Effect of two cleaning processes for bone allografts on gentamicin impregnation and in vitro antibiotic release.

Bone allografts are a useful and sometimes indispensable tool for the surgeon to repair bone defects. Microbial contamination is a major reason for discarding allografts from bone banks. To improve the number of safe allografts, we suggest chemical cleaning of the grafts followed by antibiotic impregnation. Comparison of two chemical cleaning processes for bone allografts aiming for antibiotic impregnation and consequently delivery rates in vitro. Bone chips of 5-10 mm were prepared from human femoral heads. Two cleaning methods (cleaning A and cleaning B) based on solutions containing hydrogen peroxide, paracetic acid, ethanol and biological detergent were carried out and compared. After the cleaning processes, the bone chips were impregnated with gentamicin. Bacillus subtilis bioassay was used to determine the gentamicin release after intervals of 1-7 days. Differences were compared with non-parametric Mann-Whitney U tests. The zones of inhibition obtained from the bone grafts cleaned with both cleaning processes were similar between the groups. The concentration of the released antibiotic was decreasing gradually over time, following a similar pattern for both groups. The cleaning procedure A as well as the cleaning procedure B for bone allografts allowed the impregnation with gentamicin powder in the same concentrations in both groups. The delivery of gentamicin was similar for both groups. Both cleaning procedures were easy to be carried out, making them suitable for routine use at the bone banks.

Effect of storage temperature on gentamicin release from antibiotic-coated bone chips.

Freezing is the most common method for storing bones until use in skeletal reconstruction. However, the effect of freezing on antibiotic delivery from antibiotic-coated bone has not been evaluated. In this study, we compared antibiotic delivery in vitro from gentamicin-coated human bone stored at different temperatures. Bone chips obtained from human femur heads were chemically cleaned and mixed with gentamicin sulfate. Samples were stored for 4 months at -20 °C, 4 months at -80 °C, or evaluated immediately without freezing. Antibiotic release from the bone chips was measured using Bacillus subtilis as an indicator strain. Zones of inhibition and rates of gentamicin release were similar in all three groups. Storage at -20 and -80 °C for bone allografts has no effect on gentamicin release from chemically cleaned bone chips.

Staphylococcus aureus biofilm formation and antibiotic susceptibility tests on polystyrene and metal surfaces.

AIM: We compared the MBEC™-HTP assay plates made of polystyrene with metal discs composed of TMZF(®) and CrCo as substrates for biofilm formation. METHODS AND RESULTS: Staphylococcus aureus was grown on polystyrene and on metal discs made of titanium and chrome-cobalt. Antibiotic susceptibility was assessed by examining the recovery of cells after antibiotic exposure and by measuring the biofilm inhibitory concentration (BIC). The minimal inhibitory concentration (MIC) was assessed with planktonic cells. Bacterial growth was examined by scanning electron microscopy. The antibiotic concentration for biofilm inhibition (BIC) was higher than the MIC for all antibiotics. Microscopic images showed the biofilm structure characterized by groups of cells covered by a film. CONCLUSIONS: All models allowed biofilm formation and testing with several antibiotics in vitro. Gentamicin and rifampicin are the most effective inhibitors of Staph. aureus biofilm-related infections. We recommend MBEC™-HTP assay for rapid testing of multiple substances and TMZF(®) and CrCo discs for low-throughput testing of antibiotic susceptibility and for microscopic analysis. SIGNIFICANCE AND IMPACT OF THE STUDY: In vitro assays can improve the understanding of biofilms and help developing methods to eliminate biofilms from implant surfaces. One advantage of the TMZF(®) and CrCo discs as biofilm in vitro assay is that these metals are commonly used for orthopaedic implants. These models are usable for future periprosthetic joint infection studies.

Low-energy shock waves enhance the susceptibility of staphylococcal biofilms to antimicrobial agents in vitro.

Biofilm-associated infections in wounds or on implants are difficult to treat. Eradication of the bacteria is nearly always impossible, despite the use of specific antibiotics. The bactericidal effects of high-energy extracorporeal shock waves on Staphylococcus aureus have been reported, but the effect of low-energy shock waves on staphylococci and staphylococcal biofilms has not been investigated. In this study, biofilms grown on stainless steel washers were examined by electron microscopy. We tested ten experimental groups with Staph. aureus-coated washers and eight groups with Staph. epidermidis. The biofilm-cultured washers were exposed to low-energy shock waves at 0.16 mJ/mm(2) for 500 impulses. The washers were then treated with cefuroxime, rifampicin and fosfomycin, both alone and in combination. All tests were carried out in triplicate. Viable cells were counted to determine the bactericidal effect. The control groups of Staph. aureus and Staph. epidermidis revealed a cell count of 6 × 10(8) colony-forming units/ml. Complete eradication was achieved using the combination of antibiotic therapy (single antibiotic in Staph. aureus, a combination in Staph. epidermidis) and shock wave application (p < 0.01). We conclude that shock waves combined with antibiotics could be tested in an in vitro model of infection.

