Microbiology and Infection Control Flashcards

Introduction to Pathogens and Microorganisms

• Pathogen Definition: Microorganisms that cause infection or disease in human hosts. They are microscopic and cannot be seen without a microscope.

• Non-Pathogenic Microorganisms: Microorganisms entering or residing in the body daily that do not cause disease or clinical infection.

• Normal Flora (Microbiome):

  • Definition: Beneficial microorganisms that reside naturally in and on the human body, particularly concentrated within the gastrointestinal tract and skin.

  • Functions: Essential for human health; protects against invasive pathogens, assists in breaking down and digesting food, and actively fights off infections.

  • Colloquial Term: Frequently referred to as "good bacteria."

• Primary Categories of Pathogens:

  • Bacteria: Single-celled (one-celled) microorganisms capable of independent replication. Treatable with antibiotics.

  • Viruses: Sub-cellular parasitic entities that require a host cell to replicate. Antibiotics are completely ineffective against viral infections.

• Antibiotic Overprescribing and Drug Resistance:

  • Cause: Antibiotics are frequently overprescribed for non-bacterial presentations (e.g., green nasal discharge or snot, which does not inherently denote a bacterial infection).

  • Consequence: Inappropriate administration fosters the development of Multiple Drug-Resistant Organisms (MDROs) such as Methicillin-Resistant Staphylococcus aureus (MRSA) and Vancomycin-Resistant Enterococcus (VRE), leaving clinicians with diminished therapeutic options.

• Morphological Classification of Bacteria:

  • Cocci (or Coccyx): Sphere-shaped bacteria. Example: Staphylococcus aureus (Staph aureus), which lives as normal flora on human skin.

  • Bacillus: Rod-shaped bacteria. Example: Escherichia coli (E. coli), the primary etiology of urinary tract infections (UTIs).

  • Spirillum (Perinulum): Spiral-shaped bacteria (e.g., vectors associated with viral/gastrointestinal conditions such as Chorion).

• Characteristics and Reproduction of Viruses:

  • Definition: Extremely minute microscopic parasites that enter a host cell, feed off host cellular resources, and reproduce internally.

  • Endemicity: Non-endemic to the human body (they do not naturally inhabit human tissues; they originate from external sources and always retain the potential to cause disease).

  • Antiviral Pharmacotherapy: Very few antiviral agents exist (e.g., specific formulations for Influenza, Herpes Simplex, and HIV).

  • Mechanism of Action: Antivirals do not cure viral infections; they function exclusively by halting viral cell reproduction and replication.

  • Administration Window: Antivirals such as Oseltamivir (Tamiflu) must be initiated within the first $2 - 3\,\text{days}$ of symptom onset to effectively arrest viral replication and decrease viral load/symptoms.

• Gram Staining Classification:

  • Procedure: Microscopic evaluation following application of crystal violet/safranin stains to determine bacterial cell wall composition, directly guiding targeted antibiotic selection.

  • Gram-Negative Bacteria: Retains safranin counterstain, appearing pink under microscopic evaluation.

  • Gram-Positive Bacteria: Retains crystal violet stain, appearing purple under microscopic evaluation.

Specific Pathogen Classifications and Bacterial Diseases

• Protozoa: Single-celled animal organisms typically found in water environments. Treated using antiparasitic medications. Example: Trichomonas (a sexually transmitted infection / STI).

• Fungi: Single-celled or multicellular organisms. Treated with antifungal agents available in topical creams, ointments, oral preparations, or intravenous (IV) formulations. Example: Yeast infections (Candida).

• Helminths: Parasitic worms that inhabit the gastrointestinal (GI) tract. Treated with anthelmintic/antiparasitic medications or select antibiotics. Example: Tapeworms, which can be acquired through the consumption of undercooked fish (e.g., sushi) or undercooked meats.

