Week 8 Microbiology & Infectious Disease NURS 1022 PDF

Week 8 Microbiology & Infectious Disease Microbiology & Infectious Diseases NURS 1022 Microbiology Study of microorganisms Variety of techniques used for: Visualization Identification Study of microbial function Science of microbiology Originated with invent...

Week 8 Microbiology & Infectious Disease Microbiology & Infectious Diseases NURS 1022 Microbiology Study of microorganisms Variety of techniques used for: Visualization Identification Study of microbial function Science of microbiology Originated with invention of the microscope Classification of Microorganisms Prokaryotes No membrane-bound organelles, such as a nucleus (pro, before; karyon, nucleus) Archaea, bacteria Eukaryotes With membrane-bound cell organelles Algae, fungi, protozoans Shared Properties: Methods of reproduction by cell division, binary fission, mitosis, or meiosis Presence of DNA and RNA for protein synthesis Plasma membranes Classification of Microorganisms Classification of Microorganisms (continued) Viruses Noncellular, submicroscopic particles Consist of nucleic acid surrounded by a protein coat Prions (proteinaceous infectious particles) Not cellular, not viral, lack nucleic acids Proteins that misfold and become an infectious agent When they become abnormally folded, they become infectious particles Diseases are called transmissible spongiform encephalopathies (e.g., mad cow disease, kuru) Viroids Do not have a protein coat Are plant pathogens Microorganisms in Health & Disease Microbial ecology Often deals with biofilms Interactions Mutualism Commensalism Synergism Parasitism Normal flora versus pathogens Foodborne diseases Organism/toxin contamination Waterborne diseases Organism contamination Airborne diseases Aerosols  BACTERIA  Spirochetes:  Group of helical, motile bacteria  Twisting motions of their axial fibrils  Found in various aqueous environments and in association with human or animal hosts  Pathogens Treponema pallidum—Syphilis Borrelia burgdorferi—Lyme disease Leptospira interrogans—Leptospirosis  Aerobic/Microaerophilic Helical Vibrioid Gram-Negative Bacteria  Either slightly curved or have multiple helical turns  Motile with help of flagella  Live in fresh or coastal waters  Some cause disease in humans or animals  Medically important examples Campylobacter spp Helicobacter pylori Gram-Negative Aerobic Rods and Cocci  Diverse group; extensively investigated  Widely distributed in nature  Many are human and animal pathogens  Respiratory metabolism; not fermentation  Rhizobia are soil bacteria; nitrogen fixation  Medically important examples Legionella pneumonia Neisseria gonorrhoeae Neisseria meningitides Bordetella pertussis Francisella tularensis Pseudomonas aeruginosa  Facultative Anaerobic Gram-Negative Rods  Large group of bacteria with simple nutritional requirements  Present in soil, water, intestinal tract of animals and humans  E. coli is the “workhorse” of molecular biology most strains do not cause human illness but some can cause gastroenteritis, UTIs, hemorrhagic gastritis  Rickettsias and Chlamydias  Very small gram-negative bacteria  Majority require host for replication  Generally rod-shaped but also may look coccoidal  Often cause disease  Rickettsiae need a vertebrate and an arthropod host  Chlamydias do not infect invertebrates  Rickettsiae rickettsii Rocky Mountain spotted fever (ticks)  Chlamydiae trachomatis Urogenital infections  Gram-Positive Cocci  Include aerobic and anaerobic bacteria  Range from harmless to very virulent forms  Includes Micrococcus, Staphylococcus, Streptococcus, Peptococcus  Medically important examples Staphylococcus aureus Streptococcus pyogenes Streptococcus pneumoniae Peptostreptococcus  Endospore-Forming Gram-Positive Rods and Cocci  Include Bacillus and Clostridium  Important in medicine and food industry  Spores are resistant to heat and disinfectants  Widespread in the soil  Clostridium perfringens is widely distributed in the environment  Decaying matter, marine sediment, intestinal tract of humans and other animals  Endospore-Forming Gram-Positive Rods and Cocci (continued)  Common cause of food poisoning  Bacilli are either obligate aerobes or facultative anaerobes  Clostridia are mainly obligate anaerobes  Include free-living and pathogenic species  Medically important examples Bacillus anthracis Bacillus cereus Clostridium botulinum Clostridium