Microbiology and Infection Practice Flashcards

Fundamentals of Microbiology and Microorganisms

A microorganism, or microbe, is defined as an individual living animal or plant that is so small it can be seen only with the aid of a microscope. The vast majority of microorganisms do not cause disease under normal physiological conditions. Organisms that are present all or most of the time in and on the human body are classified as endemic microorganisms. Microbiology is defined as the scientific study of microorganisms, whereas pathogens are specifically identified as harmful or disease-producing microorganisms.

Microorganisms exhibit five primary biological characteristics: metabolism, reproduction, irritability, motion, and protection. Metabolism is defined as the ability to utilize nutrients. Reproduction refers to the ability to form colonies or individual cells in order to grow larger. Irritability represents the organism's response to its environment. Motion is the capacity to move from place to place. Protection refers to survival and adaptive mechanisms such as mutation.

Requirements for Microbial Growth and Laboratory Culturing

Microbial growth depends on specific environmental conditions including oxygen, nutrient availability, temperature, moisture, pH, and light exposure. Oxygen requirements vary among organisms: obligate aerobes require oxygen for growth, whereas obligate anaerobes cannot survive in the presence of oxygen. Microbial growth necessitates the presence of organic nutrients and other chemical elements. Parasites are microorganisms that live on or within a host organism, whereas saprophytes live off the organic remains of dead plants and animals.

Temperature and environmental moisture play pivotal roles in microbial survival. The optimal temperature for most pathogenic microorganisms corresponds to normal human body temperature. Cold temperatures slow or inhibit microbial growth, whereas extreme hot temperatures actively kill microorganisms. In terms of moisture, the matter in or on which all microorganisms grow must contain available moisture or be in a liquid state. Regarding pH, microorganisms generally survive in environments with a pH that is neither excessively acidic nor excessively alkaline. Light requirements vary; while some microorganisms require light for growth, others flourish in darkness. Furthermore, many microorganisms are destroyed when exposed to the sun's ultraviolet (UV) rays.

Microbiologists grow microbes, termed cultures, under controlled laboratory conditions to determine ways to arrest their growth. Cultures are typically cultivated inside test tubes or Petri dishes containing a culture medium. Solid media contain agar, whereas liquid media are classified as nutrient broths. All culture media must start out sterile. Clinical diagnosis often utilizes a Culture and Sensitivity (C+S) test, which is ordered when an infection is suspected or known. The C+S test serves three crucial clinical purposes: identifying the specific pathogenic microorganism, determining which treatment will eliminate the microorganism, and monitoring the microorganism's response to therapy.

Structural Classification and Types of Microorganisms

Every organism is named using a two-part nomenclature system consisting of a genus name and a species name. The genus name refers to a general grouping, while the species name defines a biologically unique category. For example, Escherichia coli (E. coli) is a species found in the colon. Microorganisms are broadly categorized as either eukaryotes or prokaryotes. Organisms with a true nucleus enclosed by a nuclear membrane and containing chromosomes that divide by mitosis are called eukaryotes. Eukaryotic organisms include plants, animals, protozoa, fungi, and most algae. Conversely, prokaryotes include bacteria and cyanobacteria.

Algae are photosynthetic organisms that require sunlight and water to thrive, assist within photosynthesis, and rarely cause disease in humans. Fungi represent another eukaryotic group; an infection caused by a fungus is termed a mycosis or mycotic infection, and the study of fungi is known as mycology. Fungi encompass both yeasts and molds. Yeasts are single-celled organisms that reproduce by budding, a process requiring sugar. Candida albicans is a pathogenic yeast responsible for thrush. Molds are multicellular organisms common in the environment that grow best at room temperature. An infection caused by molds includes histoplasmosis, which affects the lungs.

Protozoa are single-celled eukaryotic microorganisms that are distinct from bacteria. Protozoa can reproduce sexually and survive in moist environments. Common non-pathogenic protozoa include amoebas and paramecia. Pathogenic protozoa are responsible for conditions such as amoebic dysentery, malaria, and trichomoniasis ("Trich").

