Bacteria Genetics & Normal Flora PDF

Batterjee Medical College Tile Bacteria Genetics & Normal flora Name :Prof. Dr. Manal El Said Designation: Head of Microbiology Department Department: Microbiology Batterjee Medical College Topic/Subject Bacteria Genetics...

Batterjee Medical College Tile Bacteria Genetics & Normal flora Name :Prof. Dr. Manal El Said Designation: Head of Microbiology Department Department: Microbiology Batterjee Medical College Topic/Subject Bacteria Genetics Transfer of Bacterial DNA Normal Flora Probiotics AMBOSS Cases References Bacteria Genetics Genetic material of bacteria consists of single circular DNA molecule Bacteria have only one copy of their genome DNA (haploid). Mutations Mutation is change in base sequence of DNA insertion of different amino acid into protein & altered phenotype. Mutations result from three types of molecular changes Transposons or Base Substitution Frame shift insertion sequences Mutations: 1-Base substitution Missense mutation different amino acid to be inserted. Mutations: 1-Base substitution Nonsense mutation termination codon stops protein synthesis prematurely & destroy protein function. Mutations: 2- Frameshift One or more base pairs are added or deleted shifts reading frame on ribosome incorporation of wrong amino acids or.production of inactive protein Mutations: 3-Transposons or insertion sequences Transposons or insertion sequences are integrated into DNA changes in genes into which they insert & in adjacent genes Transfer of DNA Within Bacterial Cells 1- Programmed rearrangements Movement of genes from inactive (storage) sites into active sites expressed new proteins. 2- Transposons Transfer of transposons (carry antibiotic resistance genes) on plasmids to other bacteria by conjugation antibiotic resistance. Transfer of DNA between Bacterial Cells Transfer of genetic information from one cell to another can occur by Conjugation Transduction Transformation Transfer of DNA between Bacterial Cells:Conjugation Conjugation: DNA (plasmid carrying antibiotic resistance gene) is transferred from one bacterium to another. Donor bacterium have "fertility" plasmid (F plasmid) carries genes for required proteins for conjugation. Pilin protein forms sex pilus (conjugation tube). NB:DNA transferred to recipient bacterium is new copy that allows donor to keep copy of DNA  Transfer of DNA between Bacterial Cells: Transduction Transduction is process by which DNA is transferred from one bacterium to another by bacterial virus (bacteriophage) Transduction Generalized Specialized  Transfer of DNA between Bacterial Cells: Transduction Generalized Transduction Cell DNA is fragmented after phage infection & pieces of cell DNA are incorporated into virus particles.  Transfer of DNA between Bacterial Cells: Transduction Specialized Transduction Lysogenic phages DNA integrated into cell DNA is excised & carries with it adjacent part of cell DNA.  Transfer of DNA between Bacterial Cells: Transformation Transformation is process by which DNA itself released from dying cells, enters recipient bacterium. https://youtu.be/MRBdbKFisgI  Normal Flora Normal flora (commensals, microbiome) are organisms that derive benefit from another host but do not damage that host. Bacteria & fungi (permanent residents) of skin, oropharynx, colon & vagina are normal flora Viruses & parasites (protozoa & helminths) are NOT normal flora.  Normal Flora Normal flora vary in number & kind from one site to another. Internal organs usually are sterile. Central nervous system, blood, lower bronchi & alveoli, liver, spleen, kidneys & bladder are free of all but occasional transient organisms.  Normal Flora Members of normal flora play role both maintenance of health & in causation of disease in three significant ways: 1- Normal flora cause disease, especially in immunocompromised & debilitated individuals. Normal flora are nonpathogens in their usual anatomic location, but they can be pathogens when leave their anatomic site.  Normal Flora 2) Constitute protective host defense mechanism. Resident normal flora occupy attachment sites on skin & mucosa that interfere with colonization by pathogenic bacteria. “Colonization resistance”: ability of members of normal flora to limit growth of pathogens (3) Serve nutritional function: produce B vitamins & vitamin K.  Important Members of the Normal Flora 1-Skin 1. Staphylococcus epidermidis (predominant ): prosthetic heart valves & prosthetic joints infections 2. Candidia albicans (Yeast) : endocarditis 2- Nose Staphylococcus aureus*: skin abscess & post-surgical wound infection 3- Oropharynx (Mouth & throat) Viridans streptococci: Subacute infective endocarditis 4- Stomach very few organisms because of low pH. *its main site is in the nose but can be present on the skin  Important Members of the Normal Flora 5-Colon > 90% of fecal flora are anaerobes 1.Bacteroides fragilis (Greatest Number; anaerobes): peritonitis 2.Escherichia coli (Most Important; facultative): urinary tract infections 6- Vagina Lactobacilli* (predominant): produces acid that keep pH of vagina low 7- Urethra Staphylococcus epidermidis: outer third of urethra Escherichia coli : colonize female urethra urinary tract infections *inhibits growth of C. albicans the cause of vaginitis Probiotics Probiotics are live, nonpathogenic bacteria that may be effective in treatment or prevention of certain human diseases. There are three beneficial effects of Probiotics : 1. Providing colonization resistance by which nonpathogen excludes pathogen from binding sites on mucosa 2. Enhancing immune response against pathogen 3. Reducing inflammatory response against pathogen. Probiotics Oral administration of live Lactobacillus rhamnosus significantly reduces the number of cases of nosocomial diarrhea in young children. Serious complications have arisen in : - highly immunosuppressed patients - patients with indwelling vascular catheters. Batterjee Medical College Case Problem -1: AMBOSS A researcher cultivates noninfectious isolate of bacteria in a culture with lysed infectious bacterial isolate. Animals exposed to bacteria grown in this culture developed symptoms of infection. Which of the following processes is most likely responsible for the described findings? a. Reassortment b. Transformation c. Generalized transduction d. Recombination Batterjee Medical College Case Problem -2: AMBOSS A researcher conducted a study using isolated strains of Klebsiella pneumoniae and Staphylococcus aureus. Klebsiella pneumoniae strain harbors plasmid conveys resistance to streptomycin. S. aureus strain is sensitive to streptomycin. Both bacterial strains are mixed in a liquid growth medium. After 2 days of incubation and subsequent transfer to a solid medium, the S. aureus strain was resistance to streptomycin. No streptomycin-resistance gene was found on the chromosomal DNA of the streptomycin-resistant S. aureus. Which of the following mechanisms is most likely responsible for this finding? a. Transformation b. Conjugation c. Transposition d. Transduction Batterjee Medical College References 1. Levinson W (2016): Review of Medical Microbiology & Immunology, 14th Ed., McGraw-Hill Companies, Inc. ISBN: 978-0-07-181812-4, 2. AMBOSS Library https://next.amboss.com/us/questions/TABN6QWdX/5/article/WM0Pn g#Zd5f80c0b0f3a51e415ac24e6e49a8b77 https://next.amboss.com/us/questions/eU55xXjkX/1 https://next.amboss.com/us/questions/eU55xXjkX/3 Batterjee Medical College Thank You