Candace J. Krepel

In Vitro Activities of Moxifloxacin against 900 Aerobic and Anaerobic Surgical Isolates from Patients with Intra-Abdominal and Diabetic Foot Infections

ABSTRACT The in vitro activities of moxifloxacin, ciprofloxacin, levofloxacin, gatifloxacin, imipenem, piperacillin-tazobactam, clindamycin, and metronidazole against 900 surgical isolates were determined using NCCLS testing methods. Moxifloxacin exhibited good to excellent antimicrobial activity against most aerobic (90.8%) and anaerobic (97.1%) microorganisms, suggesting that it may be effective for the treatment of polymicrobial surgical infections.

Preoperative Shower Revisited: Can High Topical Antiseptic Levels Be Achieved on the Skin Surface Before Surgical Admission?

BACKGROUND Skin asepsis is a sentinel strategy for reducing risk of surgical site infections. In this study, chlorhexidine gluconate (CHG) skin concentrations were determined after preoperative showering/skin cleansing using 4% CHG soap or 2% CHG-impregnated polyester cloth. STUDY DESIGN Subjects were randomized to one of three shower (4% soap)/skin cleansing (2% cloth) groups (n = 20 per group): (group 1 A/B) evening, (group 2 A/B) morning, or (group 3 A/B) evening and morning. After showering or skin cleansing, volunteers returned to the investigators laboratory where CHG skin surface concentrations were determined at five separate skin sites. CHG concentrations were compared with CHG minimal inhibitory concentration that inhibits 90% (MIC(90)) of staphylococcal skin isolates. RESULTS CHG MIC(90) for 61 skin isolates was 4.8 parts per million (ppm). In group 1A, 4% CHG skin concentrations ranged from 17.2 to 31.6 ppm, and CHG concentrations were 361.5 to 589.5 ppm (p < 0.0001) in group 1B (2%). In group 2A (4%), CHG levels ranged from 51.6 to 119.6 ppm and 848.1 to 1,049.6 ppm in group 2B (2%), respectively (p < 0.0001). CHG levels ranged from 101.4 to 149.4 ppm in the 4% CHG group (group 3A) compared with 1,484.6 to 2,031.3 ppm in 2% CHG cloth (group 3B) group (p < 0.0001). Effective CHG levels were not detected in the 4% CHG group in selected sites in seven (35%) subjects in group 1A, three (15%) in group 2A, and five (25%) in group 3A. CONCLUSIONS Effective CHG levels were achieved on most skin sites after using 4% CHG; gaps in antiseptic coverage were noted at selective sites even after repeated application. Use of the 2% CHG polyester cloth resulted in considerably higher skin concentrations with no gaps in antiseptic coverage. Effective decolonization of the skin before hospital admission can play an important role in reducing risk of surgical site infections.

Effects of maternal obesity on tissue concentrations of prophylactic cefazolin during cesarean delivery.

OBJECTIVE: To estimate the adequacy of antimicrobial activity of preoperative antibiotics at the time of cesarean delivery as a function of maternal obesity. METHODS: Twenty-nine patients scheduled for cesarean delivery were stratified according to body mass index (BMI) category, with 10 study participants classified as lean (BMI less than 30), 10 as obese (BMI 30–39.9), and nine as extremely obese (BMI 40 or higher). All patients were given a dose of 2 g cefazolin 30–60 minutes before skin incision. Antibiotic concentrations from adipose samples, collected after skin incision and before skin closure, along with myometrial and serum samples, were analyzed with microbiological agar diffusion assay. RESULTS: Cefazolin concentrations within adipose tissue obtained at skin incision were inversely proportional to maternal BMI (r=−0.67, P<.001). The mean adipose concentration was 9.4 plus or minus 2.7 micrograms/g in the lean group of women compared with 6.4 plus or minus 2.3 micrograms/g in the obese group (P=.009) and 4.4 plus or minus 1.2 micrograms/g in the extremely obese group (P<.001). Although all specimens demonstrated therapeutic cefazolin levels for gram-positive cocci (greater than 1 microgram/g), a considerable portion of obese and extremely obese did not achieve minimal inhibitory concentrations of greater than 4 micrograms/g for Gram-negative rods in adipose samples at skin incision (20% and 33.3%, respectively) or closure (20.0% and 44.4%, respectively). No significant difference in cefazolin concentration was observed in mean closure adipose, myometrial, or serum specimens across the BMI categories. CONCLUSION: Pharmacokinetic analysis suggests that present antibiotic prophylaxis dosing may fail to provide adequate antimicrobial coverage in obese patients during cesarean delivery. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov, www.clinicaltrials.gov, NCT00980486. LEVEL OF EVIDENCE: II

