidal effect and produce side effects as well. Tetracycline attacks the 30S subunit and prevents that attachment of the amino acetate to the trna, thus inhibiting the development of polypeptide chains that are used to synthesize the proteins. Due to the fact that it works against a broad spectrum of bacteria it resulted in reducing the intestinal flora which gave a chance for certain types of yeast such as Candida to increase in number. This increase of number of yeast my cause diarrhea, constipation, and even infections related to yeast. It is
specially harmful to children less than 8 and pregnant women, that s why it should not be given to them. In women it could cause Vaginal Discharge, and in children it could lead to Thrush Candidiasis in their oral cavity. General note In the fifties the four most common used drugs in Jordan were Sulfa, Tetracycline, Penicillin and Chloramphenicol. Done by : Issa Haddad