To investigate the microbial community composition and structure of the processing workshop of infant formula in Fujian Province in 2024, to reveal the microbial diversity present in the workshop as well as the changes in the distribution of microorganisms among different functional zones, and to unveil the drug resistance of the isolates.

A stratified random sampling strategy was employed to collect surface microbiota, airborne planktonic bacteria and sedimentary microbes from the selected manufactures by aseptic swabbing, six-stage Andersen air sampling, and plate exposure methods, respectively. The purified isolates were analyzed by 16S rDNA gene sequencing and multi-sequence alignment and phylogenetic tree construction were carried out using the MEGA software. To ensure taxonomic accuracy, the VITEK^® 2 Compact fully automatic microbial identification system was utilized for physiological and biochemical characterization, and phenotypic validation was performed by referring to the latest Bergey’s manual of systematic bacteriology. A dual verification framework integrating molecular and traditional phenotypic identification was thereby established. Antimicrobial susceptibility testing was performed using standardized protocols, and based on the data obtained, a heatmap was generated.

A total of 355 isolates were obtained, belonging to 19 genera. Out of these, 61.1% were Gram-positive bacteria, and 38.9% were Gram-negative bacteria, Staphylococcus, Bacillus, and Pseudomonas being the major ones, accounting for 72.95% of the total collected strains. Among them, Staphylococcus has the highest distribution rate, accounting for 33.80% of all isolated strains The phylogenetic analysis and spatial distribution pattern of Staphylococcus revealed personnel movement and material handling to be the principal contamination vectors. Antimicrobial susceptibility testing demonstrated that coagulase-negative staphylococci (CoNS) showed 100% susceptibility to teicoplanin, vancomycin and linezolid and 20%-90% susceptibility to penicillin G (benzylpenicillin), erythromycin, methicillin and clindamycin. Some of the environmental isolates showed multi-drug resistance.

Staphylococcal species were the dominant microbial population in the infant formula production environment, with workshop operators being their largest vector. The identification of antimicrobial-resistant isolates underscores the need for enhanced personnel sanitation and air purification to reduce the risk of microbial contamination.