**4.** *Staphylococcus aureus* **strains spectrum**

*Staphylococcus aureus* is a major causative agent of intramammary infections in dairy animals with potential virulence of surface components (adhesins, capsular polysaccharides, protein A), toxins, extracellular enzymes and coagulase [21]. About 74% quarter prevalence of *S. aureus* in bovine udder [22] with overall prevalence exceeding 61% in dairy animals [4]. A wide array of genotypic variations has been observed with great genetic diversity in the isolates of bovine as well as caprine origin. Some of the variants are common throughout the globe as ruminant specific *S. aureus* while others are geographic related in the literature [23]. Inflammatory respondent metabolic pathways (BoLA-DRA, GLYCAM1, FCER1G, B2M, CD74, NFKBIA and SDS), milk constituent associated (CSN2 and CSN3) and immunity related (B2M and CD74) are also specific strains of *S. aureus* of dairy mastitis [24, 25].

*Staphylococcus aureus* genotyping is mostly done by pulsed field gel electrophoresis(PFGE), multi locus sequence typing (MLST), polymerase chain reaction (PCR), *S. aureus* protein A (spa) typing, agar typing and typing on the basis of virulence and resistance coding genes [23, 26–31]. Thirty-nine electrophoretic types of *S. aureus* with diverse MLST genotyping had been reported, most of them were showed genetic heterogenicity and classified to one of the eight clonal complexes, suggestive of multiclonal nature of the *S. aureus* isolates from single dairy herd [32]. Clonal 8 complex (i.e., USA300), a lineage known for human infections, has also been isolated from bovine mastitis, suggestive of recent host shift and new adoptive genotypic strain of bovine mastitis [27].

PFGE typing of *S. aureus* from dairy origin showed that PFGE type A was significantly related to teat skin while PFGE type Q was more exclusive to milk and exhibit marked biofilm potential [33]. Overall, PFGE clusters of isolates showed same endotoxin coding genes with indistinguishable banding patterns. Phylogenetic studies based on MLST sequencing classified these clusters into clonal complexes with similar staphylococcal endotoxin genetic profiles [23]. Genotyping of dairy originated *S. aureus* showed five clonal types (PFGE A consisting on sequence type 747 [ST747] and spa type t359; PFGE B with spa type ST750 and t1180; PFGE C with spa type t605 and ST126; PFGE D with spa type t127 and ST751; PFGE F with spa type t002 and ST5). About 63% isolates harbor major clone A but negative for Panton-Valentine leukocidin and exfoliative toxin D genes [26]. Another reported PFGE typing of dairy originated *S. aureus* revealed 16 PFGE types (from A – P), with M, I and O as most frequent but not significantly variant strains in the field, respectively. PCR typing based on endotoxin genes presence showed that 11.7, 1.8, 2.7, 0.9 and 7.2% isolates carried seb, seb and sec, sec, see, and tsst-1, respectively with zero prevalence of sea and sej genes. PFGE types M and O showed clustering behavior with β-hemolysin and least prevalence of endotoxin coding genes [34].

Staphylococcal protein A types t084, t304 and t688 from subclinical mastitis showed divergent virulence and heterogenicity traits while a novel spa-type t18546 was also reported from dairy udder ailments [35]. Prevalent clonal types of *S. aureus* from bovine udder exhibited generic alterations of epigenetic modulators to surpass immune response of host. The study reported 35,878 transcripts of these strains which differ 23% from reference genomic cluster. Expressive nature of 20,756 transcripts were observed with more than 1 fragment per kilobase of transcript per million mapped fragments and 25.95% of multi-exonic genes alternatively spliced. Alternative Splicing (AS) events for more than 100 immunogenic genes were noted with 379 alternate AS events coding for transcription and splicing proteins. Spa typing of ovine originated *S. aureus* showed 14 diversified clones*,* most prominent of which were t1773, t967 and t1534 as 62.32, 5.79 and 5.79% respectively. Three novel spa types were also identified with repeats successions (07–23–12-34-12-12-23-03- 12-23), (04–31–17-24-25-17-17) and (04–31–17-24-17-17) [36].

Screening of *S. aureus* for endotoxins (SE) showed that >90% isolates were positive for SE genes while 70.1% with exaggerative response. All isolates were positive for biofilm encoding genes (icaA/D, clf/B, can, fnbA). A total of 7 spa types (1 novel spa type t17182), 5 STs, 14 SmaI-pulso-types and 3agr types (no agrII) were reported. PFGE cluster II-CC1-ST1-t127-agr III was the most prevalent clone (56.3%). Isolates of agr III (PFGE Cluster I/II-CC1-ST1-t127/2279) exhibited higher number of virulence genes than other agr types. The MSSA-ST398-t1456-agr I clone showed higher antibiotic resistance, weak biofilm expression and lower level of virulence genes expression [37]. Another study reported agr-I strain harboring penicillin resistance genes while agr-III strains were devoid of that pattern. Antimicrobial resistance encoding genes (tet (L), tet (K), erm (B) and bla (Z)) were frequent in these strains [36]. Thus, the data narrated agr-I and II as different subspecies of dairy originated *S. aureus* [38]. Disruption of the ica operon in a bappositive *S. aureus* strain showed no alteration in biofilm expression, indicating Bap gene compensatory mechanism for deficit PIA/PNAG product (a biofilm matrix polysaccharide) [39]. 17 different pulsotypes of dairy originated *S. aureus* have been reported with 24 virulence coding genes for leukocidins (lukED/lukM), pyrogenic toxin superantigen (PTSAg), haemolysins (hla-hlg), toxic-shock syndrome toxin (tst), enterotoxins (sea-seo, seu), exfoliative toxins (eta, etb), and genes for methicillin (mecA) and penicillin (blaZ) resistance. PTSAg-encoding genes and plasmid encoded sei, sed and blaZ genes were frequent in persistent intramammary ailments [40].

#### Staphylococcus aureus *and Dairy Udder DOI: http://dx.doi.org/10.5772/intechopen.95864*

*Staphylococcus aureus* classification based on *mec*A gene is narrated as methicillin susceptible (MSSA) and methicillin resistant (MRSA) strains. Studies reported 84% MSSA prevalence with MRSA isolation rate up to 4%. Spa typing of the isolates showed frequent presence of t034 and t529 in MSSA while t121 was noted in MRSA strains. Both types of isolates were positive for endotoxin B, C, D, and E. MLST and PFGE typing of isolates revealed composite genotype profile of ST 5-PFGE USA100-unknown spa type which is of hospital origin and ST 8-PFGE USA300-spa type t121 genotype, commonly designated as community-associated MRSA clone [28]. Another study reported 77.8% MRSA from goat mastitis as strong biofilm producers. Spa typing revealed 44% t127, 33.3% t2049 and 22.2% t7947 type among total MRSA isolates [41].
