Gram-positive bacteria are bacteria that give a positive result in the Gram stain test, traditionally used to classify bacteria into two broad categories according to their cell wall. Gram-positive bacteria take up the crystal violet stain used in the test, appear to be purple-coloured when seen through a microscope; this is because the thick peptidoglycan layer in the bacterial cell wall retains the stain after it is washed away from the rest of the sample, in the decolorization stage of the test. Gram-negative bacteria cannot retain the violet stain after the decolorization step, their peptidoglycan layer is much thinner and sandwiched between an inner cell membrane and a bacterial outer membrane, causing them to take up the counterstain and appear red or pink. Despite their thicker peptidoglycan layer, gram-positive bacteria are more receptive to certain cell wall targeting antibiotics than gram-negative bacteria, due to the absence of the outer membrane. In general, the following characteristics are present in gram-positive bacteria: Cytoplasmic lipid membrane Thick peptidoglycan layer Teichoic acids and lipoids are present, forming lipoteichoic acids, which serve as chelating agents, for certain types of adherence.
Peptidoglycan chains are cross-linked to form rigid cell walls by a bacterial enzyme DD-transpeptidase. A much smaller volume of periplasm than that in gram-negative bacteria. Only some species have a capsule consisting of polysaccharides. Only some species are flagellates, when they do have flagella, have only two basal body rings to support them, whereas gram-negative have four. Both gram-positive and gram-negative bacteria have a surface layer called an S-layer. In gram-positive bacteria, the S-layer is attached to the peptidoglycan layer. Gram-negative bacteria's S-layer is attached directly to the outer membrane. Specific to gram-positive bacteria is the presence of teichoic acids in the cell wall; some of these are lipoteichoic acids, which have a lipid component in the cell membrane that can assist in anchoring the peptidoglycan. Along with cell shape, Gram staining is a rapid method used to differentiate bacterial species; such staining, together with growth requirement and antibiotic susceptibility testing, other macroscopic and physiologic tests, forms the full basis for classification and subdivision of the bacteria.
The kingdom Monera was divided into four divisions based on Gram staining: Firmicutes, Gracilicutes and Mendocutes. Based on 16S ribosomal RNA phylogenetic studies of the late microbiologist Carl Woese and collaborators and colleagues at the University of Illinois, the monophyly of the gram-positive bacteria was challenged, with major implications for the therapeutic and general study of these organisms. Based on molecular studies of the 16S sequences, Woese recognised twelve bacterial phyla. Two of these were both gram-positive and were divided on the proportion of the guanine and cytosine content in their DNA; the high G + C phylum was made up of the Actinobacteria and the low G + C phylum contained the Firmicutes. The Actinobacteria include the Corynebacterium, Mycobacterium and Streptomyces genera; the Firmicutes, have a 45 -- 60 % GC content. Although bacteria are traditionally divided into two main groups, gram-positive and gram-negative, based on their Gram stain retention property, this classification system is ambiguous as it refers to three distinct aspects, which do not coalesce for some bacterial species.
The gram-positive and gram-negative staining response is not a reliable characteristic as these two kinds of bacteria do not form phylogenetic coherent groups. However, although Gram staining response is an empirical criterion, its basis lies in the marked differences in the ultrastructure and chemical composition of the bacterial cell wall, marked by the absence or presence of an outer lipid membrane. All gram-positive bacteria are bounded by a single-unit lipid membrane, and, in general, they contain a thick layer of peptidoglycan responsible for retaining the Gram stain. A number of other bacteria—that are bounded by a single membrane, but stain gram-negative due to either lack of the peptidoglycan layer, as in the Mycoplasmas, or their inability to retain the Gram stain because of their cell wall composition—also show close relationship to the Gram-positive bacteria. For the bacterial cells bounded by a single cell membrane, the term "monoderm bacteria" or "monoderm prokaryotes" has been proposed.
