Serratia - What Should You Do If You Find it in Your Herd?

Several producers have called recently to find out about Serratia marcescens mastitis after culturing milk samples from individual cows and finding Serratia as the cause of mastitis. This blog addresses their questions, decisions, and our current understanding.
Origin of Serratia marcescens

It is difficult to know where Serratia comes from without testing environmental samples, utensils, milking equipment, or milk samples from additional cows. If Serratia is found only in one cow, further environmental testing may not be worthwhile. However, if the bug is found in several cows' milk it would be important to act quickly. Serratia, although not a common cause of mastitis, is present in the cow's environment - soil, plants, feed, and water. Serratia has also been found in bedding and on the milking facility floor, indicating it may be traced back to infected cows. Serratia may originate in bedding or have leaked onto bedding from infected cows. This means that good hygiene and biosecurity are very important to prevent transfer from infected to 'clean' cows. It also means that culturing new infections - either found through DHI SCC or when fore-stripping - is important to reduce the chance of spread of Serratia. 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 'clean' cows.

Diagnosis and Severity of Serratia Mastitis Infections
Most Serratia infections will be found after a new DHI test comes back with a high cow somatic cell count (SCC). Visible signs of mastitis may only be seen in one-half of Serratia cases, meaning that visible symptoms won't always be apparent. Changes to milk are usually mild - few flakes - but infections won't cure, regardless of treatment. This means that Serratia mastitis is not a good thing, and prevention, and diagnosis through milk culturing, are important to keep infections low.

When are Serratia Mastitis Infections Most Likely to Occur?
New infections can occur at any time during lactation and may also occur during the dry period. Cows with high milk production are not at greater risk than cows with low milk production. Serratia is an "equal opportunity" bug, although is more likely to infect that next cow milked after an infected cow, and cows with poor teat ends. Because Serratia, like many environmental mastitis bugs, may be spread from cow to cow, it is important to milk infected cows last or with a milking unit used only for chronic cows.

How likely is Serratia to Cure?
Serratia is resistant to most antibiotics. One study found cure rate was only 14 percent. Mastitis treatment for Serratia rarely cures infections and is not recommended. After antibiotic treatment, milk may look better, but is usually only temporary. Because cows with Serratia mastitis are not likely to cure, emphasis should be placed on identifying new infections quickly.

How Can You Prevent and Control Serratia Mastitis Infections?
Serratia, like most mastitis bugs, plays by the numbers game. The more Serratia bugs in the cow's environment, the more likely the next cow will become infected. Teat and teat end cleanliness at milking, careful fore-stripping to prevent back splash or stripping onto cow beds, removing hair from the udder at least every 6-months, use of pre-dipping before milking will all be beneficial. In addition, reducing contact of the cow's udder with bugs between milkings, by scraping back of cow beds (where the udder rests), and applying fresh bedding frequently, will be worth your time. In herd-wide problems, quick identification of Serratia source:  cows, bedding, or teat dip, is essential to reducing infection spread.

Teat Dip and Serratia
Teat dip does not usually contain Serratia marcescens. However, Serratia is commonly resistant to chlorhexidine-gluconate or quaternary ammonium disinfectants. Consider culturing your teat dip if Serratia is found in more than one cow, and especially if one of these disinfectants is used as germicide in your teat dip. Most mastitis laboratories will culture teat dips. As long as a representative sample is sent to the laboratory, Serratia should be easy to find if present in the teat dip. A negative finding means that Serratia is not present in the teat dip sample and a positive finding means that Serratia is in the teat dip and is likely a source for new Serratia infections.

Summary
Serratia infections are relatively uncommon and it was surprising to have two calls within a short-time frame. Routine culturing was helpful to these particular farmers in that it confirmed Serratia was present in their herds. Because both producers tend to culture most new infections, they knew Serratia was not common and wanted to learn more about how to deal with the mastitis. In one case, the producer had the teat dip cultured and the result was negative. He was concerned whether a negative result meant the teat dip was not the source of the infection or the chlorhexidine teat dip was not the likely source of the cow's infection. In the other herd, Serratia was found in a good cow without previous mastitis, symptoms were atypical for the herd, and treatment was started before culture results came back from the laboratory. The producer's veterinarian recommended extended therapy because symptoms were atypical for the herd and this protocol was previously successful in curing herd mastitis infections. After treatment, mastitis was still present in the cow's quarter. The producer called to get information on what the research suggests in terms of ability to cure Serratia mastitis and whether additional treatment might be successful.

What Decisions Can Be Aided By a New Understanding About Serratia?
1). Serratia cows should be milked last or with dedicated milking units to reduce the chance of spreading infections;
2). Serratia cows should be put on the 'to cull' list. Treatment and especially re-treatment is not recommended;
3). Carefully watch for Serratia mastitis by culturing new infections;
4). Culture fresh bedding and/or teat dip (if chlorhexidine or quaternary ammonium based) if more than one case of Serratia is found;
5). Add new knowledge gained about Serratia to your tool box for quicker and profitable future mastitis decisions.

