Effect of quaternary ammonium compounds (QACs) on surface microbiota: Routine use of QAC sanitizers on utensils tends to shift the surviving microbial profile toward which group?

Introduction:
Quaternary ammonium compounds (QACs) are cationic surfactants widely used as sanitizers because they disrupt cell membranes and denature proteins. Their antimicrobial spectrum, however, is not uniform across microorganisms, and repeated use can shift the residual surface flora toward less susceptible groups.

Given Data / Assumptions:

• QACs are generally more active against Gram-positive bacteria than many Gram-negative rods.
• Environmental Gram-negative rods (e.g., Pseudomonas) can exhibit higher tolerance to QACs.
• Sanitizing reduces total counts but relative proportions can change.

Concept / Approach:
If a sanitizer preferentially kills Gram-positive organisms, then, after treatment, the fraction of Gram-negative rods among survivors may rise (even if their absolute numbers also decline). Over time, this selection pressure increases the relative prevalence of Gram-negative rods on utensils and surfaces, unless rotation of sanitizers or additional controls are employed.

Step-by-Step Solution:
Identify susceptibility pattern: Gram-positives are typically more susceptible to QACs.Infer ecological outcome: survivors skew toward Gram-negative rods.Select the option reflecting an increased percentage of Gram(-) rods after QAC use.

Verification / Alternative check:
Hygiene monitoring programs often note shifts toward QAC-tolerant Gram-negative flora, prompting sanitizer rotation or adjunct methods (e.g., oxidizing agents) to maintain control.

Why Other Options Are Wrong:

• “Favor gram positive bacteria”: Opposite of typical QAC selectivity.
• “Decrease gram positive bacteria”: True but incomplete; the question asks about the resulting increase in a group.
• “Yeasts and molds only”: Fungal susceptibility varies; not the dominant observed shift.
• “None of the above”: Contradicts observed selection patterns.

Common Pitfalls:
Assuming total count reduction equals equal efficacy across all groups; selection can still occur and should inform sanitizer rotation strategies.

Final Answer:
increase the percentage of gram(-)ve rods on utensils