Anthony E. van den Bogaard

Epidemiology of resistance to antibiotics links between animals and humans.

An inevitable side effect of the use of antibiotics is the emergence and dissemination of resistant bacteria. Most retrospective and prospective studies show that after the introduction of an antibiotic not only the level of resistance of pathogenic bacteria, but also of commensal bacteria increases. Commensal bacteria constitute a reservior of resistance genes for (potentially) pathogenic bacteria. Their level of resistance is considered to be a good indicator for selection pressure by antibiotic use and for resistance problems to be expected in pathogens. Resistant commensal bacteria of food animals might contaminate, like zoonotic bacteria, meat (products) and so reach the intestinal tract of humans. Monitoring the prevalence of resistance in indicator bacteria such as faecal Escherichia coli and enterococci in different populations, animals, patients and healthy humans, makes it feasible to compare the prevalence of resistance and to detect transfer of resistant bacteria or resistance genes from animals to humans and vice versa. Only in countries that use or used avoparcin (a glycopeptide antibiotic, like vancomycin) as antimicrobial growth promoter (AMGP), is vancomycin resistance common in intestinal enterococci, not only in exposed animals, but also in the human population outside hospitals. Resistance genes against antibiotics, that are or have only been used in animals, i.e. nourseothricin, apramycin etc. were found soon after their introduction, not only in animal bacteria but also in the commensal flora of humans, in zoonotic pathogens like salmonellae, but also in strictly human pathogens, like shigellae. This makes it clear that not only clonal spread of resistant strains occurs, but also transfer of resistance genes between human and animal bacteria. Moreover, since the EU ban of avoparcin, a significant decrease has been observed in several European countries in the prevalence of vancomycin resistant enterococci in meat (products), in faecal samples of food animals and healthy humans, which underlines the role of antimicrobial usage in food animals in the selection of bacterial resistance and the transport of these resistances via the food chain to humans. To safeguard public health, the selection and dissemination of resistant bacteria from animals should be controlled. This can only be achieved by reducing the amounts of antibiotics used in animals. Discontinuing the practice of routinely adding AMGP to animal feeds would reduce the amounts of antibiotics used for animals in the EU by a minimum of 30% and in some member states even by 50%.

Antibiotic usage in animals: impact on bacterial resistance and public health.

Antibiotic use whether for therapy or prevention of bacterial diseases, or as performance enhancers will result in antibiotic resistant micro-organisms, not only among pathogens but also among bacteria of the endogenous microflora of animals. The extent to which antibiotic use in animals will contribute to the antibiotic resistance in humans is still under much debate. In addition to the veterinary use of antibiotics, the use of these agents as antimicrobial growth promoters (AGP) greatly influences the prevalence of resistance in animal bacteria and a poses risk factor for the emergence of antibiotic resistance in human pathogens. Antibiotic resistant bacteria such as Escherichia coli, Salmonella spp., Campylobacter spp. and enterococci from animals can colonise or infect the human population via contact (occupational exposure) or via the food chain. Moreover, resistance genes can be transferred from bacteria of animals to human pathogens in the intestinal flora of humans.In humans, the control of resistance is based on hygienic measures: prevention of cross contamination and a decrease in the usage of antibiotics. In food animals housed closely together, hygienic measures, such as prevention of oral-faecal contact, are not feasible. Therefore, diminishing the need for antibiotics is the only possible way of controlling resistance in large groups of animals. This can be achieved by improvement of animal husbandry systems, feed composition and eradication of or vaccination against infectious diseases. Moreover, abolishing the use of antibiotics as feed additives for growth promotion in animals bred as a food source for humans would decrease the use of antibiotics in animals on a worldwide scale by nearly 50%. This would not only diminish the public health risk of dissemination of resistant bacteria or resistant genes from animals to humans, but would also be of major importance in maintaining the efficacy of antibiotics in veterinary medicine.

Host Specificity of Vancomycin-Resistant Enterococcus faecium

Amplified-fragment length polymorphism (AFLP) analysis was used to investigate the genetic relationships among 255 vancomycin-resistant Enterococcus faecium (VREF) strains isolated from hospitalized patients, nonhospitalized persons, and various animal sources. Four major AFLP genogroups (A-D) were discriminated. The strains of each taxon shared >/=65% of the restriction fragments. Most isolates recovered from nonhospitalized persons (75%) were grouped together with all pig isolates in genogroup A. Most isolates from hospitalized patients (84%), a subset of veal calf isolates (25%), and all isolates from cats and dogs clustered in genogroup C. Most isolates from chickens (97%) and turkeys (86%) were grouped in genogroup B, whereas most veal calf isolates (70%) clustered in genogroup D. Therefore, VREF strains are predominantly host-specific, and strains isolated from hospitalized patients are genetically different from the prevailing VREF strains present in the fecal flora of nonhospitalized persons.

