This document summarizes the normal microbial flora that inhabit the human body. It describes the different bacteria found in various parts of the body like the skin, oral cavity, intestines, urogenital tract. The document also discusses the benefits these normal flora provide, as well as potential issues like opportunistic infections when the normal flora is disrupted due to factors like antibiotic abuse, immune suppression, surgery or radiation. It introduces concepts like microeubiosis, microdysbiosis, and nosocomial infections.

1. Medical Microbiology Department of Microbiology, HMU

2. Section III Bacteriology Normal Microbial Flora in Human Body Zhao-Hua Zhong, Ph.D., Prof. Department of Microbiology Harbin Medical University

3. KEY TERMS Pathogen Opportunistic infection Microdysbiosis Translocation Medical Microecology Nosocomial Infection

4. Pathogenic Bacteria 少数 细菌总有致病性 许多 细菌具有潜在致病性 大多 细菌不具有致病性

5. Normal Microbial Flora the population of microorganisms that inhabit the skin and mucous membranes of healthy normal persons It is doubtful whether a normal viral flora exists in humans

6. Normal Microbiota= Normal Flora Normal microbiota Normal microflora Physiological microbiota

7. Normal Microbial Flora Groups Resident flora consists of relatively fixed types of microorganisms regularly found in a given area at a given age If disturbed, it promptly reestablishes itself Transient flora consists of nonpathogenic or potentially pathogenic microorganisms that inhabit the skin or mucous membranes for hours, or days

8. Transient Flora It is derived from the environment , does not produce disease, and does not establish itself permanently on the surface Members of the transient flora are generally of little significance so long as the normal resident flora remains intact If the resident flora is disturbed , transient microorganisms may colonize, proliferate, and produce disease

9. Classifications of Normal Flora Enviroment Autochthony (= aborigines) Allochthony (= foreign) Relation with host Symbiotic flora Parasitism flora

10. Microecosystem - Microecology Skin Mouth Nasopharynx Ear Eye Gastrointestine Urinary truct Reproductive tract Staphy E. coli Pseudomonas Strepto Nesseria Corynebacteria … . … .

12. Skin Flora The surface of the skin itself comprises several distinct environments the axilla (armpit) the perineum (groin) the toe webs provide typically moister regions for bacterial growth. These "tropical forest" environments often harbor the largest diversity amongst the skin flora Typical organisms include Staphylococcus aureus, Corynebacterium and some Gram-negative bacteria predominantly inhabited by Staphylococcus epidermidis and Propionobacterium

13. Oral Cavity and Nasopharyngeal Flora Streptococci predominate in the oral cavity and nasopharyngeal regions Other anaerobes and species of Neisseria Many potential pathogens may also be found in the nasopharynx of a healthy individual, providing a reservoir for infection of others These pathogens include Streptococcus pneumoniae , Neisseria meningitidis and Haemophilus influenzae

14. Intestinal Flora The intestinal tract is a rather hostile environment for microorganisms the colon may contain 10 9 to 10 11 bacteria per gram of material Most (95 - 99.9%) of these are anaerobes, represented by Bacteroides , Bifidobacterium, anaerobic streptococci and Clostridium These organisms inhibit the growth of other pathogens but some can be opportunistic (e.g. C. difficile can produce pseudomembranous colitis )

15. Urogenital Flora The urogenital tract is normally sterile with the exception of the vagina and the distal 1 cm of the urethra Vagina the genus Lactobacillus predominate in the vagina Lactobacillus generally lower the pH to around 4-5, which is optimal for the lactobacilli but inhibitory for the growth of many other bacteria Loss of this protective effect by antibiotic therapy can lead to infection by Candida ("yeast infection") Urethra may contain predominantly skin microorganisms including staphylococci, streptococci and diphtheroids

16. Normal Flora Skin Staphylococcus aureus , S. epidermidis Propionibacterium acnes Intestine Bacteroides high numbers Enterobacteriaceae low number

17. Biological Outcomes Help us by competing with pathogens such as Salmonella Help us by providing vitamins or eliminating toxins (e.g. Bacteroides) Harm us by promoting disease (e.g. dental caries) Cause neither help nor harm (e.g. "commensals")

18. Physiological Benefits Antagonism Bio-barrier: microcolony Chemical barrier Nutrient competition Provide nutrients Stimulate immune system Anti-tumor

19. 占位性生物屏障作用

20. Opportunistic Infections Compromised people normal flora Environment

21. Microeubiosis / Microdysbiosis Microeubiosis Normal flora Location Quality Quantity Host Environment Microdysbiosis Flora disequilibrium Dysbacteriosis Translocation Horizontal Vertical Blood

22. Causes of Microdysbiosis Abuses of Antibiotics Radiation Surgery Use of immune suppressors Use of hormones Acquired immune deficiency

23. Opportunistic pathogen E. coli Klebsiella Pseudomonas Enterbacteria Staphy Opportunities Translocation Dysbacteriosis Immune suppression

24. Hospital Infection Nosocomial infection Hospital-acquired infection