Transcript Normal Flora What’s growing on us?

Normal Flora
What’s growing on us?
Normal Flora (mostly
bacteria)
 In past Medical Microbiology focus on
pathogenic MOs
 Realize MOs that normally colonize humans
without harm can play role in disease
 Many innocuous NF now known to be
potentially pathogenic under certain
circumstances (what circumstances?)
 Therefore, important to acquire knowledge
about our NF
Knowledge of Normal
Flora
 Understanding of NF found at specific
body location provides insight into possible
infections that result from injury
 Knowledge of NF at a body site gives
clinician perspective on possible source
and/or significance of MOs isolated from
site of infection
Origin of Normal Flora
 Healthy fetus, in utero, is essentially free
of MOs
 Infant exposed immediately to MOs when
passing through mom’s vaginal tract and
then to MOs in environment
 Within few hours, oral and nasopharyngeal
flora of neonate established
 Within one day, resident flora of lower
intestinal tract established
Adult Normal Flora
 MOs that normally live on or in any part of
the body without causing disease
 Two basic types of NF:
 Resident NF – normally GROW on/in indicated
body site, presence fixed in well defined
distribution patterns
 Transient NF – only TEMPORARILY PRESENT
on/in indicated body site, usually don’t become
firmly entrenched but simply die within hours
Skin Normal Flora
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Staphylococcus epidermidis
Staphylococcus aureus
Propionibacterium acnes
Corynebacterium
Streptococcus species
Candida albicans
Clostridium perfringens
Skin Normal Flora
 Most skin NF found on superficial
squamous epithelium, colonizing dead cells
or closely associated with sebaceous and
sweat glands
 Secretions from these glands provide
environmental conditions and nutrients for
growth of numerous skin NF
Skin: Hostile Environment
 Subject to periodic drying
 Certain parts (folds, areas near orifices)
sufficient moisture support resident MOs
 Slightly acidic pH due to organic acids (
sebaceous & sweat glands, Staphylococcus)
prevents colonization of many MOs
 Sweat contains high NaCl, producing
hypertonic condition on skin surface that
osmotically stresses many MOs
Skin: Inhibitory Substances
 Help control colonization, overgrowth,
production of disease by resident MOs
 Remember - colonization not necessarily
mean infection and disease
 Lysozyme – produced by sweat glands and
lyse G(+) MOs
 Complex lipids – metabolized by
Propionobacterium acnes to unsaturated
fatty acids that have antimicrobial
activity (produce strong odor)
 Use of deodorants with antibacterial
substances, inhibit growth of G(+), may
lead to growth of G(-) MOs and infection
Skin Normal Flora
 Staphylococcus
epidermidis
 Staphylococcus aureus
 C+, clusters
Skin Normal flora
 Propionibacterium acnes
 B+, anaerobic
 Diphteroids (club
shaped)
 Branching bacilli
Propionibacterium acnes
 Harmless, but associated with acne during
adolescence and overproduction of sebum
by sebaceous gland
 Provides ideal environment for growth of
P. acnes and substances produced trigger
inflammatory response leading to acne
 Tetracycline (antibiotic) or accutane
(prevents sebum secretions, some severe
side effects) may be used for acne
treatment
Skin Normal Flora
 Corynebacterium
 B+, aerobic
 Diphtheroids
Skin Normal Flora
 Streptococcus species
 C+, pairs, chains
Skin Normal Flora
 Candida albicans
 Yeast, budding
 Soil & air
Skin Normal Flora
 Clostridium perfringens
 B+, anaerobic spore
former
 Soil & air
Nose & Nasopharynx (NP)
Normal Flora
 Nasopharynx (part of pharynx above soft
palate)
 Staphylococcus aureus*
 Staphylococcus epidermidis
 Diphtheroids
 Streptococcus pneumoniae*
 Haemophilus influenzae*
 Neisseria meningitidis*
 * may be causing disease if in large
numbers (relative numbers important)
Nose & NP Normal Flora
 Haemophilus influenzae
 B-, short cocobacilli
 Fastidious
Nose & NP Normal Flora
 Neisseria meningitidis
 C-, in pairs
 “coffee bean”
Oral & Oropharynx (OP)
Normal Flora
 Resist mechanical removal by adhering to
various surfaces such as gums and teeth
 MOs that can’t resist mechanical flushing
of oral cavity, swallowed, destroyed by
HCl in stomach
 Comfortable environment for MOs due to
availability of water and nutrients
Oral & OP Normal Flora
 Viridans group – α hemolytic
Streptococcus sp.
