Identification And Investigation Of Different Types Of Bacteria

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Streptococci species are commonly isolated on Blood agar, a commonly used media in microbiology laboratories. Blood agar is composed of Tryptic Soy mixed with 5% of sheep red blood cells. This media is not only used to isolate streptococci, but also staphylococci species of bacteria via hemolysis which refers to the breakdown of red blood cells in enriched agar base surrounding bacterial colonies (Gera and McIver 2013). The haemolytic properties of blood agar detect Streptococci bacteria. The process is mediated by enzymes referred to as haemolysins. Streptococci bacteria are normally classified as alpha-haemolytic or beta-haemolytic.

Alpha-haemolysis is partial or incomplete haemolysis of red blood cells. In alpha-haemolysis, agar appears dark to greenish due to the conversion of haemoglobin to biliverdin. Streptococcus pneumoniae is an example of a common bacteria displaying alpha-haemolysis. On the other hand, beta-haemolysis refers to complete haemolysis of red blood cells under the colonies resulting in a lightened or yellow colour (Spellerberg and Brandt 2016). Streptomycin is an enzyme produced by beta-haemolytic bacteria to cause complete degradation of red blood cells (Spellerberg and Brandt 2016). Beta-haemolytic bacteria can be grown on Bacitracin discs. Streptococcus pyrogenes is sensitive to this disc while other beta-haemolytic streptococci are resistant (Spellerberg and Brandt 2016). Streptococcus pneumoniae is sensitive to Optochin discs while other streptococci species are resistant.

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Nitrate reduction test can be used to identify E.coli and other members of the Enterobacteriaceae based on the ability to produce the enzyme nitrate reductase enzyme which hydrolyses nitrate ions to nitrite (Ferry et al. 2015). The product can then be degraded into various nitrogen products based on the growth environment. If an organism reduces nitrite to nitrite, the subsequent media normally forms nitrous acid. The addition of sulfalinic acid results in the formation of diazotized sulfalinic acid which reacts to produce a red coloured product, a positive indicator for the presence of nitrate (Ferry et al. 2015). If the medium fails to turn red even after the addition of various reagents, it is an indicator that the organism failed to reduce nitrate, or the organism did not denitrify nitrate to produce either molecular oxygen or ammonia. A subsequent step is normally utilized to confirm the results. The method involves the addition of powdered zinc (Ferry et al. 2015). When a tube fails to turn red after the addition of zinc, a negative result is attained. An additional test for the identification of E.coli is the indole test. The indole test is based on the reduction of sulfur-based compounds. E.coli is one of the organisms which reduces Sulphur based products to produce a positive indole test.

C- Staphylococcus aureus

The Pyrrolidinyl Aminopeptidase (PYR) test is a rapid identification test used to identify bacterial organisms which utilize the pyrrolidonyl arylamidase enzyme (Compton et al. 2017). The enzyme hydrolyses the substrate L-pyrrolidinyl-β-naphthylamide to produce a compound referred by β-naphthylamine (Surewaard et al. 2016). This compound can be detected in N, N-methylaminocinnamaldehyde to produce a bright red precipitate. After hydrolysis by the peptidase enzyme, a red colour is produced on the addition of 0.01% cinnamaldehyde reagent (Surewaard et al. 2016). The resulting visible inoculum microorganism is normally rubbed in a small area with the disk impregnated in the substrate (Surewaard et al. 2016). About two minutes are provided for the substrate to hydrolyse before the addition of the cinnamaldehyde reagent (Surewaard et al. 2016). A purple colour is then observed which serves as a positive test for the PYR test. Staphylococcus aureus produces a negative test for the PYR test while most organisms provide a positive test for the PYR test. Further additional tests which can be used to confirm the presence of the bacteria after the application of the PYR test include the nitrate reduction test described in the prior section. It is important to note that Staphylococcus aureus shows a negative test against indole implying that the organism cannot reduce sulfur-based compounds (Surewaard et al. 2016). In essence, most bacterial microorganism can be detected through the application of more than one test.