difficile Clostridium perfringens Clostridium tetani  Regular Nonsporulating Gram-Positive Rods  Obligate or facultative anaerobes  Complex nutritional requirements  Include Carnobacterium, Lactobacillus, and Listeria  Lactobacilli convert lactose and other sugars to lactic acid  Most are harmless  Some species used in industry Yogurt, cheese, sauerkraut, pickles  Listeria monocytogenes Causative agent of listeriosis  Irregular Nonsporing Gram-Positive Rods  Unusual shape  Mostly facultative anaerobes, few obligate aerobes  Medically important species Actinomyces—opportunistic Corynebacterium diphtheria—diphtheria Propionibacterium acnes—acne Actinomyces israelii—periodontal disease, lung infections  Mycobacteria  Includes gram-positive, aerobic, acid-fast rods  Widespread in water, soil, and food sources  Some are obligate intracellular parasites in humans and animals  Can colonize in host without symptoms  Infections are difficult to treat  Neither truly gram-negative or gram-positive  Naturally resistant to many antibiotics  Medically important examples Mycobacterium tuberculosis Mycobacterium leprae  VIRUSES  Viruses are microscopic particles that infect cells or other organisms  They carry DNA or RNA but cannot reproduce on their own  Obligate intracellular parasites  Infect both eukaryotes and prokaryotes viruses that infect bacteria are call “Bacteriophage (phage)”  Can be dsDNA, ssDNA, dsRNA, or ssRNA  Nucleic acid can be linear or a closed loop  Generally, species will contain one or the other  Genome Type (continued)  DNA viruses Genetic material is DNA Use DNA-dependent DNA polymerase for replication  RNA viruses Use RNA as their genetic material Do not replicate using DNA  Reverse transcribing viruses Have an RNA genome but replicate via a DNA intermediate  Viral Infections  Abortive Infection without viral production  Lytic or cytocidal Kills the host cell  Persistent Chronic: Not lytic but productive Latent: Limited synthesis—no viral synthesis Virus remains in asymptomatic host for long periods  Cold sores, shingles Slow infections: Prolonged incubation; damage might take years; followed by disease Transforming infections: Viral nucleic acid may remain indefinitely without virus production; possible oncogenic changes  Host Cell Damage  Morphological effects aka cytopathic effects Altered shape, detachment from tissue surface, lysis, membrane fusion, altered membrane permeability, inclusion bodies, cell death  Physiological effects + of viral proteins into plasma membrane—change of characteristics = altered cellular activities  Biochemical effects Inhibition or alteration of host cell’s macromolecules (e.g. DNA, RNA, large proteins)  Genotoxic effects Genotoxic substances can damage host cell DNA Mutations, Potential initiation of cancer  Major Groups of Viruses in Vertebrates  Cause disease after they break the protective barriers and gain access to underlying tissues  Most viruses are specific to a particular cell or tissue type However, a particular disease may be caused by several viruses  The genome of viruses consist of either DNA or RNA  DNA Viruses  Adenoviruses 57 adenoviral serotypes have been identified in humans Unusually stable to chemical and physical agents There is a recent interest in adenoviruses as vectors and in gene therapy Mostly respiratory illness May cause gastroenteritis, conjunctivitis, cystitis, rashes  Hepadnaviruses Cause hepatitis in humans and animals Example: Hepatitis B Can cause acute, chronic, symptomatic, or asymptomatic disease  DNA Viruses (continued)  Herpesviruses Herpes simplex 1 and 2 Varicella-zoster  Papillomaviruses and polyomaviruses Warts Possibly cervical carcinomas  Parvoviruses smallest DNA virus Only one causes human disease: B19 Others cause disease in animals  Poxviruses Largest viruses Causative agent of smallpox  RNA Viruses  Bunyaviridae Arthropod-borne  Coronaviruses largest of the RNA viruses Respiratory and enteric disease SARS (including SARS-CoV-2)  Hepatitis viruses Hepatitis (A through E, different subfamilies) Cirrhosis Hepatocellular carcinomas  RNA Viruses (continued)  Orthomyxoviruses Include influenza A, B, and C viruses Type A is most virulent in humans  Paramyxoviruses Morbillivirus, Paramyxovirus (highly pathogenic), Pneumovirus Nipah and Hendra viruses (zoonosis-causing)  Picornaviruses Important pathogens, include Enterovirus, Rhinovirus, Hepatovirus, Aphthovirus, Parechovirus, Erbovirus, Kobuvirus, Teschovirus