Antimicrobials (Cell Wall Inhibitors, Protein Synthesis Inhibitors, Fluoroquinolones) MCQs

Pharmacology · 162 free questions with answers & explanations.

1. A 30-year-old with meningococcal meningitis is started on IV penicillin G. Six hours later she develops sudden hypotension and worsening consciousness despite the organism being sensitive. The mechanism most responsible is:
2. Vancomycin inhibits bacterial cell wall synthesis by a mechanism distinct from beta-lactams. Which specific step does vancomycin target?
3. Fluoroquinolones are contraindicated in children and pregnant women primarily because of:
4. Imipenem is always combined with cilastatin in clinical formulations. The purpose of cilastatin is:
5. A hospital outbreak of MRSA is traced to a strain with vanA gene cluster. This organism, unlike typical MRSA, requires treatment with daptomycin. Why does the vanA gene confer resistance to both vancomycin AND cross-resistance to linezolid may develop?
6. Beta-lactam antibiotics act by binding PBPs (penicillin-binding proteins). In MRSA, which specific mechanism confers resistance to ALL beta-lactams including carbapenems?
7. A patient on fluoroquinolone therapy for Pseudomonas bacteremia develops treatment failure. Susceptibility testing reveals high-level fluoroquinolone resistance. Which molecular mechanism is most likely responsible?
8. Ceftaroline, a 5th-generation cephalosporin approved for MRSA, differs from earlier cephalosporins in which key property?
9. A 35-year-old patient with Gram-negative sepsis is treated with meropenem. Which pharmacokinetic/pharmacodynamic (PK/PD) parameter best predicts bactericidal efficacy of carbapenems?
10. The mechanism of beta-lactam resistance in MRSA is fundamentally different from that in beta-lactamase-producing organisms. MRSA resistance is mediated by:
11. Fluoroquinolone resistance in Gram-negative bacteria most commonly arises due to:
12. Ceftaroline, a 5th-generation cephalosporin, is unique among cephalosporins because it is active against MRSA. Its mechanism of action against MRSA is:
13. Linezolid acts on bacterial ribosomes by a unique mechanism that makes cross-resistance with other protein synthesis inhibitors unlikely. This mechanism is:
14. Ceftaroline is a fifth-generation cephalosporin with activity against MRSA. Its mechanism compared to earlier cephalosporins is BEST explained by:
15. A patient develops Clostridium difficile infection after prolonged ampicillin use. The pathogenic mechanism by which C. difficile exerts its primary cellular effect involves:
16. Resistance to fluoroquinolones in Gram-negative bacteria most commonly occurs via which mechanism?
17. Linezolid's mechanism of action is unique among protein synthesis inhibitors because it acts at:
18. A patient on long-term vancomycin therapy for MRSA endocarditis develops nephrotoxicity. The renal injury pattern and the monitoring parameter used to guide therapy are BEST described as:
19. Beta-lactam resistance in methicillin-resistant Staphylococcus aureus (MRSA) is due to production of PBP2a, encoded by the mecA gene. PBP2a confers resistance primarily by which property?
20. Ceftazidime-avibactam differs from ceftazidime alone in that avibactam inhibits which class of beta-lactamases that clavulanic acid cannot inhibit?
21. Fluoroquinolone resistance due to the plasmid-mediated qnr genes confers resistance through which mechanism?
22. A patient with hospital-acquired pneumonia is prescribed a new antibiotic that inhibits bacterial isoleucyl-tRNA synthetase, preventing aminoacyl-tRNA formation and thus protein synthesis. This drug is:
23. Vancomycin-resistant Enterococcus (VRE) with the VanA phenotype is resistant due to which precise molecular mechanism?
24. A patient is diagnosed with methicillin-resistant Staphylococcus aureus (MRSA) bacteraemia. The microbiologist confirms vancomycin MIC of 1.5 mg/L (intermediate susceptibility). Which pharmacokinetic/pharmacodynamic (PK/PD) index is most predictive of vancomycin efficacy, and what target should be achieved?
25. Linezolid, an oxazolidinone antibiotic, inhibits protein synthesis at which specific step that is unique compared to other protein synthesis inhibitors?
26. Resistance to fluoroquinolones in Gram-negative bacteria most commonly arises through mutations in which specific target, and which quinolone target does it preferentially affect?