In contrast to gram-positive bacteria, all archetypical gram-negative bacteria are bounded by a cytoplasmic membrane and an outer cell membrane. The presence of inner and outer cell membranes defines a new compartment in these cells: the periplasmic space or the periplasmic compartment; these bacteria have been designated as "diderm bacteria." The distinction between the monoderm and diderm bacteria is supported by conserved signature indels in a number of important proteins. Of these two structurally distinct groups of bacteria, monoderms are indicated to be ancestral. Based upon a number of observations including that the gram-positive bacteria are the major producers of antibiotics and that, in general, gram-negative bacteria are resistant to them, it h
Route of administration
A route of administration in pharmacology and toxicology is the path by which a drug, poison, or other substance is taken into the body. Routes of administration are classified by the location at which the substance is applied. Common examples include intravenous administration. Routes can be classified based on where the target of action is. Action may be enteral, or parenteral. Route of administration and dosage form are aspects of drug delivery. Routes of administration are classified by application location; the route or course the active substance takes from application location to the location where it has its target effect is rather a matter of pharmacokinetics. Exceptions include the transdermal or transmucosal routes, which are still referred to as routes of administration; the location of the target effect of active substances are rather a matter of pharmacodynamics. An exception is topical administration, which means that both the application location and the effect thereof is local. Topical administration is sometimes defined as both a local application location and local pharmacodynamic effect, sometimes as a local application location regardless of location of the effects.
Administration through the gastrointestinal tract is sometimes termed enteral or enteric administration. Enteral/enteric administration includes oral and rectal administration, in the sense that these are taken up by the intestines. However, uptake of drugs administered orally may occur in the stomach, as such gastrointestinal may be a more fitting term for this route of administration. Furthermore, some application locations classified as enteral, such as sublingual and sublabial or buccal, are taken up in the proximal part of the gastrointestinal tract without reaching the intestines. Enteral administration can be used for systemic administration, as well as local, such as in a contrast enema, whereby contrast media is infused into the intestines for imaging. However, for the purposes of classification based on location of effects, the term enteral is reserved for substances with systemic effects. Many drugs as tablets, capsules, or drops are taken orally. Administration methods directly into the stomach include those by gastric feeding tube or gastrostomy.
Substances may be placed into the small intestines, as with a duodenal feeding tube and enteral nutrition. Enteric coated tablets are designed to dissolve in the intestine, not the stomach, because the drug present in the tablet causes irritation in the stomach; the rectal route is an effective route of administration for many medications those used at the end of life. The walls of the rectum absorb many medications and effectively. Medications delivered to the distal one-third of the rectum at least avoid the "first pass effect" through the liver, which allows for greater bio-availability of many medications than that of the oral route. Rectal mucosa is vascularized tissue that allows for rapid and effective absorption of medications. A suppository is a solid dosage form. In hospice care, a specialized rectal catheter, designed to provide comfortable and discreet administration of ongoing medications provides a practical way to deliver and retain liquid formulations in the distal rectum, giving health practitioners a way to leverage the established benefits of rectal administration.
The parenteral route is any route, not enteral. Parenteral administration can be performed by injection, that is, using a needle and a syringe, or by the insertion of an indwelling catheter. Locations of application of parenteral administration include: central nervous systemepidural, e.g. epidural anesthesia intracerebral direct injection into the brain. Used in experimental research of chemicals and as a treatment for malignancies of the brain; the intracerebral route can interrupt the blood brain barrier from holding up against subsequent routes. Intracerebroventricular administration into the ventricular system of the brain. One use is as a last line of opioid treatment for terminal cancer patients with intractable cancer pain. Epicutaneous, it can be used both for local effect as in allergy testing and typical local anesthesia, as well as systemic effects when the active substance diffuses through skin in a transdermal route. Sublingual and buccal medication administration is a way of giving someone medicine orally.
