Survey of potential factors involved in the low frequency of CP5 and CP8 expression in Staphylococcus aureus isolates from mastitis of dairy cattle from Argentina, Chile, and Uruguay

First molecular characterization of capsule expression and antibiotic susceptibility profile of Staphylococcus aureus isolates from bovine mastitis in Jordan

Background and Aim: Bovine mastitis has long been considered the most important cause of economic losses in the dairy industry. Staphylococcus aureus is the most frequently isolated pathogen from bovine mastitis cases worldwide. Capsular polysaccharides (CPs) of serotype 5 (CP5) or serotype 8 (CP8) are the most prevalent capsule genotypes related to infections associated with S. aureus in humans. However, a variety of CPs has been reported in ruminants and other hosts. Information regarding the relationship between genotypic and phenotypic capsule variation and bovine mastitis in Jordan is scarce. Thus, we aimed to determine the prevalence of S. aureus capsule genotypes CP5 and CP8 in milk from bovine mastitis cases and the antimicrobial susceptibility profile of the recovered isolates in 27 dairy farms in Jordan. Materials and Methods: Staphylococcus aureus strains were isolated from bovine mastitis cases in two districts of Jordan. All S. aureus isolates were initially identified using conventional biochemical and microbiological methods. Subsequently, confirmation of the identity of S. aureus was performed by polymerase chain reaction (PCR) targeting nuc gene. Capsule polysaccharide typing was performed by PCR specific for CP5 and CP8. In addition, we assessed the antibiotic susceptibility profile of S. aureus isolates against commonly used antimicrobials by the disk diffusion method according to Clinical and Laboratory Standards Institute guidelines. Results: We collected 148 clinical isolates of S. aureus from bovine mastitis cases in the Zarqa (67.6%, n = 100) and Irbid (32.4%, n = 48) districts. Most isolates possessed capsule genotypes (91.3%), predominantly CP8 (88.6%). Only 8.7% of the isolates were nontypeable by PCR. In addition, we found statistically significant differences between the geographical region and the status of methicillin-resistant capsule genotypes (p < 0.05). The rates of resistance to β-lactam, macrolide, and fluoroquinolone antibiotics were very low, but resistance to tetracyclines was considerably high (22.3%). Significantly, mastitis isolates from Irbid showed a higher rate of resistance to ciprofloxacin (8.3% vs. 0%), while isolates from Zarqa showed a significantly higher rate of resistance to gentamicin (12.0% vs. 6.2%). Conclusion: We established associations between capsule genotypes and antimicrobial resistance and the pathogenic behavior of S. aureus isolated from bovine mastitis cases. Further studies are necessary to fully elucidate the role and mechanisms of capsular expression in the epidemiological and molecular variability of S. aureus in bovine mastitis.

Short communication: Association between the accessory gene regulator (agr) group and the severity of bovine mastitis caused by Staphylococcus aureus

Staphylococcus aureus can elicit mild to more severe degrees of mastitis in cattle, depending on the response of the host's immune system and the virulence factors of the specific isolate. Several virulence factors are controlled by a global regulatory system, designated accessory gene regulator (agr). Thus, the objective was to examine associations between different capsular and agr types and the severity of bovine mastitis caused by S. aureus. All isolates were obtained from bovine subclinical (n = 50), mild clinical (n = 73), and moderate clinical mastitis cases (n = 28). Isolates containing the agrI gene and lacking the agr locus (agr^-) were more prevalent among subclinical than clinical mastitis cases, whereas isolates containing the agrII and agrIII genes were more prevalent among clinical mastitis cases. The capsular types 5 (cap5) and 8 (cap8) were found in 42 and 44%, respectively, of the isolates obtained from subclinical cases and in 38.6 and 58.4%, respectively, of those isolated from clinical mastitis cases. Capsular type was not associated with type of mastitis (subclinical, mild clinical, or moderate clinical). We found a strong association between agr type and type of mastitis, suggesting that knowledge of S. aureus genetic profiles could be an additional tool to control this disease.

Capacity of two Staphylococcus aureus strains with different adaptation genotypes to persist and induce damage in bovine mammary epithelial cells and to activate macrophages

The aim of this study was to evaluate and compare the ability to adhere/internalize, persist, and induce damage in mammary epithelial cells (MAC-T) of two Staphylococcus aureus strains with different adaptation genotypes (low and high) to the bovine mammary gland (MG). Also, the phagocytic and bactericidal capacity induced after the interaction between macrophages, isolated from mammary secretion, of both S. aureus strains was evaluated. Two isolates (designated 806 and 5011) from bovine intramammary infection (IMI) harboring genes involved in adherence and biofilm production, belonging to different capsular polysaccharide (CP) type, accessory gene regulator (agr) group, pulsotype (PT) and sequence type/clonal complex (ST/CC). Strains 806 and 5011 were associated with low (nonpersistent-NP) and high (persistent-P) adaptation to the MG, respectively. Strain 5011 (P), agr group I, cap8 positive and strong biofilm producer showed higher capacity to adhere/internalize in MAC-T compared with strain 806 (NP), characterized as agr group II, cap5 positive and weak biofilm producer. Strain 5011(P) could be recovered from MAC-T lysates up to 72 h pi; while strain 806 (NP) could be recovered only at 4 h pi. Strain 5011 (P) showed greater capacity to induce apoptosis compared with strain 806 (NP) at 4, 24 and 48 h pi. Macrophages infected with strain 5011 (P) showed a greater phagocytic capacity and higher percentage of intracellular reactive oxygen species (ROS) production than strain 806 (NP). No viable bacteria were isolated from macrophages lysates stimulated with any of the S. aureus strains at 2, 4, 8 and 24 h pi. The knowledge of the molecular profile of the S. aureus strains causing bovine mastitis in a herd could become a tool to expose the most prevalent virulence gene patterns and advance in the elucidation of the pathogenesis of chronic mastitis.