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Updated: May 27, 2026
Methodology for the Study of Horizontal Gene Transfer in Staphylococcus aureus
Published on: March 10, 2017
Characterization of Staphylococcus aureus isolated from powdered infant formula milk and infant rice cereal in China
Xin Wang1, Jianghong Meng, Jing Zhang
1College of Food Science and Engineering, Northwest A & F University, Yangling, Shaanxi 712100, China.
Insights
Dry infant foods like powdered infant formula milk and infant rice cereal can be contaminated with Staphylococcus aureus. Many strains found were resistant to multiple antibiotics and carried toxin genes, posing a health risk to infants.
Area of Science:
- Food Microbiology
- Public Health
- Bacterial Pathogenesis
Background:
- Dry infant foods are not sterile and can harbor bacterial contaminants.
- Pathogenic bacteria in infant foods pose a significant risk to infant health.
Purpose of the Study:
- To determine the prevalence of Staphylococcus aureus in infant foods.
- To characterize isolated S. aureus strains for antimicrobial resistance and toxin gene profiles.
Main Methods:
- Screening of powdered infant formula milk (PIF) and infant rice cereal (IRC) samples for S. aureus.
- Antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE), and toxin gene detection (including PVL, enterotoxins).
Main Results:
- S. aureus was detected in 11.2% of PIF and 6.3% of IRC samples.
- 83.3% of isolates showed resistance to at least one antimicrobial, with high rates for erythromycin and ciprofloxacin.
- 63.0% of isolates carried toxin genes, predominantly pvl, seg, and sec.
Conclusions:
- Powdered infant formula milk and infant rice cereal in China are contaminated with S. aureus.
- Many S. aureus isolates exhibit multidrug resistance and harbor virulence factors, presenting a potential threat to infant health.
- Genetic diversity was observed among the S. aureus strains.
Abstract:
Dry infant foods are not sterile and could be contaminated with various bacteria including certain pathogens. The aim of this study was to investigate the prevalence of Staphylococcus aureus in infant foods and to characterize these strains. A total of 367 infant food samples, including 143 samples of powdered infant formula milk (PIF) and 224 samples of infant rice cereal (IRC), were collected in the Shaanxi Province of China during the period of July to August 2010 and screened for S. aureus. All S. aureus isolates were characterized by antimicrobial susceptibility testing, pulsed-field gel electrophoresis (PFGE), and detection of genes encoding enterotoxins, exfoliative toxins, Panton-Valentine leukocidin (PVL), and toxic shock syndrome toxin 1. Among all the samples examined, sixteen of 143 PIF samples (11.2%) and 14 of 224 IRC samples (6.3%) were positive for S. aureus. From these positive samples, 29 S. aureus strains were isolated from PIF and 25 from IRC. Of these S. aureus isolates, 83.3% were resistant to at least one antimicrobial, 35.2% to three or more antimicrobials. Resistance was most frequently observed to erythromycin (75.9%), followed by ciprofloxacin (51.9%) and trimethoprim/sulfamethoxazole (27.8%), while significantly fewer isolates were resistant to gentamicin (22.2%), tetracycline (18.5%), or cefoxitin (3.7%). In addition, 63.0% of isolates were positive for one or more toxin genes tested. The three most predominant toxin genes were pvl (40.7%), seg (38.9%), and sec (18.5%), followed by sea (7.4%), seb (7.4%), sed (5.6%), and see (5.6%). The ets, tsst-1, seh, sei, and sej genes were not detected. A total of 39 PFGE patterns were generated among 51 selected food isolates. Our findings indicate that PIF and IRC in the Shaanxi province were contaminated with S. aureus, and many S. aureus isolates harbored multiple toxin genes and exhibited multiple antimicrobial resistance. In addition, these S. aureus isolates were genetically diverse. The presence of S. aureus strains in these infant foods poses a potential threat to infant health.
