Bacterial Genetics and Antibiotic Resistance PDF

Antimicrobial Resistance and Antimicrobial Stewardship Dr Sumudu Withanage Department of Microbiology Outcomes Describe genetic mechanisms that cause antimicrobial resistance (AMR) Describe the methods of AMR gene transfer Describe the mechanisms of AMR Discuss factors res...

Antimicrobial Resistance and Antimicrobial Stewardship Dr Sumudu Withanage Department of Microbiology Outcomes Describe genetic mechanisms that cause antimicrobial resistance (AMR) Describe the methods of AMR gene transfer Describe the mechanisms of AMR Discuss factors responsible for the development and spread of AMR from a One Health perspective Explain what antibiotic stewardship is, its components and how to prevent antibiotic resistance Infections Self-limiting Complete recovery due to the host immune response Neutrophils Complement Interferon Antibodies ………….. Antimicrobials/ antibiotics An antimicrobial is an agent that kills microorganisms or stops their growth Bacteria Virus Fungi Parasites An antibiotic is a type of antimicrobial substance active against bacteria History of antibiotics and AMR https://i.pinimg.com/originals/e7/b2/01/e7b201640d8f000222fb8bfc6e027058.jpg Antimicrobial Resistance Antimicrobial resistance Intrinsic resistance - Some microbes are innately resistant to particular classes of antimicrobials Enterococci are intrinsically resistant to cephalosporins Anaerobes are intrinsically resistant to gentamicin Pseudomonas is intrinsically resistant to amoxycillin  Enter Clost Diphtheri Staphylo Streptoc Neisseri Haemop Enteroba Bacteroi Pseudo Acinetob Atypical ococ ridiu a coccus occus a hilus/ cteria des monas acter Bacteria cus m Moraxell a Penicillin Amoxycillin Ticarcillin Piperacillin 1st gen ceph Erythromycin Gentamicin Ciprofloxacin Tetracycline Antimicrobial resistance Acquired resistance - All microbes have the potential to acquire resistance due to changes in the DNA. Bacteria have been around longer than any living thing on earth. Binary fission – clone of the original with the same DNA Fast process - one bacterium can produce one billion clones in ten hours Bacteria mutate to protect themselves from antibiotics The mutated bacteria survive after the antibiotics are gone Eventually there are more antibiotic- resistant bacteria than non-resistiant The mutated bacteria reproduce, passing along the resistance to their offspring Bacteria can also swap genes, under the right conditions, so drug-resistant germs can share their resistance mechanisms Genetic structure Nucleus Plasmid Nucleus ✓ A circular piece of double stranded DNA lying in the cytoplasm. ✓ No nuclear membrane (prokaryote) Plasmid ✓ In addition to the nucleus one or more small circular extra- chromosomal double-stranded DNA elements. ✓ They replicate independently of the main chromosome. ✓ Carry supplementary genetic information coding for antibiotic resistance. Transposition DNA can move from the chromosome to the plasmids and vice versa This is called transposition ▪When the segments are small they’re called insertion sequences and when large, they are called transposons. Alterations in the bacterial genome Occur by two methods 1. Mutations 2. Gene transfer 1.Transformation 2.Conjugation 3.Transduction Mutations ✓Bacteria reproduce by asexual binary fission and the genome is identical in all the progeny. ✓ But occasional inaccuracies in the DNA replication process produce slightly altered DNA in progeny i.e. spontaneous mutations. Mutations 3 main types of point mutations( Affect one or two nucleotides) Deletions Insertions Substitutions Other types of mutations are Duplication Inversion Mutations…. Gene transfer Bacterial cell acquire additional genetic material by transfer of DNA between bacteria. 3 mechanisms of transfer. Transformation Conjugation Transduction Transformation Some bacteria can take up DNA from the environment (released by lysis of bacterial cells of another strain) e.g. pneumococci Neisseria spp. Once taken up, these pieces of DNA become incorporated into the bacterial chromosome by recombination. Transformation….. The transformed DNA must have been derived from a closely related strain. The pieces of DNA transferred by transformation are short and contain a very small number of genes. Conjugation A donor cell makes contact with a recipient cell through the pili and a plasmid is transferred directly from donor to recipient. e.g. E.coli Shigella spp. Salmonella spp. Transduction Transfer of genetic material between bacteria via bacterial viruses called bacteriophages. Takes place between closely related strains. Phages carrying fragments of bacterial DNA can infect another bacterium and the DNA fragment recombines with the DNA of the new host (lysogeny). Gene transfer - Summary Antibiotic resistance… Once resistance has appeared, the continuing presence of an antibiotic exerts a selection pressure in favour of resistant organisms. Therefore irrational use of antibiotics in humans and mass use of them as growth supplements in animal husbandry help to increase drug resistance. Clinical examples of acquired drug resistance ✓In treatment of tuberculosis a drug combination is used because mutants resistant to any of the drugs used are likely to be appear during treatment and have to be quickly killed by one of the combination drugs ✓ Mutations in the genes in Klebsiella can result in development of resistance to cephalosporins. This is commonly seen in hospitals ✓Acquisition of a novel PBP (PBP2a) by S. aureus resulting in resistance to cloxacillin (MRSA) Mechanisms of Antibiotic resistance (3 major methods) Antibiotic modification or inactivation by enzymes Altered target (binding) site Decreased uptake and / or efflux The multiplier effect in clinical practice Misuse of antimicrobials  increases selection of resistant strains  increases chance of patient acquiring resistant strain spread of resistant strains from person-to-person  Factors promoting emergence of antimicrobial resistance Unnecessary use (e.g. use in non-bacterial illnesses; inappropriate prophylaxis) Inappropriate use: wrong choice of antimicrobial, wrong dose or duration of treatment Poor quality drugs Unregulated over the counter sales Self-medication Use of antimicrobials as growth promoters in animal husbandry  Factors promoting spread of resistance……. Prolonged illness - increases opportunity for person- to-person spread Inadequate control of infection in health care facilities Lack of knowledge, training, guidelines for prescribers Lack of knowledge in patients Poor sanitation and overcrowding International travel and trade, population movements The implications of antimicrobial resistance Complex, multi-factorial problem Increasing morbidity and lost productivity Increases mortality Major cost implications on health care for both drugs and hospitalization  How can drug resistance be prevented Overcome patient demand Summary Training & knowledge Avoid economic incentives Regulation of animal Prescribers Appropriate husbandry antimicrobial Infection Hospital control therapy guidelines R policy & antibiotic policy Pharmaceutic al industry International Government policy policy Registration of Develop new drugs Research to address gaps pharmacy and vaccines International R surveillance Control drug promotion Monitor drug quality Antibiotic stewardship Antimicrobial stewardship (AMS) refers to coordinated efforts to promote the optimal use of antimicrobial agents, including drug choice, dosing, route, and duration of administration