Bacterial Classification and Gram Stains
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Questions and Answers

Which of the following groups of bacteria thrives in cold environments?

  • Thermophiles
  • Mesophiles
  • Psychrophiles (correct)
  • Capnophiles

What is the name given to the time required for bacterial cells to double in number?

  • Binary fission time
  • Doubling time
  • Generation time (correct)
  • Replication time

What type of environment would bacteria that require oxygen for growth be classified as?

  • Microaerophiles
  • Obligate anaerobes
  • Facultative anaerobes
  • Obligate aerobes (correct)

What type of environment would a bacterium be growing in if the solute concentration is higher outside the cell than inside?

<p>Hypertonic (C)</p> Signup and view all the answers

Which of these chemical requirements is NOT a key element needed for bacterial growth?

<p>Potassium (C)</p> Signup and view all the answers

Which type of bacteria would struggle to grow in the presence of oxygen?

<p>Obligate anaerobes (D)</p> Signup and view all the answers

What type of environment is best suited for medically important bacteria?

<p>Neutral (C)</p> Signup and view all the answers

Which of the following is a characteristic of bacteria that can grow with or without oxygen?

<p>Facultative anaerobes (C)</p> Signup and view all the answers

What is the function of the coagulase enzyme produced by Staphylococcus bacteria?

<p>Binds plasma fibrinogen to form a clot. (C)</p> Signup and view all the answers

Which characteristic is particularly associated with Staphylococcus aureus?

<p>Golden coloration on culture media. (C)</p> Signup and view all the answers

Which of the following is NOT considered a virulence factor of Staphylococcus aureus?

<p>Catalase (A)</p> Signup and view all the answers

Which condition is associated with a heat-stable enterotoxin produced by Staphylococcus aureus?

<p>Food poisoning. (C)</p> Signup and view all the answers

What is the main route of transmission for Staphylococcus aureus food poisoning?

<p>Consumption of improperly stored meat or milk products. (B)</p> Signup and view all the answers

Scalded skin syndrome, caused by Staphylococcus aureus, is characterized by which of the following symptoms?

<p>Blisters and erythema with sloughing of the skin. (B)</p> Signup and view all the answers

Which of these conditions is associated with tampon use?

<p>Toxic Shock Syndrome. (D)</p> Signup and view all the answers

What role does hyaluronidase play in the virulence of Staphylococcus aureus?

<p>It dissolves tissues. (A)</p> Signup and view all the answers

What is the Gram stain and shape of Staphylococcus bacteria?

<p>Gram-positive cocci. (D)</p> Signup and view all the answers

Which of the following describes the action of the enzyme catalase?

<p>Breaks down hydrogen peroxide. (B)</p> Signup and view all the answers

Which of the following is a characteristic of alpha-hemolytic bacteria on blood agar?

<p>Green or brown discoloration around colonies. (A)</p> Signup and view all the answers

A patient presents with a sore throat, fever, and a rash. Which bacterium is most likely the causative agent?

<p>Streptococcus pyogenes (B)</p> Signup and view all the answers

A newborn is diagnosed with meningitis and sepsis. Which bacterial species is a likely cause, given maternal colonization?

<p>Streptococcus agalactiae (D)</p> Signup and view all the answers

A patient has been diagnosed with subacute bacterial endocarditis. Which of the following is most likely to be identified?

<p>Viridans streptococci (C)</p> Signup and view all the answers

What is the primary antibiotic treatment for infections caused by most Streptococcus species?

<p>Penicillin (B)</p> Signup and view all the answers

A patient with a penicillin-resistant Streptococcus pneumoniae infection requires alternative antibiotic therapy. Which treatment is most appropriate?

<p>Vancomycin (A)</p> Signup and view all the answers

Why are beta-lactam antibiotics usually ineffective against Enterococcus infections?

<p>They are intrinsically resistant to the actions of beta-lactams (B)</p> Signup and view all the answers

Which of the following best describes the difference between colonization and infection?

<p>Colonization is when an organism is present on a body surface without causing disease, while infection occurs when organisms invade tissues and cause disease. (B)</p> Signup and view all the answers

Which of the following is a correct definition of a nosocomial infection?

<p>An infection that is acquired by a patient after admission to the hospital. (B)</p> Signup and view all the answers

What does the phrase 'portal of entry' refer to in the context of disease transmission?

<p>The place where an organism enters a vulnerable host. (A)</p> Signup and view all the answers

Which of these is NOT a primary step in an outbreak investigation?

<p>Identifying the financial costs associated with the outbreak. (B)</p> Signup and view all the answers

Which bacterial structural components are important for initiating infection and colonization?

<p>Pili, capsules, and enterotoxins. (C)</p> Signup and view all the answers

A healthcare-associated infection (HAI) is mentioned as impacting patients by:

<p>Potentially leading to increased treatment costs and extended time in hospital. (A)</p> Signup and view all the answers

What is an example of a bacterial species that is categorized as a multidrug-resistant organism?