Sublingual administration is. The word "sublingual" means "under the tongue." Buccal administration involves placement of the drug between the cheek. These medications can come in the form of films, or sprays. Many drugs are designed for sublingual administration, including cardiovascular drugs, barbiturates, opioid analgesics with poor gastrointestinal bioavailability and vitamins and minerals. Extra-amniotic administration, between the endometrium and fetal membranes nasal administration (th
Bristol-Myers Squibb Company is an American pharmaceutical company, headquartered in New York City. Bristol-Myers Squibb manufactures prescription pharmaceuticals and biologics in several therapeutic areas, including cancer, HIV/AIDS, cardiovascular disease, hepatitis, rheumatoid arthritis and psychiatric disorders. BMS' primary R&D sites are located in Lawrence, New Jersey, Hopewell Township and New Brunswick, New Jersey. BMS had an R&D site in Wallingford, Connecticut; the Squibb corporation was founded in 1858 by Edward Robinson Squibb in New York. Squibb was known as a vigorous advocate of quality control and high purity standards within the fledgling pharmaceutical industry of his time, at one point self-publishing an alternative to the U. S. Pharmacopeia after failing to convince the American Medical Association to incorporate higher purity standards. Mentions of the Materia Medica, Squibb products, Edward Squibb's opinion on the utility and best method of preparation for various medicants are found in many medical papers of the late 1800s.
Squibb Corporation served as a major supplier of medical goods to the Union Army during the American Civil War, providing portable medical kits containing morphine, surgical anesthetics, quinine for the treatment of malaria. In 1887, Hamilton College graduates William McLaren Bristol and John Ripley Myers purchased the Clinton Pharmaceutical company of Clinton, New York. In 1898, they decided to rename it Bristol and Company. Following Myers' death in 1899, Bristol changed the name to the Bristol-Myers Corporation; the first nationally recognized product was Sal Hepatica, a laxative mineral salt in 1903. Its second national success was Ipana toothpaste, from 1901 through the 1960s. Other divisions were Drackett. In 1943, Bristol-Myers acquired Cheplin Biological Laboratories, a producer of acidophilus milk in East Syracuse, New York, converted the plant to produce penicillin for the World War II Allied forces. After the war, the company renamed the plant Bristol Laboratories in 1945 and entered the civilian antibiotics market, where it faced competition from Squibb, which had opened the world's largest penicillin plant in 1944 in New Brunswick, New Jersey.
Penicillin production at the East Syracuse plant was ended in 2005, when it became less expensive to produce overseas, but the facility continues to be used for the manufacturing process development and production of other biologic medicines for clinical trials and commercial use. Bristol-Myers and Squibb merged with Bristol-Myers as the nominal survivor; the merged company became Bristol-Myers Squibb. In 1999, President Clinton awarded Bristol-Myers Squibb the National Medal of Technology, the nation's highest recognition for technological achievement, "for extending and enhancing human life through innovative pharmaceutical research and development and for redefining the science of clinical study through groundbreaking and hugely complex clinical trials that are recognized models in the industry." In 2002, the company was involved in a lawsuit of maintaining illegally a monopoly on Taxol, its cancer treatment, it was again sued for the antitrust lawsuit 5 years which cost the company $125 million for settlement.
The company was involved in an accounting scandal in 2002 that resulted in a significant restatement of revenues from 1999 to 2001. The restatement was the result of an improper booking of sales related to "channel stuffing" as the practice of offering excess inventory to customers to create higher sales numbers; the company has since settled with the United States Department of Justice and Securities and Exchange Commission, agreeing to pay $150 million while neither admitting nor denying guilt. On October 24, 2002, Bristol-Myers Squibb Co. restated earnings downward for parts of 2000 and 2001 while revising this year's earnings upward because of its massive inventory backlog imbroglio that spurred two government investigations. On March 15, 2004, Bristol-Myers Squibb Co. adjusted upward its fourth-quarter and full-year 2003 results after reversing an earlier decision about how to deal with accounting errors made in prior years. As part of a Deferred Prosecution Agreement, the company was placed under the oversight of a monitor appointed by the U.
S. Attorney in New Jersey. In addition, the former head of the Pharma group, Richard Lane, the ex-CFO, Fred Schiff, were indicted for federal securities violations. An investigation of the company was made public in July 2006, the FBI raided the company's corporate offices; the investigation centered on charges of collusion. On September 12, 2006, the monitor, former Federal Judge Frederick B. Lacey, urged the company to remove CEO Peter Dolan over the Plavix dispute; that day, BMS announced that Dolan would indeed step down. The Deferred Prosecution Agreement expired in June 2007 and the Department of Justice did not take any further legal action against the company for matters covered by the DPA. Under CEO Jim Cornelius, CEO following Dolan until May 2010, all executives involved in the "channel-stuffing" and generic competition scandals have since left the company. In 2009, a major restructuring began focusing on the pharmaceutical business and biologic products, along with productivity initiatives and cost-cutting and streamlining business operations through a multi-year program of on-going layoffs.
