A surveillance report today from European health and food safety agencies indicates that antibiotic resistance in zoonotic bacteria from humans, food, and animals on the continent remains at high levels, with notable levels of multidrug resistance in two common causes of foodborne illness in humans.
The report is based on 2016 data provided by 28 EU member states and jointly analyzed by the European Centre for Disease Prevention and Control (ECDC) and the European Food Safety Authority (EFSA). It addresses resistance in bacterial isolates of zoonotic Salmonella and Campylobacter from humans, food, and poultry, along with resistance levels and mechanisms in indicator Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) in animals and food.
Zoonotic bacteria are organisms that are transmissible between animals and humans, either through direct exposure or through consumption of contaminated meat. The ECDC and EFSA have been collecting and analyzing data submitted by EU countries on these bacteria to monitor for levels of antibiotic resistance since 2013.
Worrisome levels of multidrug resistance
Among the key findings of the report is that more than 1 in 4 (26.5%) of Salmonella isolates from human cases of Salmonellosis were multidrug-resistant, and high proportions of isolates were resistant to sulfonamides (34.6%), ampicillin (29.5%), and tetracyclines (29.2%). Among the most worrisome Salmonella serovars identified was S Kentucky; more than three-quarters of S Kentucky isolates (76.3%) were multidrug-resistant, and nearly half were resistant to at least five antibiotic classes. More than 85% of S Kentucky isolates were highly resistant to ciprofloxacin, and 19.8% were found to harbor extended-spectrum beta-lactamase (ESBL) enzymes.
About 40% of isolates from two other common Salmonella serovars, S Infantis and S Typhimurium, were multidrug-resistant, with one S Typhimurium isolate reported to be resistant to 8 of 9 tested antibiotics.
High levels of resistance were also reported in Campylobacter isolates from humans. Among isolates of C jejuni, the most common species identified in 2016, 54.6% were resistant to ciprofloxacin, with several countries (Portugal, Spain, Italy, Cyprus, Estonia, and Lithuania) reporting ciprofloxacin resistance levels of between 84% and 95%. Levels of resistance to tetracyclines in C jejuni were also high (42.8%). Among Campylobacter coli isolates, 63.8% were resistant to ciprofloxacin and 64.8% were resistant to tetracyclines. Resistance to erythromycin was higher in C coli isolates (11%) than in C jejuni isolates (2.1%).
While combined clinical and microbiological resistance to both ciprofloxacin and erythromycin—which are critically important for treatment of Campylobacteriosis—was low overall (0.6% in C jejuni and 8% in C coli), resistance to this combination was found in more than a third of all tested human Campylobacter isolates in three member states.
Campylobacter and Salmonella are the two most common foodborne zoonotic bacteria in Europe, with Campylobacter being the most-reported cause of food poisoning. Most infections occur through eating food contaminated with the bacteria, and abdominal pain and diarrhea are the main symptoms. But infections with drug-resistant Salmonella and Campylobacter can cause more severe illness.
"We are concerned to see that Salmonella and Campylobacter bacteria in humans show high levels of antimicrobial resistance," Mike Catchpole, PhD, the ECDC's chief scientist, said in an ECDC press release. "The fact that we keep detecting multidrug-resistant bacteria means that the situation in not improving. We need to investigate the origins and prevent the spread of highly resistant strains, such as ESBL-producing Salmonella Kentucky."
High levels of resistance found in poultry
Among the Salmonella isolates from poultry meat (broilers and turkeys), resistance to tetracycline, ampicillin, and sulfamethoxazole ranged from moderate to extremely high, with the highest levels of resistance to these drugs found among S Infantis isolates from broiler meat. Multidrug resistance was reported in 50.3% of Salmonella isolates from broilers and 23.7% from turkey meat. In Salmonella isolates from poultry populations, most member states reported moderate to high or extremely high resistance to tetracyclines and sulfonamides, and similar or slightly lower levels of ampicillin resistance.
Observed levels of resistance among C jejuni and C coli isolates from broilers, turkeys, and their meat to ciprofloxacin, nalidixic acid, and tetracylines were generally high (ranging from 50% to nearly 90%), but the prevalence of multidrug-resistance was low (around 1%).
Analysis of commensal E coli isolates from broilers, turkeys, and their meat found high levels of resistance to ampicillin, tetracyclines, ciprofloxacin, and sulfamethoxazole. The level of multidrug-resistance was also high (50.2% in broilers and 48.7% in turkeys), with considerable variation between the reporting member states.
Specific monitoring of commensal E coli isolates in poultry and poultry meat for production of ESBL, AmpC beta-lactamase, and carbapenemase enzymes, conducted for the first time in 2016, showed that the prevalence of ESBL-producing E coli isolates was low overall also varied widely among member states. Of note was the detection of 14 carbapenemase-producing E coli isolates from Romania and Cyprus.
Zoonotic bacteria carrying ESBL and carbapenemase enzymes are considered a public health concern because they are resistant to a wide spectrum of antibiotics, including penicillin derivatives, cephalosporins, and carbapenems—a class of last-resort antibiotics. Monitoring commensal E coli bacteria for these resistance mechanisms is important for both human and animal health because they can potentially be transferred to other types of bacteria that can spread among people and animal herds.
Also of note, two linezolid-resistant livestock-associated MRSA isolates were identified from the pig production sector in Belgium. The isolates were found to harbor a transferable linezolid resistance gene. Since linezolid is one of the last remaining treatments for highly resistant strains of MRSA, this finding could have important implications for workers on pig farms, who are the most at-risk for LA-MRSA infections.
"The detection of resistance to carbapenems in poultry and to linezolid in methicillin-resistant Staphylococcus aureus in pigs is alarming because these antibiotics are used in humans to treat serious infections," said Marta Hugas, PhD, EFSA chief scientist. "It is important that risk-managers follow-up on these findings."
Feb 27 ECDC press release