Vancomycin-Resistant Enterococci in Turkeys and Farmers

To the Editor: In enterococci vancomycin resistance of the VanA phenotype is usually due to the presence of seven genes organized in a cluster on a transposon (Tn1546).1,2 The recent emergence of v...

Different Levels of Genetic Homogeneity in Vancomycin-Resistant and -Susceptible Enterococcus faecium Isolates from Different Human and Animal Sources Analyzed by Amplified-Fragment Length Polymorphism

ABSTRACT The genetic relationship among fecal vancomycin-resistant Enterococcus faecium (VREF) and vancomycin-susceptible E. faecium (VSEF) isolates (n = 178) from the same populations of pigs, human healthy volunteers, and hospitalized patients (from The Netherlands) and chickens (from The Netherlands and Greece) was studied by amplified-fragment length polymorphism (AFLP). The majority of VREF isolates from pigs, healthy volunteers, and hospitalized patients grouped together (genetic similarity, ≥65%). In a previous AFLP study by our group the VREF isolates from hospitalized patients grouped separately, most likely because these were clinical and not fecal isolates as in the present study. Furthermore, VSEF isolates from humans and pigs were found much more genetically diverse than VREF isolates, whereas VREF and VSEF isolates from chickens clustered together in a separate genogroup (genetic similarity, ≥65%), a pattern clearly distinct from the patterns for human and pig isolates. The present study suggests that pigs are a more important source of VREF for humans than chickens and that human- and pig-derived VSEF isolates seem much more heterogeneous than VREF isolates.

Carriage of antibiotic-resistant Escherichia coli by healthy volunteers during a 15-week period

