## 4 Discussion
Reconstituted infant formula (RIF) is administered at temperatures of around 37 \({}^{\circ}\)C, which coincides with the optimum growth temperature for _C. sakazakii_. If the RIF or its leftovers in the bottle are maintained at this temperature for an extended period of time, the _C. sakazakii_ cell will proliferate to significant levels. A different scenario in which RIFs could be maintained for a long time at around 37 \({}^{\circ}\)C is utilizing a thermos instead of a baby bottle. This may happen during travel when, for convenience, RIF is stored in a thermos that maintains a consistent temperature of 37 \({}^{\circ}\)C for several hours. Moreover, the ability of the bacterium to form biofilms should not be overlooked. Based on the literature reviews, several interventions in PIFs have been successful [46]. [PERSON] and [PERSON] [47], as early as 1990, investigated the efficacy of administering acidified infant formula against Gram-negative bacteria in the stomach of hypochlorhydric premature neonates. Specifically, they conducted a double-blind trial of infant formula administration in premature infants who could not reduce the pH value below 4.0. The infant formula was fortified with 0.01-0.02 mL of 1 N HCl/mL of milk, resulting in a reduction in pH from 7.0 to 5.5. The results showed that the group with the acidified infant formula had a significantly lower stomach pH, less gastric colonization, and a lower incidence of necrotizing enterocolitis when compared to the control group. [PERSON] et al. [18] conducted a study on the antimicrobial activity of seven organic acids against four strains of _C. sakazakii_ in a synthetic medium. They subsequently opted to fortify infant formula with acetic acid and subject it to infant simulated gastric fluid. The results indicated a positive synergistic effect between the low pH of the infant's gastric fluid and acetic acid. [PERSON] et al. [48] found that the incorporation of the natural compounds citral and carvacrol into infant formula inoculated with _C. sakazakii_, together with mild heat treatment, resulted in the eradication of the opportunistic pathogenic bacterium. Additionally, [PERSON] et al. [16] incorporated tea polyphenols in powdered infant formula and found that, when combined with HCl (pH 3.55), they were able to inactivate four different strains of _C. sakazakii_. [PERSON] et al. [49] studied the addition of triglycerol monolaurate (TGML) into PIFs as a limiting factor of _C. sakazakii_ growth, and it was found that just 5 ug/mL of TGML could suppress pathogen growth below the infectious dose (10\({}^{4}\) cfu total) in simulated gastric juice. [PERSON] et al. enriched infant formula with lactic acid, copper sulfate, and monolaurin, resulting in the complete inhibition of a _C. sakazakii_ strain [50]. To the best of our knowledge, it has not been investigated whether the buffering capacity of PIF could influence the growth and/or survival of _C. sakazakii_ in combination with probiotic bacteria. For this purpose, two PIFs with different acid-buffering capacities were contaminated with _C. sakazakii_ and enriched with the probiotic bacterium BB-12\({}^{\oplus}\). The scientific hypothesis was whether, if good manufacturing practices during the preparation of RIFs are abused and _C. sakazakii_ is allowed to grow, the production of organics from the probiotic culture is able to inhibit the growth of the pathogen and whether the acid-buffering capacity of the infant formulae could be correlated with this phenomenon. The results showed that the acid-buffering capacity of an infant formula can affect the growth of _C. sakazakii_ in combination with the presence of probiotic bacteria. The strongest antimicrobial activity occurred at pH 3.65 (\(\pm\)0.02) in the co-culture of _C. sakazakii_ and BB-12\({}^{\oplus}\) in the RIF with the lower acidic buffering capacity. After 24 h of incubation at 37 \({}^{\circ}\)C, the opportunistic pathogen was below the detection limit of the method (10 cfu/mL). According to the published data, the lowest pH at which _C.