The examination of some virulence factors in S. aureus isolates obtained from the healthy human population, sheep mastitis, and cheese

Abstract.

Background

Staphylococcus aureus is responsible for many infections in humans and animals from skin and soft tissue infections to life-threatening diseases. In this study to explore the origin of S. aureus infections in humans, the antibiotic resistance profile and the variety of virulence factors in S. aureus isolates were examined in three groups: a healthy human population, cheese, and the milk of sheep with mastitis.

Aims

The examination of some virulence factors in S. aureus isolates obtained from the healthy human population, sheep mastitis, and cheese.

Methods

A total of 400 nasal swab samples from healthy students, 30 cheese samples, and 122 sheep milk samples were collected for the detection of S. aureus isolates from January 1, 2018, to March 1, 2018. The frequency of hla, hlb, Acme/arcA, pvl, and tsst-1 virulence genes and mecA gene was determined in each group by PCR assay.

Results

There was a direct relationship between the antibiotic susceptibility profile of the isolates from a healthy population and those from mastitis milk samples. Of 400 nasal samples, 15% (60/400) were positive for S. aureus, of which 60% (36/60) were positive for mecA. While 50% (15/30) of cheese samples were positive for S. aureus. of which 7 cases (46.66%, 7/15) were positive for mecA. The prevalence of S. aureus among students was dependent on gender (P=0.025). Also, 47.5% (58/122) of milk samples from sheep mastitis were positive for S. aureus, and 41.37% (24/58) were positive for the mecA gene. Based on PCR results, the highest rate of hla (68.33%, 41/60), hlb (53.33%, 32/60), and Acme/arcA (46.66%, 28/60) genes were related to a healthy population, and the highest frequency of pvl (41.38%, 24/58), and tsst-1 (27.59%, 16/58) was related to milk samples (P<0.05). A significant correlation was observed between the presence of the arginine catabolic mobile element (ACME)-arcA gene and resistance to methicillin (P<0.05).

Conclusion

The high rate of virulence factors in the S. aureus isolates obtained from mastitis and dairy products is an alert point, because they could be source of the spreading of S. aureus to humans. There is an essential need for continuous monitoring to control staphylococcal food poisoning.

Comparative Evaluation of Nested Polymerase Chain Reaction for Rapid Diagnosis of Human Brucellosis

Brucellosis is recognized as a zoonotic disease with high morbidity in the absence of treatment. The primary diagnosis of brucellosis can be effective in the achievement of satisfying treatment results and prevention of chronic infections. The present study aimed to compare the efficiency of conventional microbiological and serological approaches with nested Polymerase chain reaction (nested PCR) for rapid diagnosis of human brucellosis. A total of 120 subjects with symptoms of brucellosis were included in the study. The sensitivity and specificity of nested PCR for the detection of Brucella bacteria were compared with serological and blood culture methods. Out of 120 patients enrolled, brucellosis was detected in 73 (60.83%) cases based on serological tests with a blood culture confirmation in 8.33% of participants. Based on the obtained results, 55% of cases were positive in serum agglutination test (SAT&amp;ge;1:160), and Coombs (C-SAT&amp;ge;1:160) tests. Furthermore, seven negative SAT cases were positive in C-SAT as evidence of chronic brucellosis. The results of the 2-mercaptoethanol (2-ME) &amp;ge; 1:80 test were negative in six SAT-positive cases. Based on nested PCR results, 68.18% and 56.06% SAT positive samples were also detected by blood nested PCR and serum nested PCR, respectively. The sensitivity of blood nested PCR was significantly more than serum nested PCR, SAT&amp;ge;1:160, and blood culture (p &amp;lt;0.001). Moreover, the specificity of blood and serum nested PCR was obtained at 100%, compared to blood culture and SAT&amp;ge; 1:160. In the present study, the nested PCR was able to identify chronic brucellosis in SAT negative patients. As evidenced by the obtained results, the nested PCR showed higher efficiency for rapid diagnosis of human brucellosis, as compared to the blood culture method. Furthermore, the findings pointed to the high performance of nested PCR for rapid diagnosis of both chronic and acute brucellosis.