Reservoir Of Antimicrobial Resistance Research Articles

Less frequent Salmonella serovars as a reservoir of antimicrobial resistance

Sir, Salmonella enterica serovars Enteritidis and Typhimurium are the most frequent Salmonella serovars isolated from humans. However, a significant proportion of human Salmonella isolates belong to other serovars, for which antimicrobial susceptibility patterns are rarely reported. In Denmark, the frequency of isolation of these less frequent Salmonella serovars from human clinical samples has increased in recent years. They represented 30% of all human Salmonella isolates, which corresponded to an incidence of 10.5 per 100 000 inhabitants in 2005. From 2003 to 2005, 530 isolates belonging to these Salmonella serovars were tested for their antimicrobial susceptibility by broth microdilution (Sensititre; Trek Diagnostic Systems Ltd, East Grinstead, UK) at the Statens Serum Institut. These included 106 Salmonella Virchow, 95 Salmonella Newport, 91 Salmonella Stanley, 80 Salmonella Dublin, 53 Salmonella Hadar, 38 Salmonella Saintpaul, 32 Salmonella Derby, 20 Salmonella Uganda and 15 Salmonella Anatum obtained from sporadic clinical infections, isolated at the 16 clinical microbiology laboratories in Denmark. The MICs for these 530 human clinical Salmonella isolates were determined for ampicillin (1–32 mg/L), cefalotin (4–32 mg/L), chloramphenicol (2–64 mg/L), ciprofloxacin (0.03–4 mg/L), gentamicin (1–32 mg/L), nalidixic acid (8–64 mg/L), sulfamethoxazole (64–1024 mg/L), streptomycin (4–64 mg/L), tetracycline (2–32 mg/L) and trimethoprim (4–32 mg/L). The CLSI (formerly NCCLS) breakpoints were used. For ciprofloxacin, a breakpoint of 0.125 mg/L was also used, and for streptomycin, a breakpoint of 32 mg/L was used. Escherichia coli ATCC 25922 was used for quality control. The number of tested isolates and the percentages of resistance are reported in Table 1. Isolates belonging to some serovars, e.g. Salmonella Dublin, Salmonella Saintpaul and Salmonella Derby, were susceptible to most antimicrobials tested, whereas isolates belonging to other serovars showed much higher frequencies of resistance, e.g. Salmonella Virchow, Salmonella Newport and Salmonella Stanley. A high prevalence of multidrug resistance (resistance to four or more antimicrobial agents) was observed among isolates belonging to the following serovars: Salmonella Hadar (30%), Salmonella Virchow (25%), Salmonella Stanley (22%) and Salmonella Newport (19%). Resistance to ampicillin, chloramphenicol, streptomycin, sulfamethoxazole and tetracycline was present in Salmonella Newport (15%), Salmonella Stanley (8%) and Salmonella Virchow (1%). Resistance to these five antimicrobials could indicate the presence of the multidrug-resistant region Salmonella genomic island 1 (SGI1). This region is well described and common in Salmonella Typhimurium phage type DT104. It has also been found in other Salmonella serovars, e.g. Salmonella Newport. Of the tested Salmonella Hadar and Salmonella Virchow isolates, 87% and 80%, respectively, were resistant to nalidixic acid. However, these isolates were not resistant to ciprofloxacin when the CLSI breakpoint (4 mg/L) was used. When using the EUCAST breakpoint for ciprofloxacin (0.125 mg/L), a good consistency was observed between nalidixic acid and ciprofloxacin resistance frequencies, even though minor differences were

Prevalence and Antimicrobial Resistance of Enterococci Isolated from Retail Fruits, Vegetables, and Meats

Although enterococci are considered opportunistic pathogens, they can be reservoirs of antimicrobial resistance. Antimicrobial resistance is increasingly important because of foodborne illnesses from meat and infections from produce. From 2000 through 2001, food items (vegetables, fruits, and meats) were obtained from grocery store chains in northern Georgia and cultured for the presence of enterococci; 47.7% (189 of 396) of these samples were positive for enterococci. For the fruits and vegetables, enterococci were cultured most often from tomatoes (9 of 27 samples, 33%) and radishes (10 of 11 samples, 91%), respectively. Among the meat items tested, enterococci were isolated from 95% (21 of 22) of the chicken samples, 73% (16 of 22) of the beef samples, 95% (20 of 21) of the turkey samples, and 68% (15 of 22) of the pork samples. The predominant species identified was Enterococcus faecalis (n = 80) from meat and Enterococcus casseliflavus (n = 66) from fruits and vegetables. Although high numbers of isolates were resistant to lincomycin (176 of 185 isolates, 95.1%) and bacitracin (150 of 185 isolates, 81.1%), very few isolates were resistant to salinomycin (2 isolates, 1.1%), penicillin (3 isolates, 1.6%), or nitrofurantoin (9 isolates, 4.9%). None of the isolates were resistant to linezolid or vancomycin. These data suggest that foods commonly purchased from grocery stores are a source of enterococci; however, overall resistance to antimicrobials is relatively low.