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Pharmacokinetics, sometimes abbreviated as PK, is a branch of pharmacology dedicated to determine the fate of substances administered to a living organism. The substances of interest include any chemical xenobiotic such as: pharmaceutical drugs, food additives, etc, it attempts to analyze chemical metabolism and to discover the fate of a chemical from the moment that it is administered up to the point at which it is eliminated from the body. Pharmacokinetics is the study of how an organism affects a drug, whereas pharmacodynamics is the study of how the drug affects the organism. Both together influence dosing and adverse effects, as seen in PK/PD models. Pharmacokinetics describes how the body affects a specific xenobiotic/chemical after administration through the mechanisms of absorption and distribution, as well as the metabolic changes of the substance in the body, the effects and routes of excretion of the metabolites of the drug. Pharmacokinetic properties of chemicals are affected by the route of administration and the dose of administered drug.
These may affect the absorption rate. Models have been developed to simplify conceptualization of the many processes that take place in the interaction between an organism and a chemical substance. One of these, the multi-compartmental model, is the most used approximations to reality; the various compartments that the model is divided into are referred to as the ADME scheme: Liberation – the process of release of a drug from the pharmaceutical formulation. See IVIVC. Absorption – the process of a substance entering the blood circulation. Distribution – the dispersion or dissemination of substances throughout the fluids and tissues of the body. Metabolism – the recognition by the organism that a foreign substance is present and the irreversible transformation of parent compounds into daughter metabolites. Excretion – the removal of the substances from the body. In rare cases, some drugs irreversibly accumulate in body tissue; the two phases of metabolism and excretion can be grouped together under the title elimination.
The study of these distinct phases involves the use and manipulation of basic concepts in order to understand the process dynamics. For this reason in order to comprehend the kinetics of a drug it is necessary to have detailed knowledge of a number of factors such as: the properties of the substances that act as excipients, the characteristics of the appropriate biological membranes and the way that substances can cross them, or the characteristics of the enzyme reactions that inactivate the drug. All these concepts can be represented through mathematical formulas that have a corresponding graphical representation; the use of these models allows an understanding of the characteristics of a molecule, as well as how a particular drug will behave given information regarding some of its basic characteristics such as its acid dissociation constant and solubility, absorption capacity and distribution in the organism. The model outputs for a drug can be used in industry or in the clinical application of pharmacokinetic concepts.
Clinical pharmacokinetics provides many performance guidelines for effective and efficient use of drugs for human-health professionals and in veterinary medicine. The following are the most measured pharmacokinetic metrics: In pharmacokinetics, steady state refers to the situation where the overall intake of a drug is in dynamic equilibrium with its elimination. In practice, it is considered that steady state is reached when a time of 4 to 5 times the half-life for a drug after regular dosing is started; the following graph depicts a typical time course of drug plasma concentration and illustrates main pharmacokinetic metrics: Pharmacokinetic modelling is performed by noncompartmental or compartmental methods. Noncompartmental methods estimate the exposure to a drug by estimating the area under the curve of a concentration-time graph. Compartmental methods estimate the concentration-time graph using kinetic models. Noncompartmental methods are more versatile in that they do not assume any specific compartmental model and produce accurate results acceptable for bioequivalence studies.
