Penicillins response

A new development in the field of potentiometric enzyme sensors came in the 1980s from the work of Caras and Janata (72). They describe a penicillin-responsive device which consists of a pH-sensitive, ion-selective field effect transistor (ISFET) and an enzyme-immobilized ISFET (ENFET). Determining urea with ISFETs covered with immobilized urease is also possible (73). Current research is focused on the construction and characterization of ENFETs (27,73). Although ISFETs have several interesting features, the need to compensate for variations in the pH and buffering capacity of the sample is a serious hurdle for the rapid development of ENFETs. For detailed information on the principles and applications of ENFETs, the reader is referred to several recent reviews (27, 74) and Chapter 8. 

Directions for preparing a potentiometric biosensor for penicillin are provided in this experiment. The enzyme penicillinase is immobilized in a polyacrylamide polymer formed on the surface of a glass pH electrode. The electrode shows a linear response to penicillin G over a concentration range of 10 M to 10 M. 

Construct a calibration curve for the electrode, and report (a) the range of concentrations in which a linear response is observed, (b) the equation for the calibration curve in this range, and (c) the concentration of penicillin in a sample that yields a potential of 142 mV. 

An optimum response was defined as the greatest sensitivity, as determined by the measured potential for a standard solution of penicillin, and the largest sampling rate. The results of the optimization studies are shown in the following... 

The P-lactam antibiotics ate produced by secondary metaboHc reactions that differ from those responsible for the growth and reproduction of the microorganism. In order to enhance antibiotic synthesis, nutrients must be diverted from the primary pathways to the antibiotic biosynthetic sequences. Although most media for the production of penicillins and cephalosporins are similar, they ate individually designed for the specific requkements of the high yielding strains and the fermentation equipment used. 

One approach to combating antibiotic resistance caused by P-lactamase is to inhibit the enzyme (see Enzyme inhibition). Effective combinations of enzyme inhibitors with P-lactam antibiotics such as penicillins or cephalosporins, result in a synergistic response, lowering the minimal inhibitory concentration (MIC) by a factor of four or more for each component. However, inhibition of P-lactamases alone is not sufficient. Pharmacokinetics, stability, ability to penetrate bacteria, cost, and other factors are also important in determining whether an inhibitor is suitable for therapeutic use. Almost any class of P-lactam is capable of producing P-lactamase inhibitors. Several reviews have been pubUshed on P-lactamase inhibitors, detection, and properties (8—15). 

The changes that occur when an organism is exposed to different concentrations of penicillin provides a characteristic morphological response that... 

By virtue of their fused /3-lactam-thiazolidine ring structure, the penicillins behave as acylating agents of a reactivity comparable to carboxylic acid anhydrides (see Section 5.11.2.1). This reactivity is responsible for many of the properties of the penicillins, e.g. difficult isolation due to hydrolytic instability (B-49MI51102), antibacterial activity due to irreversible transpeptidase inhibition (Section 5.11.5.1), and antigen formation via reaction with protein molecules. 

Examine the structure of penicillin model (R=H), a model for the active compounds. What, if anything, distinguishes it from a typical amide (N,N-dimethylacetamide, for example) What is responsible for the differences Compare electrostatic potential maps for penicilhn model and dimethylacetamide. Which compound is more likely to undergo nucleophilic attack Explain. 

Suggest what precursors should be fed to cultures to produce each of the penicillins shown in Table 6.2. Read our response carefully as it contains some additional information. 

Different strains of micro-organisms are responsible for the production of either penicillins or cephalosporins. In penicillin-producing strains, an acyltransferase enzyme system is present which can remove the side chain from isopenirillin N to give 6-aminopenicillanic acid (6-APA), and which can subsequently acylate 6-APA to generate various penicillins, the most important ones being penicillin G and V(see section 6.3, Table 6.2). 

Discuss ways to promote optimal response to therapy, nursing actions to minimize adverse effects, and important points to keep in mind when educating patients about the use of penicillin. 

The expected outcomes of the patient depend on the reason for administration of penicillin but may include an optimal response to drug therapy, management of common adverse reactions, and an understanding of and compliance with the prescribed drug regimen. 

Promoting Optimal Response to Therapy The results of a culture and sensitivity test take several days because time must be allowed for the bacteria to grow on the culture media However, infections are treated as soon as possible In a few instances, the primary health care provider may determine that a penicillin is the treatment of choice until the results of the culture and sensitivity tests are known. In many instances, the primary health care provider selects a broad-spectrum antibiotic (ie, an antibiotic that is effective against many types or strains of bacteria) for initial treatment because of the many penicillin-resistant strains of microorganisms. 

FIGURE 6-20 Configuration of a penicillin sensor based on an microarray electrode coated with a pH-responsive polypyrrole. Vq = gate voltage VD = drain voltage ID = drain current PS = potentiostat CE and RE = counter and reference electrodes, respectively. (Reproduced with permission from reference 76.)... 

Contaminants of high molecular weight (considered to have arisen from mycelial residues frxm the fermentation process) may be responsible for the induction of allergy to penicillins their removal leads to a marked reduction in the antigenicity of the... 

Acute pharyngitis presents a diagnostic and therapeutic dilemma. The majority of sore throats are caused by a variety of viruses fewer than 20% are bacterial and hence potentially responsive to antibiotic therapy. However, antibiotics are widely prescribed and this reflects the difficulty in discriminating streptococcal from non-streptococcal infections clinically in the absence of microbiological documentation. Nonetheless, Strep, pyogenes is the most important bacterial pathogen and this responds to oral penicillin. However, up to 10 days treatment is required for its eradication fixm the throat. This requirement causes problems with compliance since symptomatic improvement generally occurs within 2-3 days. 

