Genetic characterization of antibiotic-resistant Staphylococcus aureus from milk in the North-West Province, South Africa

Abstract

Food borne diseases are a major public health concern worldwide. Staphylococcus aureus is one of the potential food borne pathogens which causes nosocomial and community acquired infections. In the present study, 74 representative strains of S. aureus isolated and characterized in previous study from different milk samples were subjected to random amplified polymorphic DNA (RAPD) polymerase chain reaction (PCR) and enterobacterial repetitive intergenic consensus (ERIC)-PCR to generate fingerprints to determine the genetic relationships of the isolated strains. A total of 20 RAPD patterns were generated and the number of amplified fragments obtained ranged from 0 to 8 with molecular weight ranging from 250 to 2000 bp. A dendrogram based on fingerprinting pattern grouped isolates into twelve major clusters (I-XII). In the case of ERIC-PCR 9 banding patterns were obtained with amplicons ranging from 1 to 8 and band sizes ranging from 250 to 2000 bp. A total of four major clusters (I-IV) were observed in the dendrogram based on ERIC fingerprints. The discrete banding patterns obtained both from ERIC-PCR and RAPD-PCR showed remarkably the genetic diversity of S. aureus. The findings of this study indicate that raw, bulk and pasteurized milk in the North-West Province was contaminated with toxigenic and multi-drug resistant S. aureus strains. This emphasizes the need to implement appropriate control measures to reduce contamination as well as the spread of virulent S. aureus strains to reduce the burden of disease in humans.

Keywords: ERIC-PCR; Genetic fingerprinting; Milk; RAPD-PCR; Staphylococcus aureus.

Figure 1

RAPD-PCR profiles of representative S. aureus isolates isolated from milk samples from different sampling sites. Lanes 1 = 1 Kb DNA ladder; Lanes 2–20 = A representation of the RAPD profiles for S. aureus isolates.

Figure 2

RAPD-based dendrogram showing genetic relatedness among S. aureus isolates (Z = Zeerust, RO = Rooigroond, V = Vryburg, MP/MB/M = Mafikeng, B = Disaneng, TP = Taung, CV = Carltolville, ST = Stella, R = Rustenburg, BP = Potchefstroom, PID/PIT = Setlagole).

Figure 3

ERIC-PCR profiles of representative S. aureus isolates isolated from milk samples from different sampling sites. Lanes 1 and 21 = 1 Kb DNA ladder; Lanes 2–20 A, B = A representation of the ERIC profiles for S. aureus isolates.

Figure 4

ERIC-based dendrogram showing genetic relatedness among S. aureus isolates (Z = Zeerust, RO = Rooigroond, V = Vryburg, MP/MB/M = Mafikeng, B = Disaneng, TP = Taung, CV = Carltolville, ST = Stella, R = Rustenburg, BP = Potchefstroom, PID/PIT = Setlagole).