The final outcome of the transformations that a drug undergoes in an organism and the rules that determine this fate depend on a number of interrelated factors. A number of functional models have been developed in order to simplify the study of pharmacokinetics; these models are based on a consideration of an organism as a number of related compartments. The simplest idea is to think of an organism as only one homogenous compartment; this monocompartmental model presupposes that blood plasma concentrations of the drug are a true reflection of the drug's concentration in other fluids or tissues and that the elimination of the drug is directly proportional to the drug's concentration in the organism. However, these models do not always reflect the real situation within an organism. For example, not all body tissues have the same blood supply, so the distribution of the drug will be slower in these tissues than in others with a better blood supply. In addition, there are some tissues (s
Minimum inhibitory concentration
In microbiology, the minimum inhibitory concentration is the lowest concentration of a chemical a drug, which prevents visible growth of bacterium. MIC depends on the microorganism, the affected human being, the antibiotic itself; the MIC is determined by preparing solutions of the chemical in vitro at increasing concentrations, incubating the solutions with the separate batches of cultured bacteria, measuring the results using agar dilution or broth microdilution. Results have been graded into susceptible, intermediate, or resistant to a particular antimicrobial by using a breakpoint. Breakpoints are agreed upon values, published in guidelines of a reference body, such as the U. S. Clinical and Laboratory Standards Institute, the British Society for Antimicrobial Chemotherapy or the European Committee on Antimicrobial Susceptibility Testing. There have been major discrepancies between the breakpoints from various European countries over the years, between those from the European Committee on Antimicrobial Susceptibility Testing and the US Clinical and Laboratory Standards Institute.
While MIC is the lowest concentration of an antibacterial agent necessary to inhibit visible growth, minimum bactericidal concentration is the minimum concentration of an antibacterial agent that results in bacterial death. The closer the MIC is to the MBC, the more bactericidal the compound; the first step in drug discovery is the screening of a library drug candidate for MICs against bacteria of interest. As such, MICs are the starting point for larger pre-clinical evaluations of novel antimicrobial agents. After the discovery and commercialization of antibiotics, Alexander Fleming developed the broth dilution technique using the turbidity of the broth for assessment; this is believed to be the conception point of minimum inhibitory concentrations. In the 1980s, Clinical and Laboratory Standards Institute has consolidated the methods and standards for MIC determination and clinical usage. Following the discovery of new antibacterials and their evolution, the protocols by CLSI are continually updated to reflect that change.
The protocols and parameters set by CLSI are considered to be the "gold standard" in the United States and are used by regulatory authorities, such as the FDA, to make evaluations. Nowadays, the MIC is used in antimicrobial susceptibility testing. In clinics, more than not, exact pathogens cannot be determined by symptoms of the patient. If the pathogen is determined, different serotypes of pathogens, such as Staphylococcus aureus, have varying levels of resistance to antimicrobials; as such, it is difficult to prescribe correct antimicrobials. The MIC is determined in such cases by growing the pathogen isolate from the patient on plate or broth, used in the assay. Thus, knowledge of the MIC will provide a physician valuable information for making a prescription. Accurate and precise usage of antimicrobials is important in the context of multi-drug resistant bacteria. Microbes such as bacteria have been gaining resistance to antimicrobials they were susceptible to. Usage of incompatible or sub-MIC levels of antibicrobials provides the selective pressure that has hastened the evolution of resistance in bacterial pathogens.
As such, it is important to determine the MIC in order to make the best choice in prescribing antimicrobials. MIC is used clinically over MBC because MIC is more determined. Minimum bactericidal concentration, the minimum antibacterial concentration resulting in microbial death, is defined by the inability to re-culture bacteria. In addition, drug effectiveness is similar when taken at both MIC and MBC concentrations because the host immune system can expel the pathogen when bacterial proliferation is at a standstill; when the MBC is much higher than the MIC, drug toxicity makes taking the MBC of the drug detrimental to patient. Antimicrobial toxicity can come in many forms, such as immune hypersensitivity and off-target toxicity. There are three main reagents necessary to run this assay: the media, an antimicrobial agent, the microbe being tested; the most used media is cation-adjusted Mueller Hinton Broth, due to its ability to support the growth of most pathogens and its lack of inhibitors towards common antibiotics.