D- Pseudomonas

Pseudomonas P agar can be used to differentiate strains of Pseudomonas bacteria and also the most common Pseudomonas aeruginosa. The differentiation is based on the production of pyocyanin. Of all of the species of Pseudomonas, only Pseudomonas aeruginosa produces and excretes the pigment. The medium was developed by Raney, Ward, and King to improve the production of pyocyanin. This medium contains various substances including gelatine which when digested by the organism results in the production of nitrogen. Other substances include vitamins, amino acids, and growth factors. The low amount of phosphate makes it one of the ideal medium choice considering that high amounts of phosphates inhibit the production of pyocyanin. Glycerol is added to the medium as an alternate carbon dioxide source (Costa et al. 2017). Potassium sulphate and magnesium salts are known to be activators of pyocyanin and are therefore added to the media to facilitate its production (Costa et al. 2017). The growth of Pseudomonas aeruginosa in P agar results in the production of a blue water-soluble pigment which easily diffuses into the surrounding colonies. To differentiate other species of Pseudomonas, an additional media referred to as Pseudomonas F can be added. The addition of the F agar results in the production of pyocyanin and fluorescein.

Infectious Episode


Streptococcus pneumoniae is the main cause of pneumococcal disease. Streptococcus pneumoniae causes a number of different types of diseases including pneumonia which refers to a lung infection, meningitis referring to infections covering areas of the spinal cord and brain, ear infection, sinus infection as well as bacteraemia which refers to infections of the bloodstream. Streptococcus pneumoniae is normally spread through a number of different methods including sneezing, coughing and being in close contact with an infected person. Common symptoms associated with Pneumococcus bacteria is dependent on the part of the body that is infected. The most common symptoms include coughing, fever, shortness of breath, confusion, stiff neck, disorientation, joint pains, chills, sensitivity to light, irritability, sleeplessness and ear pain. In the most severe cases, pneumococcal diseases may result in significant hearing loss or brain damage (Center for Disease Control and Prevention 2017). In other cases, it may result in death. The disease occurs globally. Travelers tend to be at a higher risk of spreading the disease especially if more time is spent in crowded settings or in close contact with children diagnosed with the diseases. It may also be spread when in close contact with children where the pneumococcal conjugate vaccine is not used. The disease is more common in developing countries as compared to developed countries. In most countries, it occurs during winter and early spring, but within the tropics, the disease occurs throughout the year (Center for Disease Control and Prevention 2017). Outbreaks of the disease tend to be common among countries which have not introduced the vaccine, but outbreaks may also be observed in clinical settings such as nursing homes and childcare centres. Several groups are easily predisposed to the disease. The high-risk group includes individual adults above 65 years and children younger than 2 years (Center for Disease Control and Prevention 2017). Individuals with a weak immune system or those with a previous history of lung disease, diabetes, HIV/AIDS and heart disease are at risk of getting the disease.


E.coli strains are largely classified as either being pathogenic or non-pathogenic. Most strains are harmless, but several serotypes are pathogenic and are linked to serious food poisoning. These strains are solely responsible for product recalls across most stores. Pathogenic strains are also linked to the majority of cases of urinary tract infections (Alteri and Mobley 2015). The other harmless strains are beneficial to the host and are involved in the production of Vitamin K and reduce the establishment of any form of pathogenic bacteria within the intestine (CDC 2015). Several strains including O104:H4 has been linked to the production of lethal toxins (Allocati et al. 2013). Food poisoning linked to E.coli largely occur as a result of failing to either washing vegetables, or undercooking poorly butchered meat (CDC 2015). The strain O157:H7 is particularly notorious for causing life-threatening complications such as haemolytic uremic syndrome which occurred in the United Arab Emirates in 2006 (Ferry et al. 2015). Treatment protocols indicate that most strains of pathogenic bacteria cause bloody diarrhoea, but enteroaggregative strains adhere and clump intestinal membrane tissues as indicated in some hospitals records in 2011 during an E.coli outbreak in Europe (Allocati et al. 2013). The severity of diseases associated with E.coli varies. The diseases tend to be more fatal in young children whose immune system has not developed considerably and in immunocompromised adults although the condition tends to be mild in most instances. An excellent example of the impact of E.coli pathogenic strains is the death of seven people in Scotland after eating poorly prepared meat. In essence, E.coli strains tend to harbour both heat-labile, and heat-labile enterotoxins which when not completely destroyed during food preparation has adverse negative effects on the body (Allocati et al. 2013). Uropathogenic strains are solely responsible for approximately 90% of all urinary tract infections (CDC 2015). In most of the ascending infections, the bacteria colonize the urethra and is spread to other parts of the bladder resulting in pyelonephritis and prostrate in males. Since women have a shorter urethra compared to men, women are more likely to be diagnosed with ascending urinary tract infections.

