MI1.{1-2,10,12-13} | General Microbiology I: History, Morphology, Sterilisation & Staining — Graded Quiz

A 35-year-old farmer presents to a rural PHC with a 3-week history of productive cough and weight loss. A ZN-stained sputum smear shows 15 acid-fast bacilli per 100 high-power fields. According to the NTEP sputum grading scale, how should this result be categorised and what is the NEXT step?

During the pre-operative check for an elective inguinal hernia repair, the theatre nurse discovers that the instrument tray was autoclaved but the autoclave's chemical indicator strip inside the pack has NOT changed colour. The steam indicator outside the pack has changed. What should the nurse do?

A medical laboratory technologist is preparing a Gram stain from a cerebrospinal fluid (CSF) specimen of a patient with meningitis. She performs the decolourisation step for 60 seconds instead of the recommended 10-15 seconds. What change in the staining result is MOST likely?

An orthopaedic surgeon needs to process flexible fibre-optic arthroscopes that cannot withstand heat. She proposes using 2% glutaraldehyde immersion for 3 hours. A resident argues that ethylene oxide (EtO) gas sterilisation should be used instead. Which statement BEST justifies using EtO over glutaraldehyde for this specific item?

A Gram stain of a mid-stream urine sample from a woman with dysuria and frequency shows numerous Gram-negative rods and >10 white blood cells per high-power field. Based on morphology alone, which organism is MOST likely responsible and what is its most distinguishing microscopic feature?

A hospital infection control committee is reviewing an outbreak of post-operative infections following arthroscopic knee surgeries. Investigation reveals that a disinfected arthroscope was rinsed with contaminated tap water after the glutaraldehyde soak. Which microorganism class is MOST likely to have survived and caused the infections, and why?

A microbiology professor demonstrates the Gram stain procedure. After adding crystal violet and Gram's iodine, she accidentally skips the decolourisation step and goes directly to safranin counterstaining. What will be the appearance of a mixed culture containing both E. coli (Gram-negative) and S. pneumoniae (Gram-positive) on the slide?

A 28-year-old MBBS intern discovers that a suspected AIDS patient's blood has splashed on a used surgical blade. To safely dispose of the blade, she needs to first disinfect the contaminated waste container. Which agent is MOST appropriate for surface decontamination of blood-splashed inanimate surfaces in this HIV exposure scenario?

A pathologist requests a Gram stain of pus from a breast abscess. The smear shows Gram-positive cocci in chains. Based on morphology, which pathogen is MOST likely, and which clinical feature would be MOST consistent with this organism?

During a cholera outbreak investigation, Koch demonstrated that Vibrio cholerae fulfils his postulates as the causative agent of cholera. However, some healthy contacts also carried the organism without disease. This observation does NOT invalidate Koch's postulates because:

A central sterile supply department (CSSD) technician notices that the biological indicator (BI) used to validate an autoclave cycle has grown spores after incubation, indicating a failed sterilisation cycle. However, 40 surgical instrument sets from that batch have already been dispatched to operating theatres. What is the MOST appropriate immediate action?

In the stool examination of a child with chronic diarrhoea, the microscopist identifies motile trophozoites with a clear ectoplasm and granular endoplasm that display directional, progressive movement. Which organism does this MOST likely represent, and what staining technique is appropriate to identify cysts of the same organism?