Depending on the pathogen and antibiotics being tested, the media can be adjusted. The antimicrobial concentration is adjusted into the correct concentration by mixing stock antimicrobial with media; the adjusted antimicrobial is serially diluted into multiple tubes to obtain a gradient. The dilution rate can be adjusted depending on the practitioner's needs; the microbe, or the inoculating agent, must come from the same colony-forming unit, must be at the correct concentration. This may be adjusted by incubation dilution. For verification, the positive control is plated in a hundred fold dilution to count colony forming units; the microbes are incubated for 16 -- 20 hours. The MIC is determined by turbidity. Kirby–Bauer test
The Enterobacteriaceae are a large family of Gram-negative bacteria. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the phylum Proteobacteria. Enterobacteriaceae includes, along with many harmless symbionts, many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis and Shigella. Other disease-causing bacteria in this family include Proteus, Enterobacter and Citrobacter. Phylogenetically, in the Enterobacteriales, several peptidoglycan-less insect endosymbionts form a sister clade to the Enterobacteriaceae, but as they are not validly described, this group is not a taxon. Members of the Enterobacteriaceae can be trivially referred to as enterobacteria or "enteric bacteria", as several members live in the intestines of animals. In fact, the etymology of the family is enterobacterium with the suffix to designate a family —not after the genus Enterobacter —and the type genus is Escherichia. Members of the Enterobacteriaceae are bacilli, are 1–5 μm in length.
They appear as medium to large-sized grey colonies on blood agar, although some can express pigments. Most have many flagella used to move about. Most members of Enterobacteriaceae have peritrichous, type I fimbriae involved in the adhesion of the bacterial cells to their hosts, they are not spore-forming. Like other proteobacteria, enterobactericeae have Gram-negative stains, they are facultative anaerobes, fermenting sugars to produce lactic acid and various other end products. Most reduce nitrate to nitrite, although exceptions exist. Unlike most similar bacteria, enterobacteriaceae lack cytochrome C oxidase, although there are exceptions. Catalase reactions vary among Enterobacteriaceae. Many members of this family are normal members of the gut microbiota in humans and other animals, while others are found in water or soil, or are parasites on a variety of different animals and plants. Escherichia coli is one of the most important model organisms, its genetics and biochemistry have been studied.
Some enterobacteria are important pathogens, e.g. Salmonella, Shigella, or Yersinia, e.g. because they produce endotoxins. Endotoxins reside in the cell wall and are released when the cell dies and the cell wall disintegrates; some members of the Enterobacteriaceae produce endotoxins that, when released into the bloodstream following cell lysis, cause a systemic inflammatory and vasodilatory response. The most severe form of this is known as endotoxic shock, which can be fatal. To identify different genera of Enterobacteriaceae, a microbiologist may run a series of tests in the lab; these include: Phenol red Tryptone broth Phenylalanine agar for detection of production of deaminase, which converts phenylalanine to phenylpyruvic acid Methyl red or Voges-Proskauer tests depend on the digestion of glucose. The methyl red tests for acid endproducts; the Voges Proskauer tests for the production of acetylmethylcarbinol. Catalase test on nutrient agar tests for the production of enzyme catalase, which splits hydrogen peroxide and releases oxygen gas.
Oxidase test on nutrient agar tests for the production of the enzyme oxidase, which reacts with an aromatic amine to produce a purple color. Nutrient gelatin tests to detect activity of the enzyme gelatinase. In a clinical setting, three species make up 80 to 95% of all isolates identified; these are Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis. Several Enterobacteriaceae strains have been isolated which are resistant to antibiotics including carbapenems, which are claimed as "the last line of antibiotic defense" against resistant organisms. For instance, some Klebsiella pneumoniae strains are carbapenem resistant. Enterobacteriaceae genomes and related information at PATRIC, a Bioinformatics Resource Center funded by NIAID Evaluation of new computer-enhanced identification program for microorganisms: adaptation of BioBASE for identification of members of the family Enterobacteriaceae Brown, A. E.. Benson's microbiological applications: laboratory manual in general microbiology. New York: McGraw- Hill
Beta-lactamases are enzymes produced by bacteria that provide multi-resistance to β-lactam antibiotics such as penicillins, cephalosporins and carbapenems, although carbapenems are resistant to beta-lactamase. Beta-lactamase provides antibiotic resistance by breaking the antibiotics' structure; these antibiotics all have a common element in their molecular structure: a four-atom ring known as a β-lactam. Through hydrolysis, the lactamase enzyme breaks the β-lactam ring open, deactivating the molecule's antibacterial properties. Beta-lactam antibiotics are used to treat a broad spectrum of Gram-positive and Gram-negative bacteria. Beta-lactamases produced by Gram-negative organisms are secreted when antibiotics are present in the environment; the structure of a Streptomyces β-lactamase is given by 1BSG. Penicillinase is a specific type of β-lactamase, showing specificity for penicillins, again by hydrolysing the β-lactam ring. Molecular weights of the various penicillinases tend to cluster near 50 kiloDaltons.