<p>MRSA (C)</p> Signup and view all the answers

If the lab starts to see an increase in the same positive cultures from a specific department, this may indicate:

<p>A possible outbreak in that department. (A)</p> Signup and view all the answers

Which transmission route is most relevant for the spread of multidrug-resistant organisms in healthcare settings?

<p>Contact transmission (A)</p> Signup and view all the answers

Which of the following is an appropriate example of a portal of exit?

<p>An infected person's respiratory system via a cough (A)</p> Signup and view all the answers

What is the primary mechanism of antibiotic resistance in Methicillin-resistant Staphylococcus aureus (MRSA)?

<p>Acquisition of the <em>mecA</em> or <em>mecC</em> gene. (B)</p> Signup and view all the answers

Which of the following represents the progression of antibiotic resistance in Staphylococcus aureus as described?

<p>Penicillin resistance → Methicillin resistance → MRSA emergence (D)</p> Signup and view all the answers

What is a common first-line treatment option for MRSA infections, especially when intravenous therapy is required?

<p>Vancomycin (A)</p> Signup and view all the answers

A patient presents with a red, swollen, painful skin infection that is exuding pus. Which of the following pathogens should be considered as the most likely cause?

<p>Methicillin-resistant <em>Staphylococcus aureus</em> (MRSA) (D)</p> Signup and view all the answers

What is a key characteristic that differentiates Staphylococcus from Streptococcus species?

<p>Catalase production (D)</p> Signup and view all the answers

Which Staphylococcus species is most associated with biofilm production and infections of prosthetic devices?

<p><em>Staphylococcus epidermidis</em> (A)</p> Signup and view all the answers

A young, sexually active female presents with a urinary tract infection. Which Staphylococcus species is most likely to be the causative agent?

<p><em>Staphylococcus saprophyticus</em> (A)</p> Signup and view all the answers

What is a characteristic shared by both Streptococcus and Enterococcus species?

<p>Gram-positive cocci morphology (D)</p> Signup and view all the answers

How does the classification of Enterococcus relate to its usual habitat?

<p>It’s traditionally known as ‘streptococci of fecal origin’. (C)</p> Signup and view all the answers

Choose the most accurate statement about MRSA colonization rates:

<p>Approximately 5% of patients in US hospitals are colonized. (B)</p> Signup and view all the answers

Flashcards

Difficult pathogens

Pathogens resistant to multiple antibiotics, e.g. MRSA, VRE.

Colonization

Presence of organisms on body surfaces without causing disease.

Infection

Organisms invade tissues causing signs and symptoms.

Nosocomial infection

Infection acquired after hospital admission.

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Transmission

Pathway by which an infection spreads to others.

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Portals of entry

Routes through which pathogens enter the body.

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Vulnerable hosts

Individuals at increased risk for infections.

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Etiologic agent

Specific pathogen responsible for an infection.

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Reservoir

Natural habitat where pathogens live and multiply.

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Mode of transmission

Method by which an infectious agent spreads.

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Staphylococcus

Gram-positive cocci in grape-like clusters, normal flora of skin and mucous membranes.

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Catalase Positive

An enzyme that breaks down hydrogen peroxide (H2O2) into bubbles, indicating Staphylococcus presence.

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Coagulase

An enzyme that binds plasma fibrinogen to form a clot, found in Staphylococcus aureus.

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Staphylococcus aureus

Most virulent staph species, golden in color, commonly found on skin and mucous membranes.

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Staphylococcus aureus Virulence Factors

Include coagulase, protein A, enterotoxins, lipase, hyaluronidase, hemolysins.

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Impetigo

A skin infection caused by Staphylococcus aureus characterized by pustules and crusty sores.

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Toxic Shock Syndrome

A severe illness linked to menstruating women, presenting with fever, vomiting, and rash.

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Food Poisoning by Staph aureus

Caused by heat-stable enterotoxins in contaminated food, leads to vomiting and diarrhea.

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Scalded Skin Syndrome

A toxin-mediated condition in infants causing skin to blister and peel, resembling scalded skin.

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Methicillin Resistant Staph aureus (MRSA)

A type of Staphylococcus aureus resistant to methicillin, complicating treatment.

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MRSA

Methicillin-resistant Staphylococcus aureus; a type of bacteria resistant to many antibiotics.

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Penicillin resistance

Resistance developed after WWII leading to the use of methicillin.

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mecA gene

Gene associated with methicillin resistance in Staphylococcus aureus.

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Vancomycin

Antibiotic used to treat MRSA infections, but may lead to VRSA.

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Community-acquired infections

Infections caused by MRSA, common in community settings.

