Short communication: Characterization of enterotoxin-producing Staphylococcus aureus isolated from mastitic cows

Abstract

Staphylococcus aureus is not only a common cause of bovine mastitis, but also an agent of food poisoning in humans. In an attempt to determine whether staphylococci causing bovine mastitis could also cause food poisoning, 60 isolates of presumed S. aureus were isolated in the period between March and August 2017 from 3,384 routine, composite, quarter milk samples of individual cows raised on 12 dairy farms in central Italy. Seventeen out of 60 isolates were confirmed as S. aureus after coagulase, thermonuclease, and biochemical tests. These isolates were analyzed by PCR for the presence of the nuc, sea, seb, sec, sed, and see genes. The positive isolates were nuc, 100% (17); sea, 35.29% (6); seb, 5.88% (1); sec, 5.88% (1); sed, 29.41% (5); and see, 47.06% (8). The isolates were also tested with 2 enzyme immunoassay diagnostic kits, one for the screening detection of the production of staphylococcal enterotoxins (SEA, SEB, SEC, SED, SEE) and one for the detection of specific enterotoxin produced by each isolate. Seven out of 17 (41.18%) were enterotoxin producers: 7 produced SEA (41.18%), 1 SEB (5.88%), 1 SEC (5.88%), 5 SED (29.41%), and 6 SEE (35.29%). To further characterize the isolates, they were analyzed by the Kirby Bauer test for susceptibility to 13 antimicrobials (ampicillin, ciprofloxacin, kanamycin, tetracycline, gentamicin, methicillin, nalidixic acid, erythromycin, amoxicillin/ clavulanic acid, streptomycin, vancomycin, neomycin, and enrofloxacin), and we detected resistance to ampicillin (52.94%), nalidixic acid (70.59%), erythromycin (5.88%), and amoxicillin/clavulanic acid (17.65%). The isolates were sensitive to the main classes of antimi-crobials used for the treatment of bovine subclinical mastitis. The presence of enterotoxin-producing isolates of S. aureus in bovine milk means that a temperature abuse or a breakdown in the thermal treatment of the milk could present a food safety risk, particularly if all enterotoxigenic isolates could potentially produce SEA in milk.

Comparison of Antibiotic Resistance Profile and Biofilm Production of Staphylococcus aureus Isolates Derived from Human Specimens and Animal-Derived Samples

“…In another recent study, sei was the second most diffuse enterotoxin in humans [12]. In addition, the animal strains showed the simultaneous presence of sea and see at 14.3%, according to another study on enterotoxin-producing S. aureus isolated from mastitic cows [26].…”

Organic Selenium Ameliorates Staphylococcus aureus-Induced Mastitis in Rats by Inhibiting the Activation of NF-κB and MAPK Signaling Pathways

“…Bacterial infection is the main etiology in bovine mastitis and a wide variety of pathogens have been reported to cause the disease ( 4 ). S. aureus is one of the most prevailing pathogenic bacteria, which causes clinical and subclinical mastitis in dairy herds ( 5 , 6 ). It was characterized by chronic, recurrent and lower cure rate in mastitis induced by S. aureus ( 7 , 8 ).…”

Microbial safety status of Serro artisanal cheese produced in Brazil

“…Safety related to CSE in Staphylococcus stains must be assessed by phenotypic and genotypic approaches to detect potential CSE producers that express this characteristic under specific conditions and might transfer these genetic elements to non-CSEproducing strains. The identification of Staphylococcus strains from artisanal cheeses that present CSE-related genes despite not being CSE producers is not uncommon (Carfora et al, 2015;Grispoldi et al, 2019). However, the CSE results of Staph.…”