Paper Example on Gram-Positive Bacterium: Streptococcus Pneumoniae

Introduction

Streptococcus pneumonia is a gram-positive bacterium that causes most of community-acquired pneumonia. Since the bacterium is gram-positive, a positive result is obtained in the Gram stain test, which is the traditional method that is commonly used to classify bacteria in their two primary categories. The bacterium’s cells are lancet-shaped cocci ad have a slightly curved outer curvature (Wang et al., 2019). Normally, the calls are viewed as pairs of cocci, but sometimes they occur in short chains and singly too. Every single cell of the bacterium has a diameter of between 0.5 and 1.25 micrometers. Streptococcus pneumonia does not form spores, and usually, they are non-motile (Yan et al., 2020). Just like the other streptococci, Streptococcus pneumonia does not contain catalase. However, they ferment glucose into lactic acid. The bacterium does not display the M protein but facilitates the hydrolysis of inulin. The cell wall composition of the bacterium is based on the presence of teichoic acid and peptidoglycan.

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Oxygen Requirements

Streptococcus pneumonia is a facultative anaerobic bacterium. Thus, the organism produces ATP through aerobic respiration in the presence of oxygen. However, in the absence of oxygen, the bacterium switches to fermentation. Thus, Streptococcus pneumonia can grow in both the presence and absence of oxygen. The bacterium depicts better growth in the presence of oxygen but can still do without it.

Temperature Requirements

Streptococcus pneumonia is mesophilic, meaning it grows best in moderate temperatures that are neither too hot nor cold. The optimum growth range of the bacterium is 30-350C (Wang et al., 2019). The bacterium is mostly found in the upper respiratory tract, including the throat and nasal passages, which have an optimum temperature.

Energy and Carbon Sources

Streptococcus pneumonia produces energy through fermentation by converting glucose into lactic acid. The bacterium obtains nitrogen and carbon through the utilization of extracellular enzyme systems. The processes of obtaining carbon and nitrogen damage hot tissues and enable the bacterium to colonize the host (Yan et al., 2020). The bacterium is capable of living on its own, but its population is threatened by the presence of Hemophilus influenzae (Wang et al., 2019). The bacterium exclusively relies on carbohydrates for its nutrition as the primary source of carbon. About 30% of Streptococcus pneumonia’s transport mechanisms are devoted to carbohydrate import. Thus, the organism is a chemoheterotroph. Streptococcus pneumonia lives in the airway where carbohydrates are scarce, so the bacterium obtains carbon by modifying and importing complex glycans. Carbohydrates are critical for two essential processes; pathogenesis and colonization.

Fastidious Bacterium

Streptococcus pneumonia is a fastidious bacterium since it has complex nutritional requirements. The bacterium can only grow if there is a culture medium with special nutrients.

Growth Characteristics

Colony Morphology

Colony morphology is a method used by scientists to describe the characteristics of a single bacterium growing on agar in a petri dish. Streptococcus pneumonia grows on blood agar, which is the most commonly used medium in the laboratory. Blood agar is enriched with tryptic soy agar with an additional 5% of sheep red blood cells (Yan et al., 2020). The blood agar is used to isolate the bacteria and contains nutrients that are essential for the growth of Streptococcus pneumonia. Blood agar is also used to identify the hemolytic properties of the bacteria. Streptococcus pneumonia is classified based on their hemolytic properties on blood agar and grouped serologically. However, Streptococcus pneumonia cannot be identified in the lab through Lancefield typing, unlike other pathogenic streptococci.

The appearance of Streptococcus pneumonia on blood agar varies depending on the encapsulation degree of the organism. The strains that are significantly and heavily strained usually have large colonies and appear grey and mucoid. The strains that are not heavily encapsulated usually have smaller colonies. Pneumococci generate pneumolysin whose function is to break down hemoglobin into a green pigment that is viewed as a significant green surrounding observed on blood agar plates as the bacterium grows (Yan et al., 2020). The ability to break down hemoglobin is referred to as α-hemolysis. A similar observation is seen when Streptococcus pneumonia colonies are growing on chocolate agar whereby green ones are observed around the bacteria.

Characteristics of Growth on a Slant in Broth

Streptococcus pneumonia can be placed in broth, which provides a growth medium for the bacteria and provides a constant provision of nutrients to allow for quick reproduction. Thus, the broth used on Streptococcus pneumonia prepares the bacteria culture for growth and cultivation for reproduction (Yan et al., 2020). The characteristic of growth is that the colonies assume the appearance of a tropical draughtsman during the development of the microbes (Wang et al., 2019). Furthermore, there is a green coloration on the surroundings of the broth.

Growth on Selective or Enriched or Differential Media

The most commonly used enriched media in the lab is sheep blood agar and chocolate agar. Selective media contains organisms that inhibit growth for some organisms, while differential media allows bacteria to be distinguished based on the type of hemolysis produced (Yan et al., 2020). When Streptococcus pneumonia is placed in a differential medium, a green surrounding is observed as the bacteria grow due to the breakdown of hemoglobin (Wang et al., 2019). In selective media, Streptococcus pneumonia appears as translucent or opaque. Small white to gray colonies can also be observed and are surrounded by a beta hemolysis zone.

Tests

Sugar fermentation tests on Streptococcus bacteria are to determine if the bacteria can ferment sugars and produce lactic acid as the end product. Streptococci cannot carry oxidative phosphorylation, and they are unable to synthesize cytochromes (Wang et al., 2019). The carbohydrate test is used to determine if the bacteria can utilize specific glucose and tests for the presence of a gas or acid after the fermentation. The first step when carrying out the carbohydrate test is by diluting the organism in a tube containing sterile water. Secondly, 1 mL of the organism is placed in the middle of the tube using a 1mL pipette. The cap is tightened, and incubation is done for twenty-four hours at 370C. The end result is the production of lactic acid as measured by the pH scale.

The phenol red glucose test contains a medium that is used as a pH indicator. The water-soluble dye changes from yellow to red when the pH of the substance is between 6.6 to 8.0, and it changes to pink when the pH is above 8.1. Thus, when testing for streptococci using the phenol red glucose test, the dye turns from yellow to red due to the production of lactic acid during oxidation.

The catalase test is another method that is commonly used to identify the microbe. Generally, the catalase test is used to differentiate between gram-positive cocci like Streptococcus pneumoniae. The bacterium is catalase-negative when cultured on fresh blood agar plates (Yan et al., 2020). The catalase test requires a specimen, which is blood. Secondly, there is a plate on blood agar. The third step is the identification of alpha-hemolytic colonies, and the test becomes negative (Wang et al., 2019). The negative result is an indication of probable Streptococcus from both the Gram and catalase tests.

The starch hydrolysis test identifies bacteria which can hydrolyze starch using specific enzymes. Iodine is used in the experiment to react with the starch and form a dark-brown color. Starch hydrolysis develops a clear zone around the bacterial growth. The oxidase characteristic of Streptococcus pneumonia tests negative.

References

Wang, H., Li, S., Xiong, C., Jin, G., Chen, Z., Gu, G., & Guo, Z. (2019). Biochemical studies of a β-1, 4-rhamnoslytransferase from Streptococcus pneumonia serotype 23F. Organic & biomolecular chemistry, 17(5), 1071-1075.

Yan, T., Tang, X., Sun, L., Tian, R., Li, Z., & Liu, G. (2020). Co infection of respiratory syncytial viruses (RSV) and streptococcus pneumonia modulates pathogenesis and dependent of serotype and phase variant. Microbial Pathogenesis, 104126.