Assessing potential routes of Streptococcus agalactiae transmission between dairy herds using national surveillance, animal movement data and molecular typing

Evaluation of Control Program Against Streptococcus agalactiae Infection in Dairy Herds During 2019–2021 in Emilia-Romagna Region, Northern Italy

Streptococcus agalactiae (group B Streptococcus, GBS) is a causative agent of mastitis in dairy cattle, mainly causing a subclinical disease associated with a high somatic cell count (SCC), and a consequent decrease in production yield and quality of milk. GBS has been almost eradicated in many Northern European countries, but there are warnings of its re-emergence as a zoonotic threat. In Italy, only two regions carry out a GBS control program: Lombardy and Emilia-Romagna. In Emilia-Romagna, the program has been in place since 2019 and provides for the bacteriological culture of bulk-tank milk (BTM) of all dairy farms every 6 months and the voluntary application of herd eradication programs in the case of positive results. To assess the progress of the program in Emilia Romagna, in terms of herd-level prevalence and GBS transmission between herds, we analyzed the results of 17,056 BTM cultures from 2,831 dairy herds, sampled bi-annually in the period 2019–2021 (six rounds total). The impact of GBS infection on SCC and milk production was also evaluated. The results show a decreasing trend in both the incidence rate (from 3.0 to 1.5%) and apparent prevalence (from 8.9 to 5.2%) of GBS over the study period. By using a susceptible-infected-susceptible (SIS) model for the estimation of the transmission parameters, a basic reproductive number R₀ of 1.4 was calculated, indicating an active spread of GBS in the dairy cattle population of the Emilia-Romagna region. GBS infected farms have a consistently higher BTM SCC than negative ones (+77,000 cells/ml), corresponding to a 0.4 kg/cow/day milk loss. Moreover, GBS infected herds resulted in almost three times more likelihood of having non-marketable milk by exceeding the legal SCC limit. This study demonstrates the need to maintain the current control program against GBS to lower its occurrence and prevent significant market losses to farmers.

Circulation of Streptococcus agalactiae ST103 in a Free Stall Italian Dairy Farm

We report here on an outbreak of mastitis caused by Streptococcus agalactiae, or group B Streptococcus, in a northern Italy (Lombardy Region) free stall dairy farm. This outbreak was unusual because it occurred in a closed dairy herd and proved to be extremely difficult to resolve even after the application of the classical control procedures, which are specifically focused on the contagious nature of S. agalactiae. In order to better understand the potential origins of the pathogen and the critical points that could impair the eradication program and to investigate the possible presence of S. agalactiae in sources outside the mammary gland, we collected 656 individual composite milk samples, 577 samples from extramammary body sites (289 rectal, 284 vaginal, and four throat samples from milking cows, dry cows, heifers, and calves), and 81 samples from the cattle environment, including the milking parlor and the barn. Twenty-two S. agalactiae isolates were obtained from lactating cows or their environment. Of these, nine were isolated from milk, two were from rectal swabs, and two were from vaginal swabs, while nine were isolated from environmental samples. Based on molecular serotyping, pilus island (PI) typing and multilocus sequence typing, all isolates belonged to serotype III, pilus type PI-1/2b, and sequence type 103 (ST103), a type previously described to have an environmental transmission cycle and a potential human origin. Once the classical mastitis control measures were supplemented with environmental hygiene measures, herd monitoring using bulk tank milk revealed no further positive results for S. agalactiae, and the outbreak was considered resolved. IMPORTANCE Streptococcus agalactiae is an important pathogen in humans and cattle. Bovine mastitis caused by this bacterium and its control are generally associated with contagious transmission between animals. More recently, the presence of a fecal-oral transmission cycle in cattle has been proposed, linked to the ability of some S. agalactiae strains to survive in the bovine gastrointestinal tract and environment. Based on analysis of 1,316 specimens from cattle and their environment on a single dairy farm, we demonstrate the presence of sequence type 103 (ST103), which may have an environmental mode of transmission. This possibility was supported by the fact that the mastitis outbreak could not be controlled through measures to prevent contagious transmission alone and required additional environmental hygiene measures to be brought to a halt. This case study highlights that measures to control animal disease need to evolve alongside the microorganisms that cause them.

Antibacterial effect of synthetic ultra-short lipopeptide on Streptococcus agalactiae and its active on bacterial mastitis in mice

Streptococcus agalactiae mastitis is one of the significant threats to the milk industry. The traditional antibiotic treatment method is easy to cause the emergence of resistant strains, and the problem of drug residue is increasingly severe. In this study, we designed and synthesized five lipopeptides. The antibacterial activity of different molecular structure lipopeptides against Streptococcus agalactiae was detected. Furthermore, the mouse mastitis model was established using Streptococcus agalactiae. The lipopeptides with better antibacterial effect were selected for the treatment experiment to evaluate the application value in the treatment of mastitis. The results showed that 4 of the synthesized lipopeptides had specific antibacterial activity. SLP3 and SLP4 have an excellent antibacterial effect and can treat murine mastitis caused by Streptococcus agalactiae infection within the safe concentration range. The results of this study can provide an excellent experimental basis for new antibiotics and clinical application in the treatment of dairy cow mastitis.