Efficacy of microbial identification system for epidemiologic typing of coagulase-negative staphylococci

The Various Roles of Fatty Acids

Lipids comprise a large group of chemically heterogeneous compounds. The majority have fatty acids (FA) as part of their structure, making these compounds suitable tools to examine processes raging from cellular to macroscopic levels of organization. Among the multiple roles of FA, they have structural functions as constituents of phospholipids which are the "building blocks" of cell membranes; as part of neutral lipids FA serve as storage materials in cells; and FA derivatives are involved in cell signalling. Studies on FA and their metabolism are important in numerous research fields, including biology, bacteriology, ecology, human nutrition and health. Specific FA and their ratios in cellular membranes may be used as biomarkers to enable the identification of organisms, to study adaptation of bacterial cells to toxic compounds and environmental conditions and to disclose food web connections. In this review, we discuss the various roles of FA in prokaryotes and eukaryotes and highlight the application of FA analysis to elucidate ecological mechanisms. We briefly describe FA synthesis; analyse the role of FA as modulators of cell membrane properties and FA ability to store and supply energy to cells; and inspect the role of polyunsaturated FA (PUFA) and the suitability of using FA as biomarkers of organisms.

Fatty acid analysis as a chemotaxonomic tool for taxonomic and epidemiological characterization of four fish pathogenic Tenacibaculum species

AIMS

In this work, fatty acid content and profiles were analysed in order to differentiate the species Tenacibaculum maritimum, Tenacibaculum gallaicum, Tenacibaculum discolor and Tenacibaculum ovolyticum that are pathogenic for cultured marine fish and to assess the potential of fatty acid profiles as a tool for epizootiological typing.

METHODS AND RESULTS

The fatty acid methylesters (FAMEs) were extracted from cells grown on marine agar for 48 h at 25 degrees C and were prepared and analysed according to the standard protocol of the MIDI/Hewlett Packard Microbial Identification System. The cellular fatty acid profiles of Tenacibaculum strains tested were characterized by the presence of large amounts of branched (36.1-40.2%) and hydroxylated (29.6-31.7%) fatty acids. The FAME products from the four species significantly (P < 0.05) differed in the content of iso-C(15:0)3-OH, iso-C(16:0)3-OH, iso-C(15:1)G, summed feature 3 (a component that contains C(16:1)omega7c and/or iso-C(15:0) 2-OH), iso-C(16:0), C(17:1)omega6c, C(15:0)3-OH, iso-C(17:0)3-OH.

CONCLUSIONS

Results of present study demonstrated the existence of differences in the fatty acids content between the T. maritimum isolates from different marine fish/geographical origin and between strains of T. maritimum, T. discolor, T. gallaicum and T. ovolyticum.

SIGNIFICANCE AND IMPACT OF THE STUDY

Profiling of fatty acids may be a useful tool to distinguish T. maritimum from other Tenacibaculum species pathogenic for fish as well as for epizootiological differentiation of T. maritimum isolates.

Use of Fatty Acid Methyl Ester Profiles to Compare Copper-Tolerant and Copper-Sensitive Strains of Pantoea ananatis