Group Milleri Streptococci in perianal infections.

BACKGROUND: Anal abscesses are commonly associated with fistulas-in-ano and are usually polymicrobial in nature, with gram-negative rods and anaerobes being the most prevalent isolates. Group Milleri Streptococci (GMS) comprise a heterogeneous group of cocci, which are capable of causing severe purulent infection with a high recurrence rate. METHOD: All anorectal infections caused by GMS, which were identified at our centre during a 4-year period were retrospectively analysed. The 18 patients with GMS-positive anorectal abscesses were matched with 36 GMS-negative anorectal abscesses to identify outcome characteristics of this clinical entity. RESULTS: During the study period, 358 patients underwent surgical treatment for anal infections; GMS were isolated in 46 individuals (13%) including 18 perianal abscesses, 11 pilonidal sinuses, eight fistulae in and nine miscellaneous infections. Seventy-two per cent of perianal GMS infections were polymicrobial with E. coli and Bacteroides fragilis being the predominant second bacteria. Nine patients (20%) developed recurrent abscesses and fistulae-in-ano and underwent additional surgical interventions with resolution at follow-up. Additional antibiotic treatment was administered in 10 patients with complex anal infections. Matched pair analysis revealed that GMS-positive perianal abscesses were more commonly polymicrobial, and that the recurrence rate was higher (55.6% GMS-positive and 22.2% GMS-negative patients, P = 0.017). CONCLUSIONS: Our data confirm the propensity of GMS to form deep and recurrent abscesses with a higher recurrence rate than non-GMS infections. First-line treatment includes surgical drainage, and antibiotic treatment may be useful in selected patients.

Group Milleri Streptococci in paediatric infections.

BACKGROUND: Group Milleri Streptococci (GMS), a subgroup of viridans streptococci, are commensals of the human respiratory, gastrointestinal and urogenital tracts. GMS tend to cause purulent infections often resulting in abscess formation. Little is known about the significance of these organisms in children. PATIENTS AND METHODS: For this retrospective study, a collection of 636 GMS positive isolates from 475 patients was used to identify 39 (8.2 %) paediatric patients (age < 18 years) with GMS infections (46 isolates) during a four-year period. RESULTS: There were 19 intra-abdominal, eleven dental/oropharyngeal, seven soft tissue and two central nervous system infections. Thirty-five patients (95 %) underwent primary surgical interventions. Furthermore, two patients - one with GMS meningitis that progressed to cerebral empyema and another with a liver abscess - initially treated with antibiotic agents alone eventually required surgical intervention to cure the infection. Only two children were treated with antibiotics alone. Polymicrobial infection was found in 22 (48 %) isolates; polymicrobial infection was most common in patients with intra-abdominal infection with 74 % and lowest in dental/oropharyngeal patients with 9 % (p = 0.001); Escherichia coli (n = 9) and Bacteroides fragilis (n = 9) were the most common secondary pathogens. Complications due to GMS infections were found in five cases (13 %). No patient died from GMS infection. Preferred antibiotics were penicillins (56 %) and cephalosporins (37 %). GMS tested susceptible to penicillin, cephalosporins, carbapenems in 100 % and clindamycin in 93 %. CONCLUSIONS: GMS infections in paediatric patients usually require both antibiotic therapy and surgical drainage. These infections may become life-threatening if not diagnosed in a timely fashion and treated aggressively.

CTX-M-1-related extended-spectrum beta-lactamases producing Escherichia coli: so far a sporadic event in Western Austria.

