Virulence Factors in Staphylococcus aureus and Quality of Raw Milk from Dairy Cows in a Semiarid Region of Northeastern Brazil

Abstract

Background: Milk quality is considered unsatisfactory in Brazil due to factors of a social, economic, cultural, and climatic nature. Mastitis is the main disease that affects dairy herds. Microorganisms of the genus Staphylococcus are the most frequently isolated pathogens in cases of mastitis in bovines. Staphylococcus aureus requires more attention because they have the ability to develop resistance to antimicrobials used in the treatment of mastitis. Thus, the aim of the present study was to evaluate virulence factors in isolates of S. aureus as well as analyze the hygienic-sanitary quality of raw milk produced on dairy farms in a semiarid region of northeastern Brazil.Material, Methods & Results: Samples were taken from milk containers at 44 properties. Fifty-eight isolates of Staphylococcus spp. were analyzed and genotypically identified as S. aureus. In the phenotypic characterization, 56.8% (33/58) of the isolates demonstrated moderate biofilm production. In the genotypic characterization (icaA, icaD and bap genes), icaA was the most representative among the isolates. No resistance to cephalothin or oxacillin was found, but 62% (36/58) of the isolates exhibited resistance to ampicillin, amoxicillin, and penicillin. In the genotypic evaluation in response to β-lactam antibiotics, 50% (29/58) of the isolates exhibited the blaZ gene. Total bacterial counts were determined based on the standard plate count and flow cytometry, for which a significant positive correlation was found (r = 0.61, P < 0.01). The somatic cell count was also performed using flow cytometry and demonstrated that 6.8% (3/44) of the properties had values above one million cells per mL. The analysis of Staphylococcus spp. revealed that 20% (9/44) of the properties had significant counts for the production of staphylococcal enterotoxins. Regarding total coliforms, 56.8% (25/44) of the milk analyzed had counts above 1.0 x 103 CFUs/mL. There were no cases of the isolation of Pseudomonas spp. Streptococcus spp. was isolated on 6.8% (3/44) of the properties. The results of the sequencing revealed one isolate to be Lactococcus lactis and two to be Enterococcus spp.Discussion: None of the 58 isolates of S. aureus was classified as negative in the phenotypic characterization of biofilmforming capacity, which suggests the presence of genes involved in this process. Studies have shown that the molecular techniques used to identify ica genes encoding biofilm synthesis are very important for the identification of virulent strains. The isolates demonstrated resistance to β-lactam antibiotics of the class of penicillins, which are the most widely employed antimicrobial agents for the treatment of diseases in dairy herds. The presence of the blaZ gene in 50% of the isolates is in agreement with data reported in other studies developed in northeastern Brazil. In 50% (29/58) of the isolates, the presence of the blaZ gene was not observed. Of these, (8/29) were resistant to ampicillin, amoxicillin and penicillin. This is due to the existence of other bacterial mechanisms. Research has shown that some isolates possessed three mechanisms (blaZ, mecA and msrA) of antimicrobial resistance simultaneously. The results of the quality analyses demonstrate that some properties produce milk of low quality, which underscores the need for management strategies directed at reducing the contamination of the product.

Virulence factors and antimicrobial resistance in Staphylococcus aureus isolated from bovine mastitis in Brazil

“…or even for other genera of medical importance. Additionally, despite the direct comparison of the results of the present study with others also conducted in Brazil is not possible, due to the difference in the distribution of the isolates (geographical and temporal) and different methodologies used to assess virulence factors and resistance genes; other studies performed in S. aureus from different Brazilian states also point to the importance of biofilm production and presence of enterotoxins and antimicrobial resistance genes (blaZ) for the pathogenesis of mastitis, besides the potential food poisoning risk associated with dairy products [5][6][7].…”

“…Indeed, studies conducted in countries from Europe, Africa, and America have reported a high prevalence of S. aureus in dairy cows reaching 41% in France (1995-2012), 47.2% in herds from Italy (2012-2013) [2], 74% in Ethiopia (2014-2015) [3], and Canada (2003)(2004)(2005) [4]. In Brazil, several studies have showed the importance of S. aureus in the epidemiology of mastitis in cattle [5][6][7][8]. Although it can be involved in clinical mastitis (especially after calving), the infection is usually subclinical, causing no visible changes in milk or udder [1].…”

Occurrence and antimicrobial susceptibility of Staphylococcus aureus in dairy farms and personnel in selected towns of West Shewa Zone, Oromia, Ethiopia

“…The high prevalence of S . aureus in this study (16.72%) might be linked to conventional hand milking, the lack of regular post-milking teat dip, dairy owners’ lack of knowledge about dry cow therapy, and operating procedures along the milk production chains [ 34 ].…”

“…The variations in the load of S . aureus between towns might be due to the differences in handling practices, sanitary conditions, and operating procedures along the milk production chain [ 34 , 36 ]. However, the total log10CFU/ml mean count of S .…”

The identification of critical lethal action in antimicrobial mechanism of glycerol monomyristate against foodborne pathogens

“…The microbial cell populations after GMM treatment were measured by the plate count method according to a previous study (42). The pathogen cells were collected as described above and resuspended to a final cell concentration of approximate 10 5 CFU/mL (OD 600 ≈ 0.05) with sterile broth.…”