Final answer:
The letter 'S' following five antibiotics in Mrs. Wallace's urine culture indicates that these antibiotics are likely to cause sensitivity or allergy in the patient.
Step-by-step explanation:
The letter 'S' that follows five antibiotics in Mrs. Wallace's urine culture indicates that these antibiotics are likely to cause sensitivity or allergy in the patient. This means that the patient may have an adverse reaction to these antibiotics. It is important for the medical professional to consider this information when deciding which antibiotics to use to treat the infection.