BACKGROUND: The present study was aimed to searching for CTX-M-type extended-spectrum beta-lactamases in community- and hospital-acquired Escherichia coli (E. coli) collected in western Austria and to investigate their clonal relatedness and their ability to spread. PATIENTS AND METHODS: All patients with E. coli positive cultures collected from a catchment population of 186,000 between January and July 2006 were enrolled into the study. CTX-M-producing E. coli were identified by antibiotic susceptibility testing and blaCTX-M multiplex PCR. Clonal relatedness was analyzed by pulsed-field gel electrophoresis (PFGE). RESULTS: In 2,042 E. coli isolates, 20 isolates (16 from urine, 4 from blood cultures) demonstrated CTX-M-1-related genes and no CTX-M-2- or CTX-M-9-related enzymes or CTX-M-15-producing strains were identified. We did not find clonal relatedness among CTX-M-1 producers isolated from the same referring center. E. coli were investigated for plasmid transfer ability of CTX-M-1-encoding genes. Plasmid digest patterns were not consistent with episomal spread of resistance loci. Transfection of CTX-M-encoding plasmids failed. CONCLUSION: Our data suggest that the emergence of CTX-M-1-producing E. coli in western Austria may be attributed to multiple independent events.

Relevance of group Milleri streptococci in thoracic surgery: a clinical update.

Group Milleri streptococci (GMS), a heterogeneous group of streptococci, are associated with purulent infections. This study was a retrospective analysis of all consecutive thoracic infections of GMS between 2001 and 2004. Of 246 surgical GMS infections, thoracic infections accounted for 4.5 per cent, including 10 pleural infections (eight empyemas and two infected pleural effusions) and one mediastinal infection. The etiology of pleural infection was parapneumonic (7), second to esophageal perforation (1), liver transplantation (1), and liver resection (1). Polymicrobial infections were present in 64 per cent. All patients underwent removal of the infected masses, including drainage (3), thoracoscopic decortication (5), thoracotomy with debridement (2), and incision with drainage (1). The case fatality rate was 9 per cent (there was one patient with congestive heart disease unfit to undergo surgical empyema evacuation) and the recurrence rate was 27.3 per cent (three patients). Combined antibiotic/surgical treatment was successful in all other cases. GMS isolates were susceptible to clindamycin and all beta-lactam antibiotics except ceftazidime, but were resistant to aminoglycosides. If found intrathoracically, GMS frequently progress to severe empyema. Therefore, timely removal of pleural collection by percutaneous drainage or surgical intervention seems indicated. If surgery is required, thoracoscopic decortication may be the preferred approach.

Clostridium difficile colitis in solid organ transplantation--a single-center experience.

Clostridium difficile (CD) is one of the most common causes of diarrhea in solid organ transplantation (SOT). Between 1996 and 2005, a total of 2474 solid organ transplants were performed at our institution, of which 43 patients developed CD-associated diarrhea. There were 3 lung, 3 heart, 20 liver, 8 kidney-pancreas, 6 kidney, 1 composite tissue, and 2 multivisceral recipients. Onset of CD infection ranged from 5 to 2453 days posttransplant. All patients presented with abdominal pain and watery diarrhea. Toxins A and B were detected using rapid immunoassay or enzyme immunoassay. Treatment consisted of reduction of immunosuppression, fluid and electrolyte replacement, metronidazole (n=20), oral vancomycin (n=20), and a combination of metronidazole and vancomycin (n=2). Toxic megacolon was seen in five patients. Two of them had colonoscopic decompression, and the remaining three required colonic resection. One of these patients died due to multiorgan failure after cured CD enteritis. The remaining patients were discharged with well-functioning grafts and all are currently alive. CD colitis was a rare complication prior to 2000; 38 of the 43 cases occurred thereafter. We conclude that CD colitis represents a severe complication following SOT. Recently, a dramatic increase in the incidence of this complication has been observed. The development of life-threatening toxic megacolon must be considered in solid organ recipients.

Inducible metronidazole resistance in nim-positive and nim-negative bacteroides fragilis group strains after several passages metronidazole containing columbia agar plates.