27. A 65-year-old immunocompromised patient is started on ceftaroline for MRSA pneumonia. Which structural feature of ceftaroline distinguishes it from other cephalosporins and confers MRSA activity?
28. A clinical isolate of Streptococcus pneumoniae shows high-level penicillin resistance. The molecular mechanism responsible is:
29. Ceftaroline is a novel cephalosporin active against MRSA. Its mechanism of anti-MRSA activity involves:
30. Tedizolid differs from linezolid in pharmacogenomic significance because its metabolic pathway avoids the drug interaction responsible for serotonin syndrome. Tedizolid's reduced interaction risk compared to linezolid is because tedizolid is:
31. A urinary tract infection with an extended-spectrum beta-lactamase (ESBL)-producing E. coli fails to respond to cephalosporins. The ESBL enzyme responsible most commonly belongs to which structural enzyme class?
32. Beta-lactamase inhibitors such as avibactam differ fundamentally from clavulanate in their mechanism. Which property best describes this difference?
33. A laboratory reports that an E. coli isolate produces an ESBL and is treated with piperacillin-tazobactam. Which mechanism specifically explains why ESBL-producing organisms may remain resistant despite a beta-lactamase inhibitor being present?
34. A patient with KPC-producing Klebsiella pneumoniae bacteraemia is treated with ceftazidime-avibactam. Four weeks later, cultures reveal avibactam resistance. Which molecular mechanism is most commonly responsible for this emergence?
35. Which pharmacokinetic/pharmacodynamic index best predicts the bactericidal efficacy of fluoroquinolones, and what implication does this have for dosing frequency?
36. A carbapenem-resistant Klebsiella pneumoniae isolate produces KPC (Klebsiella pneumoniae carbapenemase), a class A serine beta-lactamase. Which newer beta-lactam/beta-lactamase inhibitor combination would be MOST effective against this organism?
37. A mechanism of fluoroquinolone resistance in clinical bacteria involves plasmid-mediated protection of DNA gyrase via Qnr proteins. What is the PRIMARY mechanism by which Qnr proteins confer resistance?
38. Vancomycin resistance in Enterococcus faecium (VRE) most commonly results from substitution of which cell wall precursor, and which vancomycin resistance gene cluster mediates this?
39. Ceftaroline differs from earlier cephalosporins in its clinical utility against MRSA because:
40. Moxifloxacin is preferred over ciprofloxacin for community-acquired pneumonia with atypical cover because:
41. A patient develops linezolid-associated serotonin syndrome when concurrently using sertraline. The mechanism is:
42. OXA-48-type carbapenemases in Klebsiella pneumoniae are clinically important because they:
43. Vancomycin-resistant Enterococcus (VRE) carrying the vanA gene cluster exhibits resistance by which precise molecular mechanism?
44. A patient with community-acquired pneumonia fails azithromycin therapy. Sputum culture grows Streptococcus pneumoniae with high-level macrolide resistance (MIC >256 µg/mL). The MOST likely resistance mechanism is:
45. Ceftazidime-avibactam is effective against KPC-producing Klebsiella pneumoniae (CRKP) because avibactam:
46. Fluoroquinolone resistance in E. coli most commonly arises through which primary mechanism that enables subsequent higher-level resistance development?
47. Ceftaroline, a fifth-generation cephalosporin, is active against MRSA because of which unique pharmacological property?
48. A patient with carbapenem-resistant Klebsiella pneumoniae (CRKP) bacteremia requires treatment. Which combination has shown synergistic activity specifically due to inhibition of OXA-type carbapenemases?
49. Fluoroquinolone resistance in Mycobacterium tuberculosis is most commonly due to mutations in which gene?
50. Which pharmacodynamic parameter best predicts the bactericidal efficacy of fluoroquinolones and is therefore used to optimize their dosing?
51. Tedizolid is a second-generation oxazolidinone with improved activity over linezolid. Which feature explains its activity against some linezolid-resistant staphylococci carrying the cfr gene?
52. The antibacterial activity of carbapenems against MRSA is limited despite their broad-spectrum beta-lactam activity. What is the molecular basis?
53. A patient with a UTI due to E. coli fails ciprofloxacin therapy. Sequencing reveals a gyrA mutation at codon 83 (Ser83Leu). Which therapeutic choice is MOST appropriate?
