Antimicrobial resistance profiles of Staphylococcus aureus clusters on small dairy farms in southern Brazil

Abstract

In intensive dairy farming, persistent intramammary infection has been associated with specific Staphylococcus (S.) aureus strains, and these strains may be resistant to antimicrobials. The objective of this study was to evaluate the antimicrobial resistance phenotypes of S. aureus isolates and to assess the distribution and the persistence of clonal groups in small dairy herds of southern Brazil. Milk samples were collected from all lactating cows from 21 dairy farms over a two-year period, totaling 1,060 samples. S. aureus isolates were tested for susceptibility to thirteen antimicrobials using the disk diffusion method. The total DNA of the isolates was subjected to SmaI digestion followed by pulsed-field gel electrophoresis (PFGE). Banding patterns differing by ≤4 bands were considered members of a single PFGE cluster. The frequency of S. aureus isolation ranged from 3.45% to 70.59% among the 17 S. aureus-positive herds. Most S. aureus isolates (87.1%) were susceptible to all antimicrobials; resistance to penicillin (18.2%) was the most frequently observed. The 122 isolates subjected to macrorestriction analysis were classified into 30 PFGE-clusters. Among them, only 10 clusters were intermittent or persistent over the two-year period. The majority (93.6%) of isolates belonging to persistent and intermittent clusters were susceptible to all tested antimicrobials. S. aureus intramammary colonization in small dairy farms of southern Brazil is most frequently caused by sporadic PFGE clusters, although some persistent clusters can arise over time. Both sporadic and persistent isolates were highly susceptible to antimicrobials.

Genotypic and Phenotypic Evaluation of Biofilm Production and Antimicrobial Resistance in Staphylococcus aureus Isolated from Milk, North West Province, South Africa

“…It is common to observe higher rates of isolation in unpasteurized than in pasteurized milk due to the effect of heat in reducing the microbial load of pasteurized milk. Similar observations have been made in previous studies [14,21]. In a related study, Akindolire and colleagues reported 75% isolation rate of S. aureus from raw milk samples, 29% from bulk milk samples, and 13% from pasteurized milk [21].…”

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“…The high percentage of strains resistant to β-lactams in the present study was similar to that observed in other previous studies such as Daka et al, (2012), who observed that 67.9% of 78 S. aureus strains of MQ was resistant to penicillin G. In Brazil, resistance to β-lactams has also been observed between 18 to 95% in S. aureus isolated from bovine milk (CARVALHO et al, 2018;FERREIRA et al, 2016;GIRARDINI et al, 2016;MEDEIROS et al, 2009;SILVA et al, 2012). Also, a high percentage of strains in the present study were resistant to erythromycin, which results are similar to those reported in a previous study in which 17% of the strains were classified as MRSA (n = 16/93), and all were resistant to erythromycin and carried at least one resistance gene ermA, ermB or ermC (GATERMANN;KOSCHINSKI;FRIEDRICH, 2007;TÜRKYILMAZ et al, 2010).…”

Molecular characterisation of Staphylococcus aureus from some artisanal Brazilian dairies

“…Zoonotic spread of MRSA strains to humans, resulting in severe infections have been reported, clearly highlighting animals as potential reservoirs of MRSA (Girardini et al, 2016;Harrison et al, 2013;Juhász-Kaszanyitzky et al, 2007;Silva et al, 2013). Furthermore, a recent study based on a high-resolution phylogenetic approach, reported the emergence of human epidemic ca-MRSA, resulting from the adaptation of CC97 strains from bovine to human hosts (Feltrin et al, 2016;Spoor et al, 2013).…”