Veterinary Bacteriology Road Map PDF

Road map to VETM Veterinary Bacteriology Dr. Lone, DVM, PhD (Guelph, Canada), DACVM  Overview Basics of infectious disease Basic bacterial structure as applied to bacterial infectious diseases Aim is to laydown a basic simple road map of bacterial infect...

Road map to VETM Veterinary Bacteriology Dr. Lone, DVM, PhD (Guelph, Canada), DACVM  Overview Basics of infectious disease Basic bacterial structure as applied to bacterial infectious diseases Aim is to laydown a basic simple road map of bacterial infectious diseases for a veterinary medicine student, that he/she can apply when studying, identifying or diagnosing a bacterial infectious disease. What is an infectious disease? An infectious disease can be defined as an illness due to a pathogen or its toxic product, which arises through transmission from an infected person, an infected animal, or a contaminated inanimate object to a susceptible host (Seventer and Hochberg, International Encyclopedia of Public Health, 2017) Three terms to note: Pathogen or infectious agents Infection Host- A carrier for a pathogen Veterinary Infectious Diseases Infectious disease are caused by infectious agents Infectious agent (or pathogen): are cellular organisms (bacteria, fungi, parasites) or acellular particles (viruses, prions) that can cause disease as a result of multiplying or undergoing development in a susceptible host (modified CDC) A pathogen is an organism that has the capacity to cause damage in a host (Casadevall and Pirofsky) Types of infectious agents How do infectious agents cause disease? Pathogenesis is the process by which a disease or disorder develops Infectious disease pathogenesis is an outcome of an interaction between a host and pathogen Host damage can result from both infectious agent and host immune response  Infectious disease outcome Variable Environment (Environment tilts balance in favor of host or pathogen) Variable outcome (in terms of host damage and pathogen survival) (Note: Environment can be immediate, local, regional, or global includes all variables that affect life like tempt, air, nutrient availability) Environmental effects Veterinary Microbiology and Microbial Diseases, Quinn and others Variable outcome can be represented graphically 1 2 3 4 5 6 Nature Microbiolgy, Casadevall and Pirofiski Graphs 1 – 6 explanation  Outcome of Host-Pathogen interaction Commensalism: A state of host–microorganism interaction that does not result in host damage after the state is initiated. Colonization: A state of host–microorganism interaction that leads to a variable amount of host damage, from minimal to great, thereby reflecting host immune responses that have the capacity to eliminate the microorganism or to promote the development of another state. Latency: A state of host–microorganism interaction in which a microorganism persists in a host and can be associated with damage that can be evident at the cellular or tissue level, but is not associated with disease Disease: A clinical outcome of host damage that occurs after a threshold amount of damage has occurred. Please note some other definitions related to pathogenesis Virulence: The relative capacity of a microorganism to cause damage in a host. Virulence factor: Pathogen component that can damage a host. Please read the below article to get an idea about how varying terminology is used in infectious disease literature. If you don’t find time, at least go through Table 1 and Table 2 Host-Pathogen Interactions: Basic Concepts of Microbial commensalism, Colonization, Infection, and Disease. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC97744/ Summary As a veterinary doctor what problems would you encounter if you think of applying Koch’s postulates to an infectious disease in the field? Discuss Koch’s postulates 1.A particular microbe must be found in all cases of the disease and must not be present in healthy animals or humans. 2.The microbe must be isolated from the diseased animal or human and grown in pure culture in the laboratory. 3. The same disease must be produced when microbes from the pure culture are inoculated into healthy susceptiblelaboratory animals. 