54. Ceftazidime-avibactam is effective against KPC-producing Klebsiella pneumoniae but NOT against organisms producing NDM-1 metallo-beta-lactamase. Which pharmacological property of avibactam explains this limitation?
55. Extended-spectrum beta-lactamase (ESBL)-producing Escherichia coli is detected in a blood culture. Which antibiotic class is the drug of choice for definitive therapy?
56. Fluoroquinolones exert their antibacterial effect by inhibiting DNA gyrase (topoisomerase II) and topoisomerase IV. In Gram-negative bacteria, the primary target is:
57. A 55-year-old man is prescribed linezolid for vancomycin-resistant Enterococcus (VRE) bacteremia. He is also on sertraline for depression. The most serious potential drug interaction is:
58. Vancomycin exerts its cell wall inhibitory effect by binding to:
59. A patient develops Clostridioides difficile-associated diarrhoea (CDAD) after broad-spectrum antibiotic therapy. The preferred antibiotic for a first severe episode is:
60. A blood culture from a septic patient grows MRSA. The isolate is tested and shows a vancomycin MIC of 4 mcg/mL (hVISA phenotype). The MOST clinically relevant implication is:
61. The mechanism by which beta-lactamase-producing organisms resist ampicillin, and how sulbactam overcomes this resistance, involves which biochemical sequence?
62. A patient on fluoroquinolone therapy for a urinary tract infection develops tendon rupture. The sub-mechanism responsible for fluoroquinolone-induced tendinopathy involves:
63. Linezolid's pharmacological activity differs from all earlier protein synthesis inhibitors in that it:
64. A patient with a penicillin allergy develops endocarditis due to MRSA. The antibiotic of choice, which inhibits cell wall synthesis by a mechanism distinct from beta-lactams, is:
65. Which fluoroquinolone is considered 'respiratory quinolone' due to its enhanced activity against Streptococcus pneumoniae and atypical organisms, making it useful in community-acquired pneumonia?
66. Carbapenems are resistant to most beta-lactamases because of:
67. Linezolid is bacteriostatic against most gram-positive organisms but bactericidal against Mycobacterium tuberculosis. Its mechanism of action is:
68. Daptomycin is contraindicated in pulmonary infections despite being highly effective for skin and bloodstream Staphylococcal infections because:
69. Ceftriaxone is preferred over other beta-lactams for gonococcal infections primarily because of its:
70. A patient develops QT prolongation while on a fluoroquinolone. Which member of this class carries the HIGHEST risk of QT prolongation and cardiac arrhythmias?
71. Linezolid inhibits protein synthesis by binding to the 50S ribosomal subunit at a unique site. Its most serious dose-limiting adverse effect with prolonged use (>2 weeks) is:
72. A patient with nosocomial pneumonia due to MRSA is given vancomycin. The mechanism of vancomycin resistance in vancomycin-resistant enterococci (VRE) carrying the vanA gene is:
73. Linezolid, an oxazolidinone antibiotic, inhibits bacterial protein synthesis at which specific step?
74. A fluoroquinolone is described as having a C-8 methoxy group and C-7 bicyclic amine ring. These modifications PRIMARILY confer:
75. Linezolid exerts its antibacterial effect by inhibiting bacterial protein synthesis at which step?
76. A patient with community-acquired pneumonia is treated with ceftriaxone. Which statement accurately describes its pharmacokinetic advantage over cefazolin for outpatient parenteral therapy?
77. Which fluoroquinolone is classified as a 'respiratory fluoroquinolone' and is considered most active against Streptococcus pneumoniae due to its enhanced anti-pneumococcal potency?
78. Vancomycin kills bacteria by binding to the D-Ala–D-Ala terminus of peptidoglycan precursors. What consequence does this have at the molecular level?
79. A patient on ciprofloxacin for a urinary tract infection also takes an antacid containing aluminium hydroxide. Which pharmacokinetic interaction is most likely?
