Toxigenic Status of Staphylococcus aureus Isolated from Bovine Raw Milk and Minas Frescal Cheese in Brazil

Abstract

A group of 291 Staphylococcus aureus isolates from mastitic cow's milk (n = 125), bulk tank milk (n = 96), and Minas frescal cheese (n = 70) were screened for staphylococcal enterotoxin (SE) genes (sea, seb, sec, sed, see, seg, seh, sei, selj, and sell) and for the tst-1 gene encoding staphylococcal toxic shock syndrome toxin 1 by PCR assay. A total of 109 (37.5%) of the isolates were positive for at least one of these 11 genes, and 23 distinct genotypes of toxin genes were observed. Of the S. aureus isolates bearing SE genes, 17 (13.6%) were from mastitic cow's milk, 41 (41.7%) were from bulk tank milk, and 51 (72.9%) were from Minas frescal cheese. The occurrence of exclusively more recently described SE genes (seg through sell) was considerably higher (87 of 109 PCR-positive strains) than that of classical SE genes (sea through see, 15 strains). The SE genes most commonly detected were seg and sei; they were found alone or in different combinations with other toxin genes, but in 60.8% of the cases they were codetected. No strain possessed see. The tst-1 gene was found in eight isolates but none from mastitic cow's milk. Macrorestriction analysis of chromosomal DNA from 89 S. aureus isolates positive for SE gene(s) was conducted with the enzyme SmaI. Fifty-five distinct pulsed-field gel electrophoresis patterns were found, demonstrating a lack of predominance of any specific clone. A second enzyme, Apa I, used for some isolates was less discriminating than Sma I. The high genotype diversity of potential toxigenic S. aureus strains found in this study, especially from Minas frescal cheese, suggests various sources of contamination. Efforts from the entire production chain are required to improve consumer safety.

Occurrence and antibiotic resistance of enterotoxigenic Staphylococcus aureus in raw ovine and caprine milk in Greece

“…In other studies, however, the seb gene was detected in S. aureus isolates from milk and dairy products at various frequencies (Jørgensen et al 2005;Zouharova and Rysanek 2008). The fact that seb was the most commonly detected SE genotype in isolates from OM in our study is in agreement with the findings of previous studies (Arcuri et al 2010;Peles et al 2007).…”

“…None of the strains in our study harbored the see gene, in agreement with other investigations on S. aureus isolates from milk and dairy products (Arcuri et al 2010;Carfora et al 2015;Cremonesi et al 2007;Jørgensen et al 2005;Poli et al 2007;Zouharova and Rysanek 2008).…”

“…Some authors reported a predominant and systematic co-detection of seg and sei genes (Rosec and Gigaud 2002) whereas others have reported their presence individually or in different combinations with other se genes (Arcuri et al 2010;Cremonesi et al 2007;Zouharova and Rysanek 2008). The association between seg and sei has been attributed to their location within the same gene cluster (egc) in the genomic island mSAb (also known as SaPIn3/m3) (Malachowa and DeLeo 2010).…”

“…In our study, one isolate harboring only the seg gene was found. The occurrence of strains harboring only seg or sei may be explained by mispriming due to a point mutation in one of these genes or the existence of variants in the egc cluster, combinations of toxingene-containing mobile elements such as plasmids and genomic islands in the same strain, or even a new type of genetic mobile element (Arcuri et al 2010).…”

“…Since, to date, no commercial tests for the "new" types of SEs exist, S. aureus isolates containing the corresponding genes should be considered as potential SE producers. Α review of the literature seems to indicate an increase in the number of potentially enterotoxigenic S. aureus isolates from milk and dairy products carrying "new" SE genes in addition to the classical ones (Arcuri et al 2010;Rosec and Gigaud 2002;Zouharova and Rysanek 2008). It should be noted, however, that in our study the prevalence of se genes may have been underestimated because only the isolates testing positive for SE production via immunoassays were tested with PCR, as well as due to the fact that the isolates were not tested for the presence of the recently described se genes (sek-ser and seu).…”