Enteroviruses and rhinoviruses are two main causes of a variety of human illness  RNA Viruses (continued)  Rhabdoviruses Infect plants, insects, fish, birds, mammals, including humans Rabies virus belongs to this group Rabies previously fatal until development of vaccine (can be given post exposure also)  Reoviruses Not associated with a particular disease Rotavirus: Gastroenteritis, common in children, accounts for ~50% of all cases of diarrhea in children requiring hospitalization  RNA Viruses (continued)  Retroviruses Oncovirinae, Lentivirinae, Spumavirinae Example: HIV (caused by lentivirus)  Togaviruses Alphavirus- infectious arthritis, encephalitis, fever Rubivirus—rubella virus  Flaviviruses Yellow fever, encephalitis, dengue fever, hepatitis C, West Nile virus EUKARYOTIC MICROORGANISMS  Fungi:  Study of fungi = Mycology  Few fungi are pathogenic and virulent  Immune system usually fights fungal invasion  Have important symbiotic relationships with other organisms  Play a major role in decomposition  Mycorrhizae: Fungi on roots of plants  Fungal colonies are vegetative  They are free-living and heterotrophic  They appear as yeast, molds, fleshy fungi  Have cell wall composed of strong flexible polysaccharide called chitin  Penicillium 1. hypha 2. conidiophore 3. phialide 4. conida 5. septa Yeast Molds Spores from green mold growing on an orange, 1000×  Protozoans  Defined by three common characteristics Eukaryotes, Unicellular, Lack a cell wall  Many are free-living; others are potential parasites of humans and other animals  Diverse group of microbes  With the exception of one subgroup, they are motile due to cilia, flagella, and/or pseudopodia  Require moist environment to survive  Most live in ponds, streams, lakes, and oceans  Characteristics of Protozoans (continued)  Most are chemoheterotrophs and obtain nutrients from various sources Bacteria Decaying organic matter Other protozoans Host tissue  When environment becomes unfavorable for feeding, many enter a dormant stage (cyst)  Cysts can be distributed by air, which may play a role in transmitting diseases such as amoebic dysentery  Helminths  Not microbes  Interesting to microbiologists because parasitic helminths produce microscopic infective and diagnostic stages in life cycle  Often found in blood, feces, and urine  Many parasitic helminths spend much of their life cycle in a mammalian host  Most of the helminths affecting humans are either flatworms or roundworms  Adult animals usually large enough to be seen with the naked eye  Eggs and larvae (microscopic)  Classification of Helminths  Platyhelminths—flatworms Trematodes Lung fluke, liver fluke, blood fluke  All named by definite host tissue Cestodes or tapeworms Intestinal parasites  Nematodes—roundworms Enterobius vermicularis Pinworm—spends life in human host Eggs transmitted to other host by fomite Ascaris lumbricoides Human parasite without intermediate host Necator americanus and Ancylostoma duodenale Hookworm Small intestine of humans  Infectious Disease Advanced Pathophysiology & Microbiology NURS 2020  Symbiosis  Describes a close relationship between two different types of organisms in a community  Mutualism Both members benefit from the interaction  Commensalism One organism benefits, and the other is neither harmed nor helped  Parasitism One organism benefits while the other is harmed slightly or may be killed Pathogen: A parasite that causes disease  Amensalism One organism can hamper or prevent the growth/survival of another without being affected by the other organism  Normal Flora  Newborns’ first contact to microbes—birth canal  Followed by breathing  Followed by feeding  Throughout life microbes will establish residency in mucous membranes open to the environment  Normal Flora (continued)  Resident flora Remain part of the normal flora throughout life of a person  Transient flora Found in the same locations as a resident microbe Only remain for a few hours, days, or months before they vanish e.g. Bacillus laterosporus intermittently present in intestines (helps suppress fungi such as Candida)  Opportunistic Pathogens  Pathogen—a microorganism that is capable of causing disease  Balance between normal flora and human host is maintained but when balance is interrupted—microbes of the normal flora can become opportunistic pathogens  These organisms do not cause disease in