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Staphylococcus epidermidis

Coagulase-negative Staphylococcus; low virulence, opportunistic infections.

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Biofilms

Protective layer formed by bacteria like Staphylococcus epidermidis on devices.

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Catalase negative

Characteristic of Streptococcus; does not bubble in hydrogen peroxide.

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E. faecalis

Main species of Enterococcus causing human infections, found in intestines.

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Bacteremia

Presence of bacteria in the bloodstream, sometimes caused by infections like MRSA.

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Gram-negative bacteria

Bacteria that stain pink during the Gram stain process.

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Mycoplasma

Bacteria that lack a cell wall and do not stain in Gram staining.

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Psychrophiles

Bacteria that thrive in cold temperatures (4-15°C).

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Mesophiles

Bacteria that grow best at moderate temperatures (30-35°C).

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Thermophiles

Bacteria that flourish in hot environments (50-60°C or more).

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Obligate aerobes

Bacteria that require oxygen for growth.

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Facultative anaerobes

Bacteria that can grow with or without oxygen.

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Generation time

The time taken for one bacterial cell to divide into two cells.

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Enterococcus faecium

A bacterium with relatively low virulence causing UTIs, endocarditis, and wound infections.

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Hemolysis Types

Classification of bacteria based on their hemolytic activity: Alpha (ɑ), Beta (β), Gamma (ɣ).

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Alpha Hemolysis

Bacteria partially lyse RBCs, leading to a green/brown appearance on blood agar.

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Beta Hemolysis

Bacteria completely lyse RBCs, resulting in a clear colorless zone around colonies on blood agar.

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Group A Streptococcus

Known for causing conditions like pharyngitis, scarlet fever, and can lead to rheumatic fever and glomerulonephritis.

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Streptococcus pneumoniae

Leading cause of pneumonia, otitis media, and meningitis, typically appears as gram-positive cocci in pairs.

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Enterococcus Antibiotic Resistance

Enterococcus species are intrinsically resistant to beta-lactams (like penicillins), needing alternative treatments.

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Study Notes

Gram Stain List

  • Gram-Positive Cocci (GPC): Bacteria ending in "-coccus" (Streptococcus, Staphylococcus, Enterococcus)
  • Gram-Negative Cocci (GNC): Neisseria, Moraxella (few species)
  • Gram-Positive Bacilli (GPR): Everything else
  • No Gram-negative bacilli on Exam 1

Characteristics of Bacteria

  • Prokaryotes: Lack a true nucleus, DNA in a circular chromosome without a nuclear membrane, rigid cell walls with peptidoglycan, asexual reproduction
  • Eukaryotes: Possess a true nucleus, DNA within a membrane-bound nucleus, diverse cell wall structures, both sexual and asexual reproduction

Characteristics of Bacteria - Classification

  • Domain: Bacteria
  • Phylum: Firmicutes
  • Class: Bacilli
  • Order: Bacillales
  • Family: Staphylococcaceae
  • Genus: Staphylococcus
  • Species: aureus
  • Strain: a genetic variant or subtype (e.g., Methicillin-resistant S. aureus)
  • Genus is capitalized and either underlined or italicized
  • Species is lowercase and either underlined or italicized

Characteristics of Bacteria - Gram Stain Basis

  • Gram staining groups medically important bacteria
  • Gram-positive bacteria have a thick peptidoglycan layer and stain purple
  • Gram-negative bacteria have a thin peptidoglycan layer and stain pink/red due to their outer membrane

Characteristics of Bacteria - Gram Stain Procedure

  • Crystal Violet (CV): Attracted to negatively charged bacterial cells, enters cell wall
  • Iodine: Mordant, sets the dye (CV) in the cell wall
  • Alcohol: Decolorizer, removes the thin peptidoglycan layer in Gram-negative bacteria
  • Safranin: Counter stain, colors Gram-negative bacteria pink/red

Characteristics of Bacteria - Bacterial Growth Factors

  • Temperature: Psychrophiles (cold), Mesophiles (moderate), Thermophiles (hot)
  • Osmotic Pressure: Isotonic, hypotonic, hypertonic
  • Chemical Requirements: Carbon, water, nitrogen, sulfur, phosphorus, trace elements (iron, copper, zinc), hydrogen ion concentration (pH)
  • **Atmosphere:**Obligate aerobes, obligate anaerobes, facultative anaerobes, capnophiles

Characteristics of Bacteria - Bacterial Growth

  • Replication: Binary fission
  • Growth curve: Lag phase, Log phase, Stationary phase, Death phase

Characteristics of Bacteria - Bacterial Structures

  • Cocci: spherical bacteria
  • Bacilli: rod-shaped bacteria
  • Pleomorphic: varying shapes
  • Spirochetes: helical bacteria
  • Flagella: protein filaments for motility
  • Pili: hair-like appendages for adherence
  • Capsules: polysaccharide layers for protection and attachment.
  • Endospores: dormant forms; highly durable
  • Lipopolysaccharide (LPS): component of Gram-negative bacteria cell walls

