Question

1.Describe the difference between alpha-, beta-, and gamma-haemolysis?

2.Research the microorganisms listed below. List the full taxonomy (phylum, class, order, family, genus, species) of each microorganism, and write at least two sentences about a feature/characteristic of each microbe that you find interesting (we are using these strains in experiments in the next laboratory, so linking this feature/characteristic to the laboratory practical will assist your understanding).

Streptococcus pneumoniae: Staphylococcus aureus: Escherichia coli: Saccharomyces cerevisiae. 3.What is a microbial cultivation selective medium and why do microbiologists use them 4.In the laboratory experiment where you used the Most Probable Number method to determine the number of coliforms in the Library Pond water, you used both single strength and double-strength (double concentration) Maconkey medium. In one set of five universal vials, you inoculated 10 mL of duckpond water into 10 mL of double-strength MaConkey medium. Why do you think we used double-strength Maconkey medium instead of single strength medium for this set? 5.New Zealand drinking water standards require zero coliforms to be detected in 100 mL of sampled water. If you were unable to detect any coliform colonies on a Petrifilm sheet, would you be confident that you met NZ standards safe drinking water standards? Explain the reasons for your answer.

Answer 1

1) Hemolysis is the break down of hemoglobin. This method is used in classifying streptococcal species. The substance that causes hemolysis is called hemolysin. Hemolysis is the ability of bacterial colonies to break down hemoglobin when grown on blood agar.

Alpha hemolysis is also called green hemolysis or partial hemolysis. It is associated with reduction of red blood cells in haemoglobin. It is caused because of the color change in agar. It is caused by hydrogen peroxide produced by bacteria. This hydrogen peroxide oxidizes hemoglobin and this produces green oxidized derivative of methemoglobin.

Beta hemolysis is complete hemolysis. It breaks down red blood cell and hemoglobin completely. This hemolysis leaves a clear zone around the bacterial growth.

Gamma hemolysis is not occurring any hemolysis in the area around bacterial colony. The gamma hemolysis shows brownish colour.

2)

a) Streptococcus pneumoniae:

Phylum: Firmicutes.

Class: Bacilli

Order: Lactobacillales

Family: Streptococcaceae

Genus: Streptococcus

Species: Species of streptococcus based on their hemolytic properties.  Alpha hemolytic or beta hemolytic.

It is a gram positive bacterium. They are found in pairs. It do not form spores. They are non motile. It is a commensal organism in the human respiratory tract, it take benefits from the human body without harming the body. It is a lancet shaped cocci. They are alpha hemolytic when cultured on blood agar.

b) Staphylococcus aureus:

Phylum: Firmicutes

Class: Bacilli

Order: Bacillales

Family: Staphylococcaceae

Genus: Staphylococcus

Species: Staphylococcus aureus

It is a gram positive bacterium with round shaped. It is a member of microbiota of body. It is found in the upper respiratory tract and on skin. It is also called "golden grape cluster berry". It is so called because of its clustered appearance on gram stain. Its presence in body is pathogenic.

c) Escherichia coli:

Phylum: Proteobacteria

Class: Gammaproteobacteria

Order: Enterobacteriales

Family: Enterobacteriaceae

Genus: Escherichia

Species: Escherichia coli

It is a gram negative bacteria. It is a facultative anaerobic. It is found in the lower intestine of warm blooded animals. It will not form spores. It can be motile or non motile, rod shaped and it grow on MacConkey agar.

d) Saccharomyces cerevisiae:

Phylum: Sac fungi

Class: Saccharomycetes

Order: Saccharomycetales

Family: Saccharomycetaceae

Genus: Saccharomyces

Species: Saccharomyces cerevisiae

It is a species of yeast. It is used in baking, wine making, brewing. It is originally isolated from grape's skin. It is also called brewer's yeast. colonies of these grow rapid and mature in 3 days. They are moist, flat and smooth. They have the ability to ferment various carbohydrates.

3) Selective media are used for the growth of selected micro organisms. It is used to grow micro organisms that are resistant to certain features. This is used by microbiologists to grow specially selected micro organisms. In this method all micro organisms will not be grown. So culture of the selected micro organisms can be done effectively with this method.

4)  MacConkey Broth (Double strength) is used for detection of bacteria responsible for food poisoning ,for isolation, identification and enumeration.

MacConkey single strength is used for the isolation of coliforms and intestinal pathogens in water, dairy products and biological specimens.

5)  NZ water is universally safe to drink because major contaminating organisms such as Protozoa and Cryptosporidium are removed or reduced to safe levels.  All NZ water is chlorinated. Maximum amount of substances or organisms or contaminants or residues that may be present in drinking water are removed in this process. The supply of this water also meet the quality requirements. So, NZ standards meet safe drinking water standards.