Staphylococcus aureus is responsible for a variety of skin infections which require therapeutic approaches different from those of streptococcal infections. Staphylococcal celluhtis is indistinguishable clinically from streptococcal cellulitis and responds to cloxacillin or flucloxacillin, but generally fails to respond to penicillin owing to penicillinase (/3-lactamase) production. Staphylococcus aureus is an important cause of superficial, localized skin sepsis which varies ftom small pustules to boils and occasionally to a more deeply invasive, suppurative skin abscess known as a carbuncle. Antibiotics are generally not indicated for these conditions. Pustules and boils settle with antiseptic soaps or creams and often discharge spontaneously, whereas carbuncles frequently require surgical drainage. Staphylococcus aureus may also cause... 

Penicillin is the dmg of choice for the treatment of group B streptococcal, meningococcal and pneumococcal infections but, as discussed earlier, CSF concentrations of penicillin are significantly influenced by the intensity of the inflammatoiy response. To achieve therapeutic concentrations within the CSF, high dosages are required, and in the case of pneumococcal meningitis should be continued for 10-14 days. 

Since the initial report of the pH responsive CHEMFET in 1970, CHEMFET s for other species such as Ca , Na", and penicillin have been descril d. In addition, some of these devices have been tested for in vivo or on-line continuous whole blood monitoring. While problems associated with mass production of the more complex CHEMFET s such as those employing enzymes (for example, with the penicillin CHEMFET) have not yet been fully solved, the technology for mass production of the relatively simple pH CHEMFET is api rently now available and problems noted with early devices attributable to irreversible SiO changes and... 

The antibiotic activity of certain (3-lactams depends largely on their interaction with two different groups of bacterial enzymes. (3-Lactams, like the penicillins and cephalosporins, inhibit the DD-peptidases/transpeptidases that are responsible for the final step of bacterial cell wall biosynthesis.63 Unfortunately, they are themselves destroyed by the [3-lactamases,64 which thereby provide much of the resistance to these antibiotics. Class A, C, and D [3-lactamases and DD-peptidases all have a conserved serine residue in the active site whose hydroxyl group is the primary nucleophile that attacks the substrate carbonyl. Catalysis in both cases involves a double-displacement reaction with the transient formation of an acyl-enzyme intermediate. The major distinction between [3-lactamases and their evolutionary parents the DD-peptidase residues is the lifetime of the acyl-enzyme it is short in (3-lactamases and long in the DD-peptidases.65-67... 

T cells control these learned responses and decide which tools to use in the reaction. Sometimes they choose several different tools at once, and multiple reactions ensue, such as when a person becomes sensitized to penicillin and has not only anaphylaxis but hemolytic anemia and serum sickness. There are different types of T cells, and they communicate either directly with other cells or by chemical messages called cytokines. The pattern of cytokines released is one way T cells have of determining which kind of response will occur. They are broadly called Thl andTh2 responses, with Thl mostly responding to infections and Th2 often producing allergy or asthma. 

Hypersensitivity reactions with P-lactam antibiotics, especially penicillin, may encompass any of the type I through IV Gell-Coombs classifications. The most common reactions are maculopapular and urticarial eruptions.7 While rare (less than 0.05%), anaphylaxis to penicillins causes the greatest concern because they are responsible for the majority of drug-induced anaphylaxis deaths in patients, accounting for 75% of all ana-i phylaxis cases in the United States.5,8 The treatment of ana-I phylaxis is given in Table 51-2.9... 

There is concern regarding administration of dexamethasone to patients with pneumococcal meningitis caused by penicillin- or cephalosporin-resistant strains, for which vancomycin would be required. Animal models indicate that concurrent steroid use reduces vancomycin penetration into the CSF by 42% to 77% and delays CSF sterilization due to reduction in the inflammatory response.23 Treatment failures have been reported in adults with resistant pneumococcal meningitis who were treated with dexamethasone, but the risk-benefit of using dexamethasone in these patients cannot be defined at this time. Animal models indicate a benefit of adding rifampin in patients with resistant pneumococcal meningitis whenever dexamethasone is used.21,23... 

Some compounds exhibit pH behavior in which a bell-shaped curve is obtained with maximum instability at the peak [107]. The peak corresponds to the intersection of two sigmoidal curves that are mirror images. The two inflection points imply two acid and base dissociations responsible for the reaction. For a dibasic acid (H2A) for which the monobasic species (HA-) is most reactive, the rate will rise with pH as [HA-] increases. The maximum rate occurs at pH = (pA) + pK2)/2 (the mean of the two acid dissociation constants). Where an acid and base react, the two inflections arise from the two different molecules. The hydrolysis of penicillin G catalyzed by 3,6-bis(di-methylaminomethyl)catechol [108], is a typical example. For a systematic interpretation of pH-degradation profiles, see the review papers by van der Houwen et al. [109] and Connors [110]. 

Tubular secretion is the transfer of substances from the peritubular capillaries into the renal tubule for excretion in urine. This process is particularly important for the regulation of potassium and hydrogen ions in the body it is also responsible for removal of many organic compounds from the body. These may include metabolic wastes as well as foreign compounds, including drugs such as penicillin. Most substances are secreted by secondary active transport. 

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