Prevalence in Singapore of enterococci with high-level resistance to aminoglycosides and comparison of three methods for their detection

Carriage of resistant microorganisms in repatriates from foreign hospitals to The Netherlands

In a prospective survey conducted between May 1998 and September 2001, the prevalence of carriage of methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE) and gentamicin-resistant Gram-negative bacilli (GGNB) was determined in 1167 patients repatriated from foreign hospitals to The Netherlands. Swab specimens, demographic data and clinical data were obtained during transfer of the patients from the foreign hospitals. The total prevalence of carriage of resistant microorganisms was 18.2%. MRSA was carried by 2.7% of all patients, and by 4.7% of the patients repatriated to a Dutch hospital. Antimicrobial treatment (adjusted odds ratio (OR) 3.4; 95% confidence interval (CI) 1.2-9.7), length of stay in a foreign hospital of > 14 days (adjusted OR 5.4; 95% CI 2.3-12) and artificial ventilation (adjusted OR 8.5; 95% CI 1.8-41) were risk factors for carriage of MRSA. VRE and GGNB were isolated from 2.7% and 14.1% of the patients, respectively. Transfer from Asia, and southern, southeastern and eastern Europe, were risk factors for carriage of GGNB. These carriage rates were high compared to those found in patients in Dutch hospitals, where the rates are < 1% for MRSA, 2% for VRE, and 4.5% for GGNB. The highest risk of acquisition of GGNB was associated with the country from where the patient was repatriated, rather than with the antimicrobial treatment received by the individual patient in the foreign hospital.

Iron chelators protect from aminoglycoside-induced cochleo- and vestibulo-toxicity

The attenuation of gentamicin-induced hearing loss by iron chelators and radical scavengers has recently been demonstrated in guinea pig in vivo. The present study investigated whether this protective treatment is effective against hearing loss and vestibular damage caused by other aminoglycosides. In a direct comparison, dihydroxybenzoate was chosen over deferoxamine because of its more effective action against gentamicin-induced hearing loss. Guinea pigs received daily injections of kanamycin (250 mg/kg/d) or streptomycin (300 mg/kg/d) for 23 d to induce severe cochlear or vestibular toxicity, respectively. Kanamycin injections resulted in a progressive threshold shift of 60 to 80 dB at 18 kHz, while streptomycin injections induced only a small threshold shift. In contrast, streptomycin abolished almost all vestibular responses. Coinjection of aminoglycosides with a mixture of dihydroxybenzoate (100 mg/kg/d) and mannitol (30 mg/kg/d) significantly attenuated kanamycin-induced hearing loss and protected against streptomycin-induced vestibulotoxicity. DHB/mannitol did not affect serum levels or the antibacterial efficacy of either aminoglycoside. This study supports the idea that iron and free radicals play a critical role in the toxic side effects of aminoglycoside antibiotics. Furthermore, the previously proposed therapeutic protection is not limited to gentamicin but applicable to other aminoglycosides as well.

Comparison of three methods for the molecular typing of Singapore isolates of enterococci with high-level aminoglycoside resistances

Enterococci are frequently isolated as nosocomial pathogens and have often acquired intrinsic drug resistances. Molecular typing techniques have been developed to assist in epidemological and infection control measures. This study investigates enterococci with high-level aminoglycoside resistance (HLAR) from the National University Hospital (NUH) of Singapore, and evaluates and compares three methods for typing: restriction enzyme analysis by conventional gel electrophoresis [restriction fragment length polymorphism (RFLP)], pulsed-field gel electrophoresis (PFGE), and polymerase chain reaction (PCR) using random amplified polymorphic DNA (RAPD). Fifty-two isolates of Enterococcus faecalis and 13 isolates of Enterococcus faecium were used for the study. The numbers of patterns obtained for E. faecalis and E. faecium were 26 and 4, respectively by the RFLP method, and very similar discrimination was obtained by PFGE. RAPD PCR results were not reliably reproducible. A single pattern type by RFLP accounted for 16 of the E. faecalis isolates, suggesting hospital spread.

Characterization of enterococci isolated from human and nonhuman sources in Brazil

A total of 330 enterococci strains isolated from several human (272 strains) and animal (27) clinical specimens and environmental sources (31) in Brazil were identified to species level. Major human sources included urine (48.5%), blood (15.8%), and wounds (9.5%). Human isolates were identified as Enterococcus faecalis (90.0%), E. faecium (6.9%), E. gallinarum (1.1%), E. durans (0.8%), E. casseliflavus (0.4%), E. raffinosus (0.4%), and E. mundtii (0.4%). Strains isolated from animals were composed of E. hirae (40.7%), E. faecalis (33.3%), E. faecium (18.5%), and E. casseliflavus (7.5%). Among environmental isolates, 42.0% were E. faecalis, 35.4% E. faecium, 13.0% E. hirae, 6.4% E. casseliflavus, and 3.2% E. durans. Antimicrobial susceptibility tests were performed for 200 strains. Overall, high-level resistance (HLR) to aminoglycosides was found in 66 (33.0%) of the strains tested. HLR to gentamicin was detected in 11.5% of the strains, whereas 19.0% of the strains showed HLR to streptomycin and 26.0% showed HLR to kanamycin. Five (22.7%) of the E. faecium strains were resistant to ampicillin [minimum inhibitory concentration (MIC) > 32 micrograms/ml]. Vancomycin MIC50 and MIC90 were 2 and 4 micrograms/ml, respectively; only eight strains (identified as E. casseliflavus or E. gallinarum) had MIC of 8 micrograms/ml. No beta-lactamase activity was detected by the nitrocefin test.