Characteristics of Bacteria - Microbiome and Microbiota

  • Microbiome: genetic material of all microbes in the human body
  • Microbiota: community of microbes on or inside the human body
  • Biofilm: Assemblage of microbes adhering to a surface

Host-Parasite Interaction

  • Host: organism being infected
  • Parasite: invader or agent
  • Pathogen: microorganism capable of causing disease
  • Primary pathogen: frequently causes disease in healthy hosts
  • Opportunistic pathogen: causes disease in immunocompromised hosts
  • Host barriers: microbiome (normal flora), anatomic barriers (skin), stomach acid, white blood cells, antibodies.

Additional (Bacteria)

  • Bacteremia: bacteria multiplying in the bloodstream
  • Virulence: ability of an organism to produce disease
  • Pyogenic: pus-producing

Hospital Epidemiology

  • HAI: healthcare-associated infection.
  • Colonization: presence of organism without disease
  • Infection: organisms invade body tissues
  • Nosocomial infection: infection acquired in a hospital setting
  • Transmission : Portal of entry, vulnerable hosts, Organism, Reservoir, Portal of exit, contact, droplets, air
  • Steps in outbreak investigation: identify agent, eliminate, prevent, prevent future
  • Laboratory in outbreak: seeing same positive cultures in a specific department

Sterilization & Disinfection/Infection Control

  • Antiseptic: inhibits microbial growth
  • Aseptic: used to sterilize (used in surgery, phlebotomy)
  • Cide/Cidal: to kill
  • Stasis/Static: prevent multiplication. (Without necessarily killing)
  • Disinfectant: kill equipment and surfaces
  • Methods for sterility control: Heat (moist and dry), Autoclave, Pasteurization, Flame, Membrane filtration, High-efficiency particulate air (HEPA) filters, Radiation (UV light, ionization)

Staphylococcus aureus

  • "Aureus" = golden
  • Often colonizes skin, nose, armpits, and groin
  • Virulence factors: Coagulase, Protein A, Enterotoxins, Lipase, Hyaluronidase, Hemolysins
  • Diseases (Staph aureus): Skin infections (impetigo, furuncles, carbuncles, pyogenic abscesses, scalded skin syndrome), Food poisoning (toxin-mediated), Toxic Shock Syndrome (associated with menstruation and tampon usage).
  • MRSA: Methicillin-resistant Staphylococcus aureus (Antibiotic resistance.)

Coagulase-negative Staphylococcus species

  • Staphylococcus epidermidis: Colonizes most people, low virulence, forms biofilms. Associated with bacteremia and device-related infections
  • Staphylococcus saprophyticus: May have affinity for the urethra and bladder epithelium, linked with urinary tract infections, resistant to Novobiocin

Streptococcus

  • Gram-positive cocci in chains
  • Normal flora of upper respiratory and intestinal tracts
  • Catalase-negative, compared to Staph
  • Types based on hemolysis: Alpha (partially hemolyzes), Beta (completely hemolyzes), Gamma (no hemolysis)

Enterococcus

  • Gram-positive cocci
  • Often part of the streptococci intestinal flora
  • Relativley low virulence
  • Causes UTIs, endocarditis, wound infections

Moraxella catarrhalis

  • Gram-negative diplococci
  • Normal flora in upper respiratory tract.
  • Not fastidious
  • Common in otitis media, sinusitis in children, pneumonia in the elderly

Neisseria gonorrhoeae

  • Obligate human pathogen
  • Causes localized inflammation, “Gonococcus,” “GC”
  • Transmitted primarily by sexual contact, rarely lethal
  • Quickly killed in blood stream
  • Often resistant to penicillin
  • Women - endocervix, Men - urethra
  • Can cause pelvic inflammatory disease (PID) and ectopic pregnancies if left untreated.

Neisseria meningitidis

  • Obligate human pathogen
  • Normal nasopharyngeal flora in some
  • Life-threatening infections
  • Causes meningitis, septicemia.
  • Transmitted by respiratory droplets

Gram Positive Bacilli

  • Spore formers: Bacillus spp, Clostridium spp.
  • Opportunistic pathogens: Corynebacterium spp., Gardnerella vaginalis
  • **Strict pathogens:**Nocardia spp., Corynebacterium diphtheriae, Listeria monocytogenes

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Exam 1 Review PATH 3100-001 PDF

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Test your knowledge on bacterial classification and the Gram stain technique with this quiz. Explore the characteristics that distinguish Gram-positive and Gram-negative bacteria, as well as the classification hierarchy from domain to species. Perfect for microbiology students and enthusiasts alike.

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