Phenotypic and genotypic characterization of Streptococcus Uberis isolated from mastitic cow's milk

Abstract EN

A total number of 240 milk samples was collected from clinical (88 quarter milk samples; QMS), subclinical (108 QMS) and bulk tank (44 BTM) cow's milk selected from different dairy farms for detection of some phenotypic virulence factors and some putative virulence associated genes by polymerase chain reaction (PCR) in the isolated S.

uberis strains.

Also detection of antibiotic resistance for the isolated strains using conventional assay was applied.

Using biochemical tests and molecular assay, the confirmed S.

uberis strains was 48 out of 74 Streptococcus species (64.9%).

The % of S.

uberis isolation from the total examined milk samples was 20%.

The higher S.

uberis incidence was detected in bulk tank milk samples (45.5%) followed by clinical and subclinical milk samples (18.2 % and 11.1%, respectively).

In studying the phenotypic virulence factors of the collected S.

uberis isolates, it was found that β-haemolysis and positive CAMP factor like reaction were detected in only 6.25% of S.

uberis isolates for each of them, while slime production as indicator for biofilm formation was detected in 75% of these isolates.

A total of 48 isolates was tested for their in vitro antimicrobial sensitivity.

Some of the isolates were highly sensitive to a limited number of antibiotics.

On the other hand, the majority of the isolates were highly resistant to a large number of other antibiotics.

In studying the genotypic virulence genes, gapC gene was detected in all the isolated strains of S.

uberis while oppF, cfu and sau genes were detected in 93.8%, 68.8% and 62.5%, respectively.

On the contrary, lbp gene couldn't be detected in any of the isolated strains of S.

uberis.

At least 2 of the five different virulence genes were detected in each isolate of S.

uberis.

There were some strains harboring 4 virulence genes and the higher rate of these strains was detected in that isolated from clinical mastitis.

Moreover, the higher strains harboring 3 virulence genes were detected in that isolated from subclinical mastitis.

In conclusion, it was observed that S.

uberis should be given a great concern as a threat for the dairy cows.

As it caused both clinical and subclinical mastitis as well as it was isolated with high percentage in BTM.

Moreover, this pathogen nowadays emerges as resistance to different antimicrobial agents especially for those commonly utilized.

Furthermore, S.

uberis harbors different virulence factors and genes that capable it to persist in the mammary gland of the dairy animals for a long time and speeding of infection from cow to cow may occur resulting in higher prevalence rates of infection between different dairy farms.