Microbiology and Immunology

1. Cytokines are mediators that regulate immunological, inflammatory and reparative host response.
2. They are produced by cells like lymphocytes, macrophages, platelets, etc.
3. Their action is local not systemic.
4. They have effect on growth and differentiation of various cells.

Candida cultures can be obtained on  Sabouraud’s agar. Other media used to culture fungi are cornmeal agar and Czapek-Dox medium.

Mechanism of Action - Alkylation of amino, carboxyl, etc., group of proteins.
Use: To sterilized heat-labile instruments  like dental equipment, heart lung machines, etc.
Disadvantage: It is potentially mutagenic and carcinogenic.

Kaposi’s sarcoma is a highly vascular (angioblastic) tumour of the skin characterized by soft purplish plaques and papules.

Mitis-Salivarius-Bacitracin agar (MSA) with 20% sucrose and 0.2 U bacitracin/ml is a selective medium for streptococcus mutans.
Bacitracin present in the medium suppresses the growth of most non-S.mutans colonies.

B-hemolytic streptococci are classified on the basis of group-specific C carbohydrate antigen on cell wall into 20 lancefield groups (A To V except I and J).
Group A streptococci are further classified by serological typing of (M) proteins into Griffith types.

1. It is also called endocarditis lenta.
2. It is caused by the streptococcus viridans group, enterococci.
3. It occurs on damaged valves.
4. Acute endocarditis-main cause is staphylococcus aureus. Acute endocarditis is more fatal than subacute bacterial endocarditis.

IgA is involved in protection against caries as it inhibits adherence of microorganism to the mucosal surfaces and therefore their disposal by swallowing. IgA is also the major immune globulin in salvia. It is also used in the preparation of caries vaccine for prevention of dental caries because of the above said reason.

Interferons are a family of host-coded proteins produced by cells on induction by viral inducer. Interferon does not act on virus, but it renders other host cells refractory to virus. Interferons (IFNs) are natural cell-signaling proteins produced by the cells of the immune system of most vertebrates in response to challenges, such as viruses, parasites and tumour cells.

Koch’s postulates were first indicated by Henle but enumerated by Koch and they determine whether a microorganism is pathogenic or not.

EBV is a causative agent of

1.  Infectious mononucleosis
2.  Burkitt’s lymphoma 
3.  Nasophanygeal carcinoma.

T-cells produce lymphokines, cytokines and induce cell-mediated immunity (CMI). Delayed hypersensitivity refers to appearance of reaction after 48-42 hours. It is medicated by T-lymphocytes. Delayed hypersensitivity is cell-mediated immunity.

Transduction - It is transfer of portion of DNA, from one bacterium to another by a bacteriophage. It can be a transfer of DNA, episomes or plasmids. It is the most widespread mechanism of gene transfer in prokaryotes.

Nosocomial infections are hospital-acquired infections, which develop in hospitalized patients. Streptococcus pyogenes was the most important causative organism in the ICU,  but due to antibiotic sensitivity, it is now hardly encountered.

Polymerase chain reaction is the gold standard for diagnosis in all of HIV.
Reverse transcriptase PCR is sensitive for viral nucleic acid (RNA). It can detect a single copy of RNA or proviral DNA from infected cells.

The resident normal microbial flora cannot be completely or permanently removed, while transient ones are temporary. The number of superficial microorganisms can be diminished completely eradicated.

Neisseria, salmonella typhi and legionella can survive intracellularly but not S.pyogenes.

1. Neisseria meningitidis is found in spinal even inside leucocytes (intracellularly).
2. Legionella can enter alveolar macrophages.
3. Salmonella typhi can multiply within polymorphs, and hence can resist intracellular killing.

Four subclasses of IgG and their distribution are as follows:

1. IgG1-65% (Max)
2. IgG2-23%
3. IgI3-8%
4. IgG4-4%(Min)

Mycoses are fungal infections, e.g., superficial mycoses, systemic mycoses.
Mycotic abscess-soft cystic mass with slight inflammation caused by hyaline and decataceous fungi and nocardia species.

1. It is also called anaphylactic, IgE or regain-dependent hypersensitivity.
2. In this, the cytotropic IgE antibodies, are fixed on surface of cells like mast cells and basophils.

Steps to disinfect blood spills:
Disposable towels or wipes should be used to wine up the spill by gloved hands.
Diluted bleach (sodium hypochlorite) solution is then used to disinfect the area. If blood is not wiped properly by towel, then disinfectant will not act.

Darkfield or phase contrast microscopy is alternative to culture methods.

The defined diagnosis of ANUG can be established mainly on the basis of clinical findings. Since,  it is a fusospirochetal infection, dark field microscopy can also be used to detect spirochetes. However, dark field microscopy is unsuitable for examining oral lesions as many nonpathogenic treponemes found in the mouth may be confused with the causative agents. Tissue culture and subsequent tissue smear can also be used to confirm ANUG.

Lactobacillus is both acidogenic and aciduric bacteria and therefore causes caries.
Acidogenic bacteria are acid-producing bacteria. The acid produced damages dentin and other mineralized structures of teeth.
Acidouric bacteria are bacteria that can grow well in acidic medium.

Opportunistic malignancies typically associated with HIV infection are Kaposi's sarcoma.

