Bacteria: Handy Sidekicks or Mini Menaces?

Not all types of bacteria are dangerous to humans—some even happen to be vital (e.g., the bacteria in the intestines or on the skin). Other bacteria are pathogenic and can result in serious and life-threatening infections. The symptoms are just as varied as the bacteria themselves. The various bacteria require unique conditions in order to survive and reproduce. Knowing the life requirements of these tiny single-celled creatures makes it possible to successfully combat them.

Bacteria are microorganisms and cannot be seen with the naked eye. They are unicellular and can vary in size between 0.2 and 5.0 micrometers (µm). Approximately 6,000 of the smallest bacteria piled together amounts to nothing larger than a single grain of sand. Despite their size, bacteria have a highly elaborate design. They have developed artful and tricky structures in order to survive.

With Built-in Airbag 

Bacteria are prokaryotes, which means that they do not possess a proper nucleus but rather a nucleus substitution. This irregularly shaped region within the cell is called the nucleoid. The DNA, the so-called prokaryotic chromosome, floats freely in the cytoplasm of the cell. The flexible cytoplasmic membrane surrounds the cell's contents, just like a small airbag serves as a buffer zone. The cytoplasmic membrane is responsible for food intake, waste excretion, and when necessary, the restoration of the cell wall. The cell wall surrounds the entire structure and provides its stability. 

Coloring methods have made it possible to distinguish bacteria based on the structure of their cell wall. Through the process of Gram staining invented by the Danish bacteriologist Hans Christian Joachim Gram (1853–1938), bacteria with a solid single-layer cell wall are colored differently than bacteria with a thin multilayer cell wall. The former type of bacteria turns a blue/violet color and is categorized as Gram-positive, while the latter type of bacteria with the intricate multilayer cell wall is Gram-negative and turns a pinkish hue.

Some bacteria possess flagella as a means of locomotion. Flagella are long, thin protein filaments that provide bacteria with a form of movement similar to that of a propeller. However, this type of movement is only possible in liquids.

Other bacteria are able to attach to the membrane of the host cell using adherence factors called adhesins. An example of an adhesin is fimbriae, also called pili, which are characterized by their hairlike structure. Some pili are so large that they have the ability to transfer genetic material between cells. This is accomplished by ringlike particles called plasmids, which dock at the host cell like space capsules.

The appearance, shape, and size of bacteria are just as diverse as the bacteria's characteristics and attributes. The Latin word bacterium was originally derived from the Greek bacterion (βακτήριον), which is defined as “small staff.” That was the very first allusion to the shape of the microorganism. With the use of a microscope, the various forms of bacteria can be categorized into three main shapes: 

1. Coccoid bacteria (sing. coccus from the Greek for sphere, berry) have the shape of a sphere or oval. If cellular division is only partially completed, larger formations of connected cocci occur: streptococci (chain formation), staphylococci (grape-like cluster), diplococci (grouping of two), tetracocci (grouping of four), or sarcina (grouping of eight or more).
2. Rod-shaped bacteria (Bacillus) can have either a thick or thin form. Their ends can be pointed, round, or even angular. 
3. Spiral-shaped bacteria (Spirochetes) are identifiable by their helical curves, sometimes featuring proper coils.

The Taxonomy of Bacteria 

In order to systematize the thousands of bacteria, they have been divided into divisions, classes, orders, families, genera, and species. The divisions place the prokaryotes into four main groups: (1) Gracilicutes, bacteria with a thin cell wall, (2) Firmicutes, bacteria with a solid cell wall, (3) Tenericutes, bacteria without any solid cell wall, and (4) Mendosicutes.

Classification of Bacteria 

(Staphylococcus aureus used as example) 

Making Babies at Room Temperature

The reproduction of bacteria is a quick and quiet process. Bacteria proliferate through an asexual cellular division. The bacterium grows and eventually becomes the mother to two daughter cells. This can occur as a budding process or through a constriction of the middle of the cell leading to a cleavage division. Reproduction allows the formation of variant bacteria through transformations and random mutations. Bacteria with pili are able to attach to other cells and pass on their genetic material. For example, if this genetic material has developed a resistance to antibiotics, this trait will be passed on, providing the host bacteria with an evolutionary selection advantage in its favor.

Bacteria pathogenic to humans require a temperature between 25º and 40º C to reproduce—the human body temperature is thus an optimal climate. If the temperature is right and if there are enough resources such as vitamins, water, and carbon, bacteria are able to double every 10 to 30 minutes. If a small bacterial family is being started as you sip your cup of coffee in the morning, a bustling pathogenic village will have already grown by the time you sit down to dinner that night.

Some bacteria can be quite poisonous as they generate toxins or enzymes (agents disruptive to proteins) that can have a pathogenic effect on humans. These excretions are produced by the bacteria as a defensive mechanism that puts other organisms at risk. Poisons that are directly produced and discharged by the bacteria are referred to as exotoxins, whereas endotoxins are poisons first released after the bacteria's death and decay.

Yet the true guerrilla fighters are those bacteria that create spores in their interior. This occurs when the living conditions have become threatening, for example, during the absence of food. These endospores protect the bacteria against negative external influences and help them survive. They are extremely resistant against heat, dryness, and chemical disinfectants and allow the bacteria to survive for decades. Some sources have even reported of a possible spore stage of centuries. The bacteria goes into a type of dormancy and only awakes when positive living conditions arrive. This spore stage is also referred to as the dormant or latent phase of a pathogen.

Many bacteria are quite helpful to their human host. Such bacteria are named non-pathogens as they are not pathogenic to humans. Other bacteria are slightly less peace loving and induce infections if the respective immunization is not present. These are referred to as obligate pathogens. When contact does not necessarily lead to an infection, the bacteria are referred to as facultative pathogen. An infection will only occur under specific circumstances, for example, during a period of immunodeficiency such as the common cold.

Every organism that requires oxygen to live is referred to as obligate aerobic. This applies likewise to bacteria. However, not all life forms require oxygen to survive. If oxygen has an explicit negative effect on bacteria, they are referred to as obligate anaerobic. The third variant of bacteria are those that are adaptable and can survive either with or without oxygen; such bacteria are referred to as facultative aerobic or anaerobic.

In the best-case scenario, the human immune system is so strong that the natural defense can defeat any infection on its own. The human body is able to heal itself. Should the immune system not properly function, an antibacterial treatment is necessary. An infection is medicinally treated by pharmaceuticals, which either kill the bacteria by damaging their cells (bactericide, bacteriolysis) or prohibit the reproduction of bacteria (bacteriostatic). Antibiotics are the main group of medications in the antibacterial treatment. Based on the sickness, a type of wide-spectrum antibiotic or small-spectrum antibiotic will be employed. The wide-spectrum antibiotic functions against an entire array of bacteria groups, whereas the small-spectrum antibiotic can only combat a select few types of bacteria but has a better ability to fight its targets. The problem of resistance development through the extensive usage of antibiotics has already been covered in taking on the challenge.

Bacteria that exist outside of the human body can be killed with disinfectants (bactericide, bacteriolysis). This can be easily accomplished with bacteria that do not produce spores or with bacteria that are not yet in there endosporal dormant stage. Bacteria in their spore stage are far more difficult to destroy.