Zoonoses: Extended-Spectrum Beta-Lactamases (ESBL) in Escherichia coli associated with animals - Q&A
Q1. What is an ESBL?
Q2.What is antimicrobial resistance?
Q3. Have ESBLs of current concern in animals in the UK arisen
from the use of antimicrobials in veterinary medicine?
Q4. Is antimicrobial resistance a threat to public health?
Q5. When and where have ESBL E. coli in animals
been found in the UK?
Q6. Have ESBL E. coli been identified in animals
other than cattle in the UK?
Q7. What is being done about the problem?
Q8. Do ESBLs pose a risk to public health?
Q9. Are ESBLs found in humans in England and Wales?
Q10. Have these particular ESBL-producing strains of E.
coli been found in humans?
Q11. How widespread are ESBL-carrying E. coli in
food-producing animals in England and Wales?
Q12. Have ESBLs been found in other bacteria in animals
in England and Wales?
Q1. What is an ESBL?
Extended-spectrum beta-lactamases (ESBLs), such as CTX-M enzymes, are proteins that confer upon their host organism – in this particular case, E. coli – the ability to resist a wide range of therapeutic beta-lactam antimicrobials (i.e. resistance to penicillins and cephalosporins).
Q2. What is antimicrobial resistance?
It is the ability of a microorganism to withstand an antimicrobial. It is widely agreed that resistant strains of bacteria found in animals have largely resulted from the general use of antimicrobial treatments in veterinary medicine and agriculture. This is an inherent risk associated with the use of antimicrobials in any species.
Q3. Have ESBLs of current concern in animals in the UK arisen from the use of antimicrobials in veterinary medicine?
The origin(s) of the ESBLs found in livestock is not known and establishing this information is one of the objectives of the ongoing investigations in this area.
Q4. Is antimicrobial resistance a threat to public health?
Yes, which is why we support a policy of responsible prescribing to maintain the effectiveness of antimicrobial agents in the treatment and prevention of microbial infections in man and animals. The use of antimicrobials in human medicine is thought to be the main factor contributing to the development of resistance in microorganisms associated with humans. However, there is international concern regarding both the potential spread of resistant bacteria and the potential transfer of resistance genes between bacteria from animals and humans.
Q5. When and where have ESBL E. coli in animals been found in the UK?
The first recorded case of E. coli containing an ESBL CTX-M enzyme isolated in food production animals on a UK farm occurred in autumn 2004. It was recovered from diarrhoeic calves that were being reared on a dairy farm in Wales. The gene encoding CTX-M-14 was identified in the isolates.
The second case in UK livestock to date was discovered in the south of England in July 2006 and also involved the death of several calves. The situation however differed to that of the first case as these had been part of a group of calves, sourced from 4 different premises and housed together at a veterinary referral centre, rather than a working farm. This E. coli isolate was found to possess a gene encoding CTX-M-15, a related but different ESBL to CTX-M-14, but still conferring similar resistance.
Since July 2006, a further ten different cattle farms have been confirmed that are positive for E. coli carrying ESBLs of the CTX-M type, although the exact gene type has not been determined yet, in all cases. Closer examination of these cases and any potential epidemiological links is currently underway.
Q6. Have ESBL E. coli been identified in animals other than cattle in the UK?
Yes. Recent investigations have identified one premises where ESBL producing E. coli have been isolated from samples taken from sheep and horses.
Strains of E. coli are naturally present in the intestine of most animals as part of the normal commensal flora (i.e. a microorganism that normally lives in close contact with a human or animal without causing any harm. This includes many of the bacteria normally present on a person's or animal's skin or intestine), and E. coli does not cause a notifiable disease in livestock.
Q7. What is being done about the problem?
Extensive investigations into the case on the Welsh farm have been carried out by the Veterinary Laboratories Agency. Hygiene management changes and the restriction of antimicrobial usage were instigated on the farm in an attempt limit selective pressure. To date, it has been found that ESBL E. coli have increased in prevalence in cattle on the farm and that the ESBL mediated resistance has been identified in a number of different strains of E. coli, indicating spread of resistance between organisms. Resistance has also been identified in E. coli on farms to which cattle have been moved for rearing or fattening.