• Staphylococcus (Staph):

  • Properties: Gram-positive, sphere-shaped bacteria (cocci) naturally residing on intact human skin. Breaches in skin integrity allow staph to enter deeper tissues and cause active infection.

  • Associated Clinical Conditions: Boils, Toxic Shock Syndrome (often associated with prolonged tampon retention), Osteomyelitis, and MRSA.

  • MRSA Characteristics: A major healthcare-associated (nosocomial) pathogen. Most strains are resistant to standard penicillin and conventional antibiotics.

  • Treatment: Requires select IV antibiotics, with IV Vancomycin serving as the primary first-line intervention.

• Streptococcus A (Group A Strep):

  • Properties: Gram-positive bacteria.

  • Associated Clinical Conditions: Strep throat, Otitis media (middle ear infection), Scarlet fever, Endocarditis, Rheumatic fever, heart valve damage, acute kidney damage, and Necrotizing fasciitis (a rare, flesh-eating strain leading to rapid tissue death).

  • Treatment Protocol: Requires a full $10\,\text{day}$ course of targeted oral antibiotics. Inadequate treatment compliance can lead to scarlet fever, rheumatic endocarditis, and acute heart failure.

• Streptococcus B (Group B Strep):

  • Properties: Gram-positive bacteria.

  • Associated Clinical Conditions: Neonatal infections (especially prevalent in premature births), including neonatal pneumonia, meningitis (inflammation of the meninges in the brain), and neonatal septicemia.

  • Screening: Pregnant mothers undergo routine Group B Strep screening (Pre-B swab) around $32 - 33\,\text{weeks}$ of gestation.

  • Treatment: Managed via IV antibiotic administration.

• Clostridium Species:

  • Properties: Gram-positive, spore-forming bacillus (rod-shaped). Highly resilient and difficult to eradicate. Spores resist alcohol-based hand rubs; effective decontamination requires physical handwashing using soap and hot water.

  • Gas Gangrene: Clostridial spores colonize necrotic tissue, releasing exotoxins that destroy adjacent healthy tissue. Bacterial gas production creates visible gas bubbles within green, necrotic tissue, producing a foul odor. Frequently necessitates surgical limb amputation.

  • Clostridium difficile (C. diff): Causes severe, profuse diarrhea (defined as $30\,\text{or more bowel movements per day}$) characterized by a distinct, highly recognizable odor detectable across long distances.

  • Etiology & Nosocomial Risk: Highly nosocomial; secondary to broad-spectrum IV antibiotic therapy that eradicates normal intestinal bacterial flora.

  • Treatment: Managed with select agents, primarily oral Vancomycin or Metronidazole (an agent with antifungal/antiprotozoal and antibacterial activity).

Gut Microbiome, Enteric Pathogens, and Systemic Viruses

• Preserving Gut Microbiome during Antibiotic Therapy:

  • Potent antibiotic regimens destroy both target pathogens and normal intestinal bacterial flora.

  • Dietary Interventions: Patients should be encouraged to consume yogurt containing live active probiotic cultures (e.g., with breakfast) to restore gut flora.

  • Pharmacological Probiotics: Probiotic supplements (e.g., Culturelle) require a formal healthcare provider prescription/order.

• Escherichia coli (E. coli):

  • Normal Habitat: Natural inhabitant of the human colon/large intestine.

  • Pathological Infections: Leading cause of nosocomial Urinary Tract Infections (UTIs), particularly in female patients due to anatomical proximity of the urethra to the anus, improper hygiene wiping technique (wiping back-to-front instead of front-to-back), and indwelling Foley catheter usage. Indwelling catheters should be removed as early as clinically feasible.

  • Pathogenic Strains (E. coli O157:H7 / pathogenic genomes): Causes severe colon infection, bloody diarrhea, and Hemolytic Viremic Syndrome (Hemolytic Uremic Syndrome), which can precipitate fatal acute renal failure. Associated with eating undercooked ground beef. Treated with antibiotics and intensive supportive care for renal failure.

