A milk‐line sampling system to detect foodborne pathogens: A field case investigation from the United States and Argentina

Abstract The objective of this short communication was to discuss two field case investigations to determine the usefulness of a milk‐line sampling device to detect bacteria either coming from a group of cows suffering from mastitis or from the milking line potentially contaminated with environmental bacteria. In Case 1, the in‐line sampling device was able to detect certain segments of the milk‐line contaminated with environmental bacteria, but not coming from the cows. In Case 2, 19 out of 25 pooled in‐line samples were in agreement with at least one of the individual sampled cows shedding either Staphylococcus or Streptococcus spp. or both, which accounted for 76% accordance between both methods. The in‐line system, although not perfect, provided a reliable method to detect individual cows shedding mastitis‐causing organisms. In conclusion, the milk‐line sampling device system was able to help identify foodborne pathogens. Regular monitoring of the microbial quality of milk through a milk‐line sampling device is recommended for groups of cows within the dairy herd to detect potential mastitis‐causing microorganisms. Furthermore, the sampling device was an effective tool to screen the efficacy of cleaning and disinfecting mechanisms of the milk lines to identify and control potential foodborne pathogens that are collected in the bulk tank.


| INTRODUC TI ON
The opportune detection and identification of the source of bacterial contamination of milk from lactating cows is essential to take preventive actions to decrease the risk of mastitis at the level of the herd and food poisoning in humans (Godden et al., 2002;Nagoette et al., 2019). Bacteria may come both from cows and their infected udders and from environmental saprophytic contamination of segments of the milk line before the milk reaches the bulk tank (Gonzalez et al., 1986;Smith et al., 1985).
QualiTru Sampling System (Oakdale, Minnesota 55,128, USA) is a sampling device that can be set up at any connection of the milking line from the parlour to the bulk tank. The system consists of a stainless steel port that can be connected to any junction of the milking line to obtain a representative milk sample from a group of DOI: 10.1002/vms3.484

C A S E R E P O R T A milk-line sampling system to detect foodborne pathogens: A field case investigation from the United States and Argentina Abstract
The objective of this short communication was to discuss two field case investigations to determine the usefulness of a milk-line sampling device to detect bacteria either coming from a group of cows suffering from mastitis or from the milking line potentially contaminated with environmental bacteria. In Case 1, the in-line sampling device was able to detect certain segments of the milk-line contaminated with environmental bacteria, but not coming from the cows. In Case 2, 19 out of 25 pooled in-line samples were in agreement with at least one of the individual sampled cows shedding either Staphylococcus or Streptococcus spp. or both, which accounted for 76% accordance between both methods. The in-line system, although not perfect, provided a reliable method to detect individual cows shedding mastitis-causing organisms. In conclusion, the milk-line sampling device system was able to help identify foodborne pathogens. Regular monitoring of the microbial quality of milk through a milk-line sampling device is recommended for groups of cows within the dairy herd to detect potential mastitis-causing microorganisms. Furthermore, the sampling device was an effective tool to screen the efficacy of cleaning and disinfecting mechanisms of the milk lines to identify and control potential foodborne pathogens that are collected in the bulk tank.

K E Y W O R D S
dairy cattle, foodborne pathogens, milk, sampling device cows or the entire milking herd. Milk-line sampling may be particularly attractive to larger herds because it allows producers to monitor the performance of several different groups of cows within the herd (Godden et al., 2002). In addition, the system could be used to monitor any potential contamination from different sections of the milk line.
In this article, we report the usefulness of a milk-line sampling device to detect bacteria either coming from a group of cows shedding mastitis-causing microorganisms or from the milking line potentially contaminated with environmental bacteria. This report summarizes two field case investigations that occurred in a dairy herd in the United States (Case 1) and in Argentina (Case 2).

| Case 1
This case occurred in a dairy farm from the south of Georgia, USA, which had a history of high Preliminary Incubation Count bacteria (>30,000 CFU) in the bulk tank milk. One group of 16 cows (#1-16) was individually sampled for an experienced veterinarian to obtain a composite of the four quarters right before milking. Before beginning milking, a line sampling device (QualiTru Sampling System, Oakdale, Minnesota 55,128, USA) was set up in the first junction of the milk-line after leaving the parlour. A sterile septum was placed in the stainless steel port. Then, a sterile 18-G needle with a line connected to a sterile bag was inserted in the septum. Before reaching the sterile bag, the line passed through a portable peristaltic pump that allowed a frequency flow sampling over the entire process run.
The pump was set up for a volume of sampling of 60 ml of milk per minute.
Individual cow composite samples (all four quarters) and milkline pooled sample were refrigerated and then transported directly to a Veterinary Diagnostic and Investigational Laboratory.
After arrival, samples were cultured for aerobic bacterial isolation and Mycoplasma sp. using standard approved methodologies.

| Case 2
This case occurred in a large dairy farm in the pampas of Argentina.
Cows were milked in seven different groups of 170 cows according to days in milk and milk production. The farm had a history of high somatic cells count (>350,000 cells/ml) and high incidence of clinical cases of mastitis. Even though the majority of cases were environmental based on previous bacteriological culture data, cows with Staphylococcus aureus and Mycoplasma spp infection were detected.
The objective was to test the ability of an in-line sampling system to detect Staphylococcus aureus in a group of cows whenever a cow was positive within that particular group. Since sampling and culturing all cows of the entire herd was not economically feasible, only a select few cows with high somatic cell counts or with clinical mastitis within a group were selected to be individually sampled and compared to the findings with the in-line sample from that group of cows.
Sampling was performed the same way as described in Case 1 and in- pooled in-line samples were in agreement with at least one of the individual samples, which accounted for 76% accordance between the two methods. In this sense, the in-line system, although not perfect, provides a reliable mechanism to detect individual cows shedding either Staphylococcus or Streptococcus spp. or both.
In conclusion, in both cases, milk-line sampling device system was able to help identify foodborne pathogens. Regular monitoring of the microbial quality of milk through a milk-line sampling device is recommended for groups of cows within the dairy herd to detect potential mastitis-causing microorganisms. Furthermore, the sampling device is an effective tool to screen the efficacy of cleaning and disinfecting mechanisms of the milk lines to identify and control the potential foodborne pathogens that are collected in the bulk tank.

E TH I C S S TATEM ENT
The authors confirm they followed the ethics policies of the journal and the University of Georgia.

ACK N OWLED G EM ENT
The authors want to acknowledge the CPES UGA Dairy Farm and Don Remigio Dairy Farm Argentina for their participation in this study

CO N FLI C T O F I NTE R E S T
The authors have no conflict of interest to declare.