80. A patient with severe penicillin allergy (anaphylaxis) requires treatment for enterococcal endocarditis. The most appropriate cell-wall-active alternative to combine with an aminoglycoside for synergy is:
81. Tigecycline differs from classical tetracyclines primarily because it:
82. Fluoroquinolones such as ciprofloxacin kill bacteria primarily by which mechanism?
83. Linezolid is used as a reserve drug for MRSA and VRE infections. Its most serious dose-limiting adverse effect with prolonged use (>2 weeks) is:
84. β-Lactamase inhibitors like clavulanic acid, sulbactam, and tazobactam are given with β-lactams because they:
85. A patient with MRSA bacteremia is treated with vancomycin. The drug exerts its bactericidal effect by:
86. Linezolid differs mechanistically from all other protein synthesis inhibitors in that it:
87. A patient with severe Pseudomonas aeruginosa pneumonia is prescribed piperacillin-tazobactam. Tazobactam is added because it:
88. Moxifloxacin is preferred over ciprofloxacin for community-acquired pneumonia due to atypical organisms because it:
89. Daptomycin is used for MRSA and VRE infections. Its mechanism of action is fundamentally different from all beta-lactams and glycopeptides because it:
90. Fosfomycin is increasingly used for uncomplicated urinary tract infections caused by ESBL-producing E. coli. Its mechanism is:
91. A 72-year-old post-surgical patient develops Clostridioides difficile colitis after cephalosporin therapy. The first-line treatment is fidaxomicin rather than oral vancomycin because fidaxomicin:
92. A 45-year-old diabetic patient is admitted with a foot infection caused by MRSA. The decision to use daptomycin is made. Daptomycin's mechanism of action is unique among antibiotics. Which statement accurately describes it?
93. A microbiologist notes that a clinical isolate of Streptococcus pneumoniae has markedly altered penicillin-binding proteins (PBPs) with reduced affinity for beta-lactams. This resistance mechanism differs from beta-lactamase production in that it:
94. Linezolid is used to treat a vancomycin-resistant Enterococcus (VRE) infection. A patient on linezolid also takes sertraline for depression. Which adverse interaction is most concerning?
95. A patient is prescribed moxifloxacin for community-acquired pneumonia. Moxifloxacin should NOT be used for urinary tract infections primarily because:
96. Vancomycin is initiated for a patient with Clostridioides difficile colitis. The clinical pharmacist notes this is the wrong route for systemic activity. Which statement correctly explains vancomycin's role in C. difficile infection?
97. Which fluoroquinolone has greatest activity against Streptococcus pneumoniae and is considered 'respiratory fluoroquinolone' due to enhanced gram-positive coverage compared to ciprofloxacin?
98. Oritavancin, a lipoglycopeptide, has a substantially longer half-life (approximately 245 hours) than vancomycin, allowing single-dose treatment of ABSSSI. Its prolonged activity is primarily due to:
99. Fosfomycin exerts its antibacterial effect by inhibiting which step in bacterial cell wall peptidoglycan synthesis?
100. Linezolid and tedizolid are oxazolidinone antibiotics active against gram-positive organisms including VRE and MRSA. Their mechanism of action is unique because they target:
101. Daptomycin's mechanism of action makes it the only antibiotic to be bactericidal in a calcium-dependent manner. This mechanism is:
102. A patient with Enterococcus faecalis endocarditis requires combination therapy for synergistic bactericidal activity. The rationale for adding an aminoglycoside to a cell-wall active agent is that:
103. Linezolid's antibacterial mechanism is unique among protein synthesis inhibitors because it:
104. A fluoroquinolone is prescribed for a urinary tract infection. Which statement about quinolone pharmacodynamics is most accurate?
105. Ceftaroline differs from earlier-generation cephalosporins principally because it:
106. A 30-year-old woman on oral contraceptives is prescribed rifampicin for a latent TB infection contact. She is counselled to use additional contraception. The pharmacokinetic basis of this drug interaction is:
107. Vancomycin inhibits cell wall synthesis by binding to D-Ala-D-Ala terminus of peptidoglycan precursors. Vancomycin-resistant Enterococcus (VRE) employs the vanA operon to replace D-Ala-D-Ala with:
108. A 45-year-old woman is started on linezolid for MRSA bacteremia. After 3 weeks she develops thrombocytopenia and peripheral neuropathy. Which mechanism explains linezolid's myelosuppression?
109. Fluoroquinolones exert bactericidal activity by trapping a ternary complex of drug-DNA-enzyme. Which specific event in this mechanism actually leads to bacterial cell death?
