Normal Flora What’s growing on us?
Normal flora (mostly bacteria) • In the past Medical Microbiology was largely focused on those organisms that were frankly pathogenic. • It is now known that those microorganisms that normally colonize the human host without disease production can play an important role in the disease process. • Many of those once considered to be innocuous members of the normal flora are now known to be potentially pathogenic under certain circumstances (what circumstances?). Therefore, it’s important to acquire knowledge about our normal flora because:
Normal Flora • An understanding of the different normal flora (NF) found at specific body locations provides greater insight into the possible infections that might result from injury to those body sites. • A knowledge of the native organisms in the infected part of the body gives the clinician perspective on the possible source and/or significance of microorganisms isolated from the site of infection.
Normal Flora • Before a discussion of adult NF begins, a discussion of how or when NF is acquired is essential. • A healthy fetus, in utero, is essentially free of microorganisms. • The infant is exposed to NF from the mom’s vaginal tract during the delivery process and to microorganisms in the environment almost immediately thereafter.
Normal Flora • Within a few hours, the oral and nasopharyngeal flora of the neonate are established. • Within one day the resident microflora of the lower intestinal tract are established. • Adult NF refers to microorganisms that normally live on or in any part of the body without causing disease. There are two basic types of NF:
Normal Flora • Resident organisms – these are organisms that normally GROW on or in the indicated body site. Their presence becomes fixed in well defined distribution patterns. • Transient organisms – These organisms are only temporarily present on or in the indicated body site. They usually don’t become firmly entrenched, but simply die within a few hours.
Normal Flora • NF of the skin • The actual physiology of the skin varies from one part of the body to another and the resident microflora reflect these variations. • The skin, itself, is not a very favorable environment for the colonization of microorganisms. • Therefore, there are few resident microorganisms, but many transient microorganisms. Why is the microenvironment hostile?:
Normal Flora • The skin is subject to periodic drying. However, in certain parts of the body (body folds or areas near orifices), there is sufficient moisture to support the growth of resident microorganisms • Skin has a slightly acidic pH due to organic acids produced by normal secretions from the sebaceous and sweat glands and by Staphylococcus epidermidis that normally resides there. This prevents the colonization by many organisms. • Sweat contains a high content of NaCl, thus producing a hypertonic condition on the skin surface that osmotically stresses many microorganisms.
Normal Flora • The skin surface contains many inhibitory substances that help control colonization, overgrowth, and production of infectious disease by resident microorganisms. Remember that colonization does not necessarily mean infection and disease. • Lysozyme – is produced by the sweat glands and acts to lyse G+ organisms, including Staph. epidermidis • Complex lipids – are metabolized by Propionobacterium acnes to unsaturated fatty acids that have antimicrobial activity. These produce a strong odor. Use of deodorants that have antibacterial substances to inhibit the growth of these G+ organisms may lead to the growth of a preponderance of G- organisms and the subsequent development of infection.
Normal Flora • Most skin NF are found on the superficial squamous epithelium colonizing dead cells or closely associated with the sebaceous and sweat glands. The secretions from these glands provide the environmental conditions and nutrients for the growth of:
Skin Normal Flora Staph. epidermidis and Staph. aureus
Skin NF Propionibacterium acnes – this is an anaerobic G+ branching bacillus
Skin NF • P. acnes is usually harmless, but has been associated with acne vulgaris (acne), particularly during adolescence when there is an overproduction of the fluid secreted by the sebaceous glands (sebum). • This provides the ideal environment for the growth of P. acnes and substances produced by the organisms may trigger an inflammatory response leading to the production of acne. • Tetracycline or accutane (prevents sebum secretions, but has some severe side effects) may be used for treatment of acne.
