Bacteriologist Interview Preparation Guide

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The cytoplasm of Gram positive bacteria are said to be more acidic
than those of Gram negative ones.
Hence the dye is said to bind with more affinity to Gram positive cells.

An organized system of meticulously constructed narrow trenches, which are partially filled with washed gravel or crushed stone, into which a pipe is placed. Discharges from septic tanks are passed through these trenches.

Primary stain: Strong Carbol Fuchsin (contain Basic fuchsin and Phenol)
Decolourizer 20% sulphuric acid
Counterstain LoelTler’s Methylene blue or 1% Malachite green, Picric acid for color-blind workers

Beaded appearance is used to describe the appearance of Mycobacterla when the cell doesn’t stain uniformly. showing stained and unstained regions. These forms are common in Mycobacterium tuberculosis while Mycobacterium bovis stains uniformly. Most saprophytic Mycobacteria stain uniformly.

Sputum smears for Mycobacterla can be stained by fluorescent dyes such as Auramine and Rhodamlne as they have affinity for mycolic acid In their cell walIs The fluorescent microscopy is useful in screening large number of specimens. Large area of smear can be quickly observed that too under high power dry objective.

The process of kdling all hying forms including spores is called sterilization and the process of killing of only the vegetative form of pathogenic bacteria as well as other microbes is disinfection

It is the cytoplasm (especially the nucleic acid) that gets stained and not the cell wall. Presence of an intact cell wall is important for retaining Gram positivity. Cell wall deficient forms such as Mycoplasma and L forms are Gram negative.

A compound of magnesium ribonucleate and basic protein concentrated at the cell membrane helps Gram positive bacteria retain the primary dye. Gram negative bacteria do not possess this substance.

Alkylation (hydrogen atom is replaced with an alkyl group) of protein. DNA. and RNA afFects bacterial metabolism and replication. EQ gas (8.5%) is often mixed with stabilizers such as CO2 (91 5%) or hydrochlorofluorocarbons (HCFC). This requires high humidity (40-80%) and long exposure times (1-6 hrs).

Decolourization is the most important step as this step differentiates between Gram positive and Gram negative bacteria. Over-decolourization can result in Gram positive bacteria appearing Gram negative and under-decolourization can result in Gram negative bacteria appearing Gram positive.

Cell wall of Gram positive bacteria are 40 times thicker than those of Gram negative cells, hence they are thought to help retain the dye-iodine complex.

☛ Tincture Iodine - 2% of Iodine in 70% alcohol - lodophore - Povidone Iodine.
☛ Name some antiseptics.
☛ Chlorhexidine. Chloroxylenol. spirit (70% alcohol), tincture of Iodine. H202.

Sludge particles which are produced in raw or settled wastewater, by the growth of organisms in aeration tanks. This is all done in the presence of dissolved oxygen. This sludge contains living organisms that can feed on incoming wastewater

Phenol. Lysol, Formaldehyde. Sodium hypochlorite.

The cell walls of Mycobacterla are made up of waxy substance, Mycolic acid that Is relatively Impermeable to ordinary stainIng techniques. But, by apphcation of heat and a mordant (phenol), the cell can be stained The purpose of heating is to soften the waxy material of the cell wall and allow the stain to enter the cell. Basic fuchsin is more soluble in phenol and phenol is a better solvent for lipids and waxes.

Cell envelope of Gram negative bacteria contains an additional membrane (outer membrane). hence containing more lipids than Gram positive bacteria. Acetone or alcohol dissolves the lipid thus forming large pores in Gram negative bacteria through which the dye-iodine complex leaks out. Alcohol/acetone dehydrates Gram positive bacteria shrinking the cell wall and the closing the pores.

3% HCI in 95% alcohol (methylated spirit). This is useful in dilrerentiating saprophytic Mycobacteria from pathogenic Mycobacteria Pathogenic Mycobacteria are both acid and alcohol fast but saprophytic Mycobacterla are only acid-fast Saprophytic Mycobacterla can get declourized by alcohol. 95% alcohol can be used as a secondary decolorizer after decolourizing with acid Especially used in staining smears prepared from urine that may contain Mycobacterium smegmatis.

An aerobic, gram negative bacteria, that is rod-shaped, which is made of non-sporogenous organisms that produce acetic acid as a waste product.

Solution A(1) contains Toluidine blue, Malachite green, Glacial acetic acid and Alcohol while solution 8(2) contains iodine and potassium iodide In distilled water.

Certain bacteria or their structures have the ability to retain the primary dye (strong carbol fuchsin) and resist clecolourization by weak mineral acids such as H2S04. HCI. Such bacteria or their structure are termed acid fast and this property is termed acid fastness. There are two types of acid fast staining, the hot method and the cold method. The hot method (Ziehl-Neelsen) involves heating the slide while the cold methods such as Kinyoun’s and Gabbett’s do not involve heating the slide.

You work great with people! This question may stump you, but as a Bacteriologist, you may work on your own more often than in a group. The interviewer wants to hear that you work well with all types of people from patients to other health care professionals.

This includes organisms that require molecular oxygen to survive (aerobic organisms), an environment that has molecular oxygen, and processes that happen only in the presence of oxygen (aerobic respiration).

Albert’s stain. Neissers stain, Ponder’s stain and Pugh’s stain They can be demonstrated as retractile bodies in wet mount or slightly more gram positive structures in Gram stain.

☛ Positive control: Staphylococci
☛ Negative control: E.coli. pus cells

At least 100 oIl Immersion fields must be viewed before declaring the smear as negative The sensitivity of smear Is low because It requires the presence of 104 bacillilml to be smear positive. If the number of bacilli is less than this, the chances of detecting them are less In such a case, the sample should be subjected to concentration techniques such as Petroff s method If the smear Es positive for AFB. it should be counted/graded Failure to detect any AFB does not rule tuberculosis Grading of smears has prognostic value.