Api 20e microbial identification kit

An API-20E Microbial Identification Kit (bioMérieux, Shanghai, China) was used (according to the manufacturer’s instructions) to identify and differentiate members of the family Enterobacteriaceae. Isolates that exhibited typical Salmonella biochemical reactions were cultured overnight at 37 °C, and then serotyped. All the isolates were serotyped according to the White–Kauffmann–Le Minor scheme based on slide agglutination with O and H antigen-specific sera. We used diagnostic sera from a Diagnostic Sera for Salmonella Kit (Tianrun, Ningbo, China).

Using NIOSH method 0800 [34 ], bacteria and fungi were sampled by an Andersen single-stage sampler with a flow rate of 28.3 L/min. The culture media was malt extract agar for airborne fungi and trypticase soy agar for bacteria. The sampling time was 10 minutes. To calculate the concentration of colonies in the culture medium, the air volume was corrected relative to the air pressure and temperature during sampling, and the bioaerosol concentration was calculated in terms of colony-forming units (CFU)/m³ . Finally, microbiological and mycological tests were performed on the plates. An API 20E microbial identification kit (bioMerieux Inc., Durham, NC, USA) was used to identify the bacterial species. None of the sawmills were equipped with local exhaust ventilation systems and none of the exposed workers wore any respiratory protective equipment.

A total of 455 E. coli isolates from the small intestinal contents or feces of piglets 20–50 days of age with postweaning diarrhea were collected from 56 large-scale swine farms in 15 provinces in China over a 3 year period (2014–2016) (Table 1). The 56 swine farms were selected by convenience sampling (Figure S1).
Black colonies with metallic luster on eosin-methylene blue plates were obtained and grown in Luria–Bertani broth for 12 h at 37 °C with shaking. For each sample, a maximum of 5 colonies were chosen based on initial morphology. The isolates were confirmed as E. coli based on standard biochemical tests using an API-20E Microbial Identification Kit (bioMérieux, MarcyI’Etoile, France) and polymerase chain reaction (PCR) amplification of the gene encoding the universal stress protein uspA [13 (link),14 ]. A maximum of three E. coli strains per sample were included in the sample collection.