ABSTRACT A survey was conducted to evaluate differences in fatty acid methyl ester (FAME) profiles among strains of Pantoea ananatis, causal agent of center rot of onion (Allium cepa), isolated from 15 different onion cultivars in three different sites in Georgia. Differences in FAME composition were determined by plotting principal components (PCs) in two-dimensional plots. Euclidean distance squared (ED(2)) values indicated a high degree of similarity among strains. Plotting of PCs calculated from P. ananatis strains capable of growing on media amended with copper sulfate pentahydrate (200 mug/ml) indicated that copper-tolerant strains grouped into tight clusters separate from clusters formed by wild-type strains. However, unlike copper-sensitive strains, the copper-tolerant strains tended to cluster by location. A total of 80, 60, and 73% of the strains from Tift1, Tift2, and Tattnall, respectively, exhibited either confluent growth or partial growth on copper-amended medium. However, all strains were sensitive to a mixture of copper sulfate pentahydrate (200 mug/ml) and maneb (40 mug/ml). When copper-tolerant clones were analyzed and compared with their wild-type parents, in all cases the plotting of PCs developed from copper-tolerant clones formed tight clusters separate from clusters formed by the parents. Eigenvalues generated from these tests indicated that two components provided a good summary of the data, accounting for 98, 98, and 96% of the standardized variance for strains Pna 1-15B, Pna 1-12B, and Pna 2-5A, respectively. Furthermore, feature 4 (cis-9-hexadecenoic acid/2-hydroxy-13-methyltetradecanoic acid) and feature 7 (cis-9/trans-12/cis-7-octadecenoic acid) were the highest or second highest absolute values for PC1 in all three strains of the parents versus copper-tolerant clones, and hexadecanoic acid was the highest absolute value for PC2 in all three strains. Along with those fatty acids, dodecanoic acid and feature 3 (3-hydroxytetradecanoic acid/14-methylpentadecenoic acid) also had an impact on the differences observed between copper-sensitive parents and copper-resistant mutants. Finding these changes in bacterial fatty acid composition could lead to the development of a laboratory assay to identify copper-tolerant strains using gas chromatography as well as providing clues to further elucidate the mode of action of copper tolerance.

Characterization of Escherichia coli isolates from different fecal sources by means of classification tree analysis of fatty acid methyl ester (FAME) profiles

Microbial source tracking (MST) methods need to be rapid, inexpensive and accurate. Unfortunately, many MST methods provide a wealth of information that is difficult to interpret by the regulators who use this information to make decisions. This paper describes the use of classification tree analysis to interpret the results of a MST method based on fatty acid methyl ester (FAME) profiles of Escherichia coli isolates, and to present results in a format readily interpretable by water quality managers. Raw sewage E. coli isolates and animal E. coli isolates from cow, dog, gull, and horse were isolated and their FAME profiles collected. Correct classification rates determined with leaveone-out cross-validation resulted in an overall low correct classification rate of 61%. A higher overall correct classification rate of 85% was obtained when the animal isolates were pooled together and compared to the raw sewage isolates. Bootstrap aggregation or adaptive resampling and combining of the FAME profile data increased correct classification rates substantially. Other MST methods may be better suited to differentiate between different fecal sources but classification tree analysis has enabled us to distinguish raw sewage from animal E. coli isolates, which previously had not been possible with other multivariate methods such as principal component analysis and cluster analysis.

Infection of a ventriculoatrial shunt with phenotypically variable Staphylococcus epidermidis masquerading as polymicrobial bacteremia due to various coagulase-negative Staphylococci and Kocuria varians

The diagnosis of bloodstream infection with coagulase-negative staphylococci is frequently based on the isolation of the same organism from more than one blood culture. Phenotypic variation is a common characteristic of pathogenic strains of Staphylococcus epidermidis which may affect species identification by the microbiology laboratory. We describe a patient with a new onset of nephritis and gram-positive bacteremia. Gram-positive cocci grew in multiple blood cultures and were identified by the Vitek 2 system as Kocuria varians, Staphylococcus hyicus, and S. epidermidis. Bacterial isolates grew on blood agar and Congo red agar plates as two distinct morphotypes and exhibited phenotypic variation. Neither morphotype could be identified by the API-Staph assay. Cellular fatty acid analysis identified one of the morphotypes as S. epidermidis but could not identify the other morphotype. All isolates were found to be identical by pulsed-field gel electrophoresis, and both colonial morphotypes were identified as S. epidermidis by 16S ribosomal gene sequencing. Phenotypic variation of S. epidermidis may affect identification to the species level by phenotype-based identification systems. Caution should be exercised when differentiating between true infection and contamination based on strain identification.