Bacterial Anatomy, Cytology, and Genetics

Many of the microbes studied in relation to illness are in the scientific category known as prokaryotes. Prokaryotes are divided into two distinct categories: Archaea and Bacteria. Prokaryotes can live in environments where eukaryotes cannot live. Anatomically, prokaryotes are very small organisms that possess a rigid cell wall but no nucleus. The cell architecture of a prokaryote consists of three main regions: the cell envelope, appendages, and the cytoplasmic region containing genetic material (DNA and RNA).

The bacterial cell envelope consists of the capsule, surface components, the cell wall, and the plasma membrane. Cell wall structural differences dictate Gram staining characteristics: Gram-positive (+) bacterial cell walls allow stain retention, holding onto the stain and turning purple, whereas Gram-negative (-) bacteria do not hold the stain, appearing thin and pink. Appendages include flagella and fimbriae or common pili. Flagella enable tactic behavior, allowing the organism to move toward or away from stimuli such as light (phototaxis). Fimbriae and common pili are short, hair-like projections that provide bacteria with a better ability to adhere to target cells. The cytoplasmic region contains chromosomes, ribosomes, and inclusion materials reserved for later use, such as fat.

Bacterial Classification, Reproduction, and Pathogenicity

Bacteria may be classified according to their flagella, shape, motility, Gram stain result, and relationship to oxygen, although these characteristics do not always separate organisms cleanly. Morphologically, a round or spherical bacterium is called a coccus (plural: cocci). A rod-shaped bacterium is known as a bacillus (plural: bacilli). A spiral-shaped bacterium has the name spirillum (plural: spirilla or spirochete). Common morphological arrangements include diplococci, staphylococci, streptococci, bacilli, and spirilla or spirochetes.

Bacteria reproduce and transfer genetic material through three processes: conjugation, transduction, and transformation. Conjugation involves direct cell-to-cell contact where DNA crosses a sex pilus to the new cell. Transduction occurs when genes are transferred by a virus. Transformation involves DNA acquired directly from the environment after being released by another cell. When conditions are unfavorable to their growth, certain bacteria develop a spore and go into a dormant phase, allowing them to survive extreme conditions. All pathogenic bacteria die at water's boiling point except for spore formers.

To be pathogenic, bacteria must possess the ability to colonize and invade the host, resist or endure to withstand antibacterial defenses, and form substances that are toxic to the host. Examples of pathogenic bacteria include Neisseria gonorrhoeae (causes gonorrhea), Rickettsia rickettsii (causes Rocky Mountain spotted fever), and Streptococcus pneumoniae (causes pneumonia).

Virology and Common Viral Agents

Viruses are non-cellular agents that rely on the host to survive. Structurally, viruses are protein-covered sacs containing genetic material in the form of either DNA or RNA, along with other organic materials. When a virus enters the cell of a living organism, the host cell becomes a culture medium for viral reproduction.

Examples of viruses include poxviruses, adenoviruses, and picornaviruses. Poxvirus causes smallpox. Adenovirus causes conjunctivitis. Picornavirus causes the common cold and upper respiratory infections.

Antimicrobial Resistance and Healthcare-Associated Infections

The most common method of development of antimicrobial-resistant microorganisms occurs when invading microorganisms survive exposure to antimicrobial drugs and transfer their resistance to future generations. To prevent the development of drug-resistant microorganisms, clients must take antimicrobial drugs only as prescribed for the entire period prescribed, discuss the necessity of antibiotics for mild infections with healthcare providers, never share antimicrobial drugs with others, and never use antibiotics for viral infections, as antibiotics do not treat viral infections such as colds and flu.

Risk factors for clients in healthcare facilities developing resistant infections include a compromised immune system, a break in the skin, the presence of a central or peripheral IV catheter, invasive medical procedures, serious underlying disorders, previous exposure to antimicrobial drugs, repeated hospitalizations, very old age or very young age, and previous infections by multidrug-resistant organisms.

