Metabolites of bovine-associated non-aureus staphylococci influence expression of Staphylococcus aureus agr-related genes in vitro

Abstract

Communications via quorum sensing (QS) between non-aureus staphylococci (NAS) and Staphylococcus (S.) aureus in the bovine mammary gland remains largely unexplored. We determined whether 34 S. chromogenes, 11 S. epidermidis, and 14 S. simulans isolates originating from bovine milk samples and teat apices were able to regulate the QS of S. aureus, and if so, how in vitro growth inhibition of S. aureus by NAS, or NAS metabolites, or NAS cells themselves play a role in this process. In co-culture with S. aureus we observed that these 3 NAS species in general downregulated the expression of rnaIII, the effector molecule of the QS system, but this effect was more pronounced in S. chromogenes and S. simulans isolates than in S. epidermidis isolates. In vitro growth inhibition of S. aureus by NAS resulted in a small underestimation of the downregulating effect of NAS on rnaIII expression of S. aureus. Additionally, the culture supernatant of these NAS isolates and supernatant treated with proteinase K expressed greater regulatory activity over S. aureus virulence genes rnaIII, hla, and spa than washed NAS cells suspended in sterile water. These microbial interactions may influence S. aureus virulence and pathogenesis within the host. Isolation and identification of NAS metabolites affecting the QS system of S. aureus might help to develop alternative strategies for treatment and control of S. aureus mastitis.

Bovine-associated non-aureus staphylococci suppress Staphylococcus aureus biofilm dispersal in vitro yet not through agr regulation

“…The capacity to produce biofilm was observed in 8.8% (3/34), 72.7% (8/11) and 35.7% (5/14) of the S. chromogenes , S. epidermidis and S. simulans isolates, respectively (Additional file 1 ). Also, 100% (34/34) of the S. chromogenes isolates has the capacity to inhibit growth of S. aureus in vitro at least partially, whilst this was true for 45.4% (5/11) and 100% (14/14) of the S. epidermidis and S. simulans isolates, respectively [ 19 ] (Additional file 1 ). Seventy-nine (27/34), 27.3 (3/11) and 100% (14/14) of the S. chromogenes , S. epidermidis , and S. simulans isolates, respectively, repressed the S. aureus agr system [ 19 ] (Additional file 1 ).…”

“…First, the presence of genes related to biofilm formation (biofilm genotype) and the capacity to produce biofilm (biofilm phenotype) were mapped for 59 bovine NAS isolates originating from milk or TA (Additional file 1 ). The capacity to inhibit the growth of S. aureus 8325-4 (an agr + strain) in vitro (in vitro growth inhibition capacity) and to modulate the agr system of S. aureus 8325-4 ( agr interaction capacity) for the 59 NAS isolates was known from previous work [ 19 ] (Additional file 1 ).…”

“…The potential growth inhibition of S. aureus 8325-4 by the NAS isolates was evaluated before [ 19 ] (Additional file 1 ). Following the methodology described by De Vliegher et al [ 13 ], the pattern of the in vitro growth inhibition of the S. aureus strain 8325-4 by the NAS isolates was classified as NAS exhibiting no growth inhibition, partial inhibition, or total inhibition.…”

“…Some NAS isolates were able to repress the agr system of S. aureus 8325-4 by downregulating the rnaIII expression [ 19 ] (Additional file 1 ). As described by Canovas et al [ 42 ], the effect of NAS isolates on S. aureus agr was classified as none, weak, moderate, or strong.…”

“…They are commonly considered to be minor mastitis pathogens causing only a slight increase of the milk somatic cell count (SCC) [ 10 – 12 ] with no impact on milk yield. Other studies have suggested a protective effect of bovine NAS against, among other bacteria, S. aureus [ 13 – 17 ], including the repression of agr related virulence factors of S. aureus [ 18 , 19 ].…”