Thanks to Dr. Frank Welcome for guidance about teat dip culturing and Cornell QMPS for their summary of Serratia Research.

Milking Management and Gloves: A Historical Perspective on Use

Historical Background on 'Glove Use' as a Strategy to Reduce Infection Transfer

I'm currently working on several fact sheets for National Mastitis Council (NMC) meetings which are coming up in early February and am also preparing for winter workshops that will be held on 'Milking Management' (see December blogs). As part of the process, I'm reviewing lots of research to trace origin of why certain procedures and control methods are recommended. I thought I'd share some of the highlights of my findings.

It is recommended by NMC, that strong but thin disposable gloves, similar to what surgeons and health professionals wear in the hospital, be worn by all folks doing the milking on-farm. It is also recommended that these gloves be sanitized periodically or changed as needed. Gloves should be thrown away at a minimum after each milking and new gloves worn at the start of the next milking. The rationale for wearing gloves and potential impact on disease control may seem pretty obvious but we still have many farmers and employees who refuse to consider wearing gloves for various reasons. I've also found over the last 3-years of field work that many farms save gloves used at one milking and reuse them at the next to 'save money'.

My thought was that maybe there is some 'ammunition' in the research data to convince folks to wear gloves, and to encourage quick replacement or sanitizing of  'gloves at risk'. This 'ammunition' would then be used in education to persuade and overcome feelings by some farmers and employees that 'gloves are uncomfortable', 'cost too much', and/or 'affect ability to effectively palpate the udder or otherwise perform tasks that require 'feeling' or tactile senses needed when milking and diagnosing problems with the udder'.

Where and Why Did Glove Use in the Medical Profession Originate?

The 'data' or 'validation' will follow in upcoming blogs but this blog shares a historical perspective from the medical literature and which I think is both interesting and 'fun'.

The first article I found on rationale or initiation for glove use was in the medical literature in a British Medical Journal published in 1933. My thought was that if I could find the original rationale or reference, this may be helpful to get more dairy producers and their employees to wear gloves while milking and thereby reduce risk of spreading mastitis from infected cows to healthy cows.

So how did glove use start? Basically, glove use was initiated to protect a woman's hands from an unsightly rash and chemical reaction and because of a romance between this assistant and the doctor in charge. Glove use initially expanded partially due to ego. Health care professionals felt they looked more like 'experts' when wearing gloves. Glove use then expanded and continued based on a desire by health professionals to protect themselves from disease and also to protect transfer of diseases from diseased patients to healthy patients (albeit immunocompromised - e.g., in hospital for another ailment). Research provided the cause and effect or rationale. Hands harbor bacteria. Gloves, when used properly, may reduce the chance or risk of transferring bacteria. AIDS has probably been the number one reason for expanded glove use in the medical profession. It is possible, when one's own health is at stake, health care professionals are more likely to adhere to a particular protocol - like wearing gloves.

There are still plenty of  instances or examples in the medical literature where health care workers forget to fully cleanse gloved hands or replace used gloves and where bacteria are transferred via gloved hands or non-gloved hands from diseased patients to healthy patients. The presence of Methicillin Resistant Staph. aureus (MRSA) in hospitals and impact, especially in immunocompromised patients, may be reinforcing and expanding adherence to glove use by health care workers. Regardless, even when their own potential health is at stake, folks have to be continually reminded through 'data' and other means, that hands - even with glove use, - are a major means of transferring disease from one patient to other patients.

The actual historical quote of how glove use started

The original story is attributed to Dr. F.L. Reichert, and related to an event in 1891. Enjoy!

"(Dr.)W.S. Halstead of Baltimore introduced the use of rubber gloves as a protection both for patient and for surgeon in 1891. Halstead first introduced rubber gloves into his theatre a year or so earlier, in the winter of 1889-90 for a slightly different purpose. The nurse in charge of the operating room had complained to him that the solution of mercuric chloride used in sterilizing the hands had caused dermatitis on her forearms and hands. In Halstead's own words: "As she was an unusually efficient woman, I gave the matter my consideration and one day in New York requested the Goodyear Rubber Company to make as an experiment two pairs of thin rubber gloves with gauntlets (e.g., a dress glove extending over the wrist). On trial these proved to be satisfactory (so) that additional gloves were ordered."  Later the assistant in charge of instruments was given gloves. The operator wore them at first only when making exploratory incisions into joints. After a time men who had grown accustomed to wearing gloves as assistants came to wear them habitually as operators, because they felt more expert with gloves than without."

"It is interesting that the use of rubber gloves in surgery was not the result of an inspiration to eliminate the hands as a source of infection during the operation. Their use was a matter of slow evolution, first as a protection for the hands of the assistants from irritating solutions, then as an added precaution on the part of the operator in exploring joints, later as an aid to the operative dexterity of those accustomed to gloves as assistants, and finally as a regular adornment to be worn invariably in all cases, clean and septic, by the operator and all members of the operating team." "The unusually efficient woman" for whom it all began in due course became Mrs. Halstead".

More actual data to follow.... ;-)