1.  Antigen-combining site of an antibody is at amino terminus.
2.  It has both light and heavy chains.
3. The amino acid sequence in aminoterminal is variable. This variable region determines immunological specificity.

Adjuvants are the substances added to vaccines to improve their humoral antibody response. In DPT vaccine, aluminium phosphate and aluminium are used as adjuvants.

Viruses do not have a cellular organization. They are acellular. They have only one type of nucleic acid either DNA or RNA. They also do not have enzymes for protein and nucleic acid synthesis. So, they have characteristics of both living organisms and nonliving objects.

Herpangia
a.  It is caused by coxsackie virus.
b.  It is related to intraoral lesions.
c.  C/F – sore throat, cough, low grade fever, vesicles,  which rupture to form ulcers on anterior faucial pillars, hard and soft palate and posterior pharyngeal walls.

Widal test
It is a serological test to diagnose typhoid.
It measures H and Q agglutinins for typhoid and paratyphoid bacilli. It is a tube agglutination reaction.
Causes of false negative widal are
a. Carrier state
b. Inadequate amount of bacterium in the host
c. Technical errors
d.  Previous antibiotic treatment

Chemiclave is a machine which sterilizes instruments with high pressure, high temperature water and some chemicals like alcohol and formaldehyde vapour. It is therefore a sterilization unit that uses chemicals under pressure.

For screening of syphilis – VDRL, TPHA or combination is used.
Regain test are done to monitor patient’s response after treatment as they become negative after treatment, e.g., VDRL, tests.
TPHA cannot be used to evaluate syphilis after treatment as its titre remains low even after treatment but never zero.

Aspergillus causes opportunistic infection in immunocompromized patients and debilitated hosts like HIV, diabetes and other immunocomprmised. Other opportunistic fungal infection in diabetes is candidiasis.

Glutraladehyde is a high-level disinfection and instruments should be immersed in it for 20 minutes to avoid corrosion.
About glutraldehyde

1. It is effective against tubercle bacilli, fungi and viruses.
2. It has no deleterious effect on lenses of instruments, therefore used to sterilize bronchoscopes, etc.

Agglutination reactions-it is a reaction between a particulate antigen and its antibody, which results in the formation of clumps. For example:
a.  Slide agglutination-blood grouping
b.   Comb‘s test

Secondary syphilis
a.  It occurs 1-3 months after healing of primary lesion.
b.  Characteristic mucous patches, condylomata lata, popular rashes are present.
c.  It is the most infection stage.

Chronic carrier state is the most common with hepatitis B infection. HBV is a blood- borne virus. Medical and paramedical, staff of blood banks, dialysis units and sex workers are the high-risk groups.

Antirabies vaccine – They are of two types: neural vaccines and nonneural vaccines.
Semple vaccine is most widely used vaccine and it consists of 5% suspension of sheep brain infected with fixed virus and which is inactivated by phenol.
BPL vaccine is a modification of semple vaccine in which B-propiolactone is used as an inactivating agent.

Negative staining by India ink is used to demonstrate capsules. In these films, capsule is seen as a halo around bacteria.

For diagnosis of typhoid bacilli, blood is collected and is inoculated into a bile broth culture bottle.

Immunoglobulins are proteins with known antibody activity and they are synthesized by plasma cells, which are activated B-cell.

Erythroblastosis fetalis is an hemolytic disease of the newborn. It classically results from Rh incompatibility when  Rh negative mother carries a foetus,  which is Rh positive. Such Rh positive RBC of foetus when comes in contact with the blood of mother, it stimulates maternal antibody production against Rh antigens. The first pregnancy may be normal, but in subsequent pregnancy, these antibodies lyse foetal RBC causing anaemia and even death. However, maternal sensitization and antibody production can be prevented by injecting mother with Rh (D) immunoglobulin at parturition.

Holding period in an autoclave is 121^oC for 12 min at 15 lbs pressure or 134^oC at 30 lbs pressure for 3 minutes.

IgG and IgM fix the complement system by classical pathway and IgA participates in complement fixation by alternate pathway.

A bacterial spore is a dormant, tough, and nonreproductive structure produced by bacteria.

1.  It is a chronic granulomatous infection caused by actinomyces israelli mainly.
2. Actinomyces are true bacteria; however, they superficially resemble resemble fungi, and hence called ray fungus. Actinomyces are positive bacteria.
3.  Actinomycosis is also called lumpy jaw.

The plasma protein and their fractions can be separated by electrophoretic method,  which depends upon electric charge of the proteins and difference in their rate of migration.
Maximum mobility in electrophoresis is shown by albumin and minimum by y-globulin.

Bacillus stearo thermophilus is thermophilic and its spores are killed by an exposure of compressed steam for 12 minutes at 121⁰C; therefore, its spores are used to test the efficacy of moist heat sterilization (autoclave). Other means to test efficacy of moist heat sterilization are chemical indicators, autoclave tapes and thermocouples.

Psychrophilic bacteria-bacteria that can grow best at temperatures below 20^oC, e.g., soil and water saprophytes and may cause spoilage of refrigerated foods.

Negri bodies are the intracytoplasmic inclusion bodies present in the brain cells of animal suffering from rabies. Diagnosis of rabies post mortem is done by demonstration of negri bodies in the brain.