General Microbiology

General Microbiology Indian Medical PG Question 1: Which of the following is NOT a mechanism of antibiotic resistance?

• A. Efflux pump activity
• B. Inactivation by enzymes such as beta-lactamase
• C. Modification of drug target sites
• D. Increased drug absorption (Correct Answer)

General Microbiology Explanation: ***Increased drug absorption*** - **Increased drug absorption** would lead to a higher intracellular concentration of the antibiotic, making it *more potent* against the bacteria rather than contributing to resistance. - Antibiotic resistance mechanisms aim to *reduce the effective concentration* of the drug at its target site or *alter the target itself*. *Efflux pump activity* - **Efflux pumps** are bacterial membrane proteins that actively pump antibiotics out of the bacterial cell [3]. - This mechanism *reduces the intracellular concentration* of the antibiotic, preventing it from reaching its therapeutic target [3]. *Inactivation by enzymes such as beta-lactamase* - Bacteria can produce enzymes like **beta-lactamase** that *chemically modify or degrade* the antibiotic molecule, rendering it inactive [2]. - This is a common mechanism of resistance against **beta-lactam antibiotics** (e.g., penicillin, cephalosporins) [2]. *Modification of drug target sites* - Bacteria can develop mutations that *alter the structure of the antibiotic's target site*, such as a bacterial ribosome or cell wall component [1]. - This change in the target means the antibiotic can no longer bind effectively or interfere with cellular processes, thus *losing its efficacy* [1].

General Microbiology Indian Medical PG Question 2: It is true regarding normal microbial flora present on skin and mucous membrane that

• A. It is difficult to permanently eradicate by antimicrobial agents (Correct Answer)
• B. It is absent in the stomach due to acidic pH
• C. It establishes in the body only after the neonatal period
• D. The flora in the small bronchi is similar to that of the trachea

General Microbiology Explanation: ***It is difficult to permanently eradicate by antimicrobial agents*** - The **normal flora** colonizes various body sites, often forming **biofilms** or residing in protected niches, making complete eradication challenging even with potent antimicrobials. - While antimicrobials can reduce microbial populations, the remaining organisms, or recolonization from external sources, can lead to the re-establishment of the flora. *It is absent in the stomach due to acidic pH* - The stomach is not entirely sterile; **acid-tolerant bacteria**, such as *Helicobacter pylori*, can colonize the gastric mucosa. - While the **acidic pH** limits the diversity and number of microbes, some still persist, particularly in the mucus layer. *It establishes in the body only after the neonatal period* - **Colonization with normal flora** begins at birth, with exposure to maternal vaginal and fecal flora during passage through the birth canal. - Environmental exposure and feeding patterns further shape the microbial composition throughout the **neonatal period** and infancy. *The flora in the small bronchi is similar to that of the trachea* - The **lower respiratory tract**, including the small bronchi and alveoli, is generally considered **sterile or has very sparse flora** due to mucociliary clearance and immune defenses. - The **trachea** does have a transient flora, but it is distinct from and much richer than the extremely sparse flora, if any, found in the small bronchi.

General Microbiology Indian Medical PG Question 3: Blood culture is positive in which infection caused by Staphylococcus aureus?

• A. Infective endocarditis (Correct Answer)
• B. Impetigo
• C. Toxic Shock Syndrome (TSS)
• D. Staphylococcal Scalded Skin Syndrome (SSSS)

General Microbiology Explanation: ***Infective endocarditis*** - **Infective endocarditis** is characterized by the presence of bacteria in the bloodstream, leading to a **positive blood culture** [2]. *Staphylococcus aureus* is a common cause, particularly in intravenous drug users [1], [2]. - The infection involves the **endothelial lining of the heart**, often affecting heart valves, causing vegetations that can shed bacteria into the circulation [2], [3]. *Toxic Shock Syndrome (TSS)* - TSS is caused by toxins (e.g., **TSST-1**) produced by *Staphylococcus aureus*, not by the direct presence of bacteria in the bloodstream in high numbers that would consistently yield a positive blood culture. - While *S. aureus* is present, the systemic effects are primarily **toxin-mediated**, and blood cultures are often negative. *Impetigo* - Impetigo is a **superficial skin infection** caused by *Staphylococcus aureus* or *Streptococcus pyogenes*. - It does not involve systemic bacteremia, so **blood cultures are typically negative**. *Staphylococcal Scalded Skin Syndrome (SSSS)* - SSSS is a **toxin-mediated disease** caused by exfoliatin toxins produced by *Staphylococcus aureus*. - The bacteria usually remain localized at the site of infection (e.g., nose, throat, or skin), and **blood cultures are generally negative**.

