Characterization of Staphylococcus aureus Strains Isolated from Raw Milk Utilized in Small-Scale Artisan Cheese Production

2011 ◽  
Vol 74 (8) ◽  
pp. 1353-1358 ◽  
Author(s):  
DENNIS J. D'AMICO ◽  
CATHERINE W. DONNELLY

Staphylococcus aureus is an important agent of bacterial mastitis in milking animals and of foodborne intoxication in humans. The purpose of this study was to examine the genetic and phenotypic diversity, enterotoxigenicity, and antimicrobial resistance of S. aureus strains isolated from raw milk used for the production of artisan cheese in Vermont. Cross-tabulations revealed that the 16 ribotypes identified among the 90 milk isolates examined were typically associated with a specific animal species and that more than half of these ribotypes were unique to individual farms. In general, specific EcoRI ribotypes were commonly associated with specific phenotypical characteristics, including staphylococcal enterotoxin production or the lack thereof. Limited antimicrobial resistance was observed among the isolates, with resistance to ampicillin (12.51%) or penicillin (17.04%) most common. Two isolates of the same ribotype obtained from the same farm were resistant to oxacillin with 2% NaCl. More than half (52.22%) of isolates produced toxin, and 31 of the 32 isolates solely produced staphylococcal enterotoxin type C. Although these data demonstrate that S. aureus strains found in raw milk intended for artisan cheese manufacture are capable of enterotoxin production, staphylococcal enterotoxin C is not typically linked to foodborne illness. Because S. aureus is a common contaminant of cheese, an understanding of the ecology of this pathogen and of the antimicrobial susceptibility and toxigenicity of various strains will ultimately contribute to the development of control practices needed to enhance the safety of artisan and farmstead cheese production.

2020 ◽  
Vol 83 (10) ◽  
pp. 1822-1828
Author(s):  
LIVIA SCHWENDIMANN ◽  
THOMAS BERGER ◽  
HANS-ULRICH GRABER ◽  
SUSANN MEIER ◽  
JÖRG HUMMERJOHANN ◽  
...  

ABSTRACT To reduce the number of cheese with potential Staphylococcus aureus contamination reaching consumers, European legislation has stipulated that all cheese must be tested for coagulase-positive staphylococci (CPS) at the point in production when numbers are expected to be highest. When CPS counts exceed 105 CFU/mL, staphylococcal enterotoxin (SE) tests must be conducted. When SE tests are positive, the cheese must be destroyed. Manufacturers of Swiss Alpine cheese are exempt from this legislation because SE formation in hard cheese is expected to be very unlikely because of the high scalding temperatures used for cheeses during production, which inactive CPS in the curd. However, this assumption has not been scientifically tested. A laboratory-scale cheese production experiment was performed in which the conditions corresponded to certain limitations in practical cheesemaking conditions such as temperature and time exposure as for production of Gruyere or Tete de Moine Swiss type cheeses. Raw milk aliquots (200 mL) were inoculated with five strains of CPS, and scalding temperatures of 46 to 56°C were used during cheese production. The temperatures applied after the curd was pressed were meant to reproduce the temperature curve in the peripheral zone of a real cheese wheel. Contrary to expectations, SE formation occurred and differed according to the scalding temperature (52 to 56°C). The differences in SE formation were more associated with strain type rather than temperature. These results indicate that the mechanisms of SE formation in cheese require further study. HIGHLIGHTS


2021 ◽  
Vol 53 (2) ◽  
Author(s):  
Ivana Ljevaković-Musladin ◽  
Marina Vodnica-Martucci ◽  
Marija Krilanović ◽  
Lidija Kozačinski

Staphylococcus aureus is a well-known op¬portunistic pathogen that causes a wide range of acute and chronic diseases in both humans and animals. Staphylococcal food poisoning is just one of many diseases caused by this bacterium. The causative agents are entero¬toxins produced by enterotoxigenic strains of S. aureus during its growth in favourable conditions in food. Epidemiological data show that S. aureus is often found in raw milk cheeses and accordingly, cheeses are often implicated in food poisoning outbreaks. Since there are no data on the nature of S. aureus isolated from cheese produced in Croatia, the aim of this study was to determine the occur¬rence, enterotoxin production capability and antimicrobic susceptibility of S. aureus iso¬lates from domestic cheeses produced in the Dubrovnik area. A total of 30 cheese samples were analysed, and 18 samples (60%) were highly contaminated with S. aureus strains. The contamination level ranged from 3.94 to 6.26 log10 cfu/g. Such a high level of contami¬nation was supported by an inappropriate temperature regime above 8°C during market sale. Although highly contaminated, staphy¬lococcal enterotoxins were not detected in any of the cheese samples. A total of 180 coagu¬lase-positive isolates were collected from 18 cheese samples, 175 of which were confirmed as S. aureus by the latex agglutination test. En¬terotoxin production was detected in 35 iso¬lates (20%), and of these 32 isolates produced staphylococcal enterotoxin C. The other three isolates presumably produced enterotoxin E. Antibiotic resistance was detected in 1.1% of isolates and only to mupirocin. However, a full comprehensive conclusion on the nature of S. aureus isolates cannot be achieved with¬out determining its genotype characteristics for the presence of staphylococcal enterotoxin genes and molecular typing, to determine the origin of the isolates.


Author(s):  
Fatima N. Aziz ◽  
Laith Abdul Hassan Mohammed-Jawad

Food poisoning due to the bacteria is a big global problem in economically and human's health. This problem refers to an illness which is due to infection or the toxin exists in nature and the food that use. Milk is considered a nutritious food because it contains proteins and vitamins. The aim of this study is to detect and phylogeny characterization of staphylococcal enterotoxin B gene (Seb). A total of 200 milk and cheese samples were screened. One hundred ten isolates of Staphylococcus aureus pre-confirmed using selective and differential media with biochemical tests. Genomic DNA was extracted from the isolates and the SEB gene detects using conventional PCR with specific primers. Three staphylococcus aureus isolates were found to be positive for Seb gene using PCR and confirmed by sequencing. Sequence homology showed variety range of identity starting from (100% to 38%). Phylogenetic tree analyses show that samples (6 and 5) are correlated with S. epidermidis. This study discovered that isolates (A6-RLQ and A5-RLQ) are significantly clustered in a group with non- human pathogen Staphylococcus agnetis.


2019 ◽  
Vol 42 ◽  
pp. e45231
Author(s):  
Camila Lampugnani ◽  
Maike Taís Maziero Montanhini ◽  
Maria Emilene Martino Campos‐Galvão ◽  
Luis Augusto Nero ◽  
Luciano dos Santos Bersot

This study aimed to isolate Staphylococcus aureus in refrigerated raw cow milk, and identify the presence of enterotoxin-expression genes, enterotoxin production and adherence ability, and antimicrobial resistance potential of the isolated strains. Fifty raw milk samples obtained in different dairy farms were analyzed for S. aureus and evaluated in the isolates the presence of genes associated with the production of major staphylococcal enterotoxins and biofilm formation. In vitro assays were also performed to evaluate the production of enterotoxins and adherence ability, and the antimicrobial resistance. One half (25/50) of raw milk samples presented coagulase-positive staphylococci and 95.2% of the isolates were confirmed to be S. aureus. Among them, 42.4% were carrying genes for enterotoxins production; however, only one isolate was able to produce enterotoxins. All S. aureus isolates were carrying at least two genes associated with biofilm formation and 95.2% isolates was able to adhere upon the in vitro assay. All isolates demonstrated antimicrobial resistance potential to one or more of the tested antibiotics.


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