Antibacterial Mechanisms of Action and Resistance PDF

Antibacterial Mechanisms of Action and Bacterial Resistance Mechanisms Karizza Mae M. Villora, RMT, MSMTc CHAPTER 12 Antimicrobial agents include antibacterials, antifungals, antiseptics, antibiotics, preservatives, sterilants...

Antibacterial Mechanisms of Action and Bacterial Resistance Mechanisms Karizza Mae M. Villora, RMT, MSMTc CHAPTER 12 Antimicrobial agents include antibacterials, antifungals, antiseptics, antibiotics, preservatives, sterilants, and disinfectants all have the capacity to kill or suppress the growth of microorganisms. Antimicrobial drug resistance was observed soon after the discovery of antibiotics. It is a natural consequence of drug exposure and results from the use and inappropriate use of antimicrobial agents. The World Health Organization (WHO) estimates that by the year 2050 there will be at least 10 million deaths per year due to infections with drug-resistant bacteria.  Antibiotic stewardship refers to the appropriate use of antimicrobials to maximize their current effects and improve the chances of their being available for future generations. Antimicrobial Targets and Mechanisms of Action Inhibition of Bacterial Cell Wall Biosynthesis Inhibition of Folate Synthesis Interference with DNA Replication Interference with DNA Transcription Interference of mRNA Translation ❤(❁´◡`❁)❤  Inhibition of Bacterial Cell Wall Biosynthesis Gram-positive and gram-negative bacteria have a multilayered cell wall structure composed of an inner cytoplasmic membrane, a peptidoglycan layer, and in gram-negative bacteria, a second outer membrane  Inhibition of Bacterial Cell Wall Biosynthesis Peptidoglycan Structure: Alternating disaccharides (NAG, NAM) with peptide cross-links. peptide consists of L- and D-amino acids, which typically end in D-alanyl-D-alanine (D-Ala-D-Ala) sequence critical for cross-linking and drug targeting.  Inhibition of Bacterial Cell Wall Biosynthesis Peptidoglycan Biosynthesis Stages: 1. synthesis of precursors in the cytoplasm 2. transport of lipid-bound precursors across the cytoplasmic membrane 3. insertion of glycan units into the cell wall 4. transpeptidation linking and maturation. D-Cycloserine and bacitracin inhibit the first two steps, respectively. Most commonly used inhibitors of cell wall biosynthesis β-lactams (e.g. penicillin and cephalosporins) ○ compounds act by forming covalent complexes with enzymes that generate the mature peptidoglycan molecule. ○ Bind PBPs, inhibit cross-linking, cause lysis. penicillin-binding proteins (PBPs). Glycopeptides (eg. vancomycin, dalbavancin, teicoplanin) ○ Bind D-Ala-D-Ala, block transpeptidation, effective for Gram-positives., Inhibition of Folate Synthesis The pathway is mediated by two key enzymes, dihydropteroate synthase and dihydrofolate reductase, which mediate the formation of tetrahydrofolate (THF) from dihydrofolate Eg: Sulfamethoxazole (SMZ), Trimethoprim (TMP)  Interference with DNA Replication Quinolones affect DNA replication by targeting topoisomerases II (DNA gyrase) and IV, enzymes considered important in controlling DNA topology, replication, and decatenation at the end of bacterial DNA replicative cycle.  Interference with DNA Transcription Rifampin The principle therapeutic use of rifampin is in combination with other antibacterial classes to treat Mycobacterium tuberculosis infection. The target of rifampin in M. tuberculosis is the RNA polymerase β subunit at an allosteric site, with the subsequent blocking of RNA chain elongation. As a result, RNA transcription is aborted at the initiation step.  Interference of mRNA Translation Aminoglycosides Tetracycline Macrolides(erythromycin, clarithromycin, and azithromycin) Ketolides Oxazolidinones Glyclycyclines Streptogramin  xacin Rif cillins cef enem am  vancin mycin, mixin zolid mycin, mixin  micin, mycin cycline mycin mycin, pristin Mechanisms of Antimicrobial Resistance Tolerance property of dormant, nongrowing bacteria (persisters) in which drug targets are inactive, allowing bacteria to avoid damage and survive. Persister cells are subpopulations of bacteria deep in a biofilm that can differentiate into a phenotypically resistant state ○ have been shown to carry mutations in promoter genes. ○ When conditions are favorable for growth (e.g., no anti-microbial present) these bacteria will resume growth.  Resistance to antimicrobial agents INTRINSIC RESISTANCE ACQUIRED RESISTANCE innate characteristic of the caused by changes in the usual microorganism and are genetic makeup of a microorganism, leading to altered transmitted to progeny cellular physiology and structure. vertically. Examples: Example: Efflux, Target site modification, Biofilms, Impermeability, Efflux, Acquisition of new targets, Enzymatic Inactivation Enzymatic Inactivation of Antimicrobial Agents  β-Lactamase Inhibitors They act by preventing the degradation of β-lactam antibiotics have little antimicrobial activity of their own used in combination with specific antibiotics. Antimicrobial Susceptibility Testing Karizza Mae M. Villora, RMT, MSMTc CHAPTER 13 Antimicrobial Susceptibility Testing performed on bacteria and fungi isolated from clinical specimens to determine which anti-microbial agents might be effective in treating infections caused by these organisms. disk diffusion dilution (minimal inhibitory concentration [MIC]) method. Factors to Consider When Determining Whether Testing Is Warranted: Body site from which the bacterium was isolated Presence of other organisms and quality of the specimen from which the organism was grown Host’s status  Body Site Normal microbiota E. coli - lower GI viridans group streptococci - throat Coagulase-negative staphylococci - wound Yeasts - isolated in low numbers in vaginal specimens or in the throa Presence of Other Bacteria and Quality of Specimen The isolation of an organism in pure culture is less likely to represent contamination than a mixed culture. a pure culture of E. coli at more than 10^5 CFU/mL would likely represent true infection and would be tested. a few K. pneumoniae organisms in the presence of oropharyngeal flora in a sputum culture may not be significant.  Host Status Species usually viewed as normal microbiota might be responsible for an infection and therefore may require testing in an immunocompromised patient. Selecting Antimicrobial Agents for Testing and Reporting  Selection of Test Batteries 10 to 15 antimicrobial agents for routine testing against the Enterobacteriaceae, Pseudomonas spp., nonfastidious gram-negative bacilli (e.g., Acinetobacter spp., Stenotrophomonas maltophilia, and Burkholderia cepacia), staphylococci, and enterococci. Reporting of Susceptibility Test Results Reporting of Susceptibility Test Results Traditional Antimicrobial Susceptibility Test Methods