Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food

Sulfites and other preservatives are considered food additives to limit
bacterial contamination, and are generally regarded as safe for
consumption by governmental regulatory agencies at concentrations up to
5000 parts per million (ppm). Consumption of bactericidal and
bacteriostatic drugs have been shown to damage beneficial bacteria in
the human gut and this damage has been associated with several diseases.
In the present study, bactericidal and bacteriostatic effects of two
common food preservatives, sodium bisulfite and sodium sulfite, were
tested on four known beneficial bacterial species common as probiotics
and members of the human gut microbiota. Lactobacillus species casei, plantarum and rhamnosus, and Streptococcus thermophilus
were grown under optimal environmental conditions to achieve early log
phase at start of experiments. Bacterial cultures were challenged with
sulfite concentrations ranging between 10 and 3780 ppm for six hours. To
establish a control, a culture of each species was inoculated into
media containing no sulfite preservative. By two hours of exposure, a
substantial decrease (or no increase) of cell numbers (based on OD₆₀₀
readings) were observed for all bacteria types, in concentrations of
sulfites between 250–500 ppm, compared to cells in sulfite free media.
Further testing using serial dilution and drop plates identified
bactericidal effects in concentrations ranging between 1000–3780 ppm on
all the Lactobacillus species by 4 hours of exposure and bactericidal effects on S. thermophilus in 2000ppm NaHSO₃ after 6 hours of exposure.