Week 10 Review Sheet 1




November13, 2014


  1. Distinguish between Bactericidal, Bacteriostatic, Virucidal and Fungistatic

Accordingto Lammer (2014), bactericidal means capable of killing a bacteria.This refers to things like antibiotics, antiseptics and disinfectantswhich are capable of killing bacteria. Bacteriostatic on the otherhand means capable of inhibiting growth or reproduction of bacteria.Virucidalmeans capable of destroying a virus or neutralizing it. On the otherhand Fungistaticmeans inhibiting growth of fungi (Sibal, Lin &amp Jogia, 2013).

  1. Control cultures

Themain reason for control cultures is to prove that it is actually thedisinfectant that killed the bacteria. If the bacteria exposed to thedisinfectant dies but the ones in the control culture die too, thenit is probable to conclude that it is not the disinfectant thatcaused that. However, if the ones in the culture control live and theones exposed to disinfectant die, then the disinfectant will be theorigin of death (Lämmler, 2014).

  1. Factors affecting disinfectants

Sibalet al, (2013) connotes a number of factors that affect disinfectants,this include both physical and chemical factors: temperature, pH,relative humidity and water hardness. It can be depicted that mostdisinfectants increase their activity with an increase intemperature.

  1. Resistance of bacteria

Themicroorganisms DNA is different than others, it is this fact thatexplains resistance of certain microorganism as explained bySrivastava &amp Srivastava (2003). These different DNA strands canhave resistances to some things that others don`t. However if anorganism is only partially exposed to a disinfectant it may growresistant and more powerful. This creates more powerful strains ofviruses and bacteria which can be deadly.

  1. Susceptible microorganisms

Microorganismsvary in their degree of susceptibility to disinfectants. In general,Gram-positive bacteria are more susceptible to chemical disinfectantswhile mycobacteria or bacterialendosporesare more resistant (Srivastava &amp Srivastava, 2003).


  1. Antimicrobial resistance susceptibility

Antimicrobialresistance susceptibility is the ability of bacteria and othermicroorganisms to resist the effects of an antibiotic to which theywere once sensitive. Antibiotic resistance is a major concern ofoveruse of antibiotics also known as drug resistance (Lammer, 2014).

  1. Pure culture use

Apure culture is used mainly because there is need to ensure thatantibiotic sensitivity tests succeed since they are used to see howfar organism`s growth is interrupted by antibiotics. If a pureculture is not used, then the activity of the contaminated microbewill interfere with accuracy of the result (Sibalet al., 2013).

  1. Mixed cultures

Sibalet al. (2013)asserts that it is not advisable to use mixed culture in thisscenario, this is because reactions of bacterial mixtures arecompletely unpredictable. They further depict that the moment thereis a mixture in the cultures error results are prone to be attained.

  1. Factors influencing accuracy of results

Lammer(2014) depicts some of the factors that affect accuracy of results intests undertaken to determine microorganisms like bacteria. Thesefactors are:-

  • pH of medium used

  • Moisture

  • Medium components

  • amount of organism

Growth control tube gives an illustration on the behavior of the bacteria under normal conditions while the sterility control tube correlates data on the behavior of bacteria under neutralized conditions (Srivastava &amp Srivastava, 2003).

Exercise 3

  1. IMViC

Indole, the Methyl Red, the Voges-Proskauer and the Citrate Test. The IMViC tests are a group of individual tests used in microbiology lab testing to identify an organism in the coliform group.

These IMViC tests are useful for differentiating the family Enterobacteriaceae, especially when used alongside the Urease test (Sibal et al., 2013).

  1. Differentiation

Urea is a waste product of protein metabolism that is excreted in the urine. The enzyme urease hydrolyzes urea to form ammonia. This causes an increase in pH, which is detected by the phenol red indicator turning a dark pink to red color. Strong urease activity is characteristic, and mostly limited to all Proteus species. However, Morganella spp., and some Klebsiella, Yersinia, Citrobacter, Enterobacter, Providencia, and Pantoea spp. may also be positive. Phenylalanine is an amino acid that, upon deamination by oxidase enzymes, results in the formation of phenylpyruvic acid. The deamination of phenylalanine to phenylpyruvic acid is detected by the addition of a Ferric Chloride Reagent. That reacts with the by-product to produce a light to deep green color. In the family Enterobacteriaceae, only members of the Proteus, Providencia and Morganella group are capable of deaminating phenylalanine (Lämmler, 2014).