Organisms and situations that cause Healthcare-Associated Infections (HAIs) include Methicillin-resistant Staphylococcus aureus (MRSA, including golden staph, healthcare-associated HA-MRSA, and epidemic EMRSA), Vancomycin-resistant enterococci (VRE, such as Clostridium difficile, also known as C. difficile), Penicillin-resistant Streptococcus pneumoniae (PRSP), the virus causing Severe Acute Respiratory Syndrome (SARS), Extended-spectrum $\beta$-lactamases (ESBLs, which are resistant to cephalosporins), New Delhi metallo-$\beta$-lactamase (NDM, made by gram-negative organisms such as Escherichia coli and Klebsiella pneumoniae), and Carbapenem-resistant Klebsiella pneumoniae (CRKP or CRYP).

Etiology, Infectious Diseases, and the Chain of Infection

Etiology is defined as the specific cause of disease. An infectious disease is a disease caused by pathogenic microorganisms that increase in number and produce clinical symptoms of illness. Many infectious diseases are communicable. An epidemic occurs when a large number of people in the same area are infected in a relatively short time.

Diseases spread if the Chain of Infection remains unbroken. The Chain of Infection contains six sequential links: causative agent, reservoir, portal of exit, vehicle of transmission, portal of entry, and susceptible host.

The causative agent is the pathogenic microorganism itself. The reservoir is any place where a pathogen can survive before moving to another place where it can multiply, which may be living beings or inanimate objects. Ways to break the chain at the reservoir level include standard precautions, sterilizing items, disinfecting, using single-use items, properly discarding disposable equipment, changing dressings when needed, using biohazard bags and sharps containers, using personal protective equipment (PPEs), and performing frequent and thorough handwashing.

The portal of exit is the route by which the pathogen escapes from the reservoir, including all body orifices and natural body fluids. Ways to break the chain at the portal of exit include handwashing, appropriate waste disposal, careful management of secretions and drainage, standard precautions, avoiding talking, sneezing, or coughing over open wounds or sterile fields, wearing masks, and implementing infection controls or isolation.

The vehicle of transmission is the means by which the pathogen moves to a new host, including direct contact, indirect contact, human carriers, airborne transmission, foodborne transmission, waterborne transmission, and vectors.

The portal of entry is the place where the pathogen gains access to the new host, entering through the respiratory, gastrointestinal, urinary, or reproductive systems, or through breaks in the skin or mucous membranes. Common entry sites include open wounds, surgical incisions, injection puncture sites, and body orifices into which catheters are inserted. Ways to break the chain at the portal of entry include standard precautions, keeping skin clean and dry, applying moisturizers, proper manicure and pedicure care, proper positioning, proper linen management, keeping urine collection bags lower than the client, disinfecting as needed, covering wounds, and utilizing sterile technique.

The susceptible host is an individual whose body defenses are inadequate to resist infection, with ill or inactive people being more susceptible. Risk factors increasing host susceptibility include chronic fatigue, poor nutrition, injury, shock, trauma, medication side effects, emotional factors, and extreme age (infants, young children, and older adults). Ways to break the chain at the susceptible host level include treating underlying conditions, providing adequate rest and skin care, offering nutritional support, reducing anxiety, encouraging adequate fluid intake, promoting coughing and deep breathing, administering immunizations, and practicing infection control.

Pathogen Toxins, Stages of Infection, and Host Susceptibility

Toxins cause harmful effects in the host body by traveling through the circulatory system to damage other body cells. Endotoxins are structural parts of the cell walls of gram-negative bacteria; when the microorganism dies, the cell wall decays and releases the toxins. Exotoxins are toxins manufactured directly by the microorganism and excreted into the surrounding tissue.

The normal course of an infection follows four distinct stages: incubation, prodromal, full stage, and convalescence. The incubation period is the time from when the pathogen enters the body to the appearance of the first symptoms of illness. The prodromal stage is the period from the onset of initial symptoms to more severe symptoms. The full stage of infection occurs when symptoms are acute and specific to the type of infection. Convalescence is the stage during which the acute symptoms of the infection subside and the person recovers.

Several factors other than the strength of the body's natural defenses determine whether disease-causing microorganisms will ultimately cause an infection: the specific portal of entry, the number of microorganisms, the virulence (pathogen strength), and host resistance.