Cotton has become the foremost well-liked material in several clothes. Owing to its absorption and breathability, it comforts the user and additionally, stand out as wonderful natural media for the survival of microorganisms, as a result of their hydrophilic nature, non-toxicity and ability to act as a decent media to grow. In special environments like those prevailing in hospitals, the concentrations of infective microorganism populations are typically abundant over those within the traditional environments. Even the clean human skin can have a large number of microbial populations, which are estimated to be in the range of 100-1000 microbes per cm . Growth of microbes on cotton textile makes an unpleasant odour, reduce the quality and value of textile.
1.4 Common microorganisms
1.4.1 Types of microbes and their activities
Microbes are the most abundant organisms present in the environment and are of minute in microscopic dimensions, very small to be seen by the naked eye. They must be magnified by an electron or optical microscope in order to be observed. The most common types of microorganisms are bacteria, viruses, protozoans, some fungi, yeasts, and some algae . Viruses are the simplest of the forms, which are neither living nor non-living with simple genetic material; either DNA or RNA often considered as particles, associated with proteins of the viral shell which is known as capsid that together form an infectious agent of cells. They are not capable of independent reproduction and show portion of properties of organisms . Bacteria are prokaryotes, meaning that they do not posses an organized cell nucleus separated from the protoplasm by a membrane-like nuclear envelope. Many microorganisms are eukaryotic organisms, having their nuclear material organized within a nucleus bound by nuclear membrane [20-22]. Protozoans are single-celled microorganisms that are often motile usually using cilia or flagellae for propulsion; while some protozoans are colonial and are capable to reproduce by binary fission. Fungi are another eukaryotic organisms with a chitinous cell walls, and they lack flagella [20, 21]. Microorganisms are extremely important group of organisms in ecology as primary producers as well as agents of decompose of dead organisms. Fungi play an essential role in breaking down organic matter and thereby allowing nutrients to be recycled continuously in nature .
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Microorganisms are well adopted to live in diverse environments with adverse conditions, where they can flourish. As such, different microorganisms are growing in specific environments, where they apt very much and they have different mechanisms to thrive in the environmental condition. Human skin act as a good media to grow microbes as body temperature and human secretions are a good source with nutrients are readily supplied. The colonization of different types of microbes such as genera Staphylococcus and Streptococcus on skin help to protect surface from colonization by undesirable disease-causing microorganisms. The majority of those skin microbes are found on the top most layers of the skin, in the upper regions of the hair follicles as well as more moisture-accumulating regions, such as the armpit, in between the toes and groin. Colonisation density of bacteria is high as one hundred thousand per square inch in such moisture laden areas due to the favourable conditions found without harming the host. But this type of symbiosis can be exemplified by the adverse health effects of the host, when the symbiotic balance between host and microorganism is disturbed . The scientists proved that bacterial organisms cause specific diseases once they are out of control and the best-known such opportunistic bacteria is Escherichia coli, is able to enter the internal body and cause diseases like, intestinal illness and sometimes even do more severe damage to kidneys and the urinary tract. Bacteria including Staphylococcus and Streptococcus, which are normal microbial flora living on the skin, can also cause infection when they gain entry to other pasts of the body as well, such as through a cut or malfunctioning immune system. Staphylococcus aureus is the leading cause of hospital acquired infections of all the gram-positive bacteria, which may cause illnesses such as strep throat, pneumonia, and blood infections. These strains are hardly controllable once they enter into body as they are resist to many antibiotics.
1.4.2 Cell wall structure of bacteria
The study of bacterial ultra structure began in 1884, with the further development of method of staining of bacteria by Danish pathologist Hans Christian Joachim Gram. He observed that some of the cells remained purple, while rest are not. Bacteria that remained purple were termed positive and others did not were called negative. Even after long time, this gram staining method is still considered as a perfect differential test to determine the cell wall structure of bacteria . The structural difference of two cell walls are the distinguishing feature between gram positive and negative bacteria which is illustrated in Figure 1.3 [21, 23]. The cell wall of gram positive bacteria is a thick layer of a cross-linked polysaccharide comprising up to ninety percent of the weight of the cell wall that is easily stained by gentian violet, while the cell wall of a gram negative bacterium consists of a single thin layer of polysaccharide comprises only about twenty percent of the weight of the cell wall and is covered by a lipid layer that resists the gentian violet, but can be stained by safranine. Peptidoglycan serves as the skeleton of bacteria which is present in both gram-positive and gram-negative bacteria that enables the bacterium to maintain its shape. This rigid layer is a network of two sugars N-acetyl glucosamine and N-acetyl muramic acid; that are cross-linked with each other by amino acid bridges [20, 21]. The latter sugar is unique to the peptidoglycan, and is found only in bacteria.
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Figure 1.3: Structures of (a) Gram-positive cell wall; a thick, single layer of a cross-linked peptidoglycan sac and (b) Gram-negative cell walls; thin layer of peptidoglycan and is covered by a lipid by layer
(Adapted from Mason K.A., Losos J.B., Singer S.R., Biology. 9 ed. 2011, New York: McGraw-Hill)
1.5 Anti-microbial agents
According to the mode of action against bacteria anti-microbial agents can be categorised into two types . Bacteriostatic agents inhibit the growth and multiplication of bacteria upon exposure to microbes and once the agent is removed, cells once again multiply. Other type is bactericidal agents which do not stop the growth just by inhibiting, but also cause the bacterial cell to death.
The anti-bacterial molecules directly interfere with the bacterial metabolic pathways, inhibition of protein, nucleic acid or cell wall synthesis. There are three mechanisms proposed. Antimicrobial agents are classified by their specific modes of action against bacterial cells. These agents may interfere with cell wall synthesis, inhibit protein synthesis, interfere with nucleic acid synthesis or inhibit a metabolic pathway. The modes of action of antimicrobial agents are similar regardless of type of cell wall . Only difference between two are the way of entry of anti-microbial agent into the cell. Antimicrobial agents that interfere with cell wall synthesis cause burst of cell due to formed defects in the cell wall by blocking peptidoglycan synthesis, while others block metabolic pathways which will eventually cause the cell death .