ANAEROBES AS NORMAL FLORA AND SOURCE OF BIOACTIVE COMPOUNDS
Composition of normal flora
The human body mucosal and epithelial surfaces are colonized with aerobic and anaerobic micro-organisms.1 Anaerobes outnumber aerobic bacteria on all mucosal surfaces, and certain organisms predominate in the different sites (Table 1). Differences in the environment, such as oxygen tension, pH and variations in the ability of bacteria to adhere to these surfaces, account for changing patterns of colonization. Microflora also varies in different sites within the body. In the oral cavity the organisms in the buccal folds vary in their concentration and strains types from those isolated from the tongue or gingival sulci. The prevailing organisms in one body system tend to belong to certain major bacterial species. The relative and total counts of organisms can be affected by various factors, such as age, diet, anatomic variations, illness, hospitalization and antimicrobial therapy. However, these predictable pattern of bacterial flora remain stable through life.
Recognizing the flora at certain sites is useful for predicting which organisms may be involved in an infection adjacent to that location and can assist in the selection of empiric antimicrobial therapy, even before the exact microbial etiology is known. The clinical microbiology laboratory considers the site`s normal flora and chooses selective culture media that interferes with the growth of certain bacteria.
Recognizing the flora at certain sites is useful for predicting which organisms may be involved in an infection adjacent to that location and can assist in the selection of empiric antimicrobial therapy, even before the exact microbial etiology is known. The clinical microbiology laboratory considers the site`s normal flora and chooses selective culture media that interferes with the growth of certain bacteria.
The anaerobic skin flora is made up of Propionibacterium2 ( mostly Propionibacterium acnes ) and Peptostreptococcus spp. The perineum and lower extremity are colonized by colonic and vaginal flora.
The upper airways flora (oral, nasopharynx and oropharynx) is complex and contains many types of anaerobes. 1 Their distribution within the mouth is a function of their adherence and susceptibility to oxygen. The ratio of anaerobic bacteria to aerobic bacteria in saliva is approximately 10:1. The total count of anaerobic bacteria in the saliva and elsewhere in the oral cavity reach 107–108 bacteria/ml. The predominant anaerobes in the upper airways include Fusobacterium spp. (especially Fusobacterium nucleatum), pigmented Prevotella and Porphyromonas spp., Prevotella oralis and Peptostreptococcus spp.They also predominate in oropharyngeal, otolaryngologic and pulmonary infections.
The gastrointestinal flora varies at different levels. The stomach acidity reduces the number of organisms swallowed from the oropharynx. The stomach, duodenum, jejunum and proximal ileum normally contain few bacteria. The bacterial counts in the small intestine are relatively low, with total counts of 102–105 organisms/ml. However, the flora becomes more complex, and the number of species increases in the distal portion of the gastrointestinal tract. Interruption in intestinal motility may result in an increase in the number of bacteria. The organisms that predominate up to the ileocecal valve are Gram-positive facultative, whereas below that structure Bacteroides, Peptostreptococcus and Clostridium spp., and coliform bacteria predominate.3 The mean number of bacteria in the colon exceeds 1011 bacteria/g fecal material. Approximately 99.9% of these bacteria are anaerobic (ratio of aerobes to anaerobes is 1:1000–10,000). In the colon 300–400 different species or types of bacteria can be found.
Indigenous microflora of the colon
The female genital flora is composed of mixed aerobic and anaerobic flora. However, the concentration and type of bacteria is less stable and can be influenced by antimicrobial therapy, pregnancy and gynecologic surgery. A concentration of 108 organisms/ml is present during the reproductive years. Changes occur in the number of organisms at the various stages of the menstrual cycle.4 The predominant aerobic organisms are lactobacillus, and the predominant anaerobic bacteria are anaerobic Lactobacillus, Peptostreptococcus, Prevotella, Bacteroides spp. and Clostridium spp. Other anaerobic include Porphyromonas. Fusobacterium, Bilophilia, Bifidobacterium, Actinomyces,Eubacterium, and Propionibacterium spp. Enterobacteriaceae can be found in postmenopausal flora. Bacterial vaginosis is associated with an increase in the number of anaerobic flora and a decrease in the concentration of lactobacilli.5
The role of bacterial flora in infections
Most anaerobic infections originate from the endogenous mucosal membrane and skin flora. Anaerobes belonging to the indigenous flora of the oral cavity can be recovered from adjacent infections, such as cervical lymphadenitis, subcutaneous abscesses and burns in proximity to the oral cavity, human and animal bites, paronychia, tonsillar and retropharyngeal abscesses, chronic sinusitis, chronic otitis media, periodontal abscess, thyroiditis, aspiration pneumonia, and bacteremia associated with one of the above infections.3 The predominant anaerobes in these infections are Prevotella,Prevotella, Porphyromonas, Fusobacterium and Peptostreptococcus spp., which are all part of the normal flora of the mucous surfaces of the oropharynx (Tables 2,3).