Antibiotic resistance among fecal indicator bacteria from healthy individually owned and kennel dogs.

Escherichia coli and Enterococcus faecalis strains isolated from anal swabs of clinically healthy dogs were examined for the presence of acquired antimicrobial resistance. The strains originated from dogs of 92 different owners and from eight breeding kennels. The purpose of the present study was to evaluate the resistance situation in the intestinal flora of the dog to assess the possible role of the dog flora as a reservoir of antimicrobial resistance. Multiple resistance was rarely found in E. coli strains collected from individually owned dogs, in contrast with strains from kennel dogs. Resistance to ampicillin, trimethoprim, and sulfamethoxazole was significantly less prevalent in E. coli from privately owned dogs than in strains from kennel dogs. Resistance rates against tetracycline and macrolides were unexpectedly high in E. faecalis strains. Two and three E. faecalis strains from individually owned dogs and kennel dogs, respectively, were resistant to gentamicin, an antibiotic often used for treating enterococcal infections in humans. This study demonstrates that resistance percentages may fluctuate with the choice of dog population. The observed antimicrobial resistance percentages indicate that the flora of healthy dogs may act as a reservoir of resistance genes.

Microbial flora of hands of homemakers

Objectives and methods: Because of increasing concern about antimicrobial resistance in the community, aerobic flora of hands of 224 healthy homemakers in northern Manhattan, New York, were examined. Results: Mean log colony-forming unit counts before and after handwashing were 5.72 and 5.69, respectively, P =.60; mean number of species identified/sample was 3.6 before washing and 3.3 after (P =.02). After handwashing gram-negative bacteria were isolated from 75.1% of subjects; yeast from 32.9%; and Staphylococcus aureus from 18.5%, 1 of which (2.4%) was oxacillin-resistant. Generally, these community isolates were more sensitive than isolates from inpatients in the local hospital, although community isolates of Pseudomonas aeruginosa were significantly more resistant than inpatient isolates for 4/10 agents tested. Conclusions: Hands of healthy persons in the community were usually colonized with gram-negative bacteria, a single handwash had little impact on microbial counts, and hands of healthy adults may increasingly become one reservoir for antimicrobial resistance. (Am J Infect Control 2002;31:72-9.)

Detección de Enterococcus resistentes a altos niveles de aminoglucósidos y resistentes a glucopéptidos en Lactuca sativa (lechuga)

The aim of this study was to assess the presence of enterococci highly resistant to aminoglycosides and glycopeptides in foods eaten uncooked, in order to evaluate their role as reservoirs of antimicrobial resistance. We isolated 92 strains of enterococci from 79 samples of lettuce grown on farms near the city of Corrientes (Argentina). Enterococci were identified by standard methods. Antimicrobial susceptibility was determined by growth in azide dextrose broth supplemented with 500 microg/ml of gentamicin and 2,000 microg/ml of streptomycin, and by disk diffusion technique using disks with high levels of aminoglycosides, vancomycin and teicoplanin, in Müller Hinton agar. The most frequently detected species was E. faecium (32.61%), followed by E. faecalis (21.74%), E. gallinarum (13.04%), E. casseliflavus and E. mundtii (7.60%), E. hirae, (6.52%), E. durans (4.35%), E. raffinossus and E. saccharolyticus (2.17%), E. avium and E. malodoratus (1.10%). High-level resistance to streptomycin and gentamicin was found in 2 strains of E. Faecium. Resistance to streptomycin alone was observed in 2 strains of E. faecium, in 3 of E. hirae and in 1 of E. mundtii. Resistance only to gentamicin was not observed in any strain. None of the isolates showed glycopeptide resistance, except the intrinsically resistant species (E. gallinarum and E. casseliflavus). These results confirm the presence of enterococci within the community having susceptibility profiles similar to those of strains found in hospitals.