The implementation of control measures for contagious mastitis pathogens has successfully reduced the prevalence of these organisms in U.S. dairy herds. However, dairy producers continue to struggle with the control of environmental pathogens. Serratia spp. are Gram-negative bacteria, similar in structure to Escherichia coli and Klebsiella spp. The most common mastitis-causing species is Serratia marcescens. However, the treatment and control of these organisms is similar across all species of Serratia.
Commonly, these organisms are found in soil and plant matter (including feed). Therefore, cows on pasture or cows housed on organic bedding material may be at an increased risk for mastitis caused by Serratia spp. Herd outbreaks of Serratia mastitis have occurred in herds where Serratia grew in bedding and/or teat dip. Poor udder cleanliness and damaged teat ends also appear to increase risk of spreading Serratia to uninfected cows.
Serratiaspp. infect uninfected cows through environmental contact. As with control of all environmental organisms, maintaining a clean and dry environment for cows is of utmost importance. Similarly, using inorganic bedding (sand) also reduces environmental contamination by these bacteria. However, it is important to remember that recycled sand can serve as a source of environmental contamination as organic matter accumulates in the bedding material.
Practices for controlling Serratia spp. include implementing proper milking procedures and maintaining a clean and dry housing environment containing appropriate bedding materials.
At milking time, all quarters should be forestripped to begin the milk let-down process. Using an efficacious pre-milking teat disinfectant following forestripping is particularly important in controlling this mastitis-causing pathogen. Chlorhexidine is not an effective killing agent for Serratia spp.; therefore, producers with herds experiencing Serratia mastitis should choose a pre-milking teat disinfectant containing an alternative active ingredient. The pre-milking teat disinfectant should remain on the teats for 30 seconds and should be removed with either a paper towel or a single-use clean and dry cloth towel. When these guidelines are followed, the time from start of manual stimulation (forestripping or wiping) until unit attachment is in the range of 60–120 seconds, an appropriate period of time for milk let-down to occur.
In addition, reducing teat end exposure between milkings, by scraping the back of cow stalls (where the udder rests) and applying fresh bedding frequently, will be worth your time. When herd-wide infection occurs, quick identification of the Serratia source—cows, teat dip, or bedding—is essential to reduce the spread of the infection.
Although teat dip does not usually contain Serratia marcescens, teat disinfectants can become contaminated with these organisms on-farm. Furthermore, Serratia spp. are commonly resistant to chlorhexidine-gluconate disinfectants. Therefore, if a container of disinfectant containing one of these active ingredients becomes contaminated, the continued use of this disinfectant on the farm can pose a threat to the rest of the herd. Dairy producers should consider culturing their teat dip if Serratia spp. is found in more than one cow, and especially if a chlorhexidine-gluconate disinfectant is used as germicide in the teat dip. Moreover, it is important to remember that the product should only be removed from the original container. Leftover teat disinfectant from teat dipping cups should never be poured back into the original container or re-used for a subsequent milking.
New infections can occur at any time during lactation and may also occur during the dry period. However, cows in early lactation are at an increased risk for new infections due to the increased stress and immune suppression associated with the postpartum period. Cows with high milk production are not at greater risk than cows with low milk production.
Serratiais resistant to most antibiotics, and, therefore, cure rates are limited. Thus, intramammary antibiotic treatment is not recommended. Some veterinarians have found limited success with the infusion of sterile saline into the gland. This treatment acts to alter the osmolarity and, thus, may aid in the elimination of bacteria present in the gland. Veterinary consultation is recommended prior to the start of any treatment protocol. Due to the limited cure rates with the previously discussed options, emphasis needs to be placed on prevention of these infections, rather than on treatment.
Christina S. Petersson-Wolfe, Sandy Costello, and John Currin, Virginia Tech