Microbial Flora and Pathogenicity

2 February 2017

Microbial Flora & Microbial Pathogenicity There are many ways and at many levels a microorganisms can interact with humans.

Microorganisms regularly found at any anatomical site are collectively referred to as normal flora. The normal flora present in the body is highly complex and consists of more than 200 species of bacteria. The residency of normal flora depends upon several factors, including age, genetics, sex, nutrition and diet of the person. Therefore, humans have a mutualistic relationship with many of the microorganisms of their indigenous microflora.The normal flora is beneficial from the host a supply of a stable environment and constant temperature, nutrients, protection, and transport. Nutritional benefits, stimulation of the immune system, and colonization strategies are acquired by the host from the normal flora. The normal flora exhibits a tissue preference for colonization.

Microbial Flora and Pathogenicity Essay Example

This is referred to as tissue tropism. This is due to the host has the essential growth factor and nutrients for a particular microflora. Besides, the normal flora can specifically colonize to a particular tissue with capsules, fimbriae, and cell wall components.In addition, some of the indigenous bacteria are able to construct bacteria biofilms on a tissue surface. There are two types of normal flora found which are resident microflora and transient microflora. Resident microflora is defined as the organisms that are always present in the body while transient microflora is those present temporarily and under certain conditions. Human is first colonized by a normal flora at the moment of birth and passage through the birth canal.

A fetus has no normal flora.During and after delivery, a newborn is exposed to many microorganisms from its mother, food, air, and basically everything that in contact with the infants. The resident microflora of the skin consists of bacteria and fungi which is approximately 30 different types. The high amount of microorganisms can be found at moist and warm condition in hairy areas of the body where there are many sweat and oil glands, such as under the arms, the groin, moist folds between the toes and fingers. Whereas at dry, calloused areas of skin have fairly low amount of bacterial cells.The majority of skin microorganisms are found on the most superficial layers of the skin and upper part of the hair follicle. They consist of Staphylococcus epidermis and Micrococcus app and corynebacteria.

These are considered as commensal ad generally nonpathogenic. However, pathogenic Staphylococcus aureus is found on the face and hands, particularly in individuals who are nasal carriers. The respiratory tract can be divided into upper respiratory and the lower respiratory tract. The nares are mainly colonized, predominantly with Staphylococcus epidermis and corynebacteria with Straphylococcusaureas.The healthy sinuses, in contrast are sterile. The lower respiratory tract is usually free of microbes, mainly because of the efficient cleaning action of the ciliated epithelium which lines the tract. For the microflora in the conjunctiva, numbers of bacteria may be cultivated from the normal conjunctiva but the number of organisms is usually small.

Staphylococcus epidermis and certain coryneforms are dominant. Staphylococcus aureus, some streptococci, Haemophilusspp. and Neisseria spp. are usually found.Blinking every second and lachrymal secretions give no opportunity for microorganisms to colonize the conjunctiva without special mechanisms to attach to the epithelial surfaces and the ability to withstand attack by lysozyme. The presence of nutrients, epithelial debris, and secretions makes the mouth a favorable habitat for a great variety of bacteria. If dental hygiene is not taken care well, this will allows growth of these bacteria, with development of dental caries, gingivitis, and more severe periodontal disease.

There are several microbes which have been isolated from healthy human mouths.It includes Gram-positive and Gram-negative bacteria (both cocci and bacilli), spirochetes, and sometimes yeast, moldlike organisms, protozoa, and viruses. The bacteria include species of Actinomyces, Bacteroides, Fusobacterium, Lactobacillus, Porphyromonas, Neisseria, Veillonella, and Streptococcus. A various species of ? -hemolytic streptococci is the most common organisms in the indigenous microflora of the mouth. In the other hand, the urogenital tract consists of urinary tract and the various parts of the male and female reproductive systems.The healthy kidneys, ureters, and urinary bladder are sterile. Moreover, urine is normally sterile, since the urinary tract is flushed with urine every few hours.

However, the flora of the anterior urethra, suggests that the area may be inhabited by a relatively consistent normal flora consisting of Staphylococcus epidermis, Streptococcus (Enterococcus) faecalis, and some alpha-hemolytic streptococci. The reproductive systems of both men and women are usually sterile, with the exception of the vagina. Through the childbearing years, vaginal secretions are acidic which is around pH4. to 5. 0, encouraging the growth mainly of lactobacilli. The metabolic by-product of lactobacilli, especially lactic acid, inhibits growth of bacteria vaginosis (BV). A decrease in the number of lactobacilli can lead to overgrowth of other bacteria like Bacteroides spp.

