Types of Bacteria

Different types of bacteria

Bacteria can be classified into four separate types according to their shape, though there can be considerable variation within these shape classes and there are some bacteria that do not conform to any of these four types. The four primary types of bacterial shapes are:

• Bacilli (rods)

• Cocci (spherical)

• Spirilla (spirals)

• Vibrio (comma-shaped)

Cocci (spheres)

Cocci bacteria are typically arranged either individually, in chains, or in clusters. While some cocci bacteria are pathogens, some are also harmless or beneficial. The word “cocci” is derived from the Greek word for “berry”, coccos. Cocci can be both Gram-positive or Gram-negative.

Table 1. Examples of cocci bacteria

Bacilli (rods)

Bacilli are bacteria species that are shaped like a rod. Bacilli can be both Gram-positive or Gram-negative.

Table 2. Examples of bacilli bacteria shapes

Bacilli can also appear grouped together as pairs (diplobacilli) or as a fence-like structure (palisades).

Spirilla (spirals)

Spirilla are spiral- or helical-shaped bacteria species, which are stereotypically Gram-negative. These bacteria typically have flagella, which are long structures used for motility.

Table 3. Examples of spirilla bacteria shapes

Some other bacteria can have shapes that do not conform to the above types of shapes, such as pleomorphic, spindles, squares, and stars.

Types of Bacterial Colonies

Bacterial colonies are classified by their morphology, which includes the bacteria’s elevation, form, and margin. The form of these colonies can be classified as:

• circular,
• filamentous,
• irregular, or
• rhizoid.

These different morphologies allow bacteria to adapt to and survive the external and internal conditions they may encounter. Bacterial morphology contributes to its survival rate against "primary" and "secondary" selective pressures.

There are generally considered to be three "primary" selective pressures and four "secondary" selective pressures. The "primary" selective pressures include:

1. The ability to obtain nutrients
2. Cellular division
3. Predation.

The "secondary" selective pressures include:

1. Surface attachment
2. Dispersion
3. Motility
4. Differentiation.

Bacterial colonies are also classified by elevation. Bacterial colonies can be:

• raised,
• crateriform,
• convex,
• flat, and
• umbonate.

Lastly, bacterial colonies are also classified by their margin, which can be:

• curled,
• entire,
• filiform,
• lobate, or
• undulate.

Types of Bacterial Infection

There are numerous different types of bacterial infection, depending on the type of bacteria involved and the location of the infection. Unlike viral infections, bacterial infections involve living organisms (bacteria are alive, while viruses are not) and are usually treated with antibiotics.

In the following sections, we will go over several bacterial species and the illnesses that may result from being infected with them.

Types of food poisoning bacteria

Food poisoning happens when a person eats food contaminated with microorganisms, many of which can be bacteria. There are many different strains of bacteria that can cause food poisoning. Although the symptoms can be quite dramatic (diarrhoea, nausea, stomach pain or cramps, vomiting), food poisoning is usually not very serious and passes on its own. However, the sick person should make sure to stay hydrated and replenish enough nutrients and minerals while going through the illness.

Escherichia coli

While you may associate its name exclusively with food poisoning, most strains of Escherichia coli are actually harmless and already live inside humans and other mammals. The few strains that are pathogenic can produce the typical symptoms of food-borne illness: abdominal cramping and diarrhoea.

E. coli is the most common cause of traveller's diarrhoea and is typically acquired through contaminated food or drink. In severe cases, E. coli can cause colitis and bloody diarrhoea. While E. coli infections are usually self-limiting, sometimes antibiotics are used in order to shorten the duration of the illness.

Helicobacter pylori

Helicobacter pylori is a stomach-inhabiting bacteria species that can cause gastritis, duodenitis, and ulcers in some infected individuals. It is important to note that the vast majority of those infected with H. pylori will not develop the disease, and roughly 50% of the human population (mostly within the developing world) is believed to be infected with the bacteria. When the organism does cause disease, symptoms may include heartburn, tarry faeces, nausea, vomiting, and pain. The disease can eventually progress to gastric cancer or even perforation into the abdominal cavity.

Vibrio cholerae

Vibrio cholerae is the causative agent in cholera, a gastrointestinal disease that is currently only known to occur in humans. Infection with V. cholerae causes severe, life-threatening diarrheal illness in about 10% of those infected while the remainder will experience only mild diarrhoea or a lack of symptoms entirely. The most common feature distinguishing cholera from other common diarrheal diseases is the "rice water" appearance of diarrhoea produced by the infected individual. This is in contrast to other bacterial diseases, such as dysentery, which may produce bloody diarrhoea.

V. cholerae is a highly contagious species that is commonly spread through contaminated food or water. This has resulted in devastating outbreaks throughout history, such as the deadly outbreak that took place in Haiti following the 2010 earthquake. While antibiotics may shorten the duration of the illness, supportive rehydration therapy is usually the most effective treatment until the self-limiting infection passes.

Some other bacteria that cause food poisoning are Salmonella, transmitted by the fecal-oral route (including the consumption of contaminated food and water and by direct animal contact) and Clostridium botulinum. C botulinum causes botulism, which is currently a farely rare but serious infection. Botulism is caused by the toxin released by C botulinum which affects the nerves and causes paralysis of the muscles, including those used to breathe. Therefore, botulism can be deadly.

Types of bacterial pneumonia

Pneumonia involves inflammation of the lungs and may be caused by bacteria, viruses, fungi, or other conditions. Symptoms usually consist of coughing, breathing difficulties, and chest pain, but may also include more generalized symptoms such as fever, nausea, and vomiting.

Bacterial pneumonia is caused by a variety of different species of bacteria, most commonly S. pneumoniae and Klebsiella pneumoniae. Bacterial pneumonia can be placed into four types:

• community-acquired,
• healthcare-associated,
• hospital-acquired, and
• ventilator-associated.

Types of bacteria in urine

Urinary tract infections (UTIs) are infections that may involve any part of the urinary tract and typically involve symptoms such as increased urination, increased urinary urgency even when the bladder is empty, painful urination, and, in some cases, fever.

UTIs occur when bacteria enter the urinary tract, which can occur in a number of ways, including through sexual intercourse and poor hygiene. For anatomical reasons, females are at a greater risk of developing UTIs than males. The bacteria that is usually associated with UTIs is E. coli (around 80% of cases), though some other bacteria species and even fungi may occasionally be involved.

Fig.1 Symptoms of a urinary tract infection

Types of bacteria in food

Bacteria in food are not always damaging to the humans that consume it. In fact, they can be extremely beneficial, helping restore and keep a healthy microbiota (gut flora) and digest difficult foods, among the most obvious functions.

There are many damaging food bacteria, as we mentioned above, like Salmonella, Vibrio cholerae, Clostridium botulinum and Escherichia coli, among others. However, there are two main types of beneficial gut bacteria that you have probably heard of: Lactobacillus and Bifidobacterium.

Overall, bacteria come in all shapes and sizes and have widely differing functions with regard to humans: they can make us sick, or even kill us, but they can also protect us and help our bodies function to their best ability.