3. Distinguishing E. coli and P. vulgaris

Srivastava &amp Srivastava (2003) depict that E. coli will produce acid from fermenting lactose in the media and thus will turn the media yellow. P. vulgaris will not and the media will remain a pinkish red color. On a TSI slant the best way to differentiate would be to see which produces H2S. This can be deduced by viewing which produced a black precipitate. The H2S will react with the Fe in the media giving rise to a black precipitate, FeS2. E. coli does not produce H2S while P. vulgaris does. Hope this helps.

  1. Why differentiate glucose non fermenters from enterobacteriaceae

It is extremely important to differentiate glucose non fermenters from enterobacteriaceae. Enterobacteriaceae is a gram negative bacterium that can cause extreme illness if cross contaminated with a glucose non fermenter (Srivastava &amp Srivastava, 2003).

Exercise 4

  1. Microscopic morphology of Streptococci and Pneumococci

One similarity about these microorganism is that both are spherical and Gram positive. However, the difference between them is that Streptococci form strings of about 10 bacteria (like a string of pearls). Pneumococci are diplococci, so they form pairs. They have a lancet shape (elongated with pointy end) (Lammer, 2014).

  1. Hemolysis

Alpha (green) hemolysis: Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha hemolysis

  1. Description

    1. Alpha hemolysis

When alpha hemolysis (α-hemolysis) is present, the agar under the colony is dark and greenish. Streptococcus pneumoniae and a group of oral streptococci (Streptococcus viridans or viridans streptococci) display alpha hemolysis. Alpha hemolysis is caused by hydrogen peroxide produced by the bacterium, oxidizing hemoglobin to green methemoglobin (Sidal et al., 2013).

    1. Beta hemolysis

A complete lysis of red cells in the media around and under the colonies: the area appears lightened (yellow) and transparent. Streptolysin, an exotoxin, is the enzyme produced by the bacteria which causes the complete lysis of red blood cells (Sidal et al., 2013).

    1. Gamma hemolysis

If an organism does not induce hemolysis, the agar under and around the colony is unchanged, and the organism is called non-hemolytic or said to display gamma hemolysis (Sidal et al., 2013)

  1. Hemolysis displayed by the group-able streptococci

Sidal et al. (2013) illustrates some of the types of hemolysis displayed by the groupable streptococci as:-

Beta, Alpha and gamma

Exercise 5

  1. What is bacteriuria? When is it significant?

Also described as bladder infection it is significant when it causes symptoms, and particularly when the bacterial head to the kidneys (Lammer, 2014).

  1. How do microorganisms enter the urinary tract?

Lammer (2014), depicts that bacteria pass through the kidney and move on to the urethra. This makes the urethra a passage or route to the kidney.

  1. Why is aseptic urine collection important when cultures are ordered?

As illustrated by Srivastava &amp Srivastava (2003), it is important to be certain that any bacteria observed came from the urinary tract and not the collection vessel hence the need to collect aseptic urine when cultures are ordered.

  1. Bacteria that can cause urinary tract infection

Below is a list of bacteria that causes urinary tract infection as postulated by Lammer (2014)

  • Staphylococcus Saprophyticus

  • Escherichia Coli

  • Enterobacter

  • Klebsiella

  • Serratia

  • Proteus

  • Pseudomonas

  1. 20 colonies

20 in .01 ml=200 in .1 ml = 2000 in 1 ml x 10x dilution factor = 20,000. This number is not significant.


Lämmler, C. (2014). Comparative Studies on Bacteriolytic Properties of Staphylococcus chromogenes and Staphylococcus hyicus. Journal Of Veterinary Medicine, Series B, 38(1-10), 468-472. doi:10.1111/j.1439-0450.1991.tb00897.x

Sibal, A., Lin, Z., &amp Jogia, D. (2013). Coagulase-negative staphylococcus endocarditis: staphylococcus lugdunensis. Asian Cardiovascular And Thoracic Annals, 19(6), 414-415. doi:10.1177/0218492311419764

Srivastava, S., &amp Srivastava, P. (2003). Understanding bacteria. Dordrecht: Kluwer Academic Publishers.