• Mycobacterium tuberculosis (TB):

  • Pathophysiology: Destroys pulmonary tissue, leaving large cavitary lesions and holes within the lungs.

  • Treatment Compliance: Requires combination multi-drug antibiotic regimens (typically $3 - 5\,\text{antibiotics}$ daily) taken for $6 - 12\,\text{months}$ (up to $1\,\text{year}$). High rates of patient non-compliance directly drive the emergence of multi-drug-resistant TB strains.

• Borrelia:

  • Vector & Pathogenesis: Transmitted from deer ticks to humans, causing Lyme disease.

  • Symptoms: Flu-like illness, cardiac dysrhythmias (irregular heartbeat), and secondary chronic arthritis.

  • Treatment: Antibiotic therapy initiated early in the course of infection.

• Rickettsia:

  • Vector & Pathogenesis: Transmitted via tick vectors, causing Rocky Mountain Spotted Fever.

  • Symptoms: High fever, petechial rash, pneumonia, and potential systemic fatality.

  • Treatment: Prompt administration of targeted antibiotics.

• Viral Pathogens and Manifestations:

  • Herpes Simplex Virus Type 1 (HSV-1): Causes fever blisters and cold sores, typically localized above the waist, though capable of spreading below the waist.

  • Herpes Simplex Virus Type 2 (HSV-2): Causes genital herpes lesions, localized below the waist.

  • Varicella-Zoster Virus (HHV-3): Initial exposure contracts Varicella (chickenpox). The virus subsequently lies dormant in neural tissue. Reactivation in older adults or immunocompromised/stressed states causes Herpes Zoster (Shingles).

  • Shingles Features: Unilateral, intensely painful, burning vesicular lesions distributed along specific dermatomal nerve pathways (e.g., belt line, rib cage, spine).

  • Antiviral Therapy: Oral or topical Acyclovir is prescribed for HSV-1, HSV-2, and Varicella-Zoster/Shingles.

  • Influenza (Flu): Characterized by myalgias (aching muscles), high fever, upper respiratory congestion, and cough. Managed with antivirals like Tamiflu (oseltamivir), which halt viral replication if administered within $2 - 3\,\text{days}$ of symptom onset.

  • Zika Virus: Transmitted by mosquito vectors; capable of vertical transmission from an infected mother to an unborn fetus. Symptoms include fever, headache, joint pain, and myalgias. Managed with supportive care, hydration, and antipyretics ($\text{pyro} = \text{fire/hot}$; antipyretics like acetaminophen/Tylenol or NSAIDs/ibuprofen lower body temperature).

  • Ebola Virus: Highly lethal virus transmitted through contact with infected blood, body fluids, or large respiratory droplets. Symptoms include severe diarrhea, bloody diarrhea, vomiting, fever, headache, profound fatigue, muscle weakness, and frank hemorrhage from mucous membranes and bodily orifices (eyes, ears, etc.). Treatment is strictly supportive (IV fluid/electrolyte replacement and maintaining $O_2$ saturation).

  • West Nile Virus: Avian reservoir transmitted to humans via mosquitoes. Causes headache, acute confusion, and fever in symptomatic individuals, though many hosts remain asymptomatic. Managed via supportive care.

• Fungal Pathogens:

  • Microsporum (Tinea Infections): Causes Ringworm and Athlete's Foot (Tinea pedis, Tinea capitis, Tinea corporis). Characterized by itchy, red-brown, circular patches on the skin and scalp. Treated with topical or oral antifungals (many available over-the-counter).

  • Candida (Yeast):

  • Thrush: Oral Candida manifestation displaying white, cottage cheese-like plaques on the tongue and oral mucosa.

  • Vaginal Candidiasis: Proliferates when broad-spectrum antibiotics destroy normal protective vaginal bacterial flora.

  • Systemic Complications: Can progress to severe fungal pneumonia and endocarditis if left untreated.

  • Treatment: Antifungal agents such as Nystatin.