their normal habitat in a healthy person Causes of Opportunistic Pathogens  Compromised immune system AIDS malnutrition stress age chemo/radiation therapy  Changes in the normal flora Normal flora is usually protective Competition no longer exists  Entrance of the normal flora into areas of the body where it is not present under normal conditions  Stages of Infection  Contamination Presence of microbes in or on the body  Infection The presence and growth of a microorganism in the body (with exception of organisms of normal flora) The microorganism must gain entry into the host and its tissues An infection does not necessarily cause disease  Portals of Entry  Sites where pathogens enter the body  Source of infection can be exogenous or endogenous Exogenous—from outside the body Endogenous—organism is already in the body (e.g., normal flora)  Portals are generally the same areas that support normal flora  Majority of pathogens have their preferred portal of entry  Some infectious agents enter via more than one portal  Skin  Thick layer of keratinized dead cells  Pathogens can enter through natural openings, such as hair follicles and sweat glands  Damage of skin—abrasions, cuts, punctures, scrapes—these open the skin and allow microbes to enter  Mucous Membranes  Gastrointestinal tract Portal of entry for pathogens present in food, liquid, and other ingested substances Enteric bacteria include: Salmonella, Shigella, Vibrio, and certain strains of E. coli Viruses include the poliovirus, hepatitis A, echovirus, and rotavirus Protozoans: Entamoeba histolytica and Giardia lamblia Helminths: Trematodes, cestodes, nematodes  Mucous Membranes (continued)  Respiratory tract Most frequently used portal of entry Pathogens enter through air, via dust particles, moisture, and respiratory droplets from infected people Bacteria—causative agents of sore throat, meningitis, diphtheria, whooping cough Viruses—agents causing the common cold, influenza, measles, mumps, rubella, and chickenpox  Mucous Membranes (continued)  Urogenital tract Pathogens usually contracted by sexual contact Girls and women who are not sexually active are susceptible to lower urinary tract infections—close proximity of anus to urethra Opportunistic infections by E. coli Vaginal yeast infections—opportunistic by overgrowth of Candida albicans  Conjunctiva Usually good barrier against infectious agents Some bacteria can easily attach to this membrane  Placenta  Usually effective barrier against microorganisms  Some microbes can cross placenta and infect the embryo or fetus—causing spontaneous abortions, birth defects, or premature births  Parenteral Route  Technically not a portal of entry and more a bypassing of portals of entry  Pathogens are directly introduced to the subcutaneous tissue Examples: Punctures by nail, thorn, contaminated needles  Cuts, bites, stab wounds, deep abrasions, surgery  Virulence and Pathogenicity  Virulence is the degree of pathogenicity or disease-provoking power of a specific microbe  Virulence is based on virulence factors  Pathogenicity is related to the number of microorganisms, portal of entry, host defense, intrinsic characteristic of organism, and virulence factors  Adhesion  First and most crucial step of infection  Without adhesion, organism will be removed by ciliary motion, sneezing, coughing, swallowing, urine flow, tears, intestinal peristalsis  Bacteria must bind to host cell by pili, fimbriae, or specific membrane receptor sites  Adhesion can be specific or nonspecific electrostatic attraction atomic & molecular vibrations  Colonization & Invasion  Human pathogens usually colonize tissues that are in contact with the external environ’t Urogenital tract, Digestive tract, Respiratory tract, Conjunctiva  Invasion - May be aided by the production of extracellular substances that disrupt host cell membranes Break down primary and 2ndary barriers of host Are called invasins - facilitates growth and spread of the pathogen  Evasion of Host Defense  Presence of capsules  Production of proteins that bind to host cell antibodies  Mutation of organism to alter it’s antigenicity  Microbe strategies to thwart host phagocytes Avoid contact with phagocytes Inhibition of phagocytic engulfment Survival inside the phagocytes Production of products that kill or damage phagocytes before or after ingestion  Toxins  Organism that produces toxins is called toxigenic Underlying mechanism