Microbiology 101: Normal Flora and Lysozyme

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Questions and Answers

What role does lysozyme play in bodily secretions?

It cleaves the peptidoglycan component of bacterial cell walls. (correct)

It promotes bacterial growth in the oral cavity.

It functions as a nutrient for bacteria.

It neutralizes toxins produced by pathogens.

Which organism is commonly found in the normal flora of the upper respiratory tract?

E. coli

Staphylococcus epidermidis (correct)

Lactobacillus

Salmonella

What is a significant benefit of normal flora in the gastrointestinal tract?

They stimulate excessive mucus production.

They lead to increased body odor.

They prevent pathogens from colonizing. (correct)

They can cause severe infections.

At what stage does the oral cavity start to become colonized with bacteria?

Within 4-12 hours after birth Signup and view all the answers

Which bacteria are primarily responsible for plaque formation in the oral cavity?

Streptococcus mutans Signup and view all the answers

What is one potential harm caused by the normal flora in the upper respiratory tract?

Opportunistic infections Signup and view all the answers

How many species of bacteria are potentially present in human saliva?

700 species Signup and view all the answers

Which structure in the respiratory tract helps to entrap pathogens?

Mucus blanket Signup and view all the answers

What condition can occur if the normal flora of the gastrointestinal tract is disrupted?

Opportunistic infections Signup and view all the answers

What primary action does lysozyme perform against bacterial cells?

Cleaves their cell wall components Signup and view all the answers

What is a significant effect of H. pylori infection on the stomach lining?

It causes ulcers by damaging the stomach lining. Signup and view all the answers

What percentage of individuals with H. pylori infection develop symptomatic peptic ulcer disease?

15% Signup and view all the answers

How does methane impact intestinal transit in humans?

It slows down intestinal transit by 59%. Signup and view all the answers

Which statement about the vaginal microbiota (VMB) is correct during puberty?

Lactobacillus becomes a major component of VMB. Signup and view all the answers

What is one of the benefits of normal flora in the urogenital tract?

Competition with pathogens for colonization sites. Signup and view all the answers

What occurs to the vaginal microbiota at menopause?

It returns to prepuberty flora. Signup and view all the answers

Which component is NOT considered a role of normal flora?

Complete eradication of all harmful microorganisms. Signup and view all the answers

What is the primary pH level of the vaginal microbiota at birth?

5 Signup and view all the answers

Which organism is the major inhabitant of the skin's normal flora?

Staphylococcus epidermidis Signup and view all the answers

In which location is Staphylococcus aureus primarily found?

Nasal passages Signup and view all the answers

What factor is NOT important in eliminating non-resident microorganisms from the skin?

Physical removal via abrasion Signup and view all the answers

Which of these organisms is commonly found in the conjunctiva's normal flora?

Staphylococcus epidermidis Signup and view all the answers

Which anaerobic bacteria are notable in the gastrointestinal tract?

Peptostreptococci Signup and view all the answers

What is a common characteristic of Staphylococcus epidermidis related to skin flora?

It is invariably found on skin and nasal membranes. Signup and view all the answers

Which of the following is a less common but notable organism in the urogenital tract?

Candida sp. Signup and view all the answers

What is a significant factor in the balance of skin flora?

Low pH levels Signup and view all the answers

What is the primary mechanism through which superantigens exert their effects on T cells?

They interact with antigen-presenting cells and T cells without entering. Signup and view all the answers

Which of the following are symptoms primarily associated with toxic shock syndrome caused by superantigens?

Rash, capillary leak, and hypotension. Signup and view all the answers

What distinguishes superantigens from traditional exotoxins?

Superantigens do not enter the host cells. Signup and view all the answers

Which of the following correctly defines endotoxins in the context of bacterial damage to host tissues?

Endotoxins are part of the bacterial cell wall and are released upon cell lysis. Signup and view all the answers

What role do cytokines play in the effects induced by superantigens?