4.The same microbe must be recovered from the experimentally infected animals and grown again in pure culture Questions to ask when dealing with infectious disease Is this infectious or non-infectious disease If suspect infectious disease Can I identify the causative infectious agent (Various algorithms for identifying different pathogens) Structure, shape, metabolic function or profile, carbohydrate, protein or genome-based identification Can I relate the clinical findings with the disease caused by the identified pathogen Pathogenesis: virulence factors vs host-response resulting in tissue damage. How to clear the infectious agent from the body (treatment) Where did the pathogen come from How did it enter the body How to control the spread of infectious agent Can we prevent the infectious disease from occurring Infectious agent categories  Cellular infectious agents A cell is a basic membrane-bound unit (microscopic biological machine) that forms basic building block of living things Membrane-bound DNA and membrane-bound organelles Prokaryotic (Single cells organisms) Eukaryotic (Single as well as multicellular organisms) Nature Education 2010  Acellular Infectious agents Virus: an infective agent that consists of a nucleic acid molecule in a protein coat, and is able to multiply only within the living cells of a host. Prion: are normal cellular proteins that have undergone conformational change as a result of post- translational processing of a normal cellular protein and thereby have become pathogenic Diagrammatic representation parvovirus (Viral Zone) Prion infectious agent Electron micrograph parvovirus (20 nm), Fenners Virology  Eukaryotic cellular infectious agents Frontiers in Microbiology Algae Chlorella Spp. Pythium insidiosum lipid bodies Prototheca Spp. nucleus Fungus-like organisms Goold et al  Size of Infectious agents I will be teaching you 1. Our eyes cannot resolve anything less than 0.1 mm in size 2. Individual cells of pathogens I will be teaching you are less then 0.1mm in size -need a microscope -except when they replicate and aggregate with one another to form colonies that can be seen by naked eye. -bacterial and fungal colonies Relative sizes of bacterial and fungal pathogens Bacterial colonies Fungal colony Bacterial biofilms are complex microbial communities encased in extracellular polymeric substances  Bacteria has only one chromosome Taken from ngsmagnified.com Staphylococcus aureus Genus Species  What is a bacterial species? Difficult to answer. Working definitions only Bacterial species: A population of cells with similar characteristics. ▪ Phenotypic ▪ Staining, shape, motility metabolism etc. ▪ Genotypic ▪ DNA-DNA hybridization ▪ a technique that measures the degree of genetic similarity between pools of DNA sequences. ▪ > 70 % DNA-DNA hybridization –same species ▪ Average nucleotide identity (ANI) ▪ is a measure of nucleotide-level genomic similarity between the conserved coding regions of two genomes. ▪ > 95% ANI- Same species Bacterial species: can be defined as monophyletic groups of isolates with genomes that exhibit at least 95% pair-wise ANI (Chan et al 2012) Phenotypic means of identifying bacterial species DNA-DN hybridization Average nucleotide identity (ANI) All steps of ANI are carried out by computer software ANI ANI is a measure of nucleotide-level genomic similarity between the conserved coding regions of two genomes Below species level categorization Type: a subgroup of bacterial species defined by some specific characteristic Strain: a pure culture (descendants of a single cell) Isolate : pure culture from wild type heterogeneous population  Example Phenotype: gram –ve rod, bile salt resistant, ferments lactose, oxidase negative, catalase positive, IMViC (+/+/-/-) Genotypic identification: ANI E. coli Species Pathogenic (miniscule) Non-pathogenic (Huge number) Diarrheagenic ETEC, EPEC, EHEC Type (Pathotype) O6:H16, O8:H9 etc. etc. O157:H7 etc. Type (Serotype) Many strains General Veterinary Bacteriology Pay attention to word general What we study here may apply to all or only few veterinary bacterial pathogens For example, we may discuss flagella. It is not found in all, but only in some bacterial pathogens. In contrast, you can divide all veterinary bacterial pathogens as gram negative or gram positive, irrespective of whether they stain with gram stain or not. Questions to ask Is this a bacterial infectious disease If suspect bacterial infectious disease Can I identify the causative infectious agent (Various algorithms for identifying different pathogens) Shape, structure, metabolic function or profile, carbohydrate, protein or genome-based identification Can I relate the clinical findings with the disease caused by the identified pathogen Pathogenesis: bacterial virulence factors vs host-response resulting in tissue damage. How to clear the infectious agent from the body (treatment) Where did the pathogen come from How did it enter the body How to control the spread of infectious agent Can we prevent the infectious disease from occurring (vaccination Shape (Microscopic) No definite shape : mycoplasma, Pelomorphic Taken from Veterinary Microbiology 4th ed, McVey and others Shape Why do you need to stain bacteria to see their shapes? Contrast (all forms of microscopy need some form of contrast enhancement) Is there a way to enhance contrast without staining bacteria? Phase contrast microscopy Use high resolution microscope for smaller structures What is resolution? Gram stain Quick and very valuable A lot of bacterial species don’t stain with gram stain, However, we still classify them as Gram positive or gram negative Why? The answer lies in bacterial cell wall structure Typical prokaryotic cell Burton’ s Micorbiology Gram positive vs Gram negative Veterinary Microbiology and Microbial Diseases, Quinn and others Cytoplasmic membrane Veterinary Microbiology by McVey and others  Cell wall Creative labs Wall teichoic acids often consist of polyribitol or polyglycerol chains (40 to 60 repeats) variably substituted with monosaccharides or D-alanine or both  Outer membrane Hydrophobic Chains Chris Whitfield, Essentials of Glycobiology 4th ed Outer-membrane Mazgaeen, International journal of Molecular Science S-layer Koneman’s Diagnostic Microbiology  Capsule Mucoid Taken from Clinical Veterinary Microbiology by Markey & others Capsule seen under Phase contrast microscope microbeonline.com Mycobacterial cell wall and cell membranes  Bacterial appendages Fimbriae and pili are hair-like appendages present on the bacterial cell wall similar to flagella. They are shorter than flagella and more in number. They are involved in the bacterial conjugation, attachment to the surface and motility. Electron micrograph showing flagella and fimbriae microbeonline.com Please note: All bacterial cell surface structures can be used in bacterial identification and typing Fimbriae Ultramicroscopic protein structures Pili and fimbriae used interchangeably Always use “pili or pilus” for conjugation (pilus-mediate joining of two bacterial cells which allows DNA transfer). Attachment and movement Types of flagella Flagellum Structure NB: When revising for bacteriology, use the Vonderviszt and Namba title since information is limited. Cytoplasm (Chromosome) Chromosome in region called nucleoid (nucleus-like) DNA much longer than cells hence twisted and packed in chromosome by supercoiling Supercoiling by topoisomerases facilitated by nucleoid-associated proteins Most bacteria possesses single copy of double-stand circular DNA; however Some bacterial species possesses two copies of circular DNA molecules Borrelia has a linear chromosome, not circular Some bacteria carry integrated bacteriophage (virus that infect bacteria) DNA DNA can be used in bacterial identification and typing  Ribosomes Ribosomes are abundant in cytoplasm S: Svedberg - the unit of sedimentation coefficient 1 - indicates the relative rate of sedimentation during ultra-centrifugation. - depends on the size, weight, and shape of particle 16S RNA gene is widely used in bacterial identification (mostly genus level)  Plasmids Extra-chromosomal double-stranded DNA Circular, but both circular and linear in Borrelia Replicate independently OriV replication origin as opposed OriC in chromosome Chromosome Number varies and controlled Plasmid Selective advantage to bacteria Virulence and antimicrobial resistance genes Taken from Veterinary Microbiology, McVey and others Cytoskeleton FTsZ Homologs to eukaryotic tubulin Cell division MreB Eukaryotic actin like Dictates cell shape and spiral and bacillus shaped bacteria Crescentin Found in spiral shaped-bacteria with a single curve Oregon State University Website Bacterial inclusions Range in complexity Organic or inorganic molecules Nutrient storage Polysaccharide, glycogen, lipids (poly beta-hydroxybutyrate) Phosphorus, sulfur Endospore formation Nutrient starvation and unfavorable environment conditions Adobe.com Spore formation B. subtilis, Mckenney et al Endospores in a stained smear from cow Thank you. In the next class, we will be discussing bacterial DNA, the most important macromolecule in a bacterial cell. Questions are most welcome. Please don’t hesitate to ask questions