by which microorganisms produce disease  Bacterial toxins may be either endotoxins (within the bacterial cell wall) or exotoxins (secreted by bacteria)  Typical toxin chemical make up either lipopolysaccharides or proteins  See table 12.5 for list of example bacterial exotoxins; table 12.6 for comparison of exotoxins & endotoxins  Exotoxins  Protein released by bacterium  During exponential growth phase  Can act at sites other than the location of infection  Toxins produced are often species specific and associated with a particular disease  Endotoxin  Lipopolysaccharides of gram-negative cell wall  Release during lysis initiated by effective host defense or by action of antibiotics  Can act on sites remote from the original site of infection  Less potent and less specific than exotoxins  Portal of Exit  Site of pathogen leaving the infected person  Often same as the portal of entry  Pathogen can also leave host by excretion/secretion  Etiology of Infectious Disease  The study of the cause of disease when an infectious agent causes pathological changes and interferes with normal body functions  Patterns of infection Infections have varied patterns and are named accordingly  Patterns of Infection  Local infections Organism enters the body and remains confined to a specific tissue  Focal infections Pathogen spreads from a local infection to other tissues  Systemic infections Infection spreads to several sites and tissue fluids, usually by the way of the circulatory system Septicemia, bacteremia, toxemia, viremia  Mixed infection Several infectious agents concurrently establish themselves at the same site  Patterns of Infection (continued)  Acute infection Appear rapidly, with severe symptoms, then vanish rapidly  Chronic infection Usually less severe symptoms, but they persist for long periods of time  Primary infection Initial infection  Secondary infection Follows primary infection, typically caused by different microbe than what caused primary infection  Subclinical infection Does not cause any apparent symptoms Can be carried over long periods of time  Epidemiology and Public Health  Epidemiology is the study of the distribution and cause of disease in populations  It serves as the foundation and logic of interventions needed in the interest of public health and preventive medicine  How many people are affected, where, the outcome of the disease (recovery, death, disability, and so on)  Epidemiology  Major importance to public health departments  Public Health Agency of Canada https://www.canada.ca/en/public-health.html  CDC is the central source of epidemiological information in the United States  Morbidity and Mortality Weekly Report (www.cdc.gov) Contains data on morbidity, incidence of specific notifiable diseases, mortality  Diseases in the Population  Can be reported by the prevalence of the disease Total number of existing cases in the entire population  By incidence The number of new cases over a certain period of time compared with the general healthy population  Changes in prevalence and incidence of diseases are generally monitored seasonally and longer  Disease Categories  Endemic disease Repeatedly present in a given population or geographical area  Sporadic disease Breaks out only occasionally  Epidemic disease Occurs with greater frequency than usual in a population of a given area  Pandemic disease Is a worldwide epidemic  Reservoirs  For an infection to continue to exist, its causative agent(s) must have a permanent place to reside  Sites where pathogens are maintained and are a source of infection are called reservoirs of infection  1. Nonliving reservoirs Include soil, water, food Soil is a great environment for pathogens, such as fungi, helminths, and bacteria  Reservoirs (continued)  2. Animal reservoirs Diseases that occur primarily in animals and can be transmitted to humans are called zoonoses Routes of zoonoses Direct contact with the infected animal Contact with animal waste Contaminated food or water Dust from contaminated hides, fur, or feathers By consuming infected animal products By insect vectors  3. Human carriers Main reservoir for human infectious agents = human body Infected but don’t have symptoms—carriers (able  Modes of Transmission  Infectious diseases By a reservoir or a portal of exit to a portal of entry of another host Autoinoculation  Infectious agents Contact transmission Vehicle transmission Vector