Phylogenetic study of Staphylococcus and Macrococcus species based on partial hsp60 gene sequences

A 600 bp partial hsp60 gene sequence has been described previously as a novel genetic marker for species identification and phylogenetic studies within the genus Staphylococcus. In the present study, the 600 bp partial hsp60 gene sequences of 40 validly described Staphylococcus species and subspecies and four Macrococcus species were PCR-amplified and sequenced. Phylogenetic analysis revealed excellent concordance between the unrooted dendrograms based on partial hsp60 and 16S rRNA gene sequences. The genus Macrococcus is clearly separated from the genus Staphylococcus, but is closely related to the 'sciuri group', the only staphylococci that are cytochrome c oxidase-positive. The remaining Staphylococcus species clustered into five broad-based subdivisions, which corresponded to the 'aureus group', the 'epidermidis group', the 'haemolyticus group', the 'saprophyticus group' and the 'intermedius group'. These results agreed remarkably well with the current taxonomy of this diverse family, which is based on classical phenotypic and biochemical testing. Furthermore, pairwise sequence comparisons indicated that the hsp60 gene is more divergent and more discriminatory than the 16S rRNA gene for species differentiation among strains of the genera Staphylococcus and Macrococcus. It is concluded that the hsp60 gene may be an efficient alternative target for taxonomic and phylogenetic studies on members of these genera.

Variation in Microbial Identification System accuracy for yeast identification depending on commercial source of Sabouraud dextrose agar

The accuracy of the Microbial Identification System (MIS; MIDI, Inc. ) for identification of yeasts to the species level was compared by using 438 isolates grown on prepoured BBL Sabouraud dextrose agar (SDA) and prepoured Remel SDA. Correct identification was observed for 326 (74%) of the yeasts cultured on BBL SDA versus only 214 (49%) of yeasts grown on Remel SDA (P < 0.001). The commercial source of the SDA used in the MIS procedure significantly influences the system's accuracy.

Epidemiological typing of Campylobacter isolates from meat processing plants by pulsed-field gel electrophoresis, fatty acid profile typing, serotyping, and biotyping

Campylobacter spp. are a leading cause of bacterial gastroenteritis. Foods of animal origin, particularly under-cooked poultry, are common sources of Campylobacter species associated with disease in humans. A collection of 110 Campylobacter jejuni and 31 C. coli human and environmental isolates from different Ontario, Canada, abattoirs were analyzed by pulsed-field gel electrophoresis, fatty acid profile typing, and biotyping. Previously collected serotyping data for the same isolates were also analyzed in this study. Pulsed-field gel electrophoresis was found to be the most discriminatory of the typing methods, followed by serotyping, fatty acid profile typing, and biotyping. A wide variety of typing profiles were observed within the isolates, suggesting that several different Campylobacter sp. strains were present within the abattoirs.

Limitations of the current microbial identification system for identification of clinical yeast isolates

The ability of the rapid, computerized Microbial Identification System (MIS; Microbial ID, Inc.) to identify a variety of clinical isolates of yeast species was compared to the abilities of a combination of tests including the Yeast Biochemical Card (bioMerieux Vitek), determination of microscopic morphology on cornmeal agar with Tween 80, and when necessary, conventional biochemical tests and/or the API 20C Aux system (bioMerieux Vitek) to identify the same yeast isolates. The MIS chromatographically analyzes cellular fatty acids and compares the results with the fatty acid profiles in its database. Yeast isolates were subcultured onto Sabouraud dextrose agar and were incubated at 28 degrees C for 24 h. The resulting colonies were saponified, methylated, extracted, and chromatographically analyzed (by version 3.8 of the MIS YSTCLN database) according to the manufacturer's instructions. Of 477 isolates of 23 species tested, 448 (94%) were given species names by the MIS and 29 (6%) were unidentified (specified as "no match" by the MIS). Of the 448 isolates given names by the MIS, only 335 (75%) of the identifications were correct to the species level. While the MIS correctly identified only 102 (82%) of 124 isolates of Candida glabrata, the predictive value of an MIS identification of unknown isolates as C. glabrata was 100% (102 of 102) because no isolates of other species were misidentified as C. glabrata. In contrast, while the MIS correctly identified 100% (15 of 15) of the isolates of Saccharomyces cerevisiae, the predictive value of an MIS identification of unknown isolates as S. cerevisiae was only 47% (15 of 32), because 17 isolates of C. glabrata were misidentified as S. cerevisiae. The low predictive values for accuracy associated with MIS identifications for most of the remaining yeast species indicate that the procedure and/or database for the system need to be improved.

Concept of segmentation in nosocomial epidemiology: epidemiological relation among antimicrobial-resistant isolates of Pseudomonas aeruginosa

Typing studies on 271 clinical strains of Pseudomonas aeruginosa isolated from the University Teaching Hospital were conducted to obtain their serotypes, antimicrobial susceptibility patterns and plasmid profiles. These strain typing data were arranged through multivariate statistical analysis by computation to classify individual strains. Plots in the scatter diagrams obtained from both principal component analysis and quantification theory type III expressed the clinical strains of P. aeruginosa with various degrees of antimicrobial resistance. Epidemiological relation among these clinical strains was analysed in those scatter diagrams by segmentation, in combination with their epidemiological information (date and place of isolation, type of specimen, etc.). The results showed that the serotype E strains both with high-level resistance to gentamicin and with a plasmid of 3.9 x 10(6) dalton, and the strains resistant to more than five antimicrobial agents, were colonized and localized each in certain clinical wards for inpatients. It was suggested that segmentation analysis could be of practical use in the management of nosocomial infection control against P. aeruginosa with antimicrobial resistance.

Analysis of whole-cell fatty acid profiles of verotoxigenic Escherichia coli and Salmonella enteritidis with the microbial identification system

Differentiation of strains within bacterial species, based on gas chromatographic analysis of whole-cell fatty acid profiles, was assessed with 115 strains of verotoxigenic Escherichia coli and 315 strains of Salmonella enteritidis. Fatty acid-based subgroups within each of the two species were generated. Variability of fatty acid profiles observed in repeat preparations from the same strain approached that observed between subgroups, limiting the usefulness of using fatty acid profiles to subgroup verotoxigenic E. coli and S. enteritidis strains.

Epidemiological typing of Bacillus spp. isolated from food

Biotypes, fatty acid profiles, and restriction fragment length polymorphisms of a PCR product (PCR-RFLP of the cereolysin AB gene) were compared for 62 isolates of the Bacillus cereus group. Eleven isolates originated from various foods, and 51 isolates were obtained from pasteurized milk which had been processed by two different dairies. The isolates were clustered into 6 biotypes, 10 fatty acid groups, or 7 PCR-RFLP clusters. Isolates with mesophilic or psychrotrophic characteristics were preferentially distributed into specific fatty acid or PCR-RFLP groups (P = 0.004). Unique fatty acid clusters were predominantly found in milk samples of each dairy (P < 0.0001), suggesting that certain dairy plants may harbor plant-specific B. cereus which might constantly contribute to postpasteurization contamination.

Ribotype diversity of Listeria monocytogenes strains associated with outbreaks of listeriosis in ruminants

Ribotyping is a molecular method for the characterization, identification, and typing of bacterial isolates that has value in epidemiological studies. To demonstrate the utility of this technique for typing of Listeria monocytogenes, four outbreaks of epizootic listeriosis in ruminants were investigated through coordinated detection and characterization methods utilizing classical microbiology and nucleic acid-based techniques. L. monocytogenes strains isolated from clinical samples and the silage consumed by the affected animals were ribotyped to establish the causal relationship between feed and the disease outbreak. For all but one outbreak, we were able to isolate L. monocytogenes strains represented by the same ribotype from both clinical and silage samples. Additional L. monocytogenes strains with ribotypes different from those of the respective clinical samples were isolated from all silage samples. This indicates that a diverse population of L. monocytogenes strains exists in farm environments, of which some may be more likely than others to cause disease.

Mineralization of 2,4,6-trinitrophenol (picric acid): characterization and phylogenetic identification of microbial strains

Four bacterial strains that use picric acid as their sole carbon and energy source were isolated. Mineralization of 14C-UL-picric acid showed that up to 65% of the radioactivity was released as 14CO2. HPLC and UV/Vis spectral analyses indicated complete degradation of picric acid by these organisms. HPLC and LC/MS analyses showed transient formation of 2,4-dinitrophenol during picric acid degradation. Degradation of picric acid was concomitant with stoichiometric release of three moles of nitrite per mole of picric acid. The four picric acid degraders were identified as close relatives of Nocardioides simplex (ATCC 6946) based on their small subunit (16S) rRNA gene sequences.

Plasmid profiling for strain differentiation and characterization of Clostridium perfringens isolates

Plasmid profiling was used for the characterization of 13 Clostridium perfringens collection strains as well as 85 clinical and food isolates. Methodological details and limitations of the plasmid isolation procedure are outlined and discussed. For 19 clinical isolates obtained during seven group outbreaks, a close connection between at least some strains from each individual outbreak was established for six of them; only results from one outbreak were completely inconclusive, due to missing plasmids in one of the two isolates. The presence of multiple plasmid types within seven out of 12 given food samples, from which at least two C. perfringens isolates were obtained, indicates the importance of multiple isolates for meaningful typing results in epidemiological investigations. By including results from a previous report from this laboratory, baseline data on plasmid profiles for a total of 133 isolates are provided. The results of this study revealed that 36% of the food isolates unrelated to disease outbreaks carried no plasmids, as compared with 19-25% among disease-related isolates. A high prevalence (24.8%) of a 8.9 +/- 0.5 MDa plasmid was found among the 133 isolates, which contributed to one of four occurrences of identical plasmid profiles among strains that were initially considered unrelated. Two of these identical plasmid profiles were found among strains from the same culture collection, indicating the possibility of a common ancestor strain or cross-contamination.

Comparison of MIDI Sherlock system and pulsed-field gel electrophoresis in characterizing strains of methicillin-resistant Staphylococcus aureus from a recent hospital outbreak

An outbreak of methicillin-resistant Staphylococcus aureus infections at the University of Utah Health Sciences Center occurred over a 7-month period. While the isolates phenotypically appeared to be similar in gross morphology and have similar Vitek antibiotic susceptibility patterns, two additional methods of strain characterization were evaluated to enhance the epidemiological investigation: pulsed-field gel electrophoresis and gas chromatography with the MIDI Sherlock system. Sherlock uses gas chromatography to qualitatively and quantitatively analyze the cellular fatty acid composition of organisms and creates two-dimensional plots based on principal-component analysis to define groups of closely related organisms. All isolates were also evaluated by digesting their chromosomal DNAs with the low-frequency-cutting enzyme SmaI and separating the restriction fragments by contour-clamped homogeneous electric field gel electrophoresis. Sample preparation for this pulsed-field gel electrophoresis included a novel cell lysis procedure involving achromopeptidase, greatly reducing the turnaround time. Isolates tested were recovered from the following: 45 suspected outbreak patients, 6 hospitalized patients believed to be unrelated to the outbreak, 6 patients from outside the hospital, and one health care practitioner implicated in the outbreak. Of 45 phenotypically similar suspect strains, 43 clustered tightly on the Sherlock two-dimensional plot. All outbreak patient isolates were also identical by pulsed-field gel electrophoresis with the exception of the same two outliers identified by Sherlock. In this epidemiologic investigation, we found an excellent correlation between the Sherlock and pulsed-field gel electrophoresis results for strain characterization of methicillin-resistant S. aureus.