Pseudomonas aeruginosa mastitis in two goats associated with an essential oil–based teat dip

Abstract

Pseudomonas aeruginosa is an opportunistic pathogen that has been associated with mastitis in dairy animals, including goats. Often, the environmental sources of the bacteria are water-related (such as hoses and muddy pastures). Mastitis attributable to P. aeruginosa was identified in 2 goats in a small herd. Efforts were made to identify environmental sources of the pathogen. Multiple samples from the goats’ environment were cultured, including water from the trough, bedding, the hose used to wash udders, and the teat dip and teat dip containers. The bacterium was isolated from the teat dip and the teat dip container. The teat dip consisted of water, liquid soap, and several drops of essential oils (including tea tree, lavender, and peppermint). This case illustrates a potential problem that may arise as a result of the use of unconventional ingredients in teat dips. The use of alternative products by goat producers is likely to increase in the future.

Pseudomonas aeruginosa is an environmental pathogen that can cause severe clinical mastitis with systemic signs as well as subclinical chronic mastitis. ⁷ In severe cases, the affected gland may be necrotic or even gangrenous ² and the milk bloody. The organism is considered an opportunistic pathogen causing disease when the environment is contaminated and when the host defenses are decreased by stress, concomitant disease, or by nutritional imbalances. ⁷ The usual environmental sources are soil and water-related sources (such as hoses used in the milking parlor, damp bedding, and muddy pastures).^2,3 Contaminated teat dip, teat wipes, and dry-cow intramammary treatment tubes have also been implicated in outbreaks of acute and subacute mastitis in dairy cows, sheep, and goats.^2,3,7,9 Free samples of teat wipes given to 11 Irish dairies that bought dry-cow intramammary treatment tubes were contaminated with P. aeruginosa and were considered the cause of mastitis in all of the herds. ³ Contaminated dry-cow intramammary infusion tubes were the cause of P. aeruginosa mastitis following calving in a dairy herd in Australia with the outbreak resulting in the loss of almost one-third of the herd (death or culling). ⁹

Antibiotic treatment is often unsuccessful in curing P. aeruginosa mastitis, and the bacteria may persist in water that has been disinfected. ⁴ Control of Pseudomonas spp. mastitis outbreaks in dairy cow herds and small ruminant flocks may take prolonged effort and strict culling of subclinical and clinical cases. ¹¹ Antibiotic treatment based on an antibiogram was unsuccessful in clearing up P. aeruginosa mastitis in an outbreak in a sheep flock and goat herd in Israel. ¹¹ However, strict culling of clinical and subclinical cases in combination with management practices such as milking clean, dry udders, postdipping teats, providing dry bedding, cleaning the water troughs, and disinfection of milking machines each time they were used was effective in eliminating cases of P. aeruginosa mastitis. ¹¹

In small ruminants, coagulase-negative staphylococci, which are environmental pathogens, cause most cases of mastitis. ¹⁰ Gram-negative pathogens are implicated infrequently in mastitis, and P. aeruginosa causes <10% of the gram-negative cases (and, therefore, a very small proportion of total mastitis cases). ⁸ An outbreak of acute P. aeruginosa mastitis in 33 milking ewes was attributed to contamination of the water used to rinse the milking equipment. ⁸ The animals became systemically ill with fever and decreased appetite as well as having firm, inflamed udders and watery milk with flecks of purulent exudate. Ten of the ewes died within 2–3 days of the onset of clinical signs. The mastitis was unilateral in all cases. ⁸

Milk samples from 2 lactating Nubian dairy goats were submitted to the Utah Veterinary Diagnostic Laboratory (UVDL; Logan, Utah) for culture in April 2014. Both animals had recently kidded and had elevated somatic cell counts (SCC) in 1 mammary gland (udder half) detected 6 days and 1 day postpartum, respectively. The SCC was tested with a goat milk SCC kit. ^a The result for both does was 3,000,000 cells/mL of milk, the maximum value of the test.