, Mobiluncus spp. , Gardnerella vaginalis, and anaerobic cocci, which in turn can lead to BV. Gastric enzymes and extremely acidic pH in gastrointestinal tract (GI) usually prevent growth of indigenous microflora, and most transient microbes are killed as they pass through the stomach.There is one bacterium named Helicobacter pylori which stay in the stomach and is a common cause of ulcers. Few microflora usually exist in the upper portion of small intestine(the duodenum) because bile inhibits their growth, while many are found in the lower parts of the small intestine (the jejunum and ileum). The colon is where it contains most of the number and variety of microorganism of any colonized area of the body. Also, many fungi, protozoa, and viruses can live in the colon.

Many of the microflora of the colon are opportunists, causing disease when they gain access to other areas of the body or when the usual balance among the microorganisms is upset. One of the example is E. coli. E. coli bacteria can be found in all individuals. They are opportunists, usually causing us no problem but they can cause urinary tract infection (UTI) when they gain access to the urinary bladder. By definition, pathogenicity is the capability to cause a disease.

Microbes express their pathogenicity by means of their virulence, which refers to the degree of pathogenicity of the microbe.There are two types of pathogen, primary pathogen which it capable of establishing disease in a previously healthy individual with intact immunological while opportunistic pathogen is those rarely cause disease in individuals. Both primary and opportunistic pathogens have virulence determinants that facilitate pathogenesis. There are two broad qualities of pathogenic bacteria that can cause disease. Firstly, the invasiveness which means is the ability to invade tissue. It encompasses mechanism for colonization, production of extracellular substances which facilitate invasion and ability to bypass or overcome host defense mechanisms.Toxigenesis is the ability to produce toxins.

Bacteria may produce two types of toxins called exotoxins and endotoxins. Exotoxins are released from bacterial cells and may act at tissue sites removed from the site of bacteria growth. Endotoxins are cell-associated substance. The first stage of microbial infection is colonization which is the establishment of the pathogen at the appropriate portal of entry. It normally requires adhesion to the mucosal surface. Adhesion is very important to allow resisting host defense, flushing action of mucous and saliva.It involves surface interaction between specific receptors on the mammalian cell membrane and the bacterial ligand on the bacterial surface.

Types of adhesions include fimbrial where it attaches on the surface of many Gram-positive and Gram-negative bacteria and fimbriae which is a thin, rigid rod-like structures. Association with infection may differ according to the type of fimbrial antigens. The invasion of a host may be aided by the production of bacterial extracellular substances. Once attached to mucosal surfaces, some pathogens exert their pathogenic effect without penetrating the host tissues.The spreading factors is where the bacterial enzymes that affect the physical properties of tissue matrices and intercellular spaces. It includes hyaluronidase, collagenase, neuraminidase, streptokinase and staphylokinase. However, some pathogenic bacteria are inherently able to resist the bactericidal components of host tissues.

Capsules are the most common mechanism to avoid phagocytosis by bacteria. All pathogens associated with meningitis and pneumonia has capsules, for instance, Streptococcus pneumonia and E. coli. Non-capsulated variants are usually less pathogenic.Capsules are polysaccharides that reduce efficiency of phagocytosis as they prevent opsonization of the bacterium by complements and are less immunogenic. In addition, M-protein is used to avoid phagocytosis. It can be found on both the cell surface and fimbriae.

It mediates attachment of the bacterium to the host epithelial cells and helps to resist phagocytosis and also increase the virulence of the species. Besides, variation of surface antigen composition during the course of infection provides a mechanism of avoidance of specific immune response directed at those antigens.The normal flora is beneficial for human in many different ways. For example, the secretion of certain intestinal bacteria provides some nutrients, particularly vitamins K and B12, panthothenic acid, pyridoxine and biotin. The normal flora is believed to help prime the immune system and thus contribute to the development of immune competence against pathogens. The mere presence of large numbers of microorganisms at certain anatomic location is beneficial, which they prevent pathogens from colonizing those location.

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