Penicillinase was the first β-lactamase to be identified. It was first isolated by Abraham and Chain in 1940 from Gram-negative E. coli before penicillin entered clinical use, but penicillinase production spread to bacteria that did not produce it or produced it only rarely. Penicillinase-resistant beta-lactams such as methicillin were developed, but there is now widespread resistance to these. Among Gram-negative bacteria, the emergence of resistance to expanded-spectrum cephalosporins has been a major concern, it appeared in a limited number of bacterial species that could mutate to hyperproduce their chromosomal class C β-lactamase. A few years resistance appeared in bacterial species not producing AmpC enzymes due to the production of TEM- or SHV-type ESBLs. Characteristically, such resistance has included oxyimino-, but not 7-alpha-methoxy-cephalosporins. Chromosomal-mediated AmpC β-lactamases represent a new threat, since they confer resistance to 7-alpha-methoxy-cephalosporins such as cefoxitin or cefotetan but are not affected by commercially available β-lactamase inhibitors, can, in strains with loss of outer membrane porins, provide resistance to carbapenems.
Members of the family express plasmid-encoded β-lactamases, which confer resistance to penicillins but not to expanded-spectrum cephalosporins. In the mid-1980s, a new group of enzymes, the extended-spectrum β-lactamases, was detected; the prevalence of ESBL-producing bacteria have been increasing in acute care hospitals. ESBLs are beta-lactamases that hydrolyze extended-spectrum cephalosporins with an oxyimino side chain; these cephalosporins include cefotaxime and ceftazidime, as well as the oxyimino-monobactam aztreonam. Thus ESBLs confer multi-resistance to related oxyimino-beta lactams. In typical circumstances, they derive from genes for TEM-1, TEM-2, or SHV-1 by mutations that alter the amino acid configuration around the active site of these β-lactamases. A broader set of β-lactam antibiotics are susceptible to hydrolysis by these enzymes. An increasing number of ESBLs not of TEM or SHV lineage have been described; the ESBLs are plasmid encoded. Plasmids responsible for ESBL production carry genes encoding resistance to other drug classes.
Therefore, antibiotic options in the treatment of ESBL-producing organisms are limited. Carbapenems are the treatment of choice for serious infections due to ESBL-producing organisms, yet carbapenem-resistant isolates have been reported. ESBL-producing organisms may appear susceptible to some extended-spectrum cephalosporins. However, treatment with such antibiotics has been associated with high failure rates. TEM-1 is the most encountered beta-lactamase in Gram-negative bacteria. Up to 90% of ampicillin resistance in E. coli is due to the production of TEM-1. Responsible for the ampicillin and penicillin resistance, seen in H. influenzae and N. gonorrhoeae in increasing numbers. Although TEM-type beta-lactamases are most found in E. coli and K. pneumoniae, they are found in other species of Gram-negative bacteria with increasing frequency. The amino acid substitutions responsible for the extended-spectrum beta lactamase phenotype cluster around the active site of the enzyme and change its configuration, allowing access to oxyimino-beta-lactam substrates.
Opening the active site to beta-lactam substrates typically enhances the susceptibility of the enzyme to β-lactamase inhibitors, such as clavulanic acid. Single amino acid substitutions at positions 104, 164, 238, 240 produce the ESBL phenotype, but ESBLs with the broadest spectrum have more than a single amino acid substitution. Based upon different combinations of changes 140 TEM-type enzymes have been described. TEM-10, TEM-12, TEM-26 are among the most common in the United States; the term TEM comes from the name of the Athenian patient from which the isolate was recovered in 1963. SHV-1 has a similar overall structure; the SHV-1 beta-lactamase is most found i