Resumen de Antimicrobial resistance: Multidrug resistance in enterotoxigenic K99 E coli infection in lambs
Emily Gascoigne, Michael Millar
WE would like to report a neonatal lamb scour investigation in which multi-antibiotic resistant enterotoxigenic Escherichia coli with K99 antigen (ETEC K99) isolates were detected in a commercial sheep flock, to illustrate to practitioners that it cannot be assumed that commonly used antibiotic preparations will be effective. The Veterinary Medicines Directorate (VMD) collates laboratory submissions (culture and sensitivity) from the APHA and has previously found that multiresistant E coli isolates were increasing, and accounted for up to 54 per cent of isolates made over the period 2011 to 2013; spectinomycin resistance was observed in 39 to 59 per cent of isolates (VMD 2013).
There are other reports of high prevalences of resistance in neonatal lambs; for example, up to 76 per cent of E coli isolates from lambs in Spain showed resistance to tetracyclines, 50 per cent showed resistance to ampicillin and 74 per cent to streptomycin (Blanco and others 1996). Surveillance in other species (domestic pets, pigs, bovids) has also identified multidrug-resistant strains of E coli (Lanz and others 2003).
In the present case, a flock of 2500 ewes (lambing single and triplet lambs indoors to facilitate adoptions) was reported to have had numerous cases of neonatal scour at the end of lambing in 2013. All indoor-born lambs were routinely treated with a spectinomycin-based product within hours of birth.
Lambs presented with scour, lethargy and anorexia within 24 to 36 hours of birth. Despite electrolyte supplementation, additional colostrum feeds and nursing, increased mortality was reported. Amoxicillin clavulanate was administered to lambs with clinical signs (8.75 mg/kg intramuscularly for three days) in addition to supportive care and improved hygiene (including udder washing in the ewes post-lambing and before colostrum feeding). There was no significant improvement noted in incidence of disease or mortality.
In 2014, spectinomycin prophylaxis continued and there were no reports of clinical disease until more than 600 of the 2500 ewes had lambed. Clinical disease reappeared and lambs were treated with long-acting amoxicillin following the onset of clinical signs.
Given that the link between hypogammaglobulinaemia, neonatal scours and lamb survival has been well documented (Vihan 1988, Hodgson and others 1999), six neonatal lambs with clinical disease were blood sampled for zinc sulphate turbidity (ZST) testing, with five of six exceeding the lower reference range (>20 ZST units) demonstrating adequate uptake of colostral antibodies. Faecal samples were submitted to the then AHVLA laboratory at Langford for culture and sensitivity testing. Enterotoxigenic E coli, positive for the K99 antigen (ETEC K99), were detected in three of five samples with E coli also isolated from the remaining two samples. Sensitivity testing was undertaken on two E coli isolates, which proved resistant to spectinomycin (25 µg), amoxicillin/clavulanic acid (30 µg), ampicillin (10 µg) and tetracycline (10 µg). The isolates were susceptible to apramycin (15 µg), neomycin (10 µg), trimethoprim/sulphamethoxazole (25 µg) and enrofloxacin (5 µg).
Consequently, the oral prophylaxis strategy was changed to include neomycin (in combination with streptomycin) and there was a noted reduction in clinical cases. Long-term antibiotic reduction strategies have been implemented on farm to reduce antibiotic dependency in accordance with industry recommendations with an emphasis on husbandry, flock health, appropriate and targeted usage, and monitoring (BVA 2009, RUMA 2013). There is also reinforced emphasis on colostrum and hygiene practices, removal of prophylactic usage and protocols for antibiotic use if onset of clinical signs is seen. Ongoing sensitivity monitoring of the resistance profile of lamb scour bacteria and usage reduction strategies have been introduced.
It should be noted that there are currently no oral antibiotic preparations apart from Spectam (Ceva Animal Health) and Oroject (Zoetis UK) licensed in the UK for prophylactic use in neonatal lambs to prevent and treat neonatal scour associated with E coli infection.
This farm situation illustrates that many E coli isolates may have multidrug resistance patterns and that it cannot be assumed that a drug will be effective because it has worked in previous years. It also highlights the importance of culture and sensitivity testing when veterinary practitioners are implementing both prophylactic and treatment antibiosis protocols in neonatal lambs.