Parasitic Organisms, Infection Chains, and Host Defenses

• Protozoan Pathogens:

  • Amoeba: Causes amoebic dysentery, resulting in severe bloody diarrhea. Capable of forming systemic abscesses in major internal organs including the liver, lungs, and brain. Treated with amoebicides and antibiotics.

  • Giardia: Causes giardiasis (severe watery diarrhea). Transmitted via unfiltered water sources or food prepared by infected individuals with inadequate hand hygiene. Treated with antibiotics.

  • Plasmodium: Transmitted via mosquitoes, causing malaria. Destroys red blood cells leading to severe anemia and cerebral malaria affecting the brain. Treated with antimalarial drugs.

• Helminthic Parasites:

  • Enterobius (Pinworms): Small, white, thread-like worms inhabiting the lower GI tract/intestines. Most common parasitic worm infection in the United States. Visible in host stool. Treated with anthelmintics.

  • Taenia (Tapeworms): Transmitted via ingested cysts in undercooked meat or fish. The worm's head (scolex) attaches to the intestinal mucosa using suckers and hook-like teeth, growing in linked segments. Causes bloody diarrhea, nutrient deprivation, and physical crawling sensations in the abdomen. Treated with anthelmintics.

• The Chain of Infection:

  1. Infectious Agent: The primary pathogen causing disease.

  2. Reservoir: The habitat or host where the pathogen lives and multiplies.

  3. Portal of Exit: The site through which the pathogen leaves the reservoir (e.g., mouth, respiratory tract, GI tract).

  4. Mode of Transmission: The mechanism by which the pathogen travels to a new host (e.g., droplets, direct contact).

  5. Portal of Entry: The site through which the pathogen enters a new host (most commonly the mouth).

  6. Susceptible Host: An individual lacking immunity in whom the pathogen can establish infection.

• Classification of Infection Types:

  • Healthcare-Associated Infections (HAIs / Nosocomial): Infections acquired within healthcare facilities (e.g., catheter-associated UTIs, central line-associated bloodstream infections, hospital-acquired pneumonia, MRSA).

  • Primary Infection: The initial localized or systemic infection caused by a primary pathogen.

  • Secondary Infection: A subsequent infection caused by a different pathogen invading while host defenses are weakened from the primary illness (e.g., contracting a GI virus following influenza).

  • Localized Infection: An infection restricted strictly to one anatomical site.

  • Systemic Infection: An infection that has disseminated throughout the bloodstream or entire human body.

• Primary Lines of Defense:

  • Intact Skin: The largest organ of the body; serves as the primary physical barrier against microbial invasion.

  • Mucous Membranes: Line body cavities open to the environment (mouth, nose, vagina), producing sticky mucus that traps invading microorganisms.

  • Gastrointestinal System: Contains gastric acid and normal resident flora that inhibit foreign pathogen growth.

• Secondary Lines of Defense:

  • Inflammatory Response: Tissue injury triggers white blood cells to release histamine, inducing local vasodilation, hyper-permeability, localized warmth, and redness. Redness and warmth reflect active white blood cell recruitment to destroy invaders.

  • Phagocytosis: Specialized phagocytic white blood cells engulf and digest ($\text{phago} = \text{eating}$) foreign microbial invaders.

  • Fever (Elevated Body Temperature): Creates a hostile, hyperthermic environment ($104^\circ\text{F}$) that inhibits pathogen replication. Low-grade fevers ($99^\circ\text{F} - 100^\circ\text{F}$) represent natural protective immune responses that should not be automatically suppressed unless causing severe dehydration, dizziness, or intense discomfort.

  • Complement Cascade: Specialized plasma proteins identify foreign antigens, attach to pathogen cell membranes, create perforations/holes, allowing fluid influx that causes the cell to swell and undergo osmotic lysis (rupture).