Previously, during the fall of 2013, the animals had clinical mastitis with a hard udder and bloody milk with clots in 1 udder half. Milk cultures were not done at this time. Both goats had been treated with the following antibiotics: ceftiofur sodium ^b (2.2 mg/kg intramuscularly [IM], every 24 h, for 3 days), oxytetracycline ^c (4.4 mg/kg IM), and florfenicol ^d (20 mg/kg IM, every 24 h, for 2 days) systemically, and ceftiofur hydrochloride ^e intramammary treatment (1 syringe of intramammary treatment infused into affected mammary gland and repeated in 24 h). In addition to antibiotic treatment, the goats had been treated by the owner with a mastitis homeopathic treatment ^f (1 mL per animal in the drinking water at each milking), garlic tea, and probiotics (the latter 2 being administered orally). The mastitis homeopathic treatment contains Bryonia alba, carbo vegetabilis, echinacea, lachesis, laccaninum, Phytolacca decandra, Ruta graveolens, silica, sulfur, alcohol, and distilled water. According to the owner, both goats recovered from the mastitis after the antibiotics and homeopathic treatments during 2013. The same udder halves were affected in both does in the fall of 2013 and in April 2014.

The goats were part of a herd of 6 lactating does milked by hand twice per day. Animals were housed outdoors but had shelter in case of bad weather and for shade. The shelter was bedded with pine shavings and was rarely used by the goats, according to the owner. Goats in the herd were fed alfalfa pellets, mixed grass–alfalfa hay, and a grain mix consisting of barley, black oil sunflower seeds, rice bran, kelp, nutritional yeast, and molasses with access to a trace mineral block and sodium bicarbonate. Milk from the goats was for family consumption only and was not pasteurized. The teat dip was a compound mixed by the owner before each milking. The teat dip container was filled with ~350 mL of tap water from the kitchen and to that was added 2–3 drops of liquid soap, and 1 drop each of tea tree oil, peppermint oil, lavender oil, and grape seed extract. In addition, the teat dip container was washed in hot water and dishwasher soap in the dishwasher nightly.

Following detection of subclinical mastitis (high SCC) in the 2 goats by the owner in the spring of 2014, aseptically collected milk samples were submitted to the UVDL for culture. The samples were transported to the laboratory by the owner with an icepack and arrived cold. The milk samples were streaked onto 5% sheep blood agar and MacConkey agar plates ^g and incubated at 37°C for ~48 h. The blood agar plates were incubated in 7% CO₂, and the MacConkey plates were incubated aerobically. Both milk samples grew pure cultures of a single colony type of bacteria on both types of media. Preliminary testing of colonies identified lactose-negative, gram-negative bacteria that were oxidase positive and indole negative and had a green tinge on the MacConkey agar. On the blood agar, the colonies were large and gray with a slight blue-to-green tinge, and there was a small zone of beta hemolysis around the colonies. The bacteria were positively identified as P. aeruginosa by a commercially available miniaturized biochemical profile kit. ^h

After receiving the milk culture results, the owner was interested in finding the source of the P. aeruginosa, and the following environmental samples were tested: water from the water trough, the teat dip, feed that was on the ground in front of the feeder, bedding (wood shavings), a swab of the hose used to fill the water trough and wash udders, and a swab of the teat dip container after milking. Before culturing, the water sample that was submitted was concentrated by filtration with a vacuum pump. ⁱ The filter pore size was 0.2 µm. The other samples were cultured on agar as described above except that the feed and bedding were put into brain–heart infusion enrichment broth ^j at a concentration of 1:10 and incubated aerobically at 37°C for ~24 h before being streaked onto the 5% sheep blood agar and MacConkey plates. In addition, milk samples from the 6 milking does were submitted for culture. Milk from the 2 previously positive does was still positive for P. aeruginosa but the bacteria were not detected in milk from the other 4 does. Pseudomonas aeruginosa was isolated from the teat dip and the teat dip container after milking. The other environmental samples were negative for P. aeruginosa. Based on the culture results, the owner culled the 2 positive does and changed to a commercial teat dip. There were no further reports of mastitis in the flock as of April 2016.