A similar correlation exists in infections associated with the gastrointestinal tract. Such infections include peritonitis after rupture of a viscus, liver and spleen abscess, abscess and wounds near the anus, intra-abdominal abscess, and bacteremia associated with any of these.3 The predominate anaerobes are B. fragilis group, Clostridium spp. (including C. perfringens) and Peptostreptococcus spp.
Another site where a correlation exists between the normal flora and the anaerobic bacteria recovered from infected sites is the genitourinary tract. The infections involved are amnionitis, septic abortion and other pelvic inflammations.3 The recovered anaerobes are usually Gram-negative bacilli and Peptostreptococcus spp. Organisms belonging to the vaginal–cervical flora are also important pathogens of neonatal infections. They can be acquired by the newborn before delivery in the presence of amnionitis, or during passage through the birth canal.
Anaerobes
as sources of health promoting bioactive compounds
Anaerobes
possess diverse physiological functions and are capable of producing
a range of bioactive compounds that can promote human health.
Anaerobes play health-promoting roles through their bioactive products as well
as by their whole cells. The bioactive compounds produced by these
microorganisms include antimicrobial agents and substances such as
immunomodulators and vitamins. Bacteriocins produced by anaerobes have been used as preservatives for decades. Because these substances are
effective at low concentrations, encounter relatively less resistance from
bacteria and are safe to use, there is a growing interest in their antimicrobial activity.
Several
antimicrobials have been recovered from the cultures of anaerobes. Closthioamide
and andrimid produced by Clostridium cellulolyticum and Pantoea agglomerans,
respectively, are examples of novel antibiotics of anaerobic bacteria origin.
As research expands more such agents may be discovered.
Anaerobes
are widely used in preparation of fermented foods and beverages. During the
fermentation processes, these micro-organisms produce a number of bioactive
compounds including anticancer, antihypertensive and antioxidant substances.
The health promoting effect of fermented food is mostly due to these bioactive
compounds.
In
addition to their products, whole cell anaerobes enhance the quality of life.
Probiotic anaerobeic bacteria have been used for many years and are achieving
growing acceptance as health promoters. Gatrointestinal anaerobes have been used to treat severe Clostridium difficile infection syndromes
including diarrhea and colitis which cannot be treated by other modalities.
Whole
cell anaerobes are also studied to detect and treat cancer. Growing evidence is emerging that anaerobic bacteria that are members of the human microbiome are
linked to individual’s overall health. A dysfunctional microbiome may be the cause of many diseases including cancer, allergy, infection, obesity,
diabetes and several other disorders. Maintaining normal endogenous microflora is believed
to alleviate some of these life threatening health problems. The use of probiotics and
prebiotics which favorably alter the number and composition of the gut
microflora is known to render a health promoting effect.
Human’s
interaction with the microbiome anaerobes is complex. The unraveling of the
associations between the human microbiome and the human body, may bring a significant shift in the way these diseases are diagnosed and treated. Application of this knowledge can enhance human health
and improve the quality of life.
REFERENCES
1. Hentges DJ.The anaerobic microflora of the human body. Clin Infect Dis. 1993 ;16 4:S175-80.
2. Brook I, Frazier EH. Infections caused by Propionibacterium species. Rev Infect Dis 1991;13:819–22.
3. Finegold SM. Anaerobic infections in humans: an overview. Anaerobe 1995;1:3–9.
3. Finegold SM. Anaerobic infections in humans: an overview. Anaerobe 1995;1:3–9.
4. Bartlett
5. Vallor AC, Antonio MA, Hawes SE, et al. Factors associated with acquisition of, or persistent colonization by, vaginal lactobacilli: role of hydrogen peroxide production. J Infect Dis. 2001;184:1431-6.
6. Mamo G. Anaerobes as Sources of Bioactive Compounds and Health Promoting Tools. Adv Biochem Eng Biotechnol. 2016 Jul 19.