• Tertiary Lines of Defense:

  • Specialized Lymphocytes:

  • T-Cells: Originate and mature in the Thymus gland. Present at birth, the thymus progressively shrinks (involutes) with age, causing diminished cell-mediated immunity in older adults.

  • B-Cells: Originate and mature within the Bone Marrow.

  • Antigen-Antibody Response: T and B lymphocytes scan surface antigens on cell membranes to differentiate "self" from "non-self," signaling phagocytes to seek and destroy non-self invaders.

Immunological Risk Factors and Infection Control Practices

• Factors Decreasing Host Defenses:

  • Age Extremes: Neonates/infants (immature, underdeveloped immune systems) and older adults (thymic involution, diminished physiological reserves).

  • Chemical Exposure: Environmental or chemical toxicity impairs immune response capacity.

  • Chronic Illness: Depletes immune reserves through persistent, low-grade systemic inflammation.

  • Lack of Exercise: Slows blood circulation and reduces lymphatic fluid movement through lymph nodes, impairing pathogen destruction.

  • Lack of Rest/Sleep: Deprives the body of cellular repair and energy restoration, increasing susceptibility to infection.

  • Elevated Stress: Chronic psychological stress elevates systemic cortisol levels (the primary stress hormone), suppressing active immune function.

  • Non-Intact Skin: Surgical wounds, skin tears, pressure ulcers, IV access sites, and venipunctures breach primary barriers, creating direct portals of entry.

  • Poor Nutrition: Malnutrition and lack of essential fruits, vegetables, and calcium-rich dairy compromise cellular defenses and normal flora balance.

• Infection Control Practices and Asepsis:

  • Standard Precautions: Fundamental safety measures applied to ALL patients across healthcare settings to prevent pathogen transmission from blood, body fluids, secretions, excretions, non-intact skin, and mucous membranes. Mandates basic hand hygiene and glove application.

  • Medical Asepsis ("Clean Technique"): Measures performed to reduce overall pathogen counts and prevent transmission (e.g., hand hygiene, clean gloves for non-sterile procedures like NG tube insertion, clean patient environment).

  • Surgical Asepsis ("Sterile Technique"): Rigorous practices designed to completely eliminate all microorganisms and spores from an area or equipment (e.g., $15\,\text{minute}$ surgical scrub, sterile gloves, sterile fields).

  • Mandatory Indications for Hand Hygiene:

  • After touching blood, body fluids, secretions, excretions, or contaminated items.

  • Immediately upon removing gloves.

  • Prior to touching a patient, invasive lines, or urinary catheters.

  • Between caring for separate patients in a shared room.

  • Upon arriving at or leaving a clinical nursing unit, break area, or meal station.

  • Prior to eating meals.

  • After using restroom facilities.

  • Whenever hands are visibly soiled.

• Transmission-Based Isolation Precautions:

  • Airborne Precautions: Indicated for microscopic, lightweight pathogen particles that remain suspended in ambient air for long durations (e.g., Mycobacterium tuberculosis, Varicella/chickenpox). Mandates negative-pressure isolation rooms and N95 respirator masks.

  • Droplet Precautions: Indicated for heavy respiratory droplets that travel approximately $30\,\text{feet}$ through the air via coughing or sneezing (e.g., Influenza). Mandates surgical masks, eye protection, and UV light wall disinfection.

  • Contact Precautions (Direct & Indirect): Indicated for pathogens transmitted via direct physical contact with an infected patient or indirect contact with contaminated environmental surfaces/fomites (e.g., enteric viruses, C. diff). Mandates gowns and gloves.

• Psychological Care for Isolated Patients:

  • Isolation produces significant psychological confinement, anxiety, and sensory deprivation.

  • Healthcare staff should dedicate time to converse with isolated patients, offer crosswords or recreational activities, and avoid expressing distaste or frustration regarding PPE protocols or entering isolation rooms.

  • Staff must recognize that while healthcare workers depart at shift end, isolated patients remain confined within their rooms continuously for days, weeks, or months.