Skin NF Diphtheroids (aerobic corynebacterium)
Skin NF Streptococcus species
Skin NF Clostridium perfringens
Skin NF Candida albicans
Normal Flora • Normal flora of the nose and nasopharynx (part of the pharynx above the soft palate) • Staph aureus* • Staph epidermidis • Diphtheroids • Streptococcus pneumoniae* • Haemophilus influenzae* • Neisseria meningitidis* • * may be causing disease if found in large numbers (relative numbers are important)
Nose/nasopharynx NF Neisseria meningitidis
Nose/nasopharynx NF Haemophilus influenzae
Normal Flora • Normal flora of the oral cavity and oropharynx • Organisms found are those that are able to resist mechanical removal by adhering to various surfaces such as the gums and teeth. • Those bacteria that can’t resist the mechanical flushing of the oral cavity are swallowed and destroyed by the HCl in the stomach. • This is a comfortable environment for microorganisms due to the availability of water and nutrients. The most common NF in this area includes:
Normal oral flora • viridans group Streptococcus species • Strep. pyogenes* • Diphtheroids • Staph. epidermidis • Staph. aureus* • Neisseria meningitidis* • Other Neisseria species • Haemophilus influenzae* • Other Haemophilus species
Normal oral flora • Candida albicans* • Actinomycetes sp.* • Lactobacillus sp. • Bacteroides sp. • Fusobacterium sp. • Enterobacteriaceae* • * these organisms are probably causing infection if they are the predominant organism found in this area or they are found in large numbers.
Normal oral flora Actinomycetes
Normal oral flora Granules of Actinomycetes
Normal oral flora Bacteroides sp.
Normal oral flora Fusobacterium sp.
Normal oral flora Fusobacterium nucleatum
Normal oral flora Lactobacillus
Normal oral flora E. coli (a member of the Enterobacteriaceae)
Normal oral flora Some of the Strep. species that adhere to the teeth (sanguis, mutans, salivarious) contribute to the formation of dental plaques and caries
Normal Flora • Normal flora of the alimentary tract • Because of the high acidic content of the stomach, very few organisms are found there. They include: • Candida sp. • Lactobacilli • A few Strep. sp. (mainly Enterococcus faecalis) • The small intestine also has few microorganisms because of the combined inhibitory effects of stomach acid, bile, and pancreatic secretions. Normal flora include:
Normal intestinal flora • Enterococcus faecalis • Lactobacilli • Diphtheroids • Candida sp. • The large intestine has the largest microbial population in the body. There are 1012 organisms excretedper gram of wet weight feces. • Over 300 different species of bacteria are normally found in the large intestine
Normal intestinal flora • The anaerobic/facultatively anaerobic ratio of organisms is 300/1 and includes the following: • Bacteroides sp. • Fusobacterium sp. • Lactobacillus • Clostridium sp. • Peptostreptococcus sp. • Staph. sp. • Enterococcus faecalis
Normal intestinal flora • Other Strep. sp. • Pseudomonas species • Enterobacteriaceae • Candida sp.
Normal intestinal flora Pseudomonas species
Normal intestinal flora Peptostreptococcus species
Normal intestinal flora • Normal physiological processes move the microorganisms through the colon so that a normal adult excretes 3X 1013 microorganisms daily. • Under normal conditions the resident flora are self-limiting. Competition( for example, colicin produced by E. coli) and mutualism between them and the host (E.coli produces vitamin K and B for the host) maintains the status quo.
Normal intestinal flora • Anything the disturbs the intestinal environment (stress, altitude change, starvation, diarrhea, antibiotics) can serve to greatly alter the normal flora leading to gastrointestinal disease such as yeast infections and antibiotic associated pseudomembraneous colitis.
Normal flora • NF of the genitourinary tract • NF of the urethra include: • Staph. epidermidis • Enterococcus faecalis • Diphtheriods • Neisseria sp. (NOTN. gonorrhoeae) • Enterobacteriaceae • NF of the vaginal tract – the microflora present on this large, moist surface area changes with the menstrual cycle. Organisms include:
Normal genitourinary flora • Lactobacillus • Bacteroides • Enterococcus sp. • Staph. epidermidis • Diphtheroids • Strep. agalactiae • Clostridium perfringens • Peptostreptococcus • Enterobacteriaceae • Candida albicans
Normal genitourinary flora • NF of the external genitalia include: • Strep. sp. • Staph. sp. • Diphtheroids • Bacteroides • Candida sp.