I always tell my students at the start of every lecture: “If a smart man can understand the entire concept in an hour, while it will take you the whole day to do so, then better start making that coffee.”

BUGS WITH THE OUR WITS versus THEIR GENES A n ASMPH FILM MICROBES & HUMANS “The global future of mankind will probably unfold as episodes of a suspense thriller that could be entitled Our Wits Versus Their Genes.” Joshua Ledeerberg Introducing

Raul V. Destura MD Consultant-Director Section of Molecular Diagnostics and Section of Clinical Microbiology The Medical City

Is a branch of science that relates to interactions between man and microorganisms. In practice, the science deals mainly with the ill health resulting from such interactions – infections or infectious diseases

The term is usually applied to any condition that: is easily transmitted between individuals is caused by an identifiable microorganism may, following initial infection, confer protection (immunity) from subsequent infection with the same microorganism.

1. The Affected Host 2. An Infectious Agent 3. The Environment

Infectious diseases in man are caused by microorganisms (living organisms of microscopic size) from the following five groups: bacteria viruses Fungi protozoa helminths.

Contain the largest number of species that are pathogenic to human Single-celled and contain both DNA and RNA and produces by binary fission A few lack all the machinery necessary for replication and must interact with host cells to reproduce (Ricketsiaceae, Anaplasmataceae, Chlamydiaceae)

Single and multicelled agents that are further differentiated into a defined nucleus and cytoplasm Yeast- single celled fungi that reproduce by binary fission Molds or Moulds – more complex multicelled organisms that reproduce by both sexual and asexual means Some are Dimorphic

Large and very complex group of microbes Include single celled animals –protozoa Others are very complex, multi-celled organisms that have well defined organs and tissues, such as GI and genital systems

Do not have complete genetic machinery for their own propagation Either a DNA or RNA Must infect other life form to survive Represent the simplest form of infectious Agents Reproduce by replication of their nucleic acid

Bacteria have been classified on the basis of their staining properties for about 120 years. The method differentiates between two major groups of bacteria with very different cell envelopes. Gram-positive bacteria retain the stain (crystal violet) and appear blue, whereas gram-negative bacteria usually appear pink due to the counterstain safranin.

Fig. 7-37b, p.232

Commercial break……..

Developed by: Hans Christian Gram, 1884 Differential stain Discriminates between different cell types – Gram positive and Gram negative

Gram positive Dark purple Gram negative Pink

Cocci in clusters: e.g. Staphylococci Cocci in chains: e.g., Streptococci

Cocci in tetrads: e.g., Micrococci Bacilli or Rods

Cocci in pairs (or Diplococci) Bacilli or Rods

Issues selective pressure antimicrobial resistance plasmid mediated chromosomally mediated

PlasmidsPlasmids Extra-chromosomal DNA multiple copy number coding pathogenesis and antibiotic resistance factors bacterial replication

Some bacteria are motile Locomotory organelles- flagella Taste environment Respond to food/poison –chemotaxis

Flagella –embedded in cell membrane –project as strand –Flagellin (protein) subunits –move cell by propeller like action

spirochetes spirochetes similar function to flagella similar function to flagella run lengthwise along cell run lengthwise along cell snake-like movement snake-like movement

Making Wall-less forms Result from action of:Result from action of: –enzymes lytic for cell wall –antibiotics inhibiting peptidoglycan biosynthesis Usually non-viableUsually non-viable Wall-less bacteria that don’t replicate:Wall-less bacteria that don’t replicate: –spheroplasts (with outer membrane) –protoplasts (no outer membrane). Wall-less bacteria that replicateWall-less bacteria that replicate –L forms

Mycloplasma Mycloplasma

Capsules and slime layers outside cell envelopeoutside cell envelope well defined: capsulewell defined: capsule not defined: slime layer or glycocalyxnot defined: slime layer or glycocalyx usually polysaccharideusually polysaccharide often lost on in vitro cultureoften lost on in vitro culture protective in vivoprotective in vivo

Dormant cellDormant cell Produced when starvedProduced when starved Resistant to adverse conditionsResistant to adverse conditions - high temperatures - organic solvents contain calcium dipicolinatecontain calcium dipicolinate Bacillus and ClostridiumBacillus and Clostridium

Portals of Entry Respiratory Gastrointestinal Genitourinary tracts Accidental Areas: mucus membranes and skin

(A) Portals of entry. (B) Portals of exit.

Source of AgentMechanism for EntryPortal of EntryExample Infected HumanAerosolRespiratoryInfluenza Virus Infected HumanDirect ContactCutaneousHerpes Simplex in wrestlers Infected HumanSexual IntercourseGenitalSyphilis; gonorrhea Infected HumanOral or nasopharyngeal secretions to eye OcularBacterial or viral conjunctivitis Contaminated EnvironmentTransfusion of Blood productsIntravascularHepatitis virus Contaminated EnvironmentFood or waterGastroentestinalEnteric bacterial and viral pathogens Infected AnimalCooling tower driftRespiratoryLegionaires Disease Infected TickAnimal biteCutaneousRabies PatientTick biteCutaneousLyme Disease PatientAspiration of endogenous floraRespiratoryBacterial Pneumonia PatientSpillage of intestinal flora through a damaged wall GastroentestinalBacterial Peritonitis PatientMigration of Bacteria from oropharynx to middle ear through Eustachian tube EarBacterial otitis media

LD50 and ID50

Some characteristics that give infectious agents a leg up in the battle with their chosen hosts Involves invasiveness and toxigenicity Not an all or none phenomenon

Adherence Initial requirement for organisms to invade hosts The process by which bacteria stick to the surface of host cells A.k.a. Adhesion and Attachment Adherence is dictated by several factors Surface hydrophobicity and net surface charge Binding molecules on bacteria (ligands) Host cel receptor interaction

Surface hydrophobicity The more hydrophobic the bacterial cell surface, the greater the adherence to the host cell Different strains of bacteria differ in hydrophobicity thus some are more virulent than others

Pili (fimbriae) Pili (fimbriae) hair-like projections of the cell sexual conjugation adhesion to host epithelium

Tissue-Degrading Enzymes Collagenase (C. perfringens) Coagulase (S. aureus) Hyaluronidase (Staph and Strep) Streptokinase (Strep) Hemolysins and Leucocidine IgA1 Proteases Allows pathogens to inactivate the primary antibody found on mucosal surfaces and thereby eliminate protection of the host by the antibody

Exotoxins and Endotoxins Properties Mechanisms

ExotoxinsEndotoxins Excreted by living cellsIntegral part of cell walls of G- bacteria Produced by both G+ and G- bacteriaFound only in G- bacteria Polypeptide; MW 10, ,000LPS complexes (Lipid A) Heat labileHeat Stable Highly antigenicWeakly Immunogenic Can be converted to toxoidsCannot be used as toxoids Highly toxic even at small dosesModerately toxic Has specific binding receptorsNo specific receptors Usually do not produce feverInduces release of IL-1 and other mediators Plasmid mediated controlChromosomally mediated

ExotoxinsEndotoxins DiptheriaPhysiologic Effects Tetanus Fever Botulism Leucopenia Gas Gangrene Hypotension Streptococcal Erythrogenic Toxins Impaired Organ Dysfunction TSST-1 C3 and complement cascade activation Exotoxins associated with diarrheal disease and food poisoning DIC

That’s why we need to make sure we clearly understand what we read!