BACKGROUND: Recent data show an emergence of resistance in the Bacteroides fragilis group against several antimicrobial agents and inducible resistance against metronidazole in nim-positive strains. The aim of the present study was to investigate inducible metronidazole resistance in nim-positive as well as in nim-negative B. fragilis group strains. MATERIALS AND METHODS: Of 18 B. fragilis strains (including four nim-positive reference strains and one ATCC strain), two Bacteroides ovatus strains, and one Bacteroides thetaiotaomicron DSM strain minimum inhibitory concentration (MIC) values for metronidazole were determined by Etest and analyzed for nim genes (nimA to -G) by PCR. For this purpose bacterial suspensions were incubated on supplemented Columbia agar plates containing metronidazole at twice the MIC value of the specific strain and incubated under anaerobic conditions for 48 hours. After incubation, growing bacteria were harvested and thereafter incubated at four times the original MIC. This procedure was repeated with increasing antibiotic concentrations. The resulting MIC values were confirmed by Etest. RESULTS: The MIC values for metronidazole of the four nim-positive reference strains ranged from 3 to 8 mg/l. The B. fragilis ATCC 25285 strain and the B. thetaiotaomicron DSM 2255 strain were nim negative with MIC values of 0.19 mg/l and 0.75 mg/l, respectively. Three clinical isolates of B. fragilis strains showed MIC values of > 256 mg/l. In all three strains, nim genes were detected by PCR. The other clinical isolates were nim negative. In these strains, MIC values ranged from 0.19 to 0.75 mg/l. After several passages on metronidazole containing agar, all B. fragilis group strains exhibited MIC values of > 256 mg/l determined by Etest. CONCLUSION: Metronidazole resistance can be selected not only in nim-positive strains but also in nim-negative strains, suggesting that mechanisms other than nim genes are involved. These findings and the emerging resistance of the B. fragilis group against several antimicrobial agents underscore the importance of susceptibility testing of anaerobes even in routine laboratories.

Influence of human ascitic fluid on the in vitro antibacterial activity of moxifloxacin.

We investigated the in vitro influence of HAF on the antibacterial activity of moxifloxacin against Escherichia coli ATCC 10798, Escherichia coli K-12, Proteus rettgeri (Sanelli), Staphylococcus aureus ATCC 25923, Staphylococcus aureus NCTC 1808 and Staphylococcus epidermidis ATCC 12228. Human ascitic fluid was obtained from 6 cirrhotic patients by paracentesis. The interaction effect was evaluated by the checkerboard technique. Our results indicate the ability of human ascitic fluid to reduce minimum inhibitory concentrations of moxifloxacin against Gram-negative bacteria, but not against Gram-positives.

Cefazolin concentrations in serum during cardiopulmonary bypass surgery.

The objective of the study was to investigate possible changes in cefazolin serum levels induced by cardiopulmonary bypass (CPB). Six cardiac male patients who underwent cardiac surgery requiring CPB took part in the study. Cefazolin 2 g was intravenously infused over 60 min before anesthesia and blood samples were taken at appropriate times after drug administration (0, 0.25, 0.5, 1, 4, 6, 8 h), 2 min before and 5 min after the beginning and 2 min before and 5 min after the end of CPB. Drug serum concentrations were determined by means of a microbiological method. Five minutes after the start of CPB, cefazolin serum levels decreased on average by 46.6% and remained steadily low until 5 min after the end of CPB. Then, they rose on average by 37.3% at 4 h and then declined slowly until the last sampling at 8 h. Cefazolin serum concentrations were low during CPB but remained in a potentially effective range for antimicrobial prophylaxis for this surgery.

A series of infections due to Capnocytophaga spp in immunosuppressed and immunocompetent patients.

OBJECTIVE: To investigate the epidemiology, microbiology and outcome of infections caused by Capnocytophaga spp. at a single center. METHODS: We report on ten documented infectious episodes caused by Capnocytophaga observed between 1994 and 1999 at the Innsbruck University Hospital. RESULTS: In seven of ten patients, Capnocytophaga septicemia was diagnosed during periods of neutropenia. In contrast, the remaining three patients had normal white blood cell counts when acquiring Capnocytophaga septicemia (one) and pleural empyema (two). Blood cultures containing long, slender, Gram-negative rods, which grew slowly under anaerobic conditions and lacked susceptibility to metronidazole, were subcultivated in a CO2-enriched atmosphere (5%). Subcultivation yielded Capnocytophaga in all ten cases within 2-12 days. The patients were then placed on appropriate antibiotic therapy, with or without additional surgical intervention, and the organism was eradicated. CONCLUSION: Identification of Capnocytophaga facilitates appropriate, and in most cases effective, antimicrobial therapy.

[Imipenem resistance in Pseudomonas aeruginosa]. / Imipenem-Resistenz bei Pseudomonas aeruginosa.

