Microbiology: Normal Flora Quiz

Human Microflora

• Human microflora includes prebiotics, probiotics, and synbiotics
• Normal flora are microorganisms that live on an organism without causing disease
• Normal flora are permanent, or fixed, in particular areas of the body
• Normal flora populations inhabit skin and mucous membranes
• Normal flora of humans are diverse
• Humans are colonized from shortly after birth, until death.

Introduction 1

• Microorganisms are omnipresent (found in water, soil, air)
• Normal flora is defined as microorganisms that live on an organism (human or animal) without causing disease
• Normal flora are also called microbiotas or microbiomes
• Normal flora are permanent or fixed micro-organisms in particular anatomic parts of healthy humans.
• A population of micro-organisms inhabits the skin/mucous membranes of healthy people
• Diversity in flora is associated with skin and mucous membranes in healthy humans
• The human body is not sterile
• Approximately 100 trillion bacteria form the normal flora of humans.
• The human microbiota represents a complex ecosystem and outnumbers human cells (approximately 37.2 trillion).
• The resident flora helps prevent colonization by infection-causing bacteria or pathogens.

Introduction 2

• The normal human body has a profuse bacterial flora, consisting of commensal bacteria
• Some commensals can become pathogenic if they leave their normal sites and breach the body's defenses
• The normal flora is physiologically static, but it is subject to constant change.

Introduction 3

• Normal flora (NF) is found at sites that communicate with the exterior (skin, mucous membranes of the nose, mouth, intestine, urogenital tracts)
• NF is relatively stable, with specific genera populating specific body sites
• NF is mostly comprised of bacterial species, and some fungi
• Viruses and parasites are not considered part of the NF

Characteristics 2

• NF is acquired rapidly during and shortly after birth and remains stable throughout life
• Factors that alter the composition of NF include local environment (pH, temperature), age/hormones, mode of birth, dietary/cultural habits, antimicrobial use, lifestyle (e.g., smoking/lysozyme secretion, douching), etc.
• Other circumstances can change the normal flora, such as admission to a hospital or long-term care facility.
• Circumstances like the environment, staff and devices within patients (e.g. intravenous lines), can alter the normal flora.

Main Types of Human Body Flora

• Resident/Normal Flora resides within the stratum corneum, skin surface, (e.g., Staphylococcus epidermidis, Staphylococcus hominis, Malassezia species)

• Resident flora is relatively fixed and permanent, commonly found in specific areas of the body

• Promptly re-establishes itself after disturbance (e.g., mouth washing, skin scrubbing).

• Can cause disease if found outside their usual site (e.g., dental extraction leading to endocarditis).

• Transient Flora, comprises non-pathogenic or potentially pathogenic microorganisms that inhabit skin or mucous membranes for hours, days, or weeks.

• Derived from the environment; doesn't permanently colonize or induce disease in the host

• Easily removed with routine hand hygiene.

Relationships of NF and host

• Microorganisms colonizing the body maintain a symbiotic relationship with human cells (healthy state)
• Mutualism: both partners benefit (e.g., Escherichia coli in the gut receives nutrients and produces vitamin K)
• Commensalism: one partner benefits, while the other is neither benefited nor harmed.

Advantages of NF (NF in health)

• Serves as "ecological niches" preventing entry of pathogenic organisms due to bacterial interference
• Competes with other pathogens for receptor sites
• Effectively competes for micronutrients
• Important in maintaining normal intestinal flora structure and function
• Their metabolism produces vitamins, especially vitamin K and B-group vitamins

Protection and Disease

• Normal flora can form layers protecting host tissues
• Normal flora produce waste products that influence immune systems
• Large inoculums, antimicrobial drugs, and other host factors can lead to disease
• Physical destruction (e.g., burns, irradiation) can alter normal flora

Advantages of NF (NF in health)

• Evoke antibody production that cross-reacts with pathogens sharing antigens
• Releases endotoxins that assist in host defenses.
• Some NF colonies have harmful effects on pathogens via bacteriocins.

Disadvantages (NF in disease)

• Pathogens spread to sterile body parts
• Normal flora in one location may cause disease in another. (e.g., intestinal perforation leading to peritonitis, or normal flora of the intestine causing urinary tract infections)
• NF in the intestine can become a cause for urinary tract infections
• Can be involved in infections during tooth extractions (e.g., Rheumatic heart disease/Infective endocarditis).
• Synergistic relationships that encourage pathogen growth.

Disadvantages (NF in disease)

• Difficulties in laboratory results from the presence of normal flora are possible.
• Opportunistic infections (e.g., Candida in immunocompromised patients) are possible due to immunosuppression
• Opportunistic infections may affect the blood stream.
• Bacterial vaginosis may result from decreased vaginal acidity.

Host Infection by Elements of the Normal Flora

• Breaches in skin surfaces or mucosal layers can lead to host infections
• NF can enter previously sterile parts of the body and become pathogens
• Infections include caries, periodontal disease, abscesses, foul-smelling discharges, and endocarditis.
• Other infections include peritonitis and urinary tract infections

Distribution of the Normal flora

• With the exception of the alimentary tract and some other surfaces, the internal organs are sterile in health. (e.g., bladder, kidneys, lungs, CNS)
• Effective local defense mechanisms maintain sterility in these sites.
• Chemical substances in serum and tissue fluids (e.g., complement, antibodies) support phagocytic activity in these locations.

