Saliva: An Oral Microbial Modulating

Agent

A seminar presentation by:

AJEIGBE Yekeen Abiola

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Department of Microbiology,

University of Ilorin, Nigeria.

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Contents Introduction

Salivary glands

General functions of the Saliva

Components of the saliva

Selected immunoactive components of the saliva

Lifestyle factors affecting salivary flow

Effects of reduced salivary flow

Oral microbiota and general health

Saliva and dental caries

Wound licking

Conclusion

References

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Introduction The oral cavity is the gateway of the body to the external

world and represents one of the most biologically complex and significant sites in the body (Amerongen and Veerman, 2002).

Present in the oral cavity of health individuals is a watery fluid known as saliva/spittle/spit/slobber. The importance of the saliva in the mouth is more than most realize and while the digestive functions of saliva are well known and publicized, the saliva also possess considerable anti-microbial functions amongst other functions(Lamont and Jenkinson, 2010).

The anti-microbial functions of saliva are quite important for healthy living.

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Physical properties of saliva

Unstimulated saliva is an hypotonic, dilute viscous solution containing both organic and inorganic substances found in the oral cavity of Homo sapiens (Lamont and Jenkinson, 2010).

Around 0.5 to 1.5 liters of saliva are secreted into the mouth each day (Jensen et al., 2003: Humphrey and Williamson, 2003).

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Salivary Glands Saliva is secreted in glands aptly called

salivary glands.

Saliva is secreted by three (3) major salivary glands namely parotid, sub-mandibular and sub-lingual (Fig 1) and these secrete about 90% of the saliva in the mouth.

Hundreds of minor salivary glands such as lingual, labial, buccal, palatine and glossopalatine glands, also secrete saliva and these accounts for the remaining 10% of saliva in the oral cavity. (Pedersen et al., 2002; Humphrey and Williamson, 2001; Cassolato and Turnbull, 2001).

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6Fig 1: Location of salivary glands in the oral cavitySource; Britannica, 2003

General functions of the salivaFood

Taste Digestion Bolus formation

Teeth and submucosa Buffer

Protection against demineralization

Lubrication

Remineralization

MIC

RO

OG

AN

ISM

S

Source: Lamont and Jenkinson, 2010; Amerongen and Veerman, 2002; Marcotte and Lavoie, 1998.

Components of the salivaDigestive components Amylase

Gustin

Buffering components Carbonic anhydrase

Statherin

Proteins

Albumin

Lysozyme

Lactoferrin

Mucin glycoprotein 1 and 2 (MG 1 and 2)

Secretory Immunoglobulin A

Cystatins

Peroxidase

Histatines

Proline-rich proteins (PRPs)

Immunoactive components

Source: Lamont and Jenkinson, 2010; Amerongen and Veerman, 2002; Marcotte and Lavoie, 1998.

Selected immunoactive components

Description: Lactoferrin (formerly known as lactotransferrin) is a glycoprotein, and a member of a transferrin family, thus belonging to those proteins capable of binding and transferring iron (Fe3+) ions (Metz-Boutique et al., 1984).

Lactoferrin

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Selected immunoactive components

Antimicrobial activities – Bacteriostatic, bactericidal, antiviral, fungicidal, anti-inflammatory. Lactoferrin affects microorganisms which are iron dependent

such as enteroinvasive E. coli HB 101, Yersinia enterocolica, Yersinia pseudo tuberculosis, Listeria monocytogenes, Streptococcus pyogenes, and Staphylococcus

Lactoferrin also reduces the entry of viruses such as Herpes simplex virus (Marchetti et al., 1996; Fujihara and Hayashi, 1995), cytomegaloviruses (Andersen et al., 2001), and the human immunodeficiency virus (Harmsen et al., 1995), respectively

Lactoferrin

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Selected immunoactive components

Immunoactivities – Lactoferrin links to free iron in the saliva causing bactericidal or

bacteriostatic effects on various microorganisms requiring iron for their survival (Kirkpatrick et al., 1971).

Lactoferrin contribute to defense against the invasion of facultative intracellular bacteria into cells by binding both target cell membrane glycoaminogly cans and bacterial invasins, which prevents pathogen adhesion to target cells (Valenti and Antonini, 2005).

Its main contribution to antiviral defense consists in its bind ing to cell membrane glycosaminoglycans (Amerongen and Veerman, 2002; Nikawa et al., 1993; Edgar, 1992).

Lactoferrin

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Selected immunoactive components

Description - Lysozyme is a single chain polypeptide of 129 amino acids cross-linked with four disulfide bridges (Jolles, 1969) and is a basic protein found in most secretions, including saliva, where it is present in high concentrations.

Salivary lysozyme originates from both the salivary gland secretions and from gingival crevicular fluid (Lamont and Jenkinson, 2010).

