Tehran University Medical Journal

Background: Bacillus cereus spores distribute widely in nature and can be isolated from different kinds of foods. This bacterium can produce diarrhea and emetic enterotoxins and syndromes. As infants are known to be more susceptible to B. cereus infection due to their incomplete intestinal flora and fast growth of this bacterium during consumption, it is very important to investigate the presence of B. cereus in infant formula and possible pathogenicity of this microorganism in infants. 

Methods: In this study, 60 samples of infant formula were examined for the presence of B. cereus. From a 1/10 dilution of each sample, a total amount of 1 ml was inoculated onto four phenol red agar plates containing mannitol, egg yolk emulsion and polymyxin B sulfate. The plates were incubated at 30°C for 24 hours. Confirmation tests were then performed on suspected colonies.

Results: Among the 60 samples, 11 samples had more than 10 cfu/g, four of which contained more than 102 cfu/g. The other 49 samples showed less than 10 cfu/g of B. cereus. 

Conclusions: We suggest that for infant formula the maximum microbial limit be reduced to less than 10 cfu/g to control B. cereus contamination and to prevent infection in infants. For this purpose, infant formula should be tested by the method and confirmation tests used in this study. In addition, susceptibility to penicillin, ß-hemolysis and growth rate at 45ºC could also be performed.

Background: In recent years, use of powdered infant formula (PIF) milk for neonates feed is increasing; therefore, the quality control (QC) of PIF products is very important. The aim of present study was detection of toxigenic Bacillus cereus species in PIF milk using PCR assay.

Methods: The cross-sectional study was carried out on 125 samples of powdered infant formula milk (PIF) purchased between March 2015 and April 2016 in Department of Pathobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran. Briefly, 0.1 dilutions were prepared and inoculated on Bacillus cereus selective media (MYP) and incubated at 30 °C for 24 hours. The suspicious colonies were verified using biochemical tests based on standard methods. Final confirmation of studied isolates was carried out by ITS gene detection using polymerase chain reaction (PCR) assay. Presence of nonhemolytic enterotoxin (NHE) (linked to diarrhoea syndrome) and emetic toxin (EM) (linked to emetic syndrome) virulence genes were investigated using polymerase chain reaction assay. 

Conclusion: Our data revealed that near 80% of Bacillus cereus isolates have emetic toxin (EM) gene, as result virulence potency of this isolates is very high. However, the low number of this organisms in foods is very important and food safety protocols for these opportunistic toxigenic bacteria should be revised. Since the pasteurization process is ineffective on B. cereus spores; therefore, spores can remain in PIF milk and the vegetative bacterial cells can cause food poisoning in neonates. Therefore, modification of foods quality control protocols is essential in order to identify virulence genes in this bacterium.