Common Anatomic Sites of the Normal Flora

• Skin: Most frequently encountered bacteria are Staph. epidermidis, various diphtheroids, propionibacterium acnes; some anaerobic bacteria also present
• Eye/Conjunctiva: Relatively free of bacteria due to lysozyme in tears and and mechanical flushing
• Nose/Nasopharynx: Sterile at birth, but colonizes rapidly (Diphtheroids, Staph., Streptococcus, Haemophilus, Moraxella.)
• Mouth: Initial inhabitants are bacteria from mother's birth canal (e.g., gram-positive aerobic spore-bearing bacilli, coliforms, proteus, lactobacilli); varied anaerobic flora present; Candida also occurs.
• Upper Respiratory Tract: Streptococcus mitis, and various other streptococci, but bronchi and alveoli are commonly sterile.

Gastrointestinal Tract (GIT)

• GIT is sterile in utero and gets colonized after birth
• Lactobacillus, Enterococcus, coliform bacilli are common inhabitants
• Changes with food type/diet
• Stomach (low pH): few organisms persist in this acidic environment
• Duodenum and ileum: sparse and mixed organisms (Enterococcus, Lactobacilli, Streptococci)
• Small intestine: fewer organisms than large intestine (Lactobacilli, Streptococcus, Clostridium, Candida, Entamoeba, Enterobacteriaceae)
• Large intestine: large number of organisms (Bacteriodes, E.Coli, Streps, Fusobacterium)
• Colon organisms are important for bile acid conversion, vitamin K production and ammonia production.

Genitourinary Tract

• Male and female genitalia have Mycobacterium smegmatis and ureaplasma
• Urethra (external): Staphylococcus epidermidis, Streptococcus faecalis, diphtheroids
• Vagina: Before puberty: staphylococci, streptococci, diphtheroids, E. coli; after puberty Lactobacillus aerophillus (pH changes with hormone levels)
• Vagina: transient Candida can cause vaginal infections
• Lactobacillus is a gatekeeper for vaginal ecosystem (maintaining pH 4.5 +/- 0.5)
• Absent lactobacillus = bacterial vaginosis

Knowledge of the normal flora of the human body

• Knowing the normal sites of bacteria in the body helps diagnose infections
• Predicting pathogens based on their preference for specific body sites
• e.g., Streptococcus pneumoniae (upper respiratory tract), Staphylococcus aureus (skin)
• Investigating abnormal bacteria in normally sterile sites (e.g., E. coli in blood may indicate intra-abdominal pathology)
• Understanding abnormal presence of Viridans Streptococcus might indicate endocarditis.

Knowledge of the normal flora of the human body (cont.)

• Knowing normal sites of bacterial presence (in the body) aids in diagnosing infections (when found in the 'wrong place')
• Guides initial treatment as knowing potential pathogens aids in the likely diagnosis of the disease and thus choosing the most effective antibiotic.
• Knowing possible influences on the normal flora (e.g. antibiotic overuse) helps predict opportunistic infections (eg. colitis due to C.difficile; Bacterial vaginosis).

Current utility of Normal flora microorganisms in health

• Ancient physicians, like Hippocrates, recognized the crucial role of food in health
• Russian scientist Ilyich Mechnikov (Eli Metchnikoff) won the Nobel Prize for his work on the bacteria in the gut and probiotics
• Probiotic foods have been shown to enhance health and possibly prevent chronic diseases
• A link between longevity and regular consumption of fermented milk (lactobacillus rich milk) has been highlighted.

Probiotics, Prebiotics and Synbiotics

• Strong relationship exists between gut flora and health/illness
• Probiotics, prebiotics and synbiotics have been identified to be important for the modulation or restoral of gut microbiota.
• These microbes are now used in the treatment and prevention of illnesses/diseases.
• Probiotics: good bacteria (e.g., lactobacilli, bifidobacteria, yeasts)
• Prebiotics: growth stimulators (e.g., non-digestible fiber-like food substances – pectin, inulin, carbs).
• Synbiotics: combination of probiotics and prebiotics; beneficial for gut health, immune modulation, cancer prevention, and inflammatory bowel disease

Probiotics

• Probiotics are preparations or products with live microbial agents which induce a health benefit on the host
• These live microbes help to inhibit the growth of harmful bacteria (via antibacterial compounds) in the gut epithelium
• Probiotics are helpful in treating disease within the gut such as Irritable bowel disease (Crohn's dx, Ulcerative colitis), Lactose intolerance or various other extra-intestinal diseases such as obesity, Type 2 DM, allergy, peptic ulcers, fatigue, aging, osteoporosis and autism.

Prebiotics

• Prebiotics are non-digestible fiber-like food substances (e.g., inulin, pectin) that induce growth or activity of microorganisms (bacteria and fungi) that promote the well-being of the host (e.g. bacteria and fungi).
• Specifically induce the growth of specific bacteria such as lactobacilli and bifidobacteria in the large intestine; these bacteria are beneficial for the health.
• Prebiotics ideally resist digestion in the upper gut, are non-absorbed, and easily fermented by good bacteria

Synbiotics

• Synbiotics are products that contain both probiotics and prebiotics.
• Probiotics and prebiotics working synergistically benefit the host.
• Synbiotics help improve the survival and implantation of live microorganisms in the gut.
• Synbiotics can be used to treat various conditions, including cancer and lipid disorders (e.g., hypercholesterolemia)

Test your knowledge on normal flora, the microorganisms that reside on the human body without causing disease. This quiz covers their characteristics, locations, and roles within the human body. Answer questions about the factors affecting normal flora and the implications of their spread.