transmission  Contact Transmission  Direct contact Direct physical contact of the pathogen between hosts without an intermediate object Person-to-person by touching, kissing, sexual intercourse Examples: Respiratory tract infections, staphylococcal infections, measles, scarlet fever, sexually transmitted diseases  Contact Transmission (continued)  Indirect contact Pathogen is transmitted by a fomite (nonliving object) Examples: Tissues, handkerchiefs, towels, bedding, toys, clothes, diapers, eating utensils, drinking cups, medical equipment and devices  Droplet transmission Infectious agents are transmitted via respiratory droplets Released by normal exhaling, laughing, coughing, or sneezing Sneezing is the most effective form  Vehicle Transmission  Requires some sort of medium  Airborne By droplet nuclei (droplets of mucous) Other aerosols Dust—via sweeping, mopping, changing bed linens, changing clothes, simple dusting Must travel more than 1 meter to be considered airborne transmission  Bodily fluid Especially healthcare workers—precautions when handling fluids that potentially can be contaminated with pathogens Blood, urine, saliva, and other bodily fluids  Vehicle Transmission (continued)  Waterborne Through untreated or poorly treated sewage Gastrointestinal diseases—giardiasis, amebic dysentery, cholera Water-borne shigellosis and leptospirosis Pathogens shed in fecal material can enter GI tract mucosa or skin and cause disease in other areas of the body  Foodborne Incompletely cooked foods; poorly processed foods; or foods prepared under unsanitary conditions, not refrigerated or poorly refrigerated Contamination by normal flora, with zoonotic pathogens or parasitic worms  Vector Transmission  Animals, especially arthropods  Biological vectors Transmit pathogen, but also serve as host for a part of the pathogen’s life cycle Biting insects, including mosquitoes, ticks, lice, fleas, blood-sucking flies or bugs, mites  Mechanical vectors Passively carry agents to a new host by their feet or other bodily parts (e.g. flies)  Vaccinations  Most effective method of preventing infectious diseases  Health Canada provides information on vaccine preventable diseases (26 as of 2-3-2023) https://www.canada.ca/en/public- health/services/diseases.html?vaccine-preventable  CDC’s Global Immunization Division (GID) Public health mission to vaccinate against deadly diseases  Prevent epidemics and pandemics  Eradicated smallpox and polio  Healthcare-Associated (Nosocomial) Infections  Acquired as a result of treatments in a hospital or hospital-like setting but are secondary to the patient’s original condition  According to the Canadian Nosocomial Infection Surveillance Program, in Canadian hospitals from 2016 to 2020, MRSA bloodstream infections increased 33% and VRE bloodstream infections increased 72%)  HAIs (healthcare-associated infections) are among the top 10 leading causes of death in the United States  Types of Nosocomial Infections  Healthcare facilities are filled with sick people capable of shedding a variety of pathogens from different ports of exit  People often have stressed, weakened, compromised/suppressed immune systems  Are more susceptible to pathogens or opportunistic organisms  Types of HAIs Exogenous  Caused by pathogens in the healthcare environment  Shed by sick people Endogenous  Caused by microbes in the normal flora of the patient  Become pathogenic due to a variety of factors Immune system decline Antimicrobial drugs Overgrowth and superinfections can occur  Iatrogenic HAIs  May result from the use of medical procedures, such as the use of catheters, invasive diagnostic procedures, and surgery  Transmission of HAIs  Principal routes Direct contact transmission from hospital staff to patient Visitors and patients Patient to patient via activities of staff Indirect contact transmission through fomites Airborne transmission through the ventilation system  Antimicrobial Resistance in Healthcare Settings  Drug-resistant pathogens are becoming an increasing threat  More than 70% of the bacteria causing these infections are resistant to at least one of the drugs commonly used to treat them  Control and Prevention  Each facility has safety programs, policies, and procedures  Aimed to prevent transmission of pathogens  Blood-borne pathogen training  Proper hand washing and other good housekeeping  Infection control committee in all accredited hospitals