Elimination of Intraluminal Colonization by Antibiotic Lock in Silicone Vascular Catheters

An in vitro model was designed to evaluate the efficacy of instilled antimicrobials to reduce or eliminate intraluminal microbial colonization. Minimal inhibitory concentration and minimal bactericidal concentration activity of appropriate test anti-infectives were determined using standard methodology against clinically derived and reference test strains commonly associated with catheter-related infection. Drug activity was validated by bioassay for the test anti-infectives. Reference and clinical test strains were inoculated to the intraluminal surface of silicone catheter segments and incubated for 30 min, after which the inoculum was replaced with total parenteral nutrition (TPN) solution and reincubated for 12 h. For 7 d, instillation of antibiotic and TPN solution was alternated every 12 h to simulate clinical conditions. On days 1, 4, and 7, catheter segments were rinsed, bisected, and sonicated for quantitative plate count to determine mean microbial counts per centimeter of catheter surface. Catheter segments were also prepared for scanning electron microscopy. A significant decrease in staphylococcal intraluminal colonization after instillation of nafcillin, ceftriaxone, gentamicin, and vancomycin was demonstrated (P < 0.001). Aztreonam, ceftriaxone, and gentamicin completely eliminated gram-negative catheter colonization (P < 0.001). Yeast was eradicated from the internal catheter surface after treatment with amphoteracin B, and fluconazole significantly decreased intraluminal colonization (P < 0.001). Results show a significant decrease in staphylococcal, gram-negative, and fungal intraluminal colonization after instillation of appropriate antimicrobial. In vitro results support early clinical success using this technique. Future studies are warranted to identify optimal drug concentrations and dosing intervals.

Anastomotic femoral pseudoaneurysm: An investigation of occult infection as an etiologic factor

Occult infection was investigated as an etiologic factor in the formation of femoral anastomotic pseudoaneurysms associated with prosthetic vascular grafts. Forty-five femoral pseudoaneurysms with no clinical evidence of infection 10 to 173 months after prosthetic graft placement were consecutively studied. The explanted Dacron or explanted polytetrafluoroethylene graft material was cultured in trypticase soy broth and ultrasonically oscillated to remove adherent bacteria. All patients were treated by excision of the pseudoaneurysm and surrounding perigraft capsule and in situ replacement with an interposition prosthetic graft. Thirty-two bacterial isolates were recovered from 27 (60%) of the specimens, with coagulase negative staphylococci (Staphylococcus epidermidis S. warneri, S. hominis, S. capitis) accounting for 24 of the recovered species. No infection of the replacement graft developed in any patient and no recurrent pseudoaneurysms were observed. Bacterial colonization may occur at implantation or during subsequent procedures when the prosthetic graft is exposed. This chronic infection can be diagnosed by means of sensitive culture techniques that dislodge adherent bacteria from the graft surface. On grounds of the observations reported in this study, there appears to be suggestive evidence that an occult infectious process may be one of the factors that play a role in the development of some femoral anastomotic pseudoaneurysms.

In vitro evaluation of the antibacterial activity of three different central venous catheters against gram-positive bacteria

