Biofilms--matrix-enclosed microbial accretions that adhere to biological or non-biological surfaces--represent a significant and incompletely understood mode of growth for bacteria. Biofilm formation appears early in the fossil record (approximately 3.25 billion years ago) and is common throughout a diverse range of organisms in both the Archaea and Bacteria lineages, including the 'living fossils' in the most deeply dividing branches of the phylogenetic tree. It is evident that biofilm formation is an ancient and integral component of the prokaryotic life cycle, and is a key factor for survival in diverse environments. Recent advances show that biofilms are structurally complex, dynamic systems with attributes of both primordial multicellular organisms and multifaceted ecosystems. Biofilm formation represents a protected mode of growth that allows cells to survive in hostile environments and also disperse to colonize new niches. The implications of these survival and propagative mechanisms in the context of both the natural environment and infectious diseases are discussed in this review.

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Bacterial biofilms: from the natural environment to infectious diseases.

Guideline for Prevention of Surgical Site Infection, 1999 ☆ ☆☆ ★ ★★

The “Guideline for Prevention of Surgical Site Infection, 1999” presents the Centers for Disease Control and Prevention (CDC)'s recommendations for the prevention of surgical site infections (SSIs), formerly called surgical wound infections. This two-part guideline updates and replaces previous guidelines.Part I, “Surgical Site Infection: An Overview,” describes the epidemiology, definitions, microbiology, pathogenesis, and surveillance of SSIs. Included is a detailed discussion of the pre-, intra-, and postoperative issues relevant to SSI genesis.

/pdf/guideline-for-prevention-of-surgical-site-infection-1999-2k3en33kqw.pdf

Guideline for Prevention of Surgical Site Infection, 1999

Biomaterials are being used with increasing frequency for tissue substitution. Complex devices such as total joint replacements and the total artificial heart represent combinations of polymers and metal alloys for system and organ replacement. The major barriers to the extended use of these devices are the possibility of bacterial adhesion to biomaterials, which causes biomaterial-centered infection, and the lack of successful tissue integration or compatibility with biomaterial surfaces. Interactions of biomaterials with bacteria and tissue cells are directed not only by specific receptors and outer membrane molecules on the cell surface, but also by the atomic geometry and electronic state of the biomaterial surface. An understanding of these mechanisms is important to all fields of medicine and is derived from and relevant to studies in microbiology, biochemistry, and physics. Modifications to biomaterial surfaces at an atomic level will allow the programming of cell-to-substratum events, thereby diminishing infection by enhancing tissue compatibility or integration, or by directly inhibiting bacterial adhesion.

https://science.sciencemag.org/content/sci/237/4822/1588.full.pdf

Biomaterial-centered infection: microbial adhesion versus tissue integration.

The adherence of coagulase-negative staphylococci to smooth surfaces was assayed by measuring the optical densities of stained bacterial films adherent to the floors of plastic tissue culture plates. The optical densities correlated with the weight of the adherent bacterial film (r = 0.906; P less than 0.01). The measurements also agreed with visual assessments of bacterial adherence to culture tubes, microtiter plates, and tissue culture plates. Selected clinical strains were passed through a mouse model for foreign body infections and a rat model for catheter-induced endocarditis. The adherence measurements of animal passed strains remained the same as those of the laboratory-maintained parent strain. Spectrophotometric classification of coagulase-negative staphylococci into nonadherent and adherent categories according to these measurements had a sensitivity, specificity, and accuracy of 90.6, 80.8, and 88.4%, respectively. We examined a previously described collection of 127 strains of coagulase-negative staphylococci isolated from an outbreak of intravascular catheter-associated sepsis; strains associated with sepsis were more adherent than blood culture contaminants and cutaneous strains (P less than 0.001). We also examined a collection of 84 strains isolated from pediatric patients with cerebrospinal fluid (CSF) shunts; once again, pathogenic strains were more adherent than were CSF contaminants (P less than 0.01). Finally, we measured the adherence of seven endocarditis strains. As opposed to strains associated with intravascular catheters and CSF shunts, endocarditis strains were less adherent than were saprophytic strains of coagulase-negative staphylococci. The optical densities of bacterial films adherent to plastic tissue culture plates serve as a quantitative model for the study of the adherence of coagulase-negative staphylococci to medical devices, a process which may be important in the pathogenesis of foreign body infections. Images

Adherence of coagulase-negative staphylococci to plastic tissue culture plates: a quantitative model for the adherence of staphylococci to medical devices.

Slime production is not a generally recognized feature of Staphylococcus epidermidis. In a recent outbreak of S. epidermidis intravascular catheter-associated sepsis, we noted that 63% of clinically implicated strains grew as a slimy film coating the culture tube walls when propagated in tryptic soy broth. Only 37% of randomly collected blood culture contaminants and skin isolates demonstrated a similar phenomenon (p less than 0.05). Transmission electron micrographs of these coating bacteria showed them to be encased in an extracellular matrix that stained with alcian blue. Slime production was most evident in autoclaved media containing Casamino Acids and glucose supplementation (0.25% wt/vol). There were strain and media preparation variability of slime production in the presence of other carbohydrates. Some strains were not able to produce slime under any of the tested conditions. The production or nonproduction of slime did not influence growth rate. When grown in vitro, slime producers accumulated on the surface of intravascular catheters as macrocolonies, whereas non-slime, producers did not. Transmission and scanning electron micrographs showed slime producers to be encased in an adhesive layer on the catheter surface, whereas nonproducers were not encased. These results suggest that slime-mediated adherence may be a critical factor in the pathogenesis of S. epidermidis infections of medical devices.

Adherence of slime-producing strains of Staphylococcus epidermidis to smooth surfaces.

On occasion, a patient may have two or more clinical cultures yielding a coagulase-negative staphylococcus If these multiple isolates have the same phenotype, one might conclude that the same strain was reisolated from the patient, indicating its persistent and pathological presence. We examined the validity of this conclusion when we applied a number of characterizing systems to a collection of 143 isolates of coagulase-negative staphylococci collected during an outbreak of intravascular catheter-associated sepsis. The probability of classifying two random isolates as the same phenotype or species was as follows: P = 0.356 for phage typing, P = 0.348 for Baird-Parker biotyping, P = 0.346 for the API STAPH-IDENT (Analytab Products) system, P = 0.327 for Bentley et al. biotyping, and P = 0.077 for antimicrobial susceptibility patterns. Although antimicrobial susceptibility patterns had the lowest probability, a variability in test results of 7.7% and a tendency for strains to have similar antibiograms effectively raised the probability to P = 0.897. The combination of the API STAPH-IDENT with antibiograms resulted in a probability of P = 0.037 to P = 0.147. When all of the above methods were used together a probability of P = 0.014 was achieved. Five patients had isolates from two or more blood cultures spaced more than 1 day apart that were identical by all of the above criteria, thus confirming prolonged bacteremia. The collection was also examined for the incidence of slime production. Slime production was not associated with any of the above groups, but was associated with symptomatic infections (P less than 0.05) and gentamicin resistance (P less than 0.01). Slime production was strain stable and was of assistance in typing strains of coagulase-negative staphylococci.

Characterization of clinically significant strains of coagulase-negative staphylococci

The virulence of two previously described Staphylococcus epidermidis strains was examined in an experimental model of foreign body infection in mice. Animals challenged with the slime-producing strain developed three times as many infections as animals challenged with the strain that did not produce slime (P less than 0.001). Bacterial isolates recovered from the infected sites retained the characteristics of the inoculated strain. Animals without foreign bodies but challenged in a similar manner with either staphylococcal strain did not become infected. Thus, the presence of a foreign body predisposed the animals to S. epidermidis infection. These results indicate that the production of slime by S. epidermidis is a stable characteristic retained after animal passage and may be important in the pathogenesis of these infections. Images

Experimental foreign body infections in mice challenged with slime-producing Staphylococcus epidermidis.

We collected and characterized 85 strains of coagulase-negative staphylococci (51 pathogens and 34 contaminants) from cerebrospinal fluid shunts. All isolates were classified by species and characterized by antimicrobial susceptibility and quantitative adherence to plastic tissue culture plates. There were more adherent organisms among pathogens than among contaminants (P less than .01). Species distribution was similar for both groups; however, 20% of the pathogens and none of the contaminants were phosphatase-negative Staphylococcus epidermidis (P less than .05). Resistance to four or more antimicrobial agents was detected in 45% of both groups. Neither species designation nor antimicrobial resistance correlated with clinical outcome. Five (83%) of six infections due to nonadherent (vs. 16 [41%] of 39 due to adherent; P less than .05) coagulase-negative staphylococci were, however, cured with antimicrobial therapy alone. Cure was highly associated with removal of the colonized shunt--38% of infected patients treated with antimicrobial therapy alone were cured, 75% treated with antimicrobial therapy and partial shunt removal were cured, and all treated with antimicrobial therapy and total shunt replacement were cured.

Coagulase-Negative Staphylococci Isolated from Cerebrospinal Fluid Shunts: Importance of Slime Production, Species Identification, and Shunt Removal to Clinical Outcome

Gordon D. Christensen

Papers

Adherence of coagulase-negative staphylococci to plastic tissue culture plates: a quantitative model for the adherence of staphylococci to medical devices.

Adherence of slime-producing strains of Staphylococcus epidermidis to smooth surfaces.

Characterization of clinically significant strains of coagulase-negative staphylococci

Experimental foreign body infections in mice challenged with slime-producing Staphylococcus epidermidis.

Coagulase-Negative Staphylococci Isolated from Cerebrospinal Fluid Shunts: Importance of Slime Production, Species Identification, and Shunt Removal to Clinical Outcome