Staphylococcus aureus

Staphylococcus aureus is a bacteria spread through direct contact through the use of either a contaminated product or inhaling droplets dispersed by coughing or sneezing. Staphylococcus aureus is predominantly present in the nose and found in approximately 30% of all of the healthy adults . Higher levels are found in people working within clinical settings due to the development of resistant forms of the bacteria against the antibiotic methicillin resulting in the commonly referred to methicillin-resistant Staphylococcus aureus (MRSA) (Surewaard et al. 2016). The bacteria is commonly spread from one person to another via direct contact resulting in a high number of people who are considered as carriers. The most common Staphylococcus aureus infection is abscess since the skin is considered as one of the preferred locations for the bacterial organism. However, the bacteria is also present in the bloodstream resulting in bacteraemia, bones (osteomyelitis) and heart valves (endocarditis) (Surewaard et al. 2016). The bacteria also accumulates on numerous medical devices including heart pacemakers, artificial joints or valves, and catheters inserted into the skin. For example, bloodstream infections occur when a catheter is inserted in a vein and remains for a significantly long period (Leung 2014). Endocarditis which occurs in the heart valves occurs when illegal drugs re-injected in a vein. Since the injections are contaminated with Staphylococcus aureus, the bacteria is easily spread through different parts of the body (Surewaard et al. 2016). Presence of the bacteria in the bloodstream also results in the infection of adjacent soft tissue and may be more common in individuals with sore foot sores associated with diabetes (Surewaard et al. 2016). Individuals diagnosed with lung infection or pneumonia are normally prescribed several different types of drugs including corticosteroids which end up suppressing the immune system. Consequently, infections associated with Staphylococcus aureus tend to become elevated during such period since the bacterial microorganism is already present within the body or the body acts as a carrier.

Pseudomonas aeruginosa

Pseudomonas aeruginosa is regarded as an opportunistic infection occurring in clinical settings. It commonly occurs among individuals with existing conditions such as cystic fibrosis and traumatic burns. It affects both immunocompetent and immunocompromised individuals. The bacteria normally take advantage of the weak immune system of an individual to produce damaging tissue toxins to various parts of the body’s system (Bassetti et al. 2018). Its treatment is difficult since the bacterial microorganism tends to be resistant against the various existing antibiotics. Pseudomonas infection occurs across most parts of the body with the most common being lungs, stomach, blood, tendons and urinary tract. Wounds, burns, and pressure sores can also become infected. Common signs and symptoms associated with Pseudomonas infection tend to differ per body part. For example, infection in the skin is associated with rashes and pimples filled with pus while infections in the ears is associated with extreme pain and a discharge (Center for Disease Control and Prevention 2018). Pseudomonas causes various types of infections ranging from urinary tract infections, soft tissue infections, bone, and joint infection, respiratory system infections, gastrointestinal infections as well as a variety of other infections among immunocompromised individuals such as HIV/AIDS and cancer (Center for Disease Control and Prevention 2018). However, higher rates of the infection have been observed in individuals with cystic fibrosis who are susceptible to lung infections. Pseudomonas is also of grave concern among cancer patients as well as burn patients. Currently, reported case fatalities associated with the bacteria microorganism stands at 50% of all reported incidences. In the United States, the Center for Disease Control and Prevention observes that the overall incidence is approximately 0.4 percent among hospitalized patients (Center for Disease Control and Prevention 2018). This translates to the fourth most common nosocomial infection accounting for the total 10.1 % reported across all clinical settings (Center for Disease Control and Prevention 2018). Within clinical settings, Pseudomonas is present in various reservoirs including respiratory equipment, mops, sinks, taps, and food. The organism is commonly reintroduced within clinical settings on vegetables, fruits and plants often brought by visitors and patients. Spread occurs through direct contact with infected personnel, ingestion of contaminated water and food and contact with reservoirs.


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