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 • 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 • 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 • 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 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
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 • Staphylococcus epidermidis • Enterococcus faecalis • Diphtheriods • Neisseria sp. (NOTN. gonorrhoeae) • Enterobacteriaceae
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
GU Tract Normal Flora: External Genitalia • Streptococcus sp. • Staphylococcus sp. • Diphtheroids • Bacteroides • Candida sp.
Class Assignment • Textbook Reading: Chapter 2 Host-Pathogen Interaction • A. The Role of the Usual Microbial Flora • Key Terms • Learning Assessment Questions