Escherichia coli strains (n=678 and n=670) isolated from faecal samples from 90 and 93 healthy volunteers of two cities, Weert and Roermond respectively, were analysed for their susceptibility to 12 antimicrobial agents during a 15-week period. Significant differences between both cities in the distribution of the MIC values were observed for apramycin, chloramphenicol, kanamycin, neomycin, nitrofurantoin, sulfamethoxazole and trimethoprim. For Weert (n=678) the antibiotic resistance percentages varied from 0.4% for nalidixic acid to 26.7% for sulfamethoxazole. For Roermond (n=670) the figures varied from 0.6% for nitrofurantoin to 37.5% for sulfamethoxazole. Resistance to amoxicillin/clavulanate was not found in either city. The most frequent pattern was resistance to sulfamethoxazole only, followed by resistance to oxytetracycline, streptomycin and sulfamethoxazole. In each individual there was only a small variation in resistance patterns of the isolates, i. e. the majority had one (n=51) or two (n=63) patterns with a maximum of five during the 15-week period. A fully susceptible pattern was found in the strains from 38 individuals. Stämme vonEscherichia coli, (n=678 und n=670), die aus Stuhlproben von jeweils 90 und 93 gesunden Freiwilligen aus zwei Städten, Weert und Roermond, gewonnen wurden, wurden auf ihre Empfindlichkeit gegenüber 12 antimikrobiellen Substanzen geprüft. Die Untersuchung lief über 15 Wochen. Für Apramycin, Chloramphenicol, Kanamycin, Neomycin, Nitrofurantoin, Sulfamethoxazol und Trimethoprim fanden sich zwischen den beiden Städten signifikante Unterschiede in den MHK-Werten. Für Weert (n=678) fanden sich Resistenzraten, die von 0,4% bei Nalidixinsäure bis 26,7% für Sulfamethoxazol reichten. In Roermond (n=670) variierten die Resistenzraten von 0,6% für Nitrofurantoin bis 37,5% für Sulfamethoxazol. In keiner der beiden Städte fand sich Resistenz gegenüber Amoxicillin-Clavulansäure. Als häufigstes Muster fand sich Resistenz gegen Sulfamethoxazol allein, es folgten Resistenz gegen Oxytetracyklin, Streptomycin und Sulfamethoxazol. Die intraindividuellen Resistenzmuster der Isolate variierten nur sehr wenig, das heißt, die meisten hatten Resistenz gegen ein (n=51) oder zwei (n=63) Antibiotika, maximal fünf während der 15 Wochen. Bei 38 Personen zeigten alle Stämme volle Empfindlichkeit gegen die Testsubstanzen.SummaryEscherichia coli strains (n=678 and n=670) isolated from faecal samples from 90 and 93 healthy volunteers of two cities, Weert and Roermond respectively, were analysed for their susceptibility to 12 antimicrobial agents during a 15-week period. Significant differences between both cities in the distribution of the MIC values were observed for apramycin, chloramphenicol, kanamycin, neomycin, nitrofurantoin, sulfamethoxazole and trimethoprim. For Weert (n=678) the antibiotic resistance percentages varied from 0.4% for nalidixic acid to 26.7% for sulfamethoxazole. For Roermond (n=670) the figures varied from 0.6% for nitrofurantoin to 37.5% for sulfamethoxazole. Resistance to amoxicillin/clavulanate was not found in either city. The most frequent pattern was resistance to sulfamethoxazole only, followed by resistance to oxytetracycline, streptomycin and sulfamethoxazole. In each individual there was only a small variation in resistance patterns of the isolates, i. e. the majority had one (n=51) or two (n=63) patterns with a maximum of five during the 15-week period. A fully susceptible pattern was found in the strains from 38 individuals.ZusammenfassungStämme vonEscherichia coli, (n=678 und n=670), die aus Stuhlproben von jeweils 90 und 93 gesunden Freiwilligen aus zwei Städten, Weert und Roermond, gewonnen wurden, wurden auf ihre Empfindlichkeit gegenüber 12 antimikrobiellen Substanzen geprüft. Die Untersuchung lief über 15 Wochen. Für Apramycin, Chloramphenicol, Kanamycin, Neomycin, Nitrofurantoin, Sulfamethoxazol und Trimethoprim fanden sich zwischen den beiden Städten signifikante Unterschiede in den MHK-Werten. Für Weert (n=678) fanden sich Resistenzraten, die von 0,4% bei Nalidixinsäure bis 26,7% für Sulfamethoxazol reichten. In Roermond (n=670) variierten die Resistenzraten von 0,6% für Nitrofurantoin bis 37,5% für Sulfamethoxazol. In keiner der beiden Städte fand sich Resistenz gegenüber Amoxicillin-Clavulansäure. Als häufigstes Muster fand sich Resistenz gegen Sulfamethoxazol allein, es folgten Resistenz gegen Oxytetracyklin, Streptomycin und Sulfamethoxazol. Die intraindividuellen Resistenzmuster der Isolate variierten nur sehr wenig, das heißt, die meisten hatten Resistenz gegen ein (n=51) oder zwei (n=63) Antibiotika, maximal fünf während der 15 Wochen. Bei 38 Personen zeigten alle Stämme volle Empfindlichkeit gegen die Testsubstanzen.

satG, Conferring Resistance to Streptogramin A, Is Widely Distributed in Enterococcus faecium Strains but Not in Staphylococci

ABSTRACT A gene almost identical to satG was isolated from anEnterococcus faecium strain. This gene was transferred to aStaphylococcus aureus recipient strain where it conferred resistance to streptogramin A. satG was found to be widely distributed among E. faecium strains but not detected among staphylococci.

Persistent rat cytomegalovirus (RCMV) infection of the salivary glands contributes to the anti-RCMV humoral immune response

The salivary glands are the major sites of persistent replication of rat cytomegalovirus (RCMV). At several months post infection (pi), infectious RCMV is usually still produced in the salivary glands but not in any other organ or tissue of the rat. To investigate whether the persistence of RCMV in the salivary glands is crucial to the pathogenesis of viral infection, we monitored the progression of RCMV-induced disease in rats from which the salivary glands had been surgically removed (desalivated) as well as in sham-operated rats, both after a lethal and sublethal challenge with RCMV. Desalivation did not have a significant effect on either RCMV-induced morbidity or mortality. As expected, at 1 year pi, relatively high levels of infectious virus were detected in the salivary glands of sham-operated rats, whereas neither infectious virus nor RCMV DNA could be detected in liver, spleen and lungs of these animals. Infectious virus and viral DNA were also undetectable in organs from desalivated animals at 1 year pi. Surprisingly, a difference was found between desalivated and sham-operated rats in the titers of anti-RCMV IgG antibodies, which were significantly higher in sham-operated rats than in desalivated animals at 183, 295 and 365 days pi. This finding indicates that the persistence of RCMV in the salivary glands may contribute significantly to the anti-RCMV humoral immunity of infected rats.