In 1997 in western Austria, 9.9% of Pseudomonas aeruginosa strains from patients of general practitioners were resistant to imipenem as well as 18.2% of the isolates from hospitals and 20.2% of the strains at a university teaching hospital. Within the hospital the imipenem resistance varied from 9.9% among out-patients to 28.7% in isolates from intensive care units. In medical/surgical words, up to 15.1% of P. aeruginosa strains were resistant to imipenem. The incidence of imipenem-resistant P. aeruginosa strains correlates to the use of carbapenems. In June 1997, 10 consecutive isolates from 8 patients were obtained and typed using restriction fragment length polymorphism analysis (RFLP) and Pyocin typing. All 10 isolates were resistant to meropenem as well as to imipenem. The finding (by RFLP and Pyocin typing) of individual bacterial types in each isolate strongly contradicts the spread of infection by cross infection. However, all patients were proven to have been treated with imipenem during the 3 months prior to testing. In 1997, 13,880 g of imipenem were used at the university hospital in Innsbruck. The use of carbapenems appears to be the main cause for the increased incidence of imipenem-resistant P. aeruginosa strains.

Tolerance and bactericidal action of N-chlorotaurine in a urinary tract infection by an omniresistant Pseudomonas aeruginosa.

N-chlorotaurine, a weak antimicrobial oxidant produced by stimulated human leukocytes, was used to treat cystitis caused by an omniresistant Pseudomonas aeruginosa. A 21-year-old male patient was treated by repeated daily lavages of the urinary bladder with an aqueous solution of 1% N-chlorotaurine for one month. N-chlorotaurine was well tolerated; no local or systemic side effects could be detected. Despite killing of > 10(6) cfu/ml of bacteria within ten minutes in vitro and in vivo, it was not possible to eradicate the Pseudomonas infection obviously caused by inflammation of the upper urinary tract and perpetuated by intravesical concrements. Nevertheless, in actually localized infection, treatment with N-chlorotaurine might be successful because of its sufficient bactericidal action.

Comparison of culture and acid-fast bacilli stain to PCR for detection of Mycobacterium tuberculosis in clinical samples.

The major drawback in effective use of polymerase chain reaction (PCR) for detecting Mycobacterium tuberculosis (MTB) in clinical samples is the presence of PCR inhibitors and unique cell components of the organism that complicate DNA extraction and subsequent PCR amplification. A PCR assay with a unique multistep DNA extraction method that minimizes these problems was compared in a prospective study to acid-fast bacilli stain (AFBS) and culture for detecting MTB in clinical samples. A total of 254 clinical specimens in two separate studies were processed for MTB by these techniques. While PCR and culture were 100% sensitive and specific, culture required up to 8 weeks of incubation and additional time to perform biochemical testing to identify the isolated micro-organism. Acid-fast bacilli stain had a specificity of about 87% and did not differentiate among Mycobacterial species. In contrast, the results from PCR were available within 48 h and did not require additional testing to attain a final result. Polymerase chain reaction was highly reliable for detection and confirmation and interpretation of positive AFBS results. The assay was easy to perform with a turn around time of about 2 days.

Changing bacterial ecology during a five-year period of selective intestinal decontamination.

The development of bacterial resistance during selective decontamination of the digestive tract (SDD) is controversial. We studied effects on bacterial resistance one year before and during a randomized, placebo-controlled trial of SDD in a surgical intensive care unit. We randomized patients within two different topical regimens (PTA, PCA) or placebo, administered four-times daily to both the oropharynx and gastrointestinal tract. All patients received intravenous ciprofloxacin (200 mg b.d.) for four days. Both SDD regimens successfully reduced aerobic Gram-negative intestinal colonization. There was no increase in resistance of Enterobacteriaceae or Pseudomonas aeruginosa. Acinetobacter calcoaceticus developed multi-resistance over one year, but differences between groups were not significant. We detected a shift towards Gram-positive organisms. Oxacillin-resistant Staphylococcus aureus increased in concert with ciprofloxacin resistance, from 17 to 80.7%, and frequencies of resistance were significantly higher in SDD patients (P < 0.001). Resistance of coagulase-negative staphylococci (CNS) to oxacillin increased initially (25 to 66.9%), but values returned to baseline in controls. Ciprofloxacin resistance in CNS remained higher (P < 0.001) in SDD-treated patients (52.5 vs. 23.3%). The incidence of late respiratory tract infections was unaltered by the prophylactic regimen (SDD 35.2%; Placebo 41.2%; n.s.). We cannot recommend SDD as a prophylactic tool in critically ill patients.

[Induction of uterine contractions by Shigella]. / Induktion uteriner Kontraktionen durch Shigellen.

The uterus-contracting properties of Shigellae in a clinically relevant dose of 10(5) organisms per ml was investigated in 17 uterine strips which where dissected during caesarean section from the lower uterine segment. A highly significant (p < 0.001) increase in uterine activity was observed.