Normal flora

• What is the definition of normal body flora?

  It refers to the population of microorganisms that inhabit the skin and mucous membranes of healthy persons.
• How does the environment affect the microbial flora at different body sites?

  Local conditions select for organisms that are suited for growth in a particular area.
• What are the two types of normal body flora?

  Resident flora and transient flora.
• What characterizes resident flora?

  It consists of relatively fixed types of microorganisms regularly found in a given area.
• What is transient flora?

  It consists of nonpathogenic or potentially pathogenic microorganisms that inhabit a body location for a limited period.
• What happens if the normal flora is disturbed?

  Transient microorganisms may colonize, proliferate, and produce disease.
• What are commensals in the context of normal body flora?

  Flora that have established a relationship with the host.
• What is a carrier in microbiology?

  A host that some pathogenic organisms may establish themselves in without manifesting symptoms.
• What is the carrier state?

  The condition of hosts that carry pathogenic organisms without showing symptoms.
• What is an example of a chronic carrier state?

  Post–Salmonella typhi infection where the organism may establish itself in the bile duct.
• How does the host-microbe relationship vary?

  It may be one of symbiosis, commensalism, or parasitism.
• What is symbiosis?

  The association of two organisms living together.
• What is an example of commensalism?

  Proteus mirabilis in the gastrointestinal tract of humans.
• What are the normally sterile sites in the human body?

  The larynx, trachea, bronchi, bronchioles, alveoli, and accessory nasal sinuses.
• How can the number of bacteria on the skin be reduced?

  By vigorous daily scrubbing with soap containing disinfectants.
• What is the significance of the skin's protective mechanisms?

  They prevent infection and protect underlying tissue from invasion by pathogens.
• What factors influence the composition of skin flora?

  The activity of sebaceous or sweat glands and environmental factors.
• What are common normal flora of the skin?

  Candida spp., Micrococcus spp., Staphylococcus spp., Clostridium spp., Propionibacterium spp.
• What is the role of the conjunctival flora?

  It is normally held in check by the flow of tears containing antibacterial lysozyme.
• What is the microbial population in the gastrointestinal tract at birth?

  The intestine is sterile.
• How does diet influence intestinal flora?

  Diet has a marked influence on the composition of intestinal and fecal flora.
• What happens to the microbial population in the stomach when acidity decreases?

  There are chances of increased numbers of organisms present in the stomach.
• What is the predominant type of flora in the adult colon?

  Obligate anaerobes make up more than 90% of the microbial flora.
• What can alter the gastrointestinal tract population?

  Antibiotics can result in eradication or suppression of certain populations.
• What is the significance of drug-resistant organisms in the intestine?

  They serve as a source of plasmid-mediated drug resistance in bacteria.
• What are common microorganisms found in the gastrointestinal tract?

  Bacteroides spp., Clostridium spp., Enterobacteriaceae, Fusobacterium spp.
• What is the typical flora of the external auditory canal?

  It usually reflects the flora of the skin.
• How does the conjunctival flora contribute to eye health?

  It is kept in check by tears that contain antibacterial lysozyme.
• What is the role of tears in the conjunctival flora?

  Tears contain antibacterial lysozyme that helps control the flora.
• What is the impact of breastfeeding on intestinal flora?

  Breast-fed children have large numbers of lactic acid streptococci and lactobacilli in their intestines.
• What happens to the microbial population in the intestines of newborns in intensive care nurseries?

  They tend to be colonized with pathogenic organisms.
• What is the typical microbial count in the colon?

  Between $10^8$ and $10^{11}$ bacteria per gram of solid material.
• What is the predominant type of flora in the large intestine?

  Obligate anaerobes far outnumber facultative gram-negative rods.
• How can antibiotic use affect the gastrointestinal flora?

  It can lead to eradication or suppression of certain populations and proliferation of others.
• What is the relationship between the gastrointestinal flora and drug resistance?

  Prevalence of drug-resistant organisms serves as a source of plasmid-mediated drug resistance.
• What is the typical range of bacteria per gram of solid material in the large intestine?

  10^10 to 10^11 bacteria
• What type of bacteria predominantly make up the microbial flora of the large intestine?

  Obligate anaerobes
• What percentage of the microbial flora in the large intestine do obligate anaerobes constitute?

  More than 90%
• Which organisms are usually present in the large intestine besides obligate anaerobes?

  Gram-positive cocci, yeasts, and Pseudomonas aeruginosa
• How can antibiotics affect the gastrointestinal tract population?

  They can eradicate or suppress certain populations and promote others