 Streptococcus pyogenes*
 Diphtheroids
 Staphylococcus epidermidis
 Staphylococcus aureus*
 Neisseria meningitidis*
 Other Neisseria species
 Haemophilus influenzae*
 Other Haemophilus sp.
Oral & OP Normal Flora
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Candida albicans*
Actinomycetes sp.*
Lactobacillus sp.
Bacteroides sp.
Fusobacterium sp.
Enterobacteriaceae*
* probably causing infection if
predominant organism found or in large
numbers
Oral & OP Normal Flora
 Some Streptococcus species
(sanguis, mutans, salivarious) adhere
to teeth and contribute to formation
of dental plaques and caries
Oral & OP Normal Flora
 Actinomyces
 B+, branching
 Forms granules
Oral & OP Normal Flora
 Lactobacillus
 B+, anaerobe
Oral & OP Normal Flora
 Bacteroides sp.
 B-, anaerobe
Oral & OP Normal Flora
 Fusobacterium sp.
 B-, anaerobe
Oral & OP Normal Flora
 Fusobacterium nucleatum
 B-, anaerobe
 Enlongated
Oral & OP Normal Flora
 Escherichia coli
 Family Enterobacteriaceae
 B-, short, coccobacilli
Gastrointestinal (GI) Tract
Normal Flora: Stomach
 Because of high acidic content very
few MOs
 Candida sp.
 Lactobacilli
 A few Streptococcus sp. (mainly
Enterococcus faecalis)
GI Tract Normal Flora:
Small Intestine
 Few MOs because inhibitory effects
of stomach acid, bile, and pancreatic
secretions
 Enterococcus faecalis
 Lactobacilli
 Diphtheroids
 Candida sp.
GI Tract Normal Flora:
Large Intestine
 Largest microbial population in human
body
 ~1012 MOs/gram feces
 Over 300 different species of
bacteria
 The anaerobic/facultatively
anaerobic bacteria ratio is 300/1
GI Tract Normal Flora: Large
Intestine
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Bacteroides sp.
Fusobacterium sp.
Lactobacillus
Clostridium sp.
Peptostreptococcus sp.
Staphylococcus sp.
Enterococcus faecalis
Other Streptococcus sp.
Pseudomonas species
Enterobacteriaceae
Candida sp.
GI Tract Normal Flora
 Pseudomonas species
 B-, soil & water
GI Tract Normal Flora
 Peptostreptococcus species
 C+, anaerobe
GI Tract Normal flora
 Normal physiological processes move MOs
through colon, adult excretes 3x1013 daily
 Under normal conditions resident NF selflimiting
 Competition of MOs ( i.e. colicin by E. coli)
 Mutualism with host (i.e. E. coli produces
vitamin K and B for host)
 Maintains status quo
GI Tract Normal flora
 Anything disturbs intestinal
environment (stress, altitude change,
starvation, diarrhea, antibiotics) can
alter NF leading to GI disease
 Yeast infections
 Antibiotic associated
pseudomembraneous colitis)
Genitourinary (GU) Tract
Normal Flora: Urethra
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Staphylococcus epidermidis
Enterococcus faecalis
Diphtheriods
Neisseria sp. (NOT N. gonorrhoeae)
Enterobacteriaceae
GU Tract Normal Flora: Vaginal
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Changes over lifetime ( i.e. menstrual cycle)
Lactobacillus (probiotic “friendly bacteria”)
Bacteroides
Enterococcus sp.
Staphylococcus epidermidis
Diphtheroids
Streptococcus agalactiae
Clostridium perfringens
Peptostreptococcus
Enterobacteriaceae
Candida albicans
GU Tract Normal Flora:
External Genitalia
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Streptococcus sp.
Staphylococcus sp.
Diphtheroids
Bacteroides
Candida sp.
Class Assignment
 Textbook Reading: Chapter 2 HostPathogen Interaction
 A. The Role of the Usual Microbial Flora
 Key Terms
 Learning Assessment Questions