Lysozyme

Selected immunoactive components

Antimicrobial activitiesBactericidal on gram positive bacteria such as

species of Micrococcus, Staphylococcus, Streptococcus, Enterococcus, Lactococcus, Aerococcus and so on.

Gram negative bacteria such as Haemophilus and Bacteroides are less susceptible due to the presence of an outer membrane and a lower proportion of peptidoglycan (Sigma, 2012).

Lysozyme

Selected immunoactive components

ImmunoactivitiesThe natural substrate for lysozyme is the peptidoglycan

layer of bacterial cell walls (Holtje, 1996). Hence, lysozyme hydrolyzes/digests the cell walls of

Gram-positive bacteria by breaking the β (1-4) bond between N-acetylmuramic acid and N-acetylglucosamine in peptidoglycan (Figure 4) and between N-acetyl-D-glucosamine residues in chitodextrin (Rupley, 1964; Holler, 1975).

Lysozyme

Selected immunoactive components

Lysozyme

Video 1: Action of lysozymeSource: Garland Science, 2009

Selected immunoactive components

Secretory Immunoglobulin A

Description - The major immunoglobulin in the salivary secretions is immunoglobulin A (IgA). This molecule is secreted as a complex with a linking chain by cells that are found close to the parotid gland. The secreted form of IgA is called secretory IgA (or S-IgA) (Marcotte and Lavoie, 1998). S-IgA is found at all mucosal sites, such as the

gastrointestinal tract, respiratory tract and urogenital tract, and it is also present in tears and breast milk (in addition to saliva) (Humphrey and Williamson, 2001).

Selected immunoactive components

Secretory Immunoglobulin A

Fig 2: Schematic representation of SIgA.Source: Marcotte and Lavoie, 1998.

Selected immunoactive components

Secretory Immunoglobulin A

Antimicrobial activities - Bactericidal, bacteriostatic, antiviral and also neutralizes enzyme toxins.

Selected immunoactive components

Secretory Immunoglobulin A

Immunoactivities – The immunoactivities of S-IgA include: Immune exclusion Inhibition of bacterial adherence Toxin neutralization Viral immunity

Selected immunoactive components

Immune Exclusion

Immune exclusion consists of limiting the penetration of antigenic materials through the mucosal epithelium. This involves the binding of SIgA antibodies with antigens, which facilitates their removal from mucosal surfaces (Marcotte and Lavoie, 1998).

Selected immunoactive components

Inhibition of bacterial adherence

The binding of SIgA to adhesins can reduce the negative surface charge and the hydrophobicity of bacteria, thus limiting the potential for ionic and hydrophobic interactions between bacteria and host receptors (Marcotte and Lavoie, 1998).

Free in saliva, polymeric IgA effectively aggregates bacteria (Lamont and Jenkinson, 2010).

Selected immunoactive components

Toxin Neutralization

SIgA can neutralize toxins by blocking their binding to cell receptors (Marcotte and Lavoie, 1998).

Glycans on S-IgA are also able to non-specifically trap bacteria (Lamont and Jenkinson, 2010).

Selected immunoactive components

Viral Immunity

SIgA plays an important role in viral immunity because of its presence at the site of initial contact between virions and host cells.

A protective effect of SIgA against respiratory and enteric viral infections has been demonstrated (Marcotte and Lavoie, 1998).

Table 1: Summary of Immunologic components of the saliva

Immunoactive

Component

Function/Activity

Cystatin Bacteriostatic

Histatin Bactericidal and fungicidal

Lactoferrin Iron sequestration

Lysozyme Bactericidal (More effective on gram positive bacteria due

to the peptidoglycan in their cell walls)

Peroxidase Bactericidal

Proline-Rich Proteins Bacteriostatic and bactericidal.

Mucin-glycoprotein 1

and 2

Bactericidal, physical removal of microorganisms

Secretory

Immunoglobulin A

Bacteriostatic, bactericidal, anti-viral, toxin neutralization

Statherin Bacteriostatic

Thrombospondin Antiviral

Source: Lamont and Jenkinson, 2010; Amerongen and Veerman, 2002; Marcotte and Lavoie, 1998.

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Inactivation of salivary defenses Some Streptococcus, Haemophilus and Neisseria

species produce proteases that specifically cleave S-IgA1, disrupting functions such as complexing and clumping (Tachezy et al., 1996).

Other bacteria produce glycan hydrolysases that cleave sugar chains from mucins. This causes changes in mucin properties making them much less efficient, both in binding bacteria and in lubrication (Lamont and Jenkinson, 2010).

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Lifestyle factors affecting salivary flow

Smoking; Certain drugs and therapies; Emotional states such as anxiety, stress and fear

(dry mouth phenomenon); Oral hygiene (Brosky, 2007).