Abstract.The aim of this study was to evaluate the activity of three different catheters against Staphylococcus aureus ATCC 29213 and the slime-producing Staphylococcus epidermidis ATCC 35984 (RP62A). Three central venous catheters were evaluated: one impregnated with silver sulfadiazine–chlorhexidine, one to which minocycline/rifampin is bonded and a novel one into which silver, platinum and carbon are incorporated. A nonantiseptic catheter was used as the control catheter. One-centimeter trisected pieces of catheter were immersed in phosphate-buffered saline (0.01 mol/l) with 0.25% dextrose and incubated. On days 1, 3, 7, 14 and 21, a 1 ml standardized inoculum was added for 30 min and then replaced with phosphate-buffered saline with 0.25% dextrose. One-third of the samples were immediately sonicated and plated to determine bacterial adherence. The remaining segments were incubated for 4 and 24 h to determine the persistence of bacterial adherence. Bacterial adherence to the catheters impregnated with silver sulfadiazine-chlorhexidine was reduced 91–98% for the first 7 days. Adherence of Staphylococcus aureus to catheters into which silver, platinum and carbon are incorporated was reduced 70% on day 1 and 35% on day 3. Adherence to minocycline/rifampin-bonded catheters was quite variable. There was an 85.6–99.8% reduction in the persistence of bacterial adherence to the three catheters compared to controls. Bacteriostatic and bactericidal studies indicated that the effluents from the catheters impregnated with silver sulfadiazine-chlorhexidine were bactericidal, while effluents from the minocycline/rifampin-bonded catheters were bacteriostatic. The antibacterial activity of the effluents from catheters impregnated with silver sulfadiazine-chlorhexidine dissipated by day 7, while the activity of effluents from the minocycline/rifampin-bonded catheters continued to show activity at day 21. No measurable antibacterial activity was detected in the effluents of the catheters into which silver, platinum and carbon are incorporated. These data suggest that catheters coated with antibiotic/antibacterial agents and the novel catheters that incorporate antiseptic agents have different activities against initial bacterial adherence. All of them, however, effectively prevent bacterial colonization by gram-positive bacteria.

Surgical sepsis: Constancy of antibiotic susceptibility of causative organisms

BACKGROUND It is well documented that antibiotic therapy exerts selective pressure on bacteria. Conversion of bacteria from susceptible to resistant to antibiotics has been observed often during antimicrobial therapy. It has been postulated that human intestinal reservoirs facilitate communication of transposons that can transfer resistance determinants among various bacterial species. METHODS This study examined the susceptibilities of organisms isolated from infected abdomens to a number of antibiotic agents during a 12-year time interval. Analysis included 1102 isolates recovered from 255 specimens, representing the following genera: Bacteroides, Clostridium, Gemella, Fusobacterium, Peptostreptococcus, Porphyromonas, Prevotella, Enterococcus, Staphylococcus, Streptococcus, Pseudomonas, and Enterobacteriaceae. Strains were tested against beta-lactam agents, beta-lactams in combination with beta-lactamase inhibitors, first, second, and third generation cephalosporins, aminoglycosides, clindamycin, metronidazole, chloramphenicol, and imipenem. RESULTS The results indicated that during a time period of more than a decade essentially no change occurred in the antibiotic susceptible fraction of all species tested. CONCLUSIONS Abdominal sepsis is caused by leakage of endogenous intestinal flora. This study suggests that the intestinal flora is not permanently affected by short-term antibiotic therapy and that older antibiotics are appropriate first-line therapeutic agents for community-acquired infections caused by normal intestinal flora.

Evidence for a Standardized Preadmission Showering Regimen to Achieve Maximal Antiseptic Skin Surface Concentrations of Chlorhexidine Gluconate, 4%, in Surgical Patients

