Characterization of coagulase-negative staphylococci by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblot analyses

SDS-PAGE and Gel IEF: Tool for Differentiation of Methicillin-Resistant and Methicillin-Sensitive Strains of Staphylococcus aureus

The methicillin-resistant Staphylococcus aureus causes difficult-to-treat healthcare-associated infections in humans. For fast and effective selection of an appropriate antibiotic therapy, it is essential to have rapid and reliable methods for differentiation of methicillin-resistant S. aureus from less dangerous methicillin-sensitive S. aureus. There have been many methods for the identification of methicillin-resistant S. aureus described but none has been accepted as an international standard. The most commonly used techniques such as phenotyping and genotyping have a few disadvantages, for instance, these techniques are not reproducible and stable. In addition, they are time-consuming, expensive, and they are not capable to distinguish all S. aureus strains. In this study, the methicillin-resistant and methicillin-sensitive S. aureus isolates obtained from patients were extracted in hot water. The released proteins were characterised by sodium dodecyl sulphate polyacrylamide gel electrophoresis and gel isoelectric focusing. These two methods were able to differentiate among tested bacterial strains. The proposed methods are time saving, they are applicable in standard biochemical laboratories, and they do not require any expensive equipment.

The use of whole-cell protein profile analysis by SDS-PAGE as an accurate tool to identify species and subspecies of coagulase-negative staphylococci

We used sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) as a tool to characterize coagulase-negative staphylococci (CoNS). Of 253 clinical isolates and 10 control strains, five species and four subspecies were analyzed. All the isolates were identified using conventional phenotypic tests and SDS-PAGE. Discrepant results between these methods, as well as less common species and subspecies, were confirmed by sodA and 16S rDNA gene sequencing. Intraspecies similarities, calculated by the Dice coefficient, were significantly higher when compared to interspecies similarities. The conventional method failed to identify eight (3.2%) molecularly defined and SDS-PAGE-determined isolates. Therefore, SDS-PAGE was able to discriminate between all unidentified or misidentified isolates using a phenotypic method. In addition, SDS-PAGE identified all atypical isolates using biochemistry and CoNS at the subspecies level.

Typing of Staphylococcus epidermidis strains by random amplification of polymorphic DNA

The polymerase chain reaction was used to obtain randomly amplified polymorphic DNA profiles for typing of Staphylococcus epidermidis strains. Epidemiologically unrelated S. epidermidis isolates were screened with randomly amplified polymorphic DNA analysis. The discriminating ability of 45 randomly designed 10-mer primers was assessed. The highest discriminatory power was obtained with the 10-mer oligonucleotide OPAM-12. In typing a total of 13 unrelated S. epidermidis strains with OPAM-12, 11 different banding profiles were obtained reproducibly by agarose gel electrophoresis. The discriminatory power of the method with OPAM-12 was estimated using the D value of Hunter and Gaston (1988) to be 0.961. A reproducibility index of 1 was obtained after typing a total of 40 cultures including 12 triplicates and one quadruplicate of the 13 unrelated strains. Following the described procedure, the randomly amplified polymorphic DNA method provided a rapid, simple and reproducible alternative to other S. epidermidis typing systems.

Update on clinical significance of coagulase-negative staphylococci

The clinical significance of coagulase-negative Staphylococcus species (CNS) continues to increase as strategies in medical practice lead to more invasive procedures. Hospitalized patients that are immunocompromised and/or suffering from chronic diseases are the most vulnerable to infection. Since CNS are widespread on the human body and are capable of producing very large populations, distinguishing the etiologic agent(s) from contaminating flora is a serious challenge. For this reason, culture identification should proceed to the species and strain levels. A much stronger case can be made for the identification of a CNS etiologic agent if the same strain is repeatedly isolated from a series of specimens as opposed to the isolation of different strains of one or more species. Strain identity initially can be based on colony morphology, and then one or more molecular approaches can be used to gain information on the genotype. Many of the CNS species are commonly resistant to antibiotics that are being indicated for staphylococcal infections, with the exception of vancomycin. The widespread use of antibiotics in hospitals has provided a reservoir of antibiotic-resistant genes. The main focus on mechanisms of pathogenesis has been with foreign body infections and the role of specific adhesins and slime produced by Staphylococcus epidermidis. Slime can reduce the immune response and opsonophagocytosis, thereby interfering with host defense mechanisms. As we become more aware of the various strategies used by CNS, we will be in a better position to compromise their defense mechanisms and improve treatment.

Effect of growth conditions on expression and antigenicity of Staphylococcus epidermidis RP62A cell envelope proteins

Staphylococcus epidermidis RP62A (ATCC 35984) was grown in tryptic soy broth (TSB), iron-depleted TSB (TSB-Fe), iron-reconstituted TSB-Fe (TSB+Fe), a chemically defined medium, and fetal calf serum (FCS) and on silastic disks in chambers that were sutured to the pig peritoneal wall. Bacterial cell wall proteins were extracted by digestion with recombinant lysostaphin, separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and detected by silver staining. Cell wall proteins from TSB-, chemically defined medium-, or FCS-grown cells had a complex profile of greater than 25 protein bands spanning the full molecular mass range. By contrast, a digest obtained from in vivo-grown cells had only five major proteins of 40 kDa or greater. Proteins of 130 and 106 kDa were present in the cell envelopes of TSB-Fe- and in vivo-grown cells but not in those grown in TSB or TSB+Fe. A 43-kDa protein expressed by in vitro-grown cells and 52- and 96-kDa proteins expressed by in vivo-grown cells reacted with antisera from pigs with the chamber implants and from catheterized, paracatheter-inoculated pigs but not with hyperimmune sera from pigs immunized with TSB-grown cells. The data indicate that S. epidermidis, growing under in vivo conditions, expresses antigens distinct from those that are grown in vitro.

Comparative evaluation of a new molecular method for typing Staphylococcus epidermidis

The discriminatory powers of several techniques for typing Staphylococcus epidermidis were evaluated in an epidemiological study of bacteria isolated from intensive care patients and from neonates. Genomic DNA fingerprinting using BclI restriction endonuclease was an effective epidemiological marker. The distinct restriction fragment profiles produced with this enzyme were highlighted with specific probes in a Southern blot technique. Cloned Escherichia coli rRNA gene probes proved to have lower discriminatory power and be less suitable for intraspecies typing. However, a panel of random genomic Staphylococcus epidermidis DNA clones provided almost the same level of discrimination as the DNA fingerprinting technique and also provided a clearer profile. DNA and gene fingerprinting techniques were reproducible and highly discriminatory compared to typing based on antigen and plasmid profiles, antibiotic susceptibility patterns and biotypes.

Identification of the innate human immune response to surface-exposed proteins of coagulase-negative staphylococci

The presumed host defense against coagulase-negative staphylococci (ConS), recognized pathogens in hosts with compromised immunity or indwelling medical devices, is opsonophagocytosis. Targets for opsonization remain unclear. Using radiolabeling techniques, we identified the surface-exposed proteins of ConS and determined the innate humoral immune responses to them among healthy adults. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of surface proteins extrinsically labeled with 125I demonstrated 20 to 30 proteins with molecular weights of 15,000 to greater than 130,000. Five to ten of these proteins were immunogenic and recognized by normal human sera, including predominant 18-, 41-, 48-, and 51-kDa proteins. We also evaluated the humoral response of cancer patients with ConS bacteremia. Patients' sera obtained before bacteremic episodes demonstrated a pattern of reactivity similar to that of normal human sera. When patients' sera obtained after bacteremic episodes were used to determine whether an expanded immune response followed infection, only one of seven showed reactivity with more proteins than seen with the innate response. Western blot (immunoblot) analysis and whole-cell enzyme-linked immunosorbent assays were also evaluated. This study identifies (i) the surface-exposed proteins available for host interaction, (ii) the innate human antibody response to these proteins, and (iii) the immune response of cancer patients with ConS bacteremia.

Application of gas-liquid chromatographic analysis of cellular fatty acids for species identification and typing of coagulase-negative staphylococci

Gas-liquid chromatography (GLC) of bacterial cellular fatty acids was used to analyze 264 isolates of coagulase-negative staphylococci, of which 178 were Staphylococcus epidermidis. The presence and amounts of individual fatty acids were determined to generate fatty acid profiles for each of the seven coagulase-negative species tested. The fatty acid profiles were then analyzed by computerized correlation and cluster analysis to calculate mean correlation values between isolates belonging to the same or different species, as well as to establish cluster analysis dendrograms. These data ultimately allowed the clustering of individual samples into species-specific clusters. Species identification by the GLC clustering was highly consistent with species identification by biochemical assays; the results were similar in 92.4% of the cases. The GLC profile correlation analysis was further used to analyze multiple blood isolates from 60 patients in order to determine the usefulness of this methodology in establishing identity, as well as differences, between consecutive patient isolates. The correlation between those multiple S. epidermidis isolates determined to be identical by standard techniques (such as the antibiogram, biotype, and plasmid profile) was significantly (P less than 0.001) higher than that between random isolates of the same species. The correlation coefficient was greater than 97 for 40 (97.6%) of the 41 patients with multiple identical blood isolates, compared with less than 95 in all 19 (100.0%) patients with multiple nonidentical isolates. The successful use of the computerized GLC analysis in this study demonstrated its appropriate application for species identification and typing of coagulase-negative staphylococci.

Defining Staphylococcus epidermidis cell wall proteins

Three Staphylococcus epidermidis isolates of differing bacteriophage types were studied to define proteins confined to the cell wall, which were surface exposed and thus available to interact with the host. Three major proteins of 37, 41, and 51 kDa were identified in all whole-cell lysates and cell wall extracts by sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis. Two additional proteins of 18 and 25 kDa became evident by using 125I labeling to delineate surface-exposed proteins. A classification scheme using P1 to P5 to delineate the 51-, 41-, 37-, 25- and 18-kDa proteins is proposed. Additionally, murine immune sera were used to identify two immunodominant proteins of 51 and 25 kDa (P1 and P4, respectively).