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Effects of hyposalivation

Xerostomia;Disruption of normal homeostasis of the oral

cavity;Increased susceptibility to a range of oral and

den tal disorders;Difficulty in taste, eating and speech (Brosky,

2007).

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Table 2: Important Oral Diseases, their manifestations and microorganisms implicated

Disease Description Microorganisms implicatedDental Caries Decay (loss) of tooth enamel (dental caries) or

dentin (dentinal caries), or root dentin (root caries)Streptococcus, Lactobacillus, Actinomyces (root caries)

Periodontitis Inflammation and either rapid (aggressive, either generalized or localized) or slower (chronic) destruction of the tissues supporting the tooth

Aggregatibacter (localized), Porphyromonas, Treponema, Tannerella, Fusobacterium, Prevotella

Gingivitis Redness and swelling (inflammation) of the gingival tissues (gums)

Actinomyces, Fusobacterium, Bacteroides, Prevotella

Pharyngitis Redness and inflammation of the pharynx. Group A Streptococcus, Neisseria, Haemophilus, Coxsackie A virus

Stomatitis Reddening and inflammation of the oral mucosa Candida albicans, Candida tropicalis, other Candida species.

Source: Lamont and Jenkinson, 2010.

Oral microbiota and general health

Saliva and dental caries

Fig 3: Factors affecting dental cariesSource: Saliva and Dental Caries, 2000

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Conclusion

Most individuals regard saliva as a nuisance and just another bodily function. However, the saliva as simple as it is may appear, represents one of the most important secretions present in the body and while we may not fully understand all its activities and interactions, we should all be grateful for such a wonderful substance and hence, take better care of our body by taking better care of our mouth.

References Amerongen A.V. and Veerman E. C. (2002). Saliva: The Defender of The Oral Cavity: Oral Dis. 8: 12-22.

Andersen J.H., Osbakk S.A., Vorland L.H., Traavik T., Gutteberg T.J. (2001): Lactoferrin And Cyclic Lactoferricin Inhibit The Entry Of Human Fibroblasts. Antiviral Research, 51: 141–149.

Cassolato S. F. and Turnbull R. S. (2003). Xerostomia: clinical aspects and treatment. Gerodontology. 20:64–77.

Harmsen M.C., Swart P.J., De Bethune M.P., Pauwels R., De Clercq E., The T.H., Meijer D.K.F. (1995): Antiviral Effects Of Plasma And Milk Proteins: Lactoferrin Shows Potent Activity Against Both Human Immunodeficiency Virus And Human Cytomegalovirus Replication In Vitro. The Journal Of Infectious Diseases, 172, 380–388

Humphrey SP, Williamson RT. A Review Of Saliva: Normal Composition, Flow, And Function. J Prosthet Dent. 2001; 85:162-169.

Jensen SB, Pedersen AM, Reibel J, Nauntofte B. Xerostomia and hypofunction of the salivary glands in cancer therapy. 2003; 11: 207–225. [12673459]

Jolles, P., Angewandte Chemie, International Edition, 8, 227-239 (1969).

Kirkpatrick C.H., Green I., Rich R.R., Schade A.L. (1971): Inhibition Of Growth Of Candida Albicans By Iron-Unsaturated Lactoferrin: Relation To Host-Defense Mechanisms In Chronic Mucocutaneous Candidiasis. The Journal Of Infectious Diseases, 124, 539–544.

Marchetti M., Longhi C., Conte M.P., Pisani S., Valenti P., Seganti L. (1996): Lactoferrin Inhib-its Herpes Simplex Virus Type 1 Adsorption To Vero Cells. Antiviral Research, 29, 221–231.

Metz-Boutique M.H., Jolles J., Mazurier J., Schoentgen F., Legrand D., Spik G., Montreuil J., Jolles P. (1984): Human Lactotransferrin: Amino Acid Sequence And Structural Comparisons With Other Transferrins. European Journal Of Biochemistry, 145, 659–676.

Nikawa H, Samaranayake LP, Tenovuo J, Pang KM, Hamada T. The Fungicidal Effect Of Hu-man Lactoferrin On Candida Albicans And Candida Krusei. Arch Oral Biol. 1993;38:1057-1063.

Pedersen AM, Bardow A, Jensen SB, Nauntofte B. Saliva and gastrointestinal functions of taste, mastication, swallowing and digestion. Oral Dis 2002;8:117–129. [12108756]

Richard J. Lamont and Howard F. Jenkinson (2010) .Oral microbiology at a glance /.(At a glance series). ISBN 978-0-8138-2892-3 (pbk. : alk. paper)

Valenti P., Antonini G. (2005): Lactoferrin: An Important Host Defense Against Microbial And Viral Attack. Cellular And Molecular Life Sciences, 62, 2576–2587.

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Thank you