Following the massive reduction in the use of antibiotics in the Netherlands (>50%) by the veterinarians over the last couple of years, they are starting to see some benefits regarding a drop in antimicrobial resistance associated with the human ‘critical use’ antimicrobials.
In comparison with 2009 (MARAN 2011), a recent report with data for 2012 (MARAN 2013) has shown a steady decrease in resistance in several species of animal, including pigs, to the ‘critical use’ antimicrobials used in human medicine. Samples of E. coli were taken from animals at slaughter for monitoring purposes.
This must be of great relief to the Dutch Authorities, to see the incidence of cephalosporin resistance is falling in chickens (-68%) already, as earlier work on samples taken in 2009 (Overdevest and others 2011) had showed that there was potentially a major problem with the transmission of extended spectrum beta-lactamases (ESBLs) containing bacteria, selected by the use of 3rd generation cephalosporins, especially in chickens and transmitted via chicken meat. Pig samples have fallen to zero, which is also very encouraging.
Using selective media, to facilitate the identity of resistant bacteria they were looking specifically for bacteria (mainly E. coli), which produced ESBLs. Samples were taken from broiler meat, pork and beef, as well as hospital patients and from blood samples from patients with E. coli bacteraemias (patients with blood infections). The genes for ESBLs were identified and confirmed and then compared (see Table 2 and Figure1).
The number of samples from chicken meat showed a high level of contamination with E. coli expressing ESBL resistance, thought to be associated with the unlicensed use of ceftiofur given by injection in eggs and day old chicks. This practice was stopped in the EU last year, as the European Medicines Agency (EMS) responded quickly and made this use contra-indicated. Other countries have also taken steps.
Contamination of chicken meat was very high with E. coli carrying ESBLs. Strong concern has been expressed by the potential risk of spreading the infection and the resistance genes to human beings from eating chicken meat in spite of cooking and the body’s natural defences. This, from an epidemiological perspective is very interesting, as the risk can be quantified at 1569:1 chance, assuming chicken is consumed twice a week/year and pork would be as low as 69559:1, on the same basis. Although the risk appears to be quite low, as chicken meat is eaten on a regular basis throughout the year, there is a definite risk of exposure. Chicken meat was shown to carry a high prevalence of CTXM-1, TEM-52 and SHV-12 ESBLs. CTXM-1 and TEM-52 genes were the major ones found in patients. These were the same whether they had been in for <2 days or >2days. CTX-14 and CTX 15 are the main human ESBLs found in hospitals etc and CTX-14 was much higher in blood infections in comparison. Of concern though, CTX-1 was also found in bacteraemias. Patients that were in hospital for >2 days had a 4 times higher CTX-15 prevalence than patients in for <2 days, suggesting that they had picked up the infection and resistance in hospital.
In spite of a recent assessment, where it was suggested that 56% of 3rd generation cephalosporin resistance was derived from poultry (Collignon and others, 2013) based on the Overdevest and others (2011) work, this may have fallen by 68% already in the Netherlands (MARAN 2013). It would appear that the authorities in a number of countries (EU & USA) have already responded to the challenge and as the Dutch have shown that a more responsible use of antibiotics is having a significant, beneficial effect on antimicrobial resistance in veterinary medicine, although this was not the case in human medicine (NETHMAP 2013) where resistance issues were reportedly still growing.