Normal FloraNormal FloraNormal FloraNormal Flora

What’s growing on us?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. (NOT N.

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