MFM - Normal Flora

normal flora is associated with what?

skin and all mucous membranes throughout life

most normal flora are what and do what?

commensals; inhabit for long periods of time without noticeable effect

what are not normal flora?

viruses and parasites

what describes true resident flora?

strains that have an established niche at one of the many body sites, which they occupy indefinitely

what describes transient flora?

acquired from environment and establish themselves briefly; do not establish as permanent members of the normal flora

normal adult has about how much bacteria on and in their body?

1.2 kg

what describes functions of normal flora?

• serves as a barrier to infection and colonization by pathogenic bacteria (antagonism)

• intestinal normal flora synthesizes some of the vitamins we require (vitamin K and Bs)

• normal flora serve to stimulate the immune system (immunologic priming)

intestinal normal flora synthesizes what vitamins that we require?

vitamin K and Bs

what describes antagonism?

normal flora prevents colonization of some locations by pathogens (in GI tract, respiratory tract)

what describes immunologic priming (PAMP/TLR)?

the normal “microbiota” helps the host respond to quickly invading pathogens

• non-pathogenic flora primes the immune system to bacteria in general

• raises our basic level of tolerance against some common pathogens

what describes opportunistic infections?

all normal flora have the potential to cause disease by gaining access to regions that do not normally contain them

what can cause opportunistic infections?

• injury

• physical destruction

• immunosuppression

ecological disruptions can lead to what?

overgrowth by indigenous bacteria

• antibiotic selection: those resistant overgrow those sensitive

• elderly patients: “failure to thrive” - malabsorption by bacterial overgrowth

pathogenic normal flora can cause the conversion of what?

non-carcinogens to carcinogens

• alters the metabolic potential of normal flora

• potential example: H. pylori

each body region has factors that influence what type of flora that will colonize that location such as?

• pH, redox potential, oxygen, water, nutrient levels

• resistance to local antibacterial substances such as bile and lysozyme

normal flora is found in what?

skin, nails, eyes, oropharynx, URT, genitalia, GI tract

tissues and body fluids such as blood are what?

sterile in health

fetus is considered what at birth?

sterile

in regards to fetuses, initial flora is acquired during and immediately after birth via what?

orderly colonization:

• normal flora from mother’s genital tract and skin

• respiratory tract of people who are present at the time (OB GYN, relatives, visitors, etc.)

the skin is home to a variety of microbial species including what?

staphylococcus aureus, staphylococcus epidermis, proprionibacterium acnes

the mouth/throat is home to a large number of what?

streptococci

a number of are involved in periodontal disease?

anaerobic bacteria (viridans group of strep)

what yeast is commonly present in the mouth?

candida albicans

E. coli and coliforms are found where?

in the large intestine/gut

lactobacilli is found where?

female genital tract

antibiotics, douches, and hormone imbalance disturb the lactobacillus population and often result in what?

vulvovaginal candidiasis

what are the three main regions of the skin where different normal flora occur?

• axilla (armpit), perineum (crotch), and toe webs

• hand, face, and trunk

• upper arms, legs, and scalp

sites with partial occlusion contain what?

more organisms (axilla & perineum vs. arms, legs, or trunk)

• differences in moisture, body temp, and concentration of surface lipids

why is the skin in general unfavorable?

• too dry for most bacteria

• too acidic for most bacteria

• rapid turnover of epithelial cells

unsaturated fatty acids produced on the skin by gram positive bacteria do what?

inhibit gram negative bacteria

sweat glands excrete what?

lysozyme, which inhibits gram positive bacteria

where do gram negative bacteria predominate?

in the axilla, perineum, and toes

staphylococcus is what?

gram positive

what is the major inhabitant of the skin?

staphylococcus epidermis

what are sites occupied by staphylococci?

• nose

• perineum

• vulvar tissue

propionibacterium is what?

gram positive

what are other flora found on the skin?

• corynebacterium

• acinetobacter

• yeasts

what part of the GI tract has the most bacteria?

colon

what describes the stomach?

contains few, if any, resident organisms in health

in regards to the stomach, most bacteria are what?

transient, passing through along with saliva, nasopharyngeal secretion, and food

what is the only true resident of the stomach (associated with ulcer formation)?

helicobacter pylori

what describes the upper small intestine?

has a scanty resident flora, except in the lower ileum where it begins to resemble that of the colon

what caries the most abundant and diverse microbiota in the body?

colon (more than 90% are anaerobes)

in the colon, obligate anaerobes are 1000 times more what?

abundant than aerobes

what are the beneficial effects of gut microbiota?

• maintain GI tract peristalsis and integrity

• synthesize vitamin K and B complex

• convert dietary carcinogens and pre-carcinogens to non-carcinogens

the massive layer of bacteria in the gut secretes what?

bacteriocins

bacteriocins do what?

• inhibit other bacteria and prevent certain bacteria from colonizing

• protects the basement epithelial cells from pathogenic bacteria by blocking adhesion

what can disrupt the layer of bacteria in the gut that secretes bacteriocins and allow pathogenic bacteria access to the epithelial cells?

antibiotic therapy

kidneys, ureters, and urinary bladder are what in healthy humans?

sterile

the upper respiratory tract filters out bacteria, so what are usually free of normal flora?

larynx, trachea, bronchi, and lungs

the respiratory tract below the larynx is protected (in health) by what?

the action of the epithelial cilia and by the movement of the muco-ciliary blanket

• only transiently inhaled organisms are encountered in the trachea and bronchi

the mouth and pharynx contain mostly what?

facultative and anaerobic bacteria

oropharynx has what?

streptococci and neisseria

what describes the progressive colonization that the oral cavity undergoes?

• sterile at birth

• within one week - normal flora moves in rapidly

• infants without teeth: streptococcus predominates

• infants with teeth: obilgate anaerobes and facultative anaerobes start colonizing the tooth surfaces (lots more anaerobic species)

• 1 year old - normal flora of an adult is present

gingivitis and periodontitis are aggravated by what?

the resident normal flora of the mouth and biofilm

what are the three factors required to produce dental caries?

• cariogenic organism (streptococcus)

• caries-producing diet (sucrose)

• susceptible host (genetic factors)

normal flora can cause infection if?

• misplaced (ex: fecal flora invades into the urinary tract

• normal flora can overgrow if the host is immuno-compromised

• normal flora with enhanced virulence can overgrow

what are the three body locations where gram stain alone will not be diagnostic due to the fact that both gram-positive and gram-negative bacteria are found there?

• nose

• oropharynx

• vagina