Amr

• Antimicrobial resistance (AMR) is a serious global public health and economic issue, with an estimated total global economic cost of $100 trillion by 2050.
• There are different mechanisms of action of antimicrobials to inhibit or kill bacteria.
• Key bacterial body parts or growth behavior linked with AMR include the cell membrane (CM), outer membrane (OM), and planktonic vs. structured dense communities (biofilms).
• Different mechanisms of AMR include mutation, alteration of cell wall, and changes in gene regulation.
• The origin and responsible agents for the dissemination of AMR genes include unregulated use of antimicrobials in animal or humans, use of feces (or water) containing AMR bacteria as fertilizer, and food containing the AMR bacteria from feces.
• AMR cases are a serious global public health and economic issue, with an estimated 1.27 million people globally dying each year due to AMR.
• The three major purposes of antimicrobial prescription are growth promotion, prophylactics, and therapeutics.
• DNA topoisomarase and DNA gyrase are key enzymes in the cell wall.
• The four major AMR mechanisms are summarized as reduced permeability, efflux pumping, drug inactivation by enzymes, and target site change, modification or protection.
• There are 5 classes of bacteria based on their cell wall architecture.
• Folic acid synthesis is a key metabolic process in the cell wall.
• DNA, RNA polymerase, and protein synthesis occur in the cell wall.
• Biofilm formation is also a mechanism of AMR in addition to the four major AMR mechanisms.
• Thick cell walls provide protection to bacteria.
• Cell wall synthesis involves DNA, RNA, and protein & metabolite.
• Bacteria are resistant to antimicrobials that act on the cell wall.
• Bacteria have a shield outside of the cell wall for protection.
• Bacteria are versatile and can survive in nature by immediately acquiring AMR to new antimicrobials.
• Antimicrobial overuse in intensive farms (pigs & poultry), dry cow therapy, and shipping of animals is banned in the EU and USA.
• The routes of AMR bacteria mobility/spread in animals, environment, water bodies, food, and humans include unregulated use of antimicrobials in animal or humans, use of feces (or water) containing AMR bacteria as fertilizer, and food containing the AMR bacteria from feces.
• Use of feces (or water) containing AMR bacteria as fertilizer is a serious global public health and economic issue, as it can spread AMR bacteria to the public via food and water.
• E test is a quantitative method for AMR detection using solid media format.
• In E test, two-fold serial dilutions of the antibiotics are made in test tubes and then immersed in a filter paper disc, which is cut and pasted onto a strip.
• Microdilution is a quantitative method for AMR detection using liquid media format.
• In macrodilution, various antimicrobial agents diluted serially in two-fold concentrations are loaded into test tubes and then inoculated with bacteria, with the last dilution that inhibited growth determined.
• The inhibition zone is measured the next day to determine if the bacteria were killed.
• Macrodilution is a quantitative method for AMR detection using liquid media format.
• In microdilution, various antimicrobial agents diluted serially in increasing two-fold concentrations are loaded into a 96-well plate and then inoculated with bacteria, with the last dilution that inhibited growth determined.
• In agar dilution, different concentrations of antimicrobials are added to culture media to determine the MIC.
• Agar dilution is a quantitative method for AMR detection using solid media format.
• In disc diffusion, different antimicrobials are diluted at a specific concentration and then applied to a filter paper disc, which is immersed in each test tube containing the diluted concentration.
• The filter paper disc is then placed on an agar plate that is already swabbed by bacteria and incubated overnight at 37C.
• Disc diffusion is a qualitative method for AMR detection using solid media format.
• The strip is placed on an agar plate that is already swabbed by bacteria and the last dilution that inhibited growth is determined.
• Mycoplasma, Chlamydia, and Coxiella have no cell wall, while Mycobacterium has a cell wall without peptidoglycan covered by mycolic acid (wax or lipids).
• The cell membrane (CM) is not stained by Gram stain.
• The CLSI manual is consulted for the interpretation of the disk diffusion inhibition zone diameter (mm) and MIC (µl/ml) of the isolate.
• The disk diffusion test protocol involves using a 4mm thick MH agar, a 6mm diameter disk, and testing at a concentration of 1-2 x 10^8 CFU/ml.
• The class and concentration of antimicrobials to be tested can include Polypeptides like Colistin, Penicillins like Ampicillin, Cephalosporins like cefotaxime, Carbapenem like meropenem, Chloramphenicol like Florfenicol, Aminoglycosides like Gentamycin, Tetracyclines like Erythromycin, Lincosamides like Pirlimycin, Sulfonamides like Trimethoprims, Rifampicin like Rifampicin, Quinolones like Ciprofloxacin.
• The CLSI manual has different cut-off values for disk diffusion inhibition zone (mm) and MIC (µl/ml) against different antimicrobials and against different pathogen species.