110. A surgeon notices that a patient receiving cefazolin prophylaxis develops a wound infection caused by methicillin-resistant Staphylococcus aureus (MRSA). The resistance mechanism in MRSA involves:
111. A patient with Gram-negative sepsis is started on imipenem-cilastatin. What is the PRIMARY purpose of combining imipenem with cilastatin?
112. A fluoroquinolone is described as having excellent activity against atypical pathogens and Streptococcus pneumoniae, making it suitable as monotherapy for community-acquired pneumonia. This drug is MOST likely:
113. Which statement about the mechanism of resistance to fluoroquinolones mediated by plasmid-encoded Qnr proteins is CORRECT?
114. A patient with penicillin allergy (anaphylaxis) requires antibiotic cover for an elective procedure. Amoxicillin-clavulanate is contraindicated. The best antibiotic alternative that covers oral streptococci for endocarditis prophylaxis is:
115. Clavulanic acid restores ampicillin activity against beta-lactamase-producing organisms. What is the primary mechanism by which clavulanic acid achieves this?
116. Linezolid inhibits bacterial protein synthesis at which specific step, making it unique among clinical protein synthesis inhibitors?
117. Fluoroquinolones are contraindicated in children because of which specific toxicity demonstrated in animal studies?
118. A patient receiving imipenem develops seizures. Which pharmacological principle explains why cilastatin is co-administered with imipenem and how it relates to this adverse effect?
119. Glycopeptide antibiotics (vancomycin, teicoplanin) inhibit bacterial cell wall synthesis by binding to which specific target?
120. Clavulanic acid potentiates amoxicillin activity against β-lactamase-producing organisms. The mechanism of clavulanic acid is:
121. Linezolid is active against VRE and MRSA by a mechanism distinct from all other protein synthesis inhibitors. Which of the following correctly describes its mechanism?
122. Vancomycin inhibits cell wall synthesis by a mechanism different from β-lactams. The specific step it inhibits is:
123. Fluoroquinolones exert bactericidal activity by inhibiting which bacterial enzyme, and what is the consequence of inhibiting this enzyme?
124. Tigecycline is categorised as a glycylcycline and differs from classic tetracyclines in being active against tetracycline-resistant organisms. The resistance mechanisms it overcomes are:
125. A microbiologist notes that a bacterial isolate produces an enzyme that opens the beta-lactam ring of penicillin. This beta-lactamase is inhibited by clavulanic acid. The mechanism by which clavulanic acid inhibits beta-lactamase is best described as:
126. Vancomycin kills bacteria by binding to the D-Ala–D-Ala terminus of peptidoglycan precursors. Vancomycin-resistant Enterococcus (VRE) modifies this target to D-Ala–D-Lac. Which property of D-Lac reduces vancomycin binding?
127. Which fluoroquinolone demonstrates the best activity against Streptococcus pneumoniae and atypical pathogens, making it suitable for community-acquired pneumonia monotherapy?
128. Linezolid inhibits bacterial protein synthesis at a step that is different from all other ribosome-targeting antibiotics. Which step does it inhibit?
129. A 28-year-old pregnant woman is found to have a beta-lactam allergy documented as anaphylaxis. She requires treatment for Streptococcus agalactiae (Group B Strep) colonization before delivery. Which is the safest alternative?
130. The mechanism by which beta-lactamase inhibitors (e.g., clavulanate) restore the activity of amoxicillin against resistant organisms is:
131. Vancomycin kills gram-positive bacteria by binding to which specific substrate?
132. A physician prescribes ciprofloxacin for a urinary tract infection. The dual bacterial targets of fluoroquinolones are:
133. Linezolid, an oxazolidinone antibiotic, acts by inhibiting bacterial protein synthesis at which specific step?
134. Which of the following is TRUE regarding the pharmacodynamic killing pattern of aminoglycosides compared to beta-lactams?
135. A patient with a serious Enterococcus faecalis endocarditis fails vancomycin monotherapy. Adding ampicillin is considered. The basis of synergy between ampicillin and vancomycin against enterococci is:
136. A patient receiving moxifloxacin develops prolonged QTc on ECG. This adverse effect is most directly related to moxifloxacin's action on:
137. Linezolid, an oxazolidinone antibiotic, carries a specific interaction risk when used with serotonergic drugs such as SSRIs. The mechanism for this interaction is:
138. Which of the following best explains why carbapenems (e.g., imipenem) have the broadest beta-lactam spectrum including activity against ESBL-producing organisms while classic penicillins fail?
