#MICROBIOLOGY(AIIMS-PG)
Q- Identify the organism by the appearance of colonies on the Regan-Lowe medium as shown in the photograph below?
A. Hemophilus influenzae
B. Bordetella Pertussis
C. Brucella melitensis
D. Mycobacterium tuberculosis
Answer is B. Bordetella Pertussis
🔹Bordetella Pertussis is an organism that shows Bisected pearls/ Mercury drops appearance of colonies on the Regan-Lowe medium as shown in the photograph above.
🔹B. pertussis is a very small Gram-negative aerobic coccobacillus that appears singly or in pairs.
🔹Its metabolism is respiratory, never fermentative, and taxonomically, Bordetella is placed among the "Gram-negative Aerobic Rods and Cocci" in Bergey's Manual. Bordetella is not assigned to any family.
🔹The bacteria are nutritionally fastidious and are usually cultivated on rich media supplemented with blood.
🔹They can be grown in synthetic medium, however, which contains a buffer, salts, an amino acid energy source, and growth factors such as nicotinamide (for which there is a strict requirement).
🔹Even on blood agar the organism grows slowly and requires 3-6 days to form pinpoint colonies.
🔹Bordetella pertussis colonizes the cilia of the mammalian respiratory epithelium. Generally, it is thought that B. pertussis does not invade the tissues, but some recent work has shown the bacterium in alveolar macrophages.
🔹The bacterium is a pathogen for humans and possibly for higher primates, and no other reservoir is known.
🔹 Whooping cough is a relatively mild disease in adults but has a significant mortality rate in infants. Until immunization was introduced in the 1930s, whooping cough was one of the most frequent and severe diseases of infants.
Extra points:
Morphology
-Capsulated
-It is a strict human pathogen
Culture
-Bordet-Gengou glycerine potato-blood agar medium is commonly used.
-Contains a high percentage of blood (20%–30%) to inactivate inhibitors in the agar.
-Mischulow’s charcoal agar
Produces bisected pearls or mercury drops colonies.
-Confluent growth present and “aluminium paint” appearance.
-Culture films have Thumbprint appearance
Virulent Factors
1. Pertussis toxin
2. Filamentous hemagglutinin (FHA) secreted protein: Piracy of Adhesins
3.Tracheal cytotoxin
Q- Features of chancroid:
A. School of fish on Gram stain
B. Painful ulcer
C. Bleeds on touch
D. Groove sign
Chose the correct Options
1. C & D
2. A, B & D
3. A, B & C
4. A, C & D
Answer is A, B and D
Chancroid is a bacterial sexually transmitted infection characterized by painful sores on the genitalia. Chancroid is known to spread from one individual to another solely through sexual contact. However, there have been reports of accidental infection through another route which is by the hand.
H.ducreyi:
▪️Bipolar starned (safety pirz) bacilli arranged in group or whorls or parallel chains (school of fish or rail-road track appearance).
▪️The ulcer may bleed or produce contagious fluid that can spread bacteria during oral, anal or vaginal intercourse
▪️So, Causative agent of Chancroid or soft sore-STD is characterized by tender, non indurated irregular genital ulceration and inguinal adenitis.
Treatment - Single oral dose of azithromycin.
Alternative ciprofloxacin for erythromycin
Q- A patient complains about nausea, vomiting and stomach cramps after attending a social gathering party, which causative organism is likely responsible for Food Poisoning within 3 hours.
A. Staphylococcus aureus
B. Salmonella
C. Clostridium botulinum
D. Clostridium perfringens
Answer is A. Staphylococcus aureus
Staphylococcus aureus food poisoning is characterized by a sudden start of nausea vomiting, and stomach cramps. Most people also have diarrhea. Incubation period is 1-6 hrs so symptoms usually develop within 30 minutes to 6 hours after eating or drinking an item containing Staph toxin and last no longer than 1 day. Severe illness is rare.
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