In this case, the combination of water, oils, and soap that constituted the teat dip supported the growth of P. aeruginosa and was not germicidal, as the owner had expected. The impact of the ineffective teat dip was significant (mastitis and eventual culling of 2 animals). It is difficult to say if 1 individual component of the teat dip was contaminated with the bacteria because, unfortunately, the essential oils and soap were not available for culture after initial results were given to the owner and she immediately switched to a commercial teat dip. The same components had been used as a teat dip during the clinical mastitis outbreak in the fall of 2013, but no testing was performed at that time. In addition, no milk cultures were performed before the mastitis was treated in 2013. Therefore, it is unclear whether the clinical mastitis reported in the fall of 2013 was caused by P. aeruginosa or by another pathogen. If it was P. aeruginosa, it is possible that the antibiotic treatment did not fully clear the bacteria from the mammary gland of the 2 does and that the more recent subclinical mastitis that was detected in April 2014 was, in fact, the result of persistent infection with P. aeruginosa. Mastitis caused by P. aeruginosa is indeed notoriously difficult to treat effectively with antibiotics. ¹¹ If this was the case, the infected does may have shed P. aeruginosa into the environment, including the teat dip when milked. This seems unlikely because the bacterium was not detected in any of the other environmental samples tested or in milk from the other 4 does. If P. aeruginosa was being shed from the 2 positive does it would have contaminated some of the other samples tested and/or caused mastitis in 1 or more of the other animals. It is more likely that bacteria in 1 or more components of the teat dip caused the April 2014 mastitis in the 2 goats. In addition, it may be surmised that previous damage to the mammary gland of these 2 animals by clinical mastitis in 2013 predisposed them to developing subclinical mastitis when exposed to P. aeruginosa in the teat dip. In contrast, the other 4 does in the milking herd, with no history of detectable mastitis were not as susceptible to infection. However, without culture results from the fall 2013 mastitis episode, it cannot be determined conclusively that the subclinical P. aeruginosa mastitis in the 2 does was a new infection. It is also possible that the soap component of the teat dip was contaminated with P. aeruginosa and not actually the essential oils. The soap was not available for culture, as stated above. Regardless, the noncommercial teat dip when considered as a whole was not an effective germicide.

Sometimes, use of alternative medicine products is driven by a scarcity of approved products on the market. However, it may also be because many commercially available iodine- and chlorine-based teat dips are not suitable for organic farming. ¹ Because of the importance of goats in agriculture worldwide ⁶ and the increasing numbers of dairy and other types of goats in the United States, ⁵ veterinary knowledge about diseases, nutrition, and management of goats is essential. The number and popularity of goats and their products have varied since their introduction into the United States by European settlers, but the trend has definitely been upward in the past few years. Annual sales of sheep and goat products increased ~30% between 2002 and 2007, and the number of goats increased by 24% in the same time period (Overview of the United States sheep and goat industry. National Agricultural Statistics Service website, United States Department of Agriculture. Available at: www.nass.usda.gov). Goats are valued in the United States for the same attributes as they are elsewhere (hardiness, compact size, meat, milk, fiber, and are able to be handled by children). As well, the goat show circuit and the use of goats as pack animals for hiking are active components of the goat industry in the United States (The goat industry: structure, concentration, demand and growth. Animal and Plant Health Inspection Service, United States Department of Agriculture. Available at: https://goo.gl/NmF2DX). Veterinary diagnosticians will increasingly encounter diagnostic samples from producers using organic or other unconventional farming techniques. This is particularly relevant with the increase in people raising goats for “niche” markets (such as the gourmet cheese market) and using alternative products in management such as essential oils as in the case described here.