Bacteria

BACTERIA

Living things are either classified into eukaryotes or prokaryotes.

Eukaryotes include plants, animals, fungi, protozoa and algae.

Prokaryotes include bacteria and archaea.

TRIVIAWhat do the bacteria Lactobacillus burglaricous and Streptococcus thermophilus have in common?Both must be present in a product for it to be labeled yogurt under U.S. Food and Drug Administration regulations.

Their genetic materials is not enclosed within a membrane.

Their DNA is not associated with histones.

They lack membrane- bound organelles.

Their cell walls are simpler

They usually divide by binary fission.

Prokaryotes

Bacteria are prokaryotic cells. Their outer surface called cell wall is composed mainly of peptidoglycan.Unlike viruses, bacteria possess both DNA & RNA.Unlike eukaryotic cells, they do not have true nucleus, lack mitochondria & have smaller ribosones (70 Svedberg units).

TRIVIAMicrofossils of bacteria living 3.4 billion years ago were found in Australia.Earth had no oxygen at the time the bacteria existed.The finding from a remote region of Western Australia lends hope that life has existed on Mars.

CLASSIFICATION

Bacterial Classification Based on Shapes

Most of the bacteria belong to three main shapes:

Rod-shaped bacteria are called bacilli - e.g. E.Coli and Salmonella

E.COLI

Spherical-shaped bacteria are called cocci - e.g. Staphylococcus and Streptococcus

Staphylococcus

Spiral-shaped bacteria are called spirilla - e.g. Treponema and Borellia

Borellia Borellia infection in human

Bacterial Classification Based on Staining MethodsBacteria are grouped as 'Gram positive' and 'Gram negative' bacteria, based on the results of Gram staining method, wherein an agent is used to bind to the cell wall of the bacteria.

Gram positive bacteria - take up crystal violet dye and retain their blue or

violet color

Gram negative bacteria - do not take up crystal violet dye, and thus appear

red or pink.

Bacteria are also classified based on the requirement of oxygen for their survival

Aerobic bacteria - Bacteria that need oxygen for their survival.

Anaerobic bacteria - Bacteria that do not require oxygen for survival.

TRIVIATuberculosisMycobacterium tuberculosisTuberculosis has ravaged the world for centuries, also known as consumption. It has been found in the spines of mummies and "in 2007 there were an estimated 13.7 million chronic active cases, 9.3 million new cases, and 1.8 million deaths, mostly in developing countries" according to the WHO. The organization has started a program that aims at saving 14 million lives between 2006 and 2015.

Aerobic bacteria, Staphylococcus aureus,, cultured on an agar plate

Clostridium perfringens bacteria are

Anaerobic Food-Borne Pathogens

Autotrophic and Heterotrophic BacteriaThis is one of the most important classification types as it takes into account the most important aspect of bacterial growth and reproduction

Autotrophic bacteria (also known as autotrophs) obtain the carbon it requires from carbon dioxide.

Heterotrophic bacteria obtain sugar from the environment they are in (for example, the living cells or organisms they are in).

TRIVIAWearing headphones for just an hour will increase the bacteria in your ear by 700 times.

Bacterial Classification Based on EnvironmentAs we mentioned earlier, bacteria are found in all types of environment. While some species of bacteria can withstand extreme conditions, others need specific moderate conditions to survive. On the basis on environmental conditions of their habitat, bacteria are classified into:

Mesophiles - which require moderate conditions to survive.

Neutrophiles - which require moderate conditions to survive.

Extremophiles - which can survive in extreme conditions.

Acidophiles - which can tolerate low pH conditions.

Alkaliphiles - which can tolerate high pH conditions.

Thermophiles - which can resist high temperature.

Psychrophilic bacteria - which can survive extremely cold conditions.

Halophiles - which can survive in highly saline conditions.

Osmophiles - which can survive in high sugar osmotic conditions.

DIAGNOSTIC TEST

SIMPLE STAINS

These make use of a single dye which can either be water or alcohol based. It is used primarily to color the organism and to demonstrate its shape and basic structure.  

Examples are crystal violet, carbon fuchsin, methylene blue and saffranin

DIFFERENTIAL STAINS  These are used to differentiate one group of bacteria from another group. There are two types of differential staining procedures, namely:

1) Gram stain - distinguishes Gram- positive bacteria from Gram- negative bacteria.

Gram- positive bacteria stain purple or

blue, while Gram- negative bacteria stain

red or pink.

All cocci are Gram- positive, except for

Neisseria, Veillonella and Branhamelia

All bacilli are Gram- negative, except for

Corynebacterium, Bacillus and

Mycobacterium.

Gram stain of Renibacterium salmoninarum

2.) Acid – fast Stain – stain used for those bacteria with high lipid content in their cell wall, hence cannot be stained using Gram stain. There are two methods of acid- fast staining, namely:

Ziel – Neelsen stain – also known as the “hot method”, because it requires steam- bathing the

organism with aqueous dye.

Kinyoun stain – also known as the “cold method”, as it does not utilize heat for staining. Acid- fast bacilli stain red with either a blue or green background, depending on the method used. The background is blue when the Ziel- Neelsen method is used, and green when the method is Kinyoun. All Mycobacteria are acid-fast. Nocardia are only partially acid-fast.

acid fast stain of Mycobacterium leprae bacteria

3. Special Stains – these are to demonstrate specific structures in a bacterial cell. For instance, metachromatic granules can be visualized using the LAMB (Loeffler alkaline methylene blue) stain. Other special stain includes Hiss stain, for demonstration of the capsule or slime layer; Dyer stain, for the cell wall; Fischer- Conn stain, for flagella; Dorner and Schaeffer, and Fulton stains, for spores; and India ink (or nigrosin) , for the demonstration of the capsule of the fungus Cryptococcus neoformans.

CULTURE MEDIA

The use of staining procedures can only give us a clue as to what probable organism is being studied. In order to identify a specific organism , culture using specific culture media is the most ideal. Media (medium) are use to grow microorganism. A culture medium is basically an aqueous solution to which all the necessary nutrients have been added.

Culture of Salmonella typhi bacteria

Culture of Pseudomonas aeruginosa bacteria

TRIVIAThe skin of the armpits can harbor up to 516,000 bacteria per square inch, while drier areas, such as the forearm, have only about 13,000 bacteria per square inch.  

Thank You Maricris T. Peregrino

BSN 4Y-12012