In total, 172 isolates of Enterobacteriaceae, Acinetobacter spp., Pseudomonas aeruginosa and Stenotrophomonas maltophilia were tested for susceptibility to colistin by agar dilution, Etest and the Vitek 2 system. Isolates with a colistin MIC < or =2 mg/L were considered to be susceptible. Fifty-four (31%) Gram-negative isolates were resistant to colistin. Categorical agreement between agar dilution and Etest was 87%, and between agar dilution and Vitek 2 was 82%. Based on the data obtained, the Vitek 2 system was unreliable for detecting colistin resistance, and results obtained by Etest may require confirmation by a standard MIC susceptibility testing method.
This study validated abbreviated methods for the presumptive identification of Staphylococcus lugdunensis and studied the antibiotic susceptibilities of 106 isolates. The combination of positive responses to ornithine and pyrrolidonyl arylamidase identified all S. lugdunensis isolates. Resistance to penicillin and methicillin was detected in 27 and 5% of isolates, respectively.Staphylococcus lugdunensis, a coagulase-negative staphylococcus, has clinical characteristics that resemble those of the coagulase-positive Staphylococcus aureus. Infections attributed to S. lugdunensis include infective endocarditis (19), bacteremia, meningitis (6), bone and joint infections (7), and softtissue infections (16). S. lugdunensis generally is susceptible to anti-staphylococcal antibiotics (18), but increasing penicillin resistance has been reported (9, 13). Meanwhile, oxacillin susceptibility breakpoints for S. lugdunensis were changed in 2005 (3), and oxacillin disc breakpoints were revised in 2005 and subsequently replaced by cefoxitin disc breakpoints in 2006 (2). The current reference method for the identification of coagulase-negative staphylococci (1) is labor-intensive. Screening for S. lugdunensis by detecting clumping factor (15, 21) or using a limited number of biochemical tests (5, 12, 15) has been proposed, but these methods have been evaluated only against small numbers of S. lugdunensis isolates.The aims of this study were to evaluate the use of simple screening strategies for the identification of S. lugdunensis, to comprehensively describe the microbiological characteristics of S. lugdunensis, and to evaluate the antibiotic susceptibility of clinical isolates.The accuracy of three abbreviated identification protocols and two commercial identification kits (ID 32 Staph and Vitek ID-GP; both from bioMérieux, France) was evaluated against a collection of coagulase-negative staphylococci that were isolated from clinical samples. Isolates from the collection were identified using a panel of 30 phenotypic and biochemical tests (1) and included Staphylococcus capitis (n ϭ 7), Staphylococcus caprae (n ϭ 5), Staphylococcus cohnii (n ϭ 2), Staphylococcus epidermidis (n ϭ 14), Staphylococcus haemolyticus (n ϭ 24), Staphylococcus hominis (n ϭ 3), Staphylococcus lugdunensis (n ϭ 46), Staphylococcus saprophyticus (n ϭ 2), and Staphylococcus warneri (n ϭ 3). The identification of 10 isolates (belonging to S. haemolyticus, S. cohnii, S. epidermidis, and S. lugdunensis) was further confirmed by sequencing a 457-bp sequence of the 16S rRNA gene (8). For the three abbreviated identification protocols, isolates were tested for the presence of pyrrolidonyl arylamidase (PYR) (Oxoid, United Kingdom), ornithine decarboxylase (BioMedia, Malaysia), and urease (BioMedia, Malaysia); trehalose utilization; alkaline phosphatase activity; and mannose utilization (the last three substances were from Rosco, Denmark). In the first identification protocol, isolates that were positive for both PYR and ornithine decarboxylase were identified as S...
Laboratory criteria were used to select coagulase-negative staphylococci isolated from nonsterile body sites for further investigation. Fifty-seven percent of the study isolates were clinically significant, predominantly causing community-acquired soft tissue infections. There were species-related differences in virulence, with 91% of Staphylococcus lugdunensis isolates clinically significant compared with 11% of S. haemolyticus isolates.Staphylococci are normal skin commensals (1) and are frequently isolated from clinical specimens. The isolation of coagulase-negative staphylococci (CoNS) from nonsterile sites is usually ignored or reported without further species level identification. Routine species level identification may better define the clinical spectrum of disease caused by CoNS. However, the reference method (7) is labor-intensive, while the use of commercial identification kits is not cost-effective.This study used a simple laboratory algorithm (Table 1) to select CoNS isolated from nonsterile sites for further investigation using an abbreviated identification scheme (4, 6). Quantitative culture using a calibrated loop system (8) was performed for urine specimens, while other specimens were inoculated using semiquantitative methods (14).CoNS were identified by Gram stain, the presence of catalase, bacitracin resistance, and the absence of free coagulase (1). Isolates positive for ornithine decarboxylase and pyrrolidonyl arylamidase (OBIS PYR; Oxoid, United Kingdom) were identified as Staphylococcus lugdunensis (9). Urinary isolates that were resistant to novobiocin, exhibited urease activity, and failed to reduce nitrates were identified as S. saprophyticus (subspecies saprophyticus) (1). Following these initial screening tests, CoNS isolates were identified to the species level by a simplified two-step identification method (6). CoNS that remained unidentified were tested using ID32 Staph (bioMérieux, France) and ID-GP cards (bioMérieux, France). Clinical details were collected retrospectively from patient case records. Statistical data were generated using StatCalc (EpiInfo; CDC). Isolates were classified as nosocomial if the sample was collected more than 48 h following admission to the hospital. All other isolates were classified as community acquired. Standardized criteria for the diagnosis of nosocomial infections were used to determine the clinical significance of test isolates (3, 5).One hundred seventy-nine CoNS isolates were cultured from 168 unique samples, which were predominantly swabs (n ϭ 126; 70%) and urine (n ϭ 25; 14%). Eighty-seven (49%) of the isolates were cultured from operative samples, and 145 (81%) of the isolates were classified as community acquired. A single colonial morphotype of CoNS was present in primary culture from 156 samples, while two morphotypes of CoNS were present in the remaining 12 samples. Nineteen (11%) CoNS isolates were isolated in mixed cultures, with Յ1ϩ growth of other organisms, predominantly diptheroids. Assessment of semiquantitative growth (14) show...
This study was performed to determine the prevalence, distribution of specimen sources, and antimicrobial susceptibility of the Acinetobacter calcoaceticus-Acinetobacter baumannii (Acb) species complex in Singapore. One hundred and ninety-three non-replicate Acb species complex clinical isolates were collected from six hospitals over a 1-month period in 2006. Of these, 152 (78·7%) were identified as A. baumannii, 18 (9·3%) as 'Acinetobacter pittii' [genomic species (gen. sp.) 3], and 23 (11·9%) as 'Acinetobacter nosocomialis' (gen. sp. 13TU). Carbapenem resistance was highest in A. baumannii (72·4%), followed by A. pittii (38·9%), and A. nosocomialis (34·8%). Most carbapenem-resistant A. baumannii and A. nosocomialis possessed the bla(OXA-23-like) gene whereas carbapenem-resistant A. pittii possessed the bla(OXA-58-like) gene. Two imipenem-resistant strains (A. baumannii and A. pittii) had the bla(IMP-like) gene. Representatives of carbapenem-resistant A. baumannii were related to European clones I and II.
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