IMPORTANCE To reduce the amount of skin surface bacteria for patients undergoing elective surgery, selective health care facilities have instituted a preadmission antiseptic skin cleansing protocol using chlorhexidine gluconate. A Cochrane Collaborative review suggests that existing data do not justify preoperative skin cleansing as a strategy to reduce surgical site infection. OBJECTIVES To develop and evaluate the efficacy of a standardized preadmission showering protocol that optimizes skin surface concentrations of chlorhexidine gluconate and to compare the findings with the design and methods of published studies on preoperative skin preparation. DESIGN, SETTING, AND PARTICIPANTS A randomized prospective analysis in 120 healthy volunteers was conducted at an academic tertiary care medical center from June 1, 2014, to September, 30, 2014. Data analysis was performed from October 13, 2014, to October 27, 2014. A standardized process of dose, duration, and timing was used to maximize antiseptic skin surface concentrations of chlorhexidine gluconate applied during preoperative showering. The volunteers were randomized to 2 chlorhexidine gluconate, 4%, showering groups (2 vs 3 showers), containing 60 participants each, and 3 subgroups (no pause, 1-minute pause, or 2-minute pause before rinsing), containing 20 participants each. Volunteers used 118 mL of chlorhexidine gluconate, 4%, for each shower. Skin surface concentrations of chlorhexidine gluconate were analyzed using colorimetric assay at 5 separate anatomic sites. Individual groups were analyzed using paired t test and analysis of variance. INTERVENTION Preadmission showers using chlorhexidine gluconate, 4%. MAIN OUTCOMES AND MEASURES The primary outcome was to develop a standardized approach for administering the preadmission shower with chlorhexidine gluconate, 4%, resulting in maximal, persistent skin antisepsis by delineating a precise dose (volume) of chlorhexidine gluconate, 4%; duration (number of showers); and timing (pause) before rinsing. RESULTS The mean (SD) composite chlorhexidine gluconate concentrations were significantly higher (P < .001) in the 1- and 2-minute pause groups compared with the no-pause group in participants taking 2 (978.8 [234.6], 1042.2 [219.9], and 265.6 [113.3] µg/mL, respectively) or 3 (1067.2 [205.6], 1017.9 [227.8], and 387.1 [217.5] µg/mL, respectively) showers. There was no significant difference in concentrations between 2 and 3 showers or between the 1- and 2-minute pauses. CONCLUSIONS AND RELEVANCE A standardized preadmission shower regimen that includes 118 mL of aqueous chlorhexidine gluconate, 4%, per shower; a minimum of 2 sequential showers; and a 1-minute pause before rinsing results in maximal skin surface (16.5 µg/cm2) concentrations of chlorhexidine gluconate that are sufficient to inhibit or kill gram-positive or gram-negative surgical wound pathogens. This showering regimen corrects deficiencies present in current nonstandardized preadmission shower protocols for patients undergoing elective surgery.

Microbiology of Explanted Suture Segments from Infected and Noninfected Surgical Patients

ABSTRACT Sutures under selective host/environmental factors can potentiate postoperative surgical site infection (SSI). The present investigation characterized microbial recovery and biofilm formation from explanted absorbable (AB) and nonabsorbable (NAB) sutures from infected and noninfected sites. AB and NAB sutures were harvested from noninfected (70.9%) and infected (29.1%) sites in 158 patients. At explantation, devices were sonicated and processed for qualitative/quantitative bacteriology; selective sutures were processed for scanning electron microscopy (SEM). Bacteria were recovered from 85 (53.8%) explanted sites; 39 sites were noninfected, and 46 were infected. Suture recovery ranged from 11.1 to 574.6 days postinsertion. A significant difference in mean microbial recovery between noninfected (1.2 isolates) and infected (2.7 isolates) devices (P < 0.05) was noted. Staphylococcus epidermidis, Staphylococcus aureus, coagulase-negative staphylococci (CNS), Peptostreptococcus spp., Bacteroides fragilis, Escherichia coli, Enterococcus spp., Pseudomonas aeruginosa, and Serratia spp. were recovered from infected devices, while commensal skin flora was recovered from noninfected devices. No significant difference in quantitative microbial recovery between infected monofilament and multifilament sutures was noted. Biofilm was present in 100% and 66.6% of infected and noninfected devices, respectively (P < 0.042). We conclude that both monofilament and braided sutures provide a hospitable surface for microbial adherence: (i) a significant difference in microbial recovery from infected and noninfected sutures was noted, (ii) infected sutures harbored a mixed flora, including multidrug-resistant health care-associated pathogens, and (iii) a significant difference in the presence or absence of a biofilm in infected versus noninfected explanted devices was noted. Further studies to document the benefit of focused risk reduction strategies to minimize suture contamination and biofilm formation postimplantation are warranted.

ANAEROBIC INFECTIONS IN THE SURGICAL PATIENT: MICROBIAL ETIOLOGY AND THERAPY

Anaerobic infections occur in surgical patients in part because of structural or functional defects in the host that (1) cause a breech in the normal mucosal barriers, (2) create localized vascular insufficiencies, or (3) produce an obstruction. Any or all of these events may compromise the oxidation-reduction potential within the tissues, encouraging rapid anaerobic growth. Although diverse anaerobic populations are spread throughout the gastrointestinal tract, a relatively limited number of organisms are responsible for clinical infection in the surgical patient. Many of these