1. Normal Flora
What’s growing on us?

2. 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

3. 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

4. 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

5. 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

6. Skin Normal Flora Staphylococcus epidermidis Staphylococcus aureus
Propionibacterium acnes
Corynebacterium
Streptococcus species
Candida albicans
Clostridium perfringens

7. 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

8. 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

9. 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

10. Skin Normal Flora Staphylococcus epidermidis Staphylococcus aureus
C+, clusters

11. Skin Normal flora Propionibacterium acnes B+, anaerobic
Diphteroids (club shaped)
Branching bacilli

12. 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

13. Skin Normal Flora
Corynebacterium
B+, aerobic
Diphtheroids

14. Skin Normal Flora
Streptococcus species
C+, pairs, chains

15. Skin Normal Flora
Candida albicans
Yeast, budding
Soil & air

16. Skin Normal Flora Clostridium perfringens B+, anaerobic spore former
Soil & air

17. 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)

18. Nose & NP Normal Flora Haemophilus influenzae B-, short cocobacilli
Fastidious

19. Nose & NP Normal Flora Neisseria meningitidis C-, in pairs
“coffee bean”

20. 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

21. 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.

22. Oral & OP Normal Flora Candida albicans* Actinomycetes sp.*
Lactobacillus sp.
Bacteroides sp.
Fusobacterium sp.
Enterobacteriaceae*
* probably causing infection if predominant organism found or in large numbers

23. Oral & OP Normal Flora
Some Streptococcus species (sanguis, mutans, salivarious) adhere to teeth and contribute to formation of dental plaques and caries

24. Oral & OP Normal Flora
Actinomyces
B+, branching
Forms granules

25. Oral & OP Normal Flora
Lactobacillus
B+, anaerobe

26. Oral & OP Normal Flora
Bacteroides sp.
B-, anaerobe

27. Oral & OP Normal Flora
Fusobacterium sp.
B-, anaerobe

28. Oral & OP Normal Flora
Fusobacterium nucleatum
B-, anaerobe
Enlongated

29. Oral & OP Normal Flora Escherichia coli Family Enterobacteriaceae
B-, short, coccobacilli

30. Gastrointestinal (GI) Tract Normal Flora: Stomach
Because of high acidic content very few MOs
Candida sp.
Lactobacilli
A few Streptococcus sp. (mainly Enterococcus faecalis)

31. GI Tract Normal Flora: Small Intestine
Few MOs because inhibitory effects of stomach acid, bile, and pancreatic secretions
Enterococcus faecalis
Lactobacilli
Diphtheroids
Candida sp.

32. 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

33. GI Tract Normal Flora: Large Intestine
Bacteroides sp.
Fusobacterium sp.
Lactobacillus
Clostridium sp.
Peptostreptococcus sp.
Staphylococcus sp.
Enterococcus faecalis
Other Streptococcus sp.
Pseudomonas species
Enterobacteriaceae
Candida sp.

34. GI Tract Normal Flora
Pseudomonas species
B-, soil & water

35. GI Tract Normal Flora
Peptostreptococcus species
C+, anaerobe

36. GI Tract Normal flora
Normal physiological processes move MOs through colon, adult excretes 3x1013 daily
Under normal conditions resident NF self-limiting
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

37. 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)

38. Genitourinary (GU) Tract Normal Flora: Urethra
Staphylococcus epidermidis
Enterococcus faecalis
Diphtheriods
Neisseria sp. (NOT N. gonorrhoeae)
Enterobacteriaceae

39. GU Tract Normal Flora: Vaginal
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

40. GU Tract Normal Flora: External Genitalia
Streptococcus sp.
Staphylococcus sp.
Diphtheroids
Bacteroides
Candida sp.

41. Class Assignment Textbook Reading: Chapter 2 Host-Pathogen Interaction
A. The Role of the Usual Microbial Flora
Key Terms
Learning Assessment Questions