Test your basic microbiology: bacterial structure and growth, Gram staining, viruses, sterilization and infection. There are two sets of 10 questions. Click an answer to see whether you are right, with a short explanation.
Set 1: Basic Microbiology I
Score0 / 0Time00:00
1.Bacterial capsules contribute to virulence mainly by helping bacteria resist:
Answer: B. The slippery polysaccharide capsule makes it hard for neutrophils and macrophages to engulf the bacteria, as in Streptococcus pneumoniae.
2.Which statement about Pseudomonas aeruginosa is NOT true?
Answer: A. P. aeruginosa has very simple nutritional needs and can use many organic compounds for growth, which is why it survives in water systems and on wet surfaces. Growth promotion test guide →
3.Colony-forming units per mL (CFU/mL) is the unit of the:
Answer: D. Plate counts (pour plate, spread plate, membrane filtration) count colonies, each arising from one or more viable cells, so results are reported in CFU. TAMC/TYMC guide →
4.Which is the correct order of taxonomic ranks, from highest to lowest?
Answer: C. A common memory aid: Dear King Philip Came Over For Good Soup.
5.The most common cause of nosocomial (hospital-acquired) infections is:
Answer: B. Most healthcare-associated infections are bacterial, for example E. coli, Staphylococcus aureus, Klebsiella, Pseudomonas and Clostridioides difficile.
6.The most frequently used portal of entry for pathogens is the:
Answer: A. The respiratory tract is the easiest and most frequently used portal of entry, because microbes are inhaled in droplets and dust.
7.Which organism is the most common cause of urinary tract infections?
Answer: A. Uropathogenic E. coli causes most community-acquired UTIs.
8.In which bacterial growth phase are secondary metabolites, such as antibiotics, mainly produced?
Answer: C. Secondary metabolites are produced mainly in the stationary phase (idiophase), when growth slows as nutrients run out.
9.Which part of the body contains the largest microbial population?
Answer: B. The colon contains the densest microbial population in the body, around 10^11 bacteria per gram of contents.
10.Which step in Gram staining is most likely to give a false result?
Answer: A. Over-decolorizing with alcohol or acetone washes crystal violet out of Gram-positive cells, so they wrongly appear Gram-negative.
Set 2: Basic Microbiology II
Score0 / 0Time00:00
1.A structural component found in all viruses is the:
Answer: C. Every virus has a protein capsid around its nucleic acid. Envelopes and spikes are found only in some viruses, and many viruses have RNA instead of DNA.
2.Which microorganisms are most likely to survive UHT treatment?
Answer: B. Bacterial endospores are the most heat-resistant form of microbial life. UHT is designed to destroy them, so surviving spores are the main cause of UHT spoilage.
3.NAM and NAG in the peptidoglycan backbone are joined by a:
Answer: C. N-acetylmuramic acid and N-acetylglucosamine alternate, joined by β-(1,4) glycosidic bonds. Lysozyme breaks exactly this bond.
4.Which of these bacteria has no cell wall?
Answer: B. Mycoplasma has no cell wall, so it is naturally resistant to beta-lactam antibiotics and is a known contaminant of cell cultures.
5.What colour are Staphylococcus aureus colonies typically?
Answer: C. S. aureus produces the golden carotenoid pigment staphyloxanthin; 'aureus' means golden.
6.Dextran, used as a plasma expander, is produced by:
Answer: D. Leuconostoc mesenteroides makes dextran from sucrose using the enzyme dextransucrase.
7.The mordant in Gram staining is:
Answer: D. Gram's iodine forms a crystal violet–iodine complex that is trapped in the thick peptidoglycan of Gram-positive cells. Crystal violet is the primary stain, alcohol the decolorizer and safranin the counterstain.
8.The standard autoclave condition for sterilization is:
Answer: C. Saturated steam at about 15 psi above atmospheric pressure reaches 121 °C, the standard condition for at least 15 minutes.
9.Human papillomaviruses cause:
Answer: A. Low-risk HPV types cause warts; high-risk types such as HPV 16 and 18 cause cervical and other cancers. Measles, shingles and mumps are caused by other viruses.
10.The endotoxin in the outer membrane of Gram-negative bacteria is:
Answer: D. The lipid A part of lipopolysaccharide (LPS) is the endotoxin, detected by the bacterial endotoxin (LAL) test in parenteral products.