6. Mamo G. Anaerobes as Sources of Bioactive Compounds and Health Promoting Tools. Adv Biochem Eng Biotechnol. 2016 Jul 19.
Table 1: Normal Flora
Predominant
| |||
No. of organisms/gr
|
anaerobic
| ||
Site
|
Aerobes
|
anaerobes
|
bacteria
|
skin
|
P. acnes
| ||
Peptostreptococcus sp.
| |||
mouth/upper respiratory tract
|
108-9
|
109-11
|
pigment Prevotella & Porphyromonas spp.
|
Fusobacterium spp.
| |||
Peptostreptococcus spp.
| |||
Actinomyces spp.
| |||
Gastrointestinal tract
| |||
upper
|
102-5
|
103-7
|
( B. fragilis group
|
( Clostridium spp.
| |||
lower
|
105-9
|
1010-12
|
( Peptostreptococcus spp.
|
( Bifidobacterium spp.
| |||
( Eubacterium spp.
| |||
female genital tract
|
108
|
109
|
Peptostreptococcus spp.
|
Prevotella bivia
| |||
Prevotella disiens
| |||
Table 2: Recovery of anaerobic bacteria in infectious sites
Infection | Peptostrepto- coccus sp. | Clostridium sp. | Bacteroides
fragilis
group
| Pigmented Prevotella and Porphyromonas | P. bivius
P. disien
| Fuso-bacterium sp. |
Bacteremia
|
1
|
1
|
2
|
1
|
0
|
1
|
Central nervous system
|
2
|
1
|
1
|
2
|
0
|
1
|
Head and neck
|
3
|
1
|
1
|
3
|
0
|
3
|
Thoracic
|
2
|
1
|
1
|
3
|
0
|
3
|
Abdominal
|
3
|
3
|
3
|
1
|
1
|
1
|
Obstetric-gynecology
|
3
|
2
|
1
|
1
|
2
|
1
|
Skin and soft tissue
|
2
|
1
|
2
|
2
|
1
|
1
|
Frequency of recovery in anaerobic infections: 0 = none, 1 = rare (1% to 33%), 2 = common (34% to 66%), 3 = very common (67% to 100%).
Table 3: Aerobic and anaerobic bacteria isolated in type of infection
Type of infection
|
aerobic and facultative organism
|
Anaerobic
|
Pleuro pulmonary
|
Streptococcus viridans
|
Pigmented Prevotella (P. denticola, P. melaninogenica, P. intermedia, P. nigrescens, P. loescheii)
|
Staphylococcus aureus*
|
Nonpigmented Prevotella (P. oris, P. buccae, P. oralis)
| |
Enterobacteriaceae *
|
Fusobacterium nucleatum (subsp. nucleatum, polymorphum)
| |
Pseudomonas aeruginosa
|
Peptostreptococcus (P. micros, P. anaerobius, P. magnus)
| |
Bacteroides fragilis group
| ||
Non-spore-forming gram-positive rods (Actinomyces, Eubacterium, Lactobacillus)
| ||
Intra-abdominal
|
Escherichia coli
Streptococcus (viridans group and group D)
Pseudomonas aeruginosa
|
Bacteroides fragilis group
Bilophila wadsworthia
Peptostreptococcus (especially P. micros)
Clostridium spp.
|
Female genital tract
|
Streptococcus (groups A, B, others)
Escherichia coli
Klebsiella pneumoniae
Neisseria gonorrhea (in sexually active patients)
Chlamydia (in sexually active patients)
Mycoplasma hominis (in postpartum patients)
|
Peptostreptococcus spp.
Prevotella (especially P. bivia, P. disiens)
Bacteroides fragilis group
Clostridium (especially C. perfringens)
Actinomyces, Eubacterium (in intrauterine contraceptive device-associated infections)
|
Skin and Soft tissue
|
Staphylococcus aureus
Streptococcus (Str. milleri group, groups A, B viridans group)
Enterococcus spp.‡
Enterobacteriaceae‡
Pseudomonas aeruginosa*
|
Peptostreptococcus (P. magnus, P. micros, P. asaccharolyticus)
Pigmented Prevotella spp.
Actinomyces spp.
Fusobacterium nucleatum
B. fragilis group‡
Clostridium spp. ‡
|
* = recovered in hospital-acquired infection
‡ = better exposure to colonic flora.