Nosocomial Pathogens Practice Questions
19 free Nosocomial Pathogens practice questions for the Microbiology. Tap an option to answer — you get instant feedback, the correct answer, and a detailed explanation for every question.
Which Gram-negative, non-fermenting bacillus is notorious for its intrinsic resistance to many antibiotics and its ability to thrive in moist hospital environments like ventilators?
- A Staphylococcus aureus
- B Streptococcus pyogenes
- C Haemophilus influenzae
- D Pseudomonas aeruginosa
Correct answer: Pseudomonas aeruginosa
Pseudomonas aeruginosa is a leading cause of nosocomial pneumonia and UTI, particularly in immunocompromised patients. Its ability to form biofilms on medical devices makes it exceptionally difficult to eradicate.
MRSA (Methicillin-Resistant Staphylococcus aureus) acquires resistance to beta-lactam antibiotics primarily through the acquisition of which gene?
- A blaZ
- B vanA
- C mecA
- D tetM
Correct answer: mecA
The mecA gene encodes an altered penicillin-binding protein (PBP2a) that has a low affinity for beta-lactam antibiotics. This allows the bacterium to continue cell wall synthesis even in the presence of methicillin, oxacillin, and cephalosporins.
Which of the following organisms is a frequent cause of catheter-associated urinary tract infections (CAUTIs) and is known for its high urease activity?
- A Proteus mirabilis
- B Enterococcus faecalis
- C Candida albicans
- D Serratia marcescens
Correct answer: Proteus mirabilis
Proteus mirabilis produces large amounts of urease, which hydrolyzes urea to ammonia, raising the pH of urine. This alkaline environment promotes the formation of struvite stones, which can obstruct urinary catheters.
Vancomycin-resistant enterococci (VRE) typically involve a change in the cell wall precursor target from D-Ala-D-Ala to which of the following?
- A D-Ala-D-Ser
- B D-Glu-D-Ala
- C L-Ala-D-Glu
- D D-Ala-D-Lac
Correct answer: D-Ala-D-Lac
VRE strains modify their peptidoglycan precursors to end in D-Alanyl-D-Lactate instead of D-Alanyl-D-Alanine. This structural change significantly reduces the binding affinity of vancomycin to the cell wall intermediate.
Which multidrug-resistant organism is often associated with military personnel returning from conflict zones and is highly resilient in the hospital environment?
- A Acinetobacter baumannii
- B Klebsiella pneumoniae
- C Burkholderia cepacia
- D Stenotrophomonas maltophilia
Correct answer: Acinetobacter baumannii
Acinetobacter baumannii, often dubbed 'Iraqibacter', is a Gram-negative coccobacillus that causes severe infections in ICU patients. It can survive on dry surfaces for weeks, facilitating its spread via healthcare workers' hands.
What is the primary mode of transmission for most nosocomial pathogens within a hospital setting?
- A Airborne droplet spread across long distances
- B Contaminated food and water from hospital sources
- C Contact spread through healthcare workers' hands
- D Endogenous mutation of the patient's own flora
Correct answer: Contact spread through healthcare workers' hands
While other routes exist, contact transmission is the most significant pathway for healthcare-associated infections. Hand hygiene remains the single most effective intervention to prevent the cross-transmission of resistant pathogens.
Which of the following fungal pathogens is a leading cause of nosocomial bloodstream infections, particularly in patients with central venous catheters?
- A Mucor indicus
- B Cryptococcus neoformans
- C Candida auris
- D Aspergillus fumigatus
Correct answer: Candida auris
Candida auris is an emerging multidrug-resistant yeast that causes outbreaks in healthcare facilities. Unlike most other Candida species, it can persist on environmental surfaces and spread between patients.
Carbapenem-resistant Enterobacteriaceae (CRE) are primarily concerning because they produce enzymes that:
- A Degrade vancomycin molecules within the periplasmic space
- B Prevent aminoglycoside uptake across the outer membrane
- C Methylate the ribosomal 16S rRNA to block protein synthesis
- D Inactivate almost all available beta-lactam antibiotics
Correct answer: Inactivate almost all available beta-lactam antibiotics
CRE produce carbapenemases (like KPC or NDM-1) which are beta-lactamases capable of hydrolyzing carbapenems, penicillins, and cephalosporins. These infections are often associated with high mortality due to limited treatment options.
Which opportunistic pathogen is characterized by the production of a red pigment called prodigiosin and is associated with hospital outbreaks of UTI and pneumonia?
- A Serratia marcescens
- B Klebsiella oxytoca
- C Enterobacter cloacae
- D Citrobacter freundii
Correct answer: Serratia marcescens
Serratia marcescens is a Gram-negative bacillus known for producing a red pigment at room temperature. It was once thought to be harmless but is now recognized as a significant cause of nosocomial infections, especially in neonatal units.
A healthcare-associated infection (HAI) is typically defined as an infection that appears how many hours or more after hospital admission?
- A 12 hours
- B 24 hours
- C 48 hours
- D 72 hours
Correct answer: 48 hours
The standard CDC definition for a healthcare-associated infection is one that was not present or incubating at the time of admission, usually manifesting 48 hours or more after the patient enters the facility.
Which of the following Gram-positive bacteria is a common skin commensal but a frequent cause of neonatal sepsis and infections of prosthetic joints?
- A Staphylococcus epidermidis
- B Streptococcus agalactiae
- C Corynebacterium diphtheriae
- D Listeria monocytogenes
Correct answer: Staphylococcus epidermidis
Staphylococcus epidermidis is a coagulase-negative staphylococcus (CoNS) that excels at forming biofilms on plastic medical devices. It is the most common organism isolated from blood cultures, though it is often a contaminant.
Which nosocomial pathogen is an obligate aerobe, often found in water reservoirs, and causes a high mortality rate in cystic fibrosis patients?
- A Burkholderia cepacia
- B Legionella pneumophila
- C Mycobacterium abscessus
- D Alcaligenes faecalis
Correct answer: Burkholderia cepacia
Burkholderia cepacia is highly resistant to multiple antibiotics and can spread between cystic fibrosis patients through social contact. Some hospitals practice 'segregation' to prevent the transmission of this virulent pathogen.
ESBL-producing bacteria (Extended-Spectrum Beta-Lactamases) are resistant to most cephalosporins but remain typically susceptible to:
- A Amoxicillin
- B Ceftriaxone
- C Carbapenems
- D Aztreonam
Correct answer: Carbapenems
ESBLs are enzymes that mediate resistance to third-generation cephalosporins and monobactams (aztreonam). Carbapenems (like imipenem or meropenem) remain the treatment of choice for serious infections caused by ESBL-producing organisms.
Which factor is the most significant risk for the development of a surgical site infection (SSI)?
- A The duration of the preoperative hospital stay
- B The use of robotic surgery vs. manual surgery
- C The age of the surgical instruments
- D The presence of a remote infection at the time of surgery
Correct answer: The duration of the preoperative hospital stay
A longer preoperative hospital stay increases the risk that the patient's skin will become colonized with hospital-acquired, multi-drug resistant flora, which can then be introduced into the surgical wound.
Which virus is a major cause of nosocomial gastroenteritis in pediatric wards, despite the availability of a vaccine?
- A Rotavirus
- B Adenovirus
- C Astrovirus
- D Sapovirus
Correct answer: Rotavirus
Rotavirus is highly contagious and stable on environmental surfaces. While vaccines have reduced the overall burden, it remains a frequent cause of hospital-acquired diarrhea in children where infection control measures fail.
What is the clinical significance of 'Stenotrophomonas maltophilia' in the hospital setting?
- A It is the primary cause of hospital-acquired meningitis
- B It is naturally resistant to carbapenems
- C It produces a food-borne enterotoxin
- D It is the only Gram-negative bacteria with a thick capsule
Correct answer: It is naturally resistant to carbapenems
Stenotrophomonas maltophilia is an opportunistic pathogen that is intrinsically resistant to carbapenems due to the production of metallo-beta-lactamases. It often emerges in patients who have received broad-spectrum antibiotic therapy.
Which procedure carries the highest risk for the development of nosocomial pneumonia?
- A Nasogastric intubation
- B Intravenous catheterization
- C Mechanical ventilation
- D Urinary catheterization
Correct answer: Mechanical ventilation
Ventilator-associated pneumonia (VAP) is a major HAI. The endotracheal tube bypasses the natural defenses of the upper airway and provides a surface for biofilm formation and the microaspiration of contaminated secretions into the lungs.
Which of the following is true regarding the 'ESKAPE' pathogens?
- A They are all Gram-positive bacteria
- B They are the only pathogens that cause nosocomial infections
- C They are organisms known to 'escape' antibiotic action
- D They are all transmitted primarily through respiratory droplets
Correct answer: They are organisms known to 'escape' antibiotic action
The acronym ESKAPE stands for Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species. These organisms are highlighted by the IDSA as the premier threats for antibiotic resistance.
What is the primary reservoir for 'Klebsiella pneumoniae' in a hospital setting?
- A The hospital water supply and plumbing system
- B Air conditioning filters and ventilation systems
- C The gastrointestinal tract of patients and staff
- D Contaminated linen and bedding
Correct answer: The gastrointestinal tract of patients and staff
Klebsiella pneumoniae is a common inhabitant of the human intestinal tract. In hospitals, colonization of the gut by resistant strains serves as a reservoir for subsequent infections of the urinary tract, lungs, or bloodstream.