139. Linezolid is used for MRSA pneumonia. Its unique mechanism distinguishing it from all other protein synthesis inhibitors is:
140. A patient with severe Clostridium difficile colitis fails metronidazole therapy. Oral vancomycin is prescribed. Why is intravenous vancomycin ineffective for C. difficile colitis?
141. Fluoroquinolones inhibit two topoisomerases. In gram-negative organisms, the primary target leading to bactericidal activity is:
142. Beta-lactam antibiotics are bactericidal because they inhibit penicillin-binding proteins (PBPs). The downstream bactericidal event that directly causes cell lysis is:
143. A 72-year-old patient with CKD (CrCl 15 mL/min) requires antibiotic therapy. Which of the following antibiotics requires the LEAST dose adjustment due to its primarily hepatic/biliary elimination?
144. A patient with MRSA bacteremia is started on vancomycin. The drug's mechanism of action involves:
145. Tigecycline is a glycylcycline antibiotic that overcomes tetracycline resistance primarily because it:
146. A fluoroquinolone is prescribed for a patient. Which pharmacodynamic index best predicts its bactericidal efficacy?
147. Imipenem is always combined with cilastatin in clinical formulations. The reason is that cilastatin:
148. A 35-year-old woman develops tendon pain and swelling while on a fluoroquinolone for a urinary tract infection. The proposed mechanism of fluoroquinolone-induced tendinopathy involves:
149. A clinical microbiology lab receives a blood culture growing MRSA. The isolate reports vancomycin MIC of 1.5 mcg/mL (still technically 'susceptible'). The patient has persistent bacteremia despite 72 hours of vancomycin therapy. The infectious disease consultant recommends switching to daptomycin. What is the mechanism underlying this 'vancomycin heteroresistance' phenomenon?
150. A 60-year-old man on hemodialysis is diagnosed with enterococcal endocarditis. Culture shows Enterococcus faecalis susceptible to ampicillin but resistant to all aminoglycosides (high-level aminoglycoside resistance, HLAR). What synergistic combination is appropriate?
151. Fluoroquinolones inhibit DNA gyrase in gram-negative bacteria and topoisomerase IV in gram-positive bacteria. Resistance mutations emerge in the 'quinolone resistance-determining region' (QRDR). The FIRST step mutation in E. coli that confers the LOWEST level of fluoroquinolone resistance occurs in which gene?
152. A clinician is treating a neutropenic febrile patient with suspected carbapenem-resistant Klebsiella pneumoniae (CR-KP) infection producing KPC enzyme. Which antibiotic combination represents the most evidence-based current approach for this infection?
153. Beta-lactam antibiotics kill bacteria through penicillin-binding protein (PBP) inhibition. Which process is DIRECTLY impaired when PBPs are inhibited, leading to cell lysis?
154. The PBP2a (encoded by mecA gene) in MRSA confers resistance to all β-lactams except newer agents. Which mechanism specifically makes ceftaroline effective against MRSA despite PBP2a?
155. Vancomycin inhibits cell wall synthesis by binding D-Ala-D-Ala terminus of peptidoglycan precursors. Vancomycin-resistant Enterococcus (VRE) with vanA gene exhibits resistance via which precise mechanism?
156. Linezolid acts at the 23S rRNA of the 50S ribosomal subunit. Its most clinically significant adverse effect with prolonged use (>2 weeks) relates to which mechanism?
157. Clavulanic acid is a mechanism-based ('suicide') β-lactamase inhibitor. What distinguishes mechanism-based inhibitors from competitive inhibitors in terms of enzyme kinetics?
158. Vancomycin acts by binding to which target in bacterial cell wall synthesis, distinguishing it from beta-lactams?
159. A patient is on ampicillin for a urinary tract infection. The organism is found to produce extended-spectrum beta-lactamase (ESBL). Which combination would be the most appropriate alternative?
160. Linezolid is an oxazolidinone antibiotic active against VRE and MRSA. Its unique mechanism is:
161. Daptomycin is used for complicated skin infections and bacteraemia caused by MRSA. It is NOT used for pneumococcal pneumonia because:
162. Ceftriaxone can be administered once daily for serious infections despite its MIC-based pharmacodynamics (time-dependent killing). This is because: