Antibiotic resistance in exopolysaccharide-forming Staphylococcus epidermidis clinical isolates from orthopaedic implant infections

The opportunistic pathogen Staphylococcus epidermidis is able to produce biofilm and to frequently cause implant infections. In recent years, it has also exhibited an increasing antimicrobial drug resistance. Here, the resistance to a panel of 16 different antibiotics in 342 clinical strains of S. epidermidis from orthopaedic implant infections has been investigated. The isolates were pheno- and genotyped for extracellular polysaccharide production, relevant to staphylococcal biofilm formation, in order to ascertain possible associations with antibiotic resistance. Approximately 10% of the isolates were found to be sensitive to all screened antibiotics. In all, 37-38% were resistant to beta-lactams such as oxacillin and imipenem, while the resistance to penicillin, ampicillin, cefazolin, cefamandole, was consistently observed in over 80% of the strains. Erythromycin- and clindamycin- resistant strains were approximately 41% and 16%, respectively. Of the isolates, 10% was resistant to chloramphenicol, 23% to sulfamethoxazole and 26% to ciprofloxacin. Resistance to vancomycin was never observed. Interestingly, exopolysaccharide-producing strains exhibited a significantly higher prevalence in the resistance to the four aminoglycosides (gentamicin, amikacin, netilmicin, tobramycin), to sulfamethoxazole and to ciprofloxacin with respect to non-producing isolates. Moreover, multiple resistance to antibiotics was more frequent among exopolysaccharide-forming strains.     

Biofilm formation by Propionibacterium acnes on biomaterials in vitro and in vivo: impact on diagnosis and treatment

Propionibacterium acnes is found increasingly as a cause of delayed infection, usually involving implanted biomaterials. Despite susceptibility to common antibiotics, such infections are very difficult to treat and usually require surgical removal of the device. Three clinical isolates of P. acnes were assessed for ability to adhere to titanium, surgical steel and silicone, with and without a plasma conditioning film. After adherence, the biomaterials were then incubated for a further 6 days and examined for biofilm development. All three isolates adhered to all three biomaterials similarly. Importantly, we were able to demonstrate biofilm formation, including production of exopolymer similar in appearance to the polysaccharide intercellular adhesin of Staphylococcus epidermidis. A case summary also demonstrated failure to eradicate P. acnes infection in a hydrocephalus shunt after prolonged treatment. The removed shunt showed obvious biofilm formation, initially obscured by exopolymer when viewed by environmental scanning electron microscopy. Biofilm development by P. acnes explains the difficulties encountered in clinical management of such infections.     

Ica-expression and gentamicin susceptibility of Staphylococcus epidermidis biofilm on orthopedic implant biomaterials

Ica-expression by Staphylococcus epidermidis and slime production depends on environmental conditions such as implant material and presence of antibiotics. Here, we evaluate biofilm formation and ica-expression of S. epidermidis strains on biomaterials involved in total hip- and knee arthroplasty [polyethylene (PE), polymethylmethacrylate (PMMA), stainless steel (SS)]. Ica-expression, assayed using real-time RT-PCR, was highest on PE as confirmed using confocal laser scanning microscopy. Yet biofilm formation by S. epidermidis was most extensive on SS, with less slime production. Ica-expression and slime production were minimal on PMMA. After 3 h of continued growth of 24 h old biofilms in the presence of gentamicin, biofilms on PE showed lower susceptibility to gentamicin, relative to the other materials, presumably as a result of the stronger ica-expression. A higher gentamicin concentration further decreased metabolic activity on all biomaterials. It is concluded that the level of biomaterial-induced ica-expression does not correlate with the amount of biofilm formed, but initially aids bacteria in surviving antibiotic attacks. Once antibiotic treatment has started however, also the antibiotic itself induces slime production and only if its concentration is high enough, killing results. Results suggest that biomaterial-associated infections in orthopedics by S. epidermidis on PE may be more difficult to eradicate than on PMMA or SS.     

Application of a feasible method for determination of biofilm antimicrobial susceptibility in staphylococci

The aim of this study was to use a practical method to determine the minimal biofilm eradication concentration (MBEC) of vancomycin and to compare the MBEC with minimal inhibitory concentration (MIC) for biofilm-producing and non-biofilm-producing isolates of staphylococci. Forty Staphylococcus spp. isolates from central venous catheter, from distinct patients, were selected for this study. The vast majority (28/30) of isolates which were biofilm-producing, presented high MBEC values (≥8 μg/mL) and could be considered as non-susceptible to vancomycin. All non-biofilm-producing isolates presented low MBEC (≤2 μg/mL) and were susceptible to vancomycin, according to CLSI breakpoints. While the MBEC and MIC values for biofilm-producing isolates differ significantly, the MBEC and MIC values for non-biofilm producers were the same. The method we have used proved to be a feasible and rapid technique to measure MBEC of Staphylococcus spp. biofilms. The method presented herein might be an alternative tool to evaluate the antibiotic susceptibility in the biofilm mode of growth; the MBEC may be a more appropriate approach to correlate the susceptibility in vitro with clinical outcome resulting from the treatment of Staphylococcus spp. infection.     

解脲脲原体生物被膜形成与耐药性的相关性研究

目的 研究解脲脲原体(Ureaplasma urealyticum,Uu)标准株及临床分离株体外形成生物被膜的能力及游离状态与形成生物被膜后药物敏感性的差异.方法 对Uu标准株3、8血清型(Uu3、Uu8)及从女性患者宫颈中分离鉴定的21株Uu临床株进行体外培养后,扫描电镜、激光共聚焦显微镜鉴定生物被膜形成,并在生物被膜形成前后进行约敏测定(四环素、红霉素、环丙沙星).配对秩和检验及x2检验分别比较Uu游离状态及形成生物被膜后最低抑菌浓度间及耐药率间的差异.结果 Uu3、Uu8及21株Uu临床株均具有体外形成生物被膜的能力.Uu形成牛物被膜后对四环素、红霉素及环丙沙星的最低抑菌浓度较游离状态明显增高(P<0.001).Uu形成生物被膜后对红霉素及环丙沙星的耐药率增高具有统计学意义(P值分别为<0.001及0.035),但对四环素的耐药率增高无统计学意义(P=0.293).结论 Uu标准株及临床株均具有体外形成生物被膜的能力,Uu形成生物被膜后对抗菌素的抵抗力增加,出现了多重耐药现象.

Abstract：

Objective To study the ability of standard strain and clinical isolates of Ureaplasma spp. to form biofilms in vitro and to compare the antibiotic susceptibility of sessile cells and their planktonic counterparts. Methods A total of 21 Ureaplasma wealyticum(Uu) isolates recovered from female patients diagnosed with cervicitis and Uu serovar 3 and Uu serovar 8( Uu3, Uu8) were included. Scanning electron microscope and confocal scanning laser microscopy were used to identify biofilm formation. Conventional antibiotic susceptibility tests and biofilm susceptibility assays for tetracycline, erythromycin and ciprofloxacin were carried out. The paired rank sum test and was applied to analyze the statistical differences between the MIC and the minimal biofilm inhibitory concentration. The x2 test was applied to analyze the statistical differences of global resistance percentages between planktonic cells and sessile cells. Results Uu3, Uu8 and 21 Uu isolates all can form biofilms in vitro. Minimal inhibitory concentration of sessile cells compared with planktonic cells were obviously higher for tetracycline, erythromycin and ciprofloxacin (P <0.001). Global resistance percentages between planktonic cells and sessile cells were different for erythromycin (9.52% vs 61.90% , P < 0. 001), ciprofloxacin ( 80. 95% vs 100% , P = 0. 035 ) and tetracycline (4. 76% vs 14.29% , P =0.293). Conclusion Uu isolates and Uu1, Uu8 all can form biofilms in vitro, and biofilm formation can strengthen resistance of Uu to antibiotics, even multidrug resistance was observed.     

解脲脲原体生物被膜形成与耐药性的相关性研究

目的 研究解脲脲原体(Ureaplasma urealyticum,Uu)标准株及临床分离株体外形成生物被膜的能力及游离状态与形成生物被膜后药物敏感性的差异.方法 对Uu标准株3、8血清型(Uu3、Uu8)及从女性患者宫颈中分离鉴定的21株Uu临床株进行体外培养后,扫描电镜、激光共聚焦显微镜鉴定生物被膜形成,并在生物被膜形成前后进行约敏测定(四环素、红霉素、环丙沙星).配对秩和检验及x2检验分别比较Uu游离状态及形成生物被膜后最低抑菌浓度间及耐药率间的差异.结果 Uu3、Uu8及21株Uu临床株均具有体外形成生物被膜的能力.Uu形成牛物被膜后对四环素、红霉素及环丙沙星的最低抑菌浓度较游离状态明显增高(P<0.001).Uu形成生物被膜后对红霉素及环丙沙星的耐药率增高具有统计学意义(P值分别为<0.001及0.035),但对四环素的耐药率增高无统计学意义(P=0.293).结论 Uu标准株及临床株均具有体外形成生物被膜的能力,Uu形成生物被膜后对抗菌素的抵抗力增加,出现了多重耐药现象.     

Sequential analysis of staphylococcal colonization of body surfaces of patients undergoing vascular surgery.

Slime-producing coagulase-negative staphylococci are pathogens in vascular surgery by virtue of their ability to adhere to and persist on prosthetic graft material. Inguinal and abdominal skin sites were cultured in 41 patients upon hospitalization, and slime production and antimicrobial susceptibility were assessed in all recovered staphylococcal isolates. Twenty-one patients eventually underwent lower-extremity revascularization. In the operative population, cultures were also obtained on the day of surgery and fifth postoperative day. All 21 patients received perioperative cefazolin. Of 327 coagulase-negative staphylococci recovered, Staphylococcus epidermidis (47%), S. haemolyticus (21%), and S. hominis (10%) were the predominant isolates. Slime-producing coagulase-negative staphylococci were recovered from 17 of 21 patients at admission but only from 8 of 21 patients on day 5 postoperation (P less than 0.05). S. epidermidis isolates demonstrated increasing multiple resistance from admission to 5 days postoperation to methicillin, gentamicin, clindamycin, erythromycin, and trimethoprim-sulfamethoxazole (P less than 0.05). All coagulase-negative staphylococcal isolates were susceptible to ciprofloxacin and vancomycin. Slime-producing capability was not associated with increased methicillin resistance for the recovered isolates. The data demonstrate that patients enter the hospital colonized with slime-producing strains of coagulase-negative staphylococci and that during hospitalization the staphylococcal skin burden shifts from a predominately susceptible to a resistant microbial population, which may enhance the importance of slime production as a risk factor in lower-extremity revascularization.     

Speciation and antibiotic susceptibility patterns of coagulase-negative staphylococci

During a six month period, 191 isolates of coagulase-negative staphylococci from blood, urine, cerebrospinal fluid and heart valves were identified to species level and tested for antimicrobial susceptibility. Seventy-one percent of isolates wereStaphylococcus epidermidis, 8 %Staphylococcus warneri, 7 %Staphylococcus hominis, 7 %Staphylococcus haemolyticus, 4 %Staphylococcus capitis, 2 %Staphylococcus saprophyticus and 1 %Staphylococcus cohnii. Approximately 4 % of isolates were felt to be associated with infection. Overall, 18% of isolates were susceptible to penicillin G, 61 % oxacillin, 98 % cephalothin, 98 % cefamandole, 72 % cefotaxime, 95 % cefsulodin, 76 % gentamicin, 64 % clindamycin and 98 % rifampicin. All isolates were susceptible to vancomycin. Vancomycin, rifampicin, cephalothin and cefamandole showed excellent activity against oxacillin-resistant isolates. With one exception, speciation was not helpful in determining whether or not an isolate was associated with infection.     

Biofilm formation by Propionibacterium acnes is associated with increased resistance to antimicrobial agents and increased production of putative virulence factors

Propionibacterium acnes plays an important role in the pathogenesis of acne vulgaris, a common disorder of the pilosebaceous follicles. Recently, it was suggested that P. acnes cells residing within the follicles grow as a biofilm. In the present study, we tested the biofilm-forming ability of several P. acnes strains in a microtiter plate model. We also evaluated the resistance of biofilm-grown P. acnes towards antimicrobial agents commonly used in the treatment of acne and the production of putative virulence factors. Our results indicate that P. acnes can form biofilms in vitro. The results also show that sessile P. acnes cells are more resistant to various commonly used antimicrobial agents than planktonic cells. In addition, sessile cells produce more extracellular lipases as well as significant amounts of the quorum-sensing molecule autoinducer-2.     

Effects of tigecycline, linezolid and vancomycin on biofilms of viridans streptococci isolates from patients with endocarditis

BACKGROUND: Endocarditis, and prosthetic valve endocarditis in particular, is a serious disease with high morbidity and mortality. We investigate the effects of tigecycline, linezolid and vancomycin on biofilms of viridans group streptococci (VGS) isolated from patients with definite native or prosthetic valve endocarditis. METHODS AND RESULTS: Ten of 20 VGS blood stream isolates from patients with endocarditis formed biofilms in the microtiter plate biofilm model. The minimal inhibitory concentrations (MIC) for tigecycline, linezolid and vancomycin were determined using the microdilution broth method. Biofilms were grown for 24 hours and were incubated with tigecycline, linezolid and vancomycin at increasing concentrations from 1-128x MIC of the isolate being tested. Biofilm thickness was quantified by measuring the optical density (OD) after dyeing it with crystal violet. The incubation of the biofilms with tigecycline, linezolid or vancomycin resulted in a significant reduction of OD compared to the control biofilm without antibiotic (p<0.05). The optical density ratio (Odr) decreased significantly at 2x MIC for tigecycline, and at 8x MIC for linezolid and vancomycin (p<0.05). Although biofilms persisted even at the highest antibiotic concentrations of 128x MIC, bacterial growth was eradicated starting at concentrations of 16x MIC for vancomycin and of 32x MIC for linezolid, but not for tigecycline, up to a concentration of 128x MIC. CONCLUSIONS: In the present study on viridans streptococci isolated from patients with endocarditis, tigecycline and linezolid reduced the density of the biofilms as effectively as vancomycin. However, linezolid and vancomycin were bactericidal at higher concentrations. Linezolid and vancomycin at very high doses may be useful in the treatment of biofilm-associated diseases caused by VGS infections.     

Assessment of pheromone response in biofilm forming clinical isolates of high level gentamicin resistant Enterococcus faecalis

Twenty five clinical isolates of high level gentamicin resistant Enterococcus faecalis were tested for their biofilm formation and pheromone responsiveness. The biofilm assay was carried out using microtiter plate method. Two isolates out of the 25 (8%) were high biofilm formers and 19 (76%) and four (16%) isolates were moderate and weak biofilm formers respectively. All the isolates responded to pheromones of E. faecalis FA2-2 strain. On addition of pheromone producing E. faecalis FA2-2 strain to these isolates, seven of 19 (37%) moderate biofilm formers developed into high biofilm formers. Similarly one of the 4 (25%) weak biofilm formers developed into high level biofilm former. Twelve (48%) of the 25 isolates were transconjugated by cross streak method using gentamicin as selective marker. This proves that the genetic factor for gentamicin resistance is present in the pheromone responsive plasmid. Among these twelve transaconjugants, seven isolates and one isolate were high biofilm formers on addition of E. faecalis FA2-2 and prior to its addition respectively. Out of the total 25 isolates, eight transconjugants for gentamicin resistance could turn to high biofilm formers on addition of the pheromone producing strain. All the isolates were resistant to more than two antibiotics tested. All the isolates were sensitive to vancomycin. The results indicate the significance of this nosocomial pathogen in biofilm formation and the role of pheromone responding clinical isolates of E. faecalis in spread of multidrug resistance genes.     

Polysaccharide intercellular adhesin or protein factors in biofilm accumulation of Staphylococcus epidermidis and Staphylococcus aureus isolated from prosthetic hip and knee joint infections

Nosocomial staphylococcal foreign-body infections related to biofilm formation are a serious threat, demanding new therapeutic and preventive strategies. As the use of biofilm-associated factors as vaccines is critically restricted by their prevalence in natural staphylococcal populations we studied the distribution of genes involved in biofilm formation, the biofilm phenotype and production of polysaccharide intercellular adhesin (PIA) in clonally independent Staphylococcus aureus and Staphylococcus epidermidis strains isolated from prosthetic joint infections after total hip or total knee arthroplasty. Biofilm formation was detected in all S. aureus and 69.2% of S. epidermidis strains. Importantly, 27% of biofilm-positive S. epidermidis produced PIA-independent biofilms, in part mediated by the accumulation associated protein (Aap). Protein-dependent biofilms were exclusively found in S. epidermidis strains from total hip arthroplasty (THA). In S. aureus PIA and proteins act cooperatively in biofilm formation regardless of the infection site. PIA and protein factors like Aap are of differential importance for the pathogenesis of S. epidermidis in prosthetic joint infections (PJI) after THA and total knee arthroplasty (TKA), implicating that icaADBC cannot serve as a general virulence marker in this species. In S. aureus biofilm formation proteins are of overall importance and future work should focus on the identification of functionally active molecules.     

解脲脲原体生物被膜形成与耐药性的相关性研究

目的 研究解脲脲原体(Ureaplasma urealyticum,Uu)标准株及临床分离株体外形成生物被膜的能力及游离状态与形成生物被膜后药物敏感性的差异.方法 对Uu标准株3、8血清型(Uu3、Uu8)及从女性患者宫颈中分离鉴定的21株Uu临床株进行体外培养后,扫描电镜、激光共聚焦显微镜鉴定生物被膜形成,并在生物被膜形成前后进行约敏测定(四环素、红霉素、环丙沙星).配对秩和检验及x2检验分别比较Uu游离状态及形成生物被膜后最低抑菌浓度间及耐药率间的差异.结果 Uu3、Uu8及21株Uu临床株均具有体外形成生物被膜的能力.Uu形成牛物被膜后对四环素、红霉素及环丙沙星的最低抑菌浓度较游离状态明显增高(P<0.001).Uu形成生物被膜后对红霉素及环丙沙星的耐药率增高具有统计学意义(P值分别为<0.001及0.035),但对四环素的耐药率增高无统计学意义(P=0.293).结论 Uu标准株及临床株均具有体外形成生物被膜的能力,Uu形成生物被膜后对抗菌素的抵抗力增加,出现了多重耐药现象.     

Antimicrobial resistance among faecal enterococci from healthy individuals in Portugal

Analysis of 247 faecal enterococcal isolates from 99 healthy Portuguese individuals during 2001 revealed the presence of enterococci resistant to vancomycin (5%) and highly resistant to streptomycin (52%), kanamycin (40%) or gentamicin (11%). Most isolates were also resistant to tetracycline, erythromycin, ciprofloxacin and quinupristin-dalfopristin. The vanA (two Tn1546 types), vanC1, erm(B), aac(6')-aph(2')-Ia, aph(3')-IIIa, vat(E) and vat(D) genes were detected. Enterococcus faecalis and Enterococcus faecium isolates with high-level resistance to gentamicin were related to Portuguese poultry isolates described previously. E. faecium isolates that were highly resistant to vancomycin or gentamicin harboured different housekeeping purK alleles associated previously with different hosts.     

In-vitro activities of cefamandole and cephalothin against 1,881 clinical isolates. A multi-center study

By use of an agardilution technic, 1,881 clinical isolates were tested against cefamandole and cephalothin. The isolates represented 18 genera, recovered in five geographically separate centers within the United States. The majority of strains were susceptible (MICs less than or equal to 8 micrograms/ml) to both drugs. Cefamandole showed greater activity against most of the bacterial pathogens. Enterococci, Serratia spp., and Acinetobacter spp. were resistant to both drugs. Cephalothin was more active against Staphylococcus aureus, and both cephalosporins were relatively inactive against methicillin-resistant strains of S. aureus. Enterobacter spp. and indole-positive Proteus spp. were susceptible to cefamandole but resistant to cephalothin.     

Antibiotic multiresistance strictly associated with IS256 and ica genes in Staphylococcus epidermidis strains from implant orthopedic infections

In this study the presence both of the ica genes, encoding for biofilm exopolysaccharide production, and the insertion sequence IS256, a mobile element frequently associated to transposons, was investigated in relationship with the prevalence of antibiotic resistance among Staphylococcus epidermidis strains. The investigation was conducted on 70 clinical isolates derived from orthopedic implant infections. Among the clinical isolates investigated a dramatic high level of association was found between the presence of ica genes as well as of IS256 and multiple-resistance to all the antibiotics tested (oxacillin, penicillin, gentamicin, erythromycin, clindamycin, chloramphenicol, sulfamethoxazole + trimethoprim, ciprofloxacin, vancomycin). Noteworthy, a striking full association between the presence of IS256 and resistance to gentamicin was found, being none of the IS256-negative strain resistant to this antibiotic. This association is probably because of the link of the corresponding aminoglycoside-resistance genes, and IS256, often co-existing within the same staphylococcal transposon. In conclusion, in orthopedics, the presence of ica genes and that of IS256 in S. epidermidis genome should both be considered as informative markers of clinically relevant strains equipped with greatest and broadest resistance potential to survive to medical treatments.     

Propionibacterium acnes types I and II represent phylogenetically distinct groups

Although two phenotypes of the opportunistic pathogen Propionibacterium acnes (types I and II) have been described, epidemiological investigations of their roles in different infections have not been widely reported. Using immunofluorescence microscopy with monoclonal antibodies (MAbs) QUBPa1 and QUBPa2, specific for types I and II, respectively, we investigated the prevalences of the two types among 132 P. acnes isolates. Analysis of isolates from failed prosthetic hip implants (n = 40) revealed approximately equal numbers of type I and II organisms. Isolates from failed prosthetic hip-associated bone (n = 6) and tissue (n = 38) samples, as well as isolates from acne (n = 22), dental infections (n = 8), and skin removed during surgical incision (n = 18) were predominately of type I. A total of 11 (8%) isolates showed atypical MAb labeling and could not be conclusively identified. Phylogenetic analysis of P. acnes by nucleotide sequencing revealed the 16S rRNA gene to be highly conserved between types I and II. In contrast, sequence analysis of recA and a putative hemolysin gene (tly) revealed significantly greater type-specific polymorphisms that corresponded to phylogenetically distinct cluster groups. All 11 isolates with atypical MAb labeling were identified as type I by sequencing. Within the recA and tly phylogenetic trees, nine of these isolates formed a cluster distinct from other type I organisms, suggesting a further phylogenetic subdivision within type I. Our study therefore demonstrates that the phenotypic differences between P. acnes types I and II reflect deeper differences in their phylogeny. Furthermore, nucleotide sequencing provides an accurate method for identifying the type status of P. acnes isolates.     

Biofilm formation by Propionibacterium acnes is a characteristic of invasive isolates

Propionibacterium acnes is a common and probably underestimated cause of delayed joint prosthesis infection. Bacterial biofilm formation is central in the pathogenesis of infections related to foreign material, and P. acnes has been shown to form biofilm both in vitro and in vivo. Here, biofilm formation by 93 P. acnes isolates, either from invasive infections ( n  = 45) or from the skin of healthy people ( n  = 48), was analysed. The majority of isolates from deep infections produced biofilm in a microtitre model of biofilm formation, whereas the skin isolates were poor biofilm producers (p <0.001 for a difference). This indicates a role for biofilm formation in P. acnes virulence. The type distribution, as determined by sequencing of recA , was similar among isolates isolated from skin and from deep infections, demonstrating that P. acnes isolates with different genetic backgrounds have pathogenic potential. The biofilm formed on plastic and on bone cement was analysed by scanning electron microscopy (EM) and by transmission EM. The biofilm was seen as a 10-μm-thick layer covering the bacteria and was composed of filamentous as well as more amorphous structures. Interestingly, the presence of human plasma in solution or at the plastic surface inhibits biofilm formation, which could explain why P. acnes primarily infect plasma-poor environments of, for example, joint prostheses and cerebrospinal shunts. This work underlines the importance of biofilm formation in P. acnes pathogenesis, and shows that biofilm formation should be considered in the diagnosis and treatment of invasive P. acnes infections.     

Effects on antibiotic resistance of Staphylococcus epidermidis following adhesion to polymethylmethacrylate and to silicone surfaces

A number of studies appears to give emphasis to the role of prosthetic materials in determining microbial adherence and resistance to host defence and drug therapy. Aim of this study was to explore whether the direct contact with biomaterial substrata of different chemical nature could influence bacterial behaviour, determining possible changes in the bacteria population as far as antibiotic resistance is concerned. To this end, susceptibility to penicillin, erythromycin, clindamycin, cefamandole, imipenem, vancomycin, ciprofloxacin. ampicillin, cefazolin, trimethoprim-sulfamethoxazole, chloramphenicol, amikacin and netilmicin was evaluated in a methicillin-, gentamicin- and tobramycin-resistant Staphylococcus epidermidis strain, after in vitro adhesion to polymethylmethacrylate (PM MA) and to silicone elastomer. The susceptibility to antibiotics of both adherent bacteria and bacteria which, although exposed to the materials, had not undergone adhesion was measured as bacterial growth inhibition area onto a plate antibiogram. according to Kirby-Bauer and using an image analyser system. The results obtained suggest that the two test materials considered in this study were capable to condition bacterial behaviour. In particular. the adhesion onto PMMA surfaces induced a marked and significant decrease in susceptibility to the following beta-lactam antibiotics: cefamandole (32%), cefazolin (23%), imipenem (27%), ampicillin (31%). Moreover, PMMA caused a lower but significant reduction in resistance to vancomycin (15%), chloramphenicol (16%), amikacin (13%). netilmicin (13%), erythromycin (11%) trimethoprim-sulfamethoxazole (13%). In contrast, the adhesion onto silicone elastomer appeared to influence bacterial changes to a lesser extent and elicited a significant decrease in susceptibility only to cefazolin (10%) and amikacin (11). Further studies are required to thoroughly investigate the mechanisms of these variations, even though, also according to other authors, one of the best conceivable conclusions is that some material substrata can lead to selection of variant adhesive bacteria with increased antibiotic resistance.     

Experimental model of biofilm implant-related osteomyelitis to test combination biomaterials using biofilms as initial inocula

Currently, the majority of animal models that are used to study biofilm-related infections use planktonic bacterial cells as initial inocula to produce positive signals of infection in biomaterials studies. However, the use of planktonic cells has potentially led to inconsistent results in infection outcomes. In this study, well-established biofilms of methicillin-resistant Staphylococcus aureus were grown and used as initial inocula in an animal model of a Type IIIB open fracture. The goal of the work was to establish, for the first time, a repeatable model of biofilm implant-related osteomyelitis, wherein biofilms were used as initial inocula to test combination biomaterials. Results showed that 100% of animals that were treated with biofilms developed osteomyelitis, whereas 0% of animals not treated with biofilm developed infection. The development of this experimental model may lead to an important shift in biofilm and biomaterials research by showing that when biofilms are used as initial inocula, they may provide additional insights into how biofilm-related infections in the clinic develop and how they can be treated with combination biomaterials to eradicate and/or prevent biofilm formation.