General Microbiology Indian Medical PG Question 4: A 25-year-old woman presents with a sudden onset of high fever, chills, and rigors. Blood cultures are pending. What is the next appropriate step in her management?

• A. Administer broad-spectrum antibiotics (Correct Answer)
• B. Wait for blood culture results
• C. Start antipyretic therapy only
• D. Order a CT scan

General Microbiology Explanation: ***Administer broad-spectrum antibiotics*** - The patient presents with classic signs of **sepsis** (high fever, chills, rigors), which is a medical emergency requiring prompt intervention [2]. - **Early administration of broad-spectrum antibiotics** is crucial to improve outcomes and reduce mortality in suspected sepsis, even before culture results are available [1]. *Wait for blood culture results* - Delaying antibiotic treatment in a patient with suspected sepsis can lead to rapid clinical deterioration and increased mortality [1]. - While blood cultures are essential to guide definitive therapy, initial empiric broad-spectrum antibiotics should not be withheld [3]. *Start antipyretic therapy only* - Antipyretics only address the symptom of fever and do not treat the underlying infection causing the fever and chills. - This approach would leave the potentially life-threatening infection untreated, leading to worsening patient condition. *Order a CT scan* - A CT scan is not the immediate priority in a patient presenting with acute signs of systemic infection and suspected sepsis. - While it may be useful later to identify a source of infection, controlling the infection with antibiotics is the most urgent step.

General Microbiology Indian Medical PG Question 5: A farmer presents with pustules that show Gram-positive cocci on smear. The culture shows beta hemolysis, and the organisms are catalase-negative. To confirm that the identified organism is group A streptococcus, which of the following tests should be performed?

• A. Bacitracin sensitivity (Correct Answer)
• B. Novobiocin sensitivity
• C. Bile solubility
• D. Optochin sensitivity

General Microbiology Explanation: ***Bacitracin sensitivity*** - **Group A Streptococcus (GAS)** is uniquely sensitive to bacitracin, distinguishing it from most other beta-hemolytic streptococci. - A definitive zone of inhibition around a **bacitracin disk** on a blood agar plate indicates GAS. *Optochin sensitivity* - This test is used to identify **Streptococcus pneumoniae**, which is alpha-hemolytic, not beta-hemolytic like the organism described. - *S. pneumoniae* is **sensitive to optochin**, while other alpha-hemolytic streptococci are resistant. *Novobiocin sensitivity* - This test is primarily used to differentiate coagulase-negative staphylococci, specifically to identify **Staphylococcus saprophyticus** (resistant) from other coagulase-negative staphylococci (sensitive). - It is not applicable to the identification of streptococci. *Bile solubility* - This test is used to differentiate **Streptococcus pneumoniae** (bile soluble) from other alpha-hemolytic streptococci. - The described organism is **beta-hemolytic**, making this test inappropriate for its identification.

General Microbiology Flashcard 1 of 5

Question: 4 Bacterial Growth Environments_____ - environment w/ O2Obligate Anaerobes - environment w/o O2Facultative Anaerobes - either w/ or w/o O2Intracellular bacteria

Answer: Obligate Aerobes

General Microbiology Flashcard 2 of 5

Question: _____ staining procedures can be used to visualise cell walls

Answer: Differential (Simple/Differential)

General Microbiology Flashcard 3 of 5

Question: The resolving power of a light microscope, shown in the image, is limited by the _____ of the light.

Answer: wavelength

General Microbiology Flashcard 4 of 5

Question: germ theory was given by

Answer: Louise pasteur

Extra Information: 

General Microbiology Flashcard 5 of 5

Question: 3 phases of bacterial growth curve: _____ phase, growth/log phase, stationary phase

Answer: lag