The finding of Salmonella Typhimurium DT 104 in calves on the premises led to an investigation to find out if there was transference of the CTX-M-14 enzyme from the E coli into the Salmonellae present on the farm. There was no evidence of this at the most recent visit in October 2006.
Investigations are also currently underway on the other farms that have been identified. This involves the collection of samples from animals and the environment on the farms and microbiological analysis and gene sequencing, carried out to determine the CTX-M enzymes present, the extent of their spread within the population and the source of the resistant E. coli isolate.
There is a monitoring scheme undertaken by the VLA, which has been rolled out across the VLA’s Regional Laboratories in 2006, to screen for ESBLs in all E. coli isolates detected in clinical material submitted to regional laboratories. This will allow improved surveillance for ESBLs in food producing animals. The development of a protocol specifically for the investigation of such cases detected on UK farms is currently being prepared by the VLA lead on antimicrobial resistance.
Q8. Do ESBLs pose a risk to public health?
In view of the gaps in knowledge we do not know what risk ESBLs in livestock pose to public health The current evidence is that the majority of strains and serotypes affecting humans are different from those identified in animals. It is hoped that the current investigations into the newly identified infected farms will enable us to learn more about this condition, the organism involved and about possible risks to public health.
Q9. Are ESBLs found in humans in England and Wales?
ESBL-producing E. coli have been a significant cause of human disease in England and Wales over the last two years. The presence of ESBL-producing E. coli can on occasion seriously affect treatment, for example, in some urinary tract infections.
Q10. Have these particular ESBL-producing strains of E. coli been found in humans?
The CTX-M enzyme types identified in E. coli from animals in the UK thus far have all been detected in E. coli from humans in the UK or internationally. With one exception, the serotypes of the E. coli strains containing ESBLs, identified in animals, are not the same as those of E. coli known to be commonly associated with human disease.
In February 2007, Defra became aware that a cattle premises in England had been found to contain ESBL E. coli of the O25 serotype. This serotype is associated with urinary tract infections in humans, although other tests have shown that the particular strain of E. coli involved in this case in cattle is not known to be commonly associated with human disease.
Q11. How widespread are ESBL-carrying E. coli in food-producing animals in England and Wales?
At the moment, this is not known. It is hoped that the current investigations will enable us to learn more about this condition. A survey of food borne pathogens in abattoirs, conducted in 2003, examined approximately 3000 strains of E. coli from cattle, sheep and pigs and no ESBLs were detected.
There is a monitoring scheme undertaken by the VLA, which has been rolled out across the VLA’s Regional Laboratories in England and Wales in 2006, to screen for ESBLs in all E. coli isolates detected in clinical material submitted to regional laboratories, this scheme has already identified a number of E. coli strains containing ESBLs. This scheme has improved surveillance for ESBLs in livestock.
Q12. Have ESBLs been found in other bacteria in animals in England and Wales?
ESBLs have not so far been detected in Salmonella spp. recovered from animals originating in England and Wales. A Salmonella Branderup isolate from a turkey derived from an imported egg was discovered to be producing an AmpC enzyme (a type of ESBL). The strain involved was indistinguishable from a Canadian Salmonella Branderup isolate, also recovered from turkeys. The results of VLA surveillance for third-generation cephalosporin resistance in Salmonella spp. in Great Britain, during 2005, are presented in table 1.
| Species | Year | No examined | ESBL positive | AmpC positive |
| Cattle | 2005 | 499 | 0 | 0 |
| Pig | 2005 | 398 | 0 | 0 |
| Poultry | 2005 | 778 | 0 | 0 |
Table 1. Results of screening Salmonella spp. isolates for resistance to third-generation cephalosporins during 2005
Page last modified:
14 March, 2007