They lead to excessive inflammatory responses. Signup and view all the answers

Which genus includes species found primarily on the skin and upper respiratory tract?

Corynebacterium Signup and view all the answers

What is a primary habitat for Lactic acid bacteria?

Mouth and gastrointestinal tract Signup and view all the answers

Which statement accurately reflects why humans do not generally become ill from normal bacterial flora?

Phagocytic cells and bactericidal compounds eliminate invading bacteria. Signup and view all the answers

Which of the following is NOT a characteristic of Enterococcus species?

Contains Corynebacterium species Signup and view all the answers

What role do neutrophils play in relation to normal bacterial flora?

They kill invading bacteria during an immune response. Signup and view all the answers

How is the environmental density of bacteria related to preventing illness?

Low density inhibits tissue conditioning for growth. Signup and view all the answers

Which of the following explains the limited colonization of normal flora in the bloodstream?

Bacteria need to mutate to survive in blood. Signup and view all the answers

Which Lactic acid bacteria is specifically mentioned as part of the normal flora?

Lactobacillus acidophilus Signup and view all the answers

What is the primary metabolic condition of the normal flora in the gastrointestinal tract?

Primarily anaerobic Signup and view all the answers

Which type of bacteria predominantly exists in the sigmoid colon and rectum?

10^10-10^11 bacteria/gram Signup and view all the answers

What percentage of fecal mass in adults is primarily composed of bacteria?

25%-35% Signup and view all the answers

What is one potential harmful effect of gastrointestinal normal flora?

Transfer of antibiotic resistance Signup and view all the answers

Which bacteria are commonly associated with the small intestine's proximal region?

Streptococci and lactobacilli Signup and view all the answers

Which gastrointestinal bacteria are implicated in causing gastric ulcers?

Helicobacter pylori Signup and view all the answers

What is a major benefit attributed to the bacteria in the distal small intestine?

Competition with pathogens for colonization sites Signup and view all the answers

Which bacteria are predominantly found in the large intestine?

Clostridia and bifidobacteria Signup and view all the answers

What is the relationship between normal flora and inflammatory bowel diseases?

Normal flora are implicated in inflammatory bowel diseases Signup and view all the answers

What is one function that gut bacteria perform in the gastrointestinal tract?

Production of substances that inhibit pathogens Signup and view all the answers

Study Notes

Microbial Flora & Bacterial Pathogenesis

Normal flora are a mixture of microorganisms regularly found at any anatomical site in a healthy person.
Normal flora compete with pathogens for attachment sites and nutrients, preventing colonization by pathogens.
This has been demonstrated in the oral cavity, intestines, skin, and vaginal epithelium.
Resident flora are microorganisms that normally occupy a particular body site.
Resident bacteria outnumber a person's own cells by 10 to 1.
The resident flora can quickly re-establish itself after disruption, which can negatively impact the immune system, increasing susceptibility to infection.

Normal Flora Types

Resident are indigenous microorganisms (flora, microbiota, normal flora).
Transient are microorganisms that colonize temporarily (hours, days, or weeks) and don't permanently establish themselves.
Internal tissues are normally sterile.

Transient Flora

Transient flora are non-pathogenic or potentially pathogenic microorganisms that inhabit the skin for hours, days, or weeks.
Transient flora do not permanently colonize or establish.
Removed easily by handwashing; found more superficially on the skin.

Relationship Between Normal Flora and Host

Commensalism: One organism benefits, and the other is unaffected.
Mutualism: Both organisms benefit (example: bacteria digest food humans cannot).
Parasitism: One organism benefits at the expense of the other (pathogens harming body).

Normal Flora Locations

Skin
Conjunctiva (eye)
Nasopharynx
Oral cavity
Gastrointestinal tract and rectum
Urogenital tract

Normal Flora - Skin

Staphylococcus epidermidis is the major inhabitant, comprising over 90% of the flora.
Staphylococcus aureus is also present, but occurrence varies with age, most common in newborns.

Factors Important in Eliminating Non-resident Microorganisms From Skin

Low pH
Fatty acids (sebaceous secretions)
Lysozyme

Normal Flora - Conjunctiva

Has a variety of bacteria, but in low numbers.
Blinking removes bacteria mechanically.
Lacrimal secretions contain lysozyme (antimicrobial agent).

Normal Flora - Upper Respiratory Tract

Nose: Staphylococcus aureus and Staphylococcus epidermidis are common.
Oropharynx: Viridans streptococci, including Streptococcus mutans.
Other species present in assorted numbers.

Normal Flora - Oral Cavity

Sterile at birth, then colonized with various species.
Develops with teeth (implicated in dental caries).
More than 700 species potentially present.

Normal Flora - Respiratory Tract

Lower respiratory tract: usually sterile,
Ciliated epithelium and mucus blanket trap pathogens.
Alveolar macrophages further protect.
Opportunistic infections if barriers are breached

Normal Flora - Gastrointestinal Tract

GI ecology varies widely along the tract.
Contains a vast number of species (e.g., >350 species in large intestine.)
Most are anaerobic bacteria.
Critical function of digesting indigestible food.
Can produce vitamins, nutrients, and compete for space with pathogens.

Normal Flora - Stomach

Helicobacter pylori is present.
Linked positively to gastric ulcers and potentially gastric cancer.
Plays a role in digestion.

Normal Flora - Large Intestine

High bacteria concentration.
Species include Bacteroides, Clostridia, and Bifidobacteria.
Can produce harmful substances and/or potentially harmful carcinogens, or have a correlation with diseases like inflammatory bowel diseases, potentially increasing the development of colon cancer.

Normal Flora - Urogenital Tract

Upper urinary tract is usually sterile; urethra may have resident flora similar to skin.
Vagina:
- Infants have flora similar to skin and intestines.
- Puberty: Lactobacillus becomes prevalent, creates acidic environment.
- Menopause: return to prepuberty flora.

Opportunistic Flora

Some normal flora can become opportunistic pathogens under certain circumstances (e.g., Staphylococcus, Enterococci, Streptococci, Pseudomonas).
Breach of skin barrier can allow normal flora to cause infection, leading to diseases like abscesses or sepsis.
Use of antibiotics can disrupt normal microbe populations, potentially allowing opportunistic pathogens to thrive.

Mechanisms of Bacterial Pathogenicity

Invasiveness describes the process of bacteria's ability to invade tissue (often by colonization and by countering the host immune defenses e.g. phagocytosis).
Toxigenicity describes the ability of bacteria produces toxins.
Toxins are divided into two types:
- Exotoxins: soluble proteins secreted by bacteria (e.g., A-B toxins, which bind to a host cell receptor and cause harm).
- Endotoxins: part of the cell wall of Gram-negative bacteria released upon cell death (e.g., Lipid A, produces fever and inflammation).

Bacterial Pathogenesis

Pathogens damage host via toxins (toxins) and/or invasion.
Bacteria employ many virulence factors (e.g., adhesins, capsules, toxins) to aid disease.
Mechanisms of evading host defense are essential for successful infection.
Host factors (e.g., host immune system and complement) greatly impact bacterial survival and pathogenicity.

Extracellular Versus Intracellular Parasitism

Extracellular parasites are destroyed by phagocytosis.
Intracellular parasites multiply within phagocytes, causing chronic diseases versus acute ones.

Barrier Systems

Host cells and membranes (physical barriers)
Production of antibodies
Phagocytic cells (e.g., macrophages, neutrophils).

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Description

Test your knowledge on the role of lysozyme and the normal flora in the human body. This quiz covers important questions about bacteria in the respiratory and gastrointestinal tracts, their benefits, and potential harms. Prepare to challenge your understanding of microbial interactions within our systems.