Which of the following is NOT effective in all cases against microorganisms?

Alcohol as an antiseptic is effective against a broad range of microorganisms, including bacteria and viruses, but there are specific limitations to its effectiveness. For instance, alcohol is not effective against certain types of spores and some non-enveloped viruses, such as norovirus. Additionally, its efficacy can be diminished in the presence of organic matter or when used in concentrations lower than 60% to 70%.

In contrast, ultrasonic cleaning is primarily a physical cleaning method that uses sound waves to remove debris, which can be highly effective in cleaning instruments but does not kill microorganisms on its own. Soap and water are effective in removing dirt and bacteria but may not eliminate all pathogens, particularly some viruses. Mechanical decontamination through methods such as scrubbing or using mechanical devices can significantly reduce microbial load but may not ensure complete disinfection.

Thus, while alcohol is a widely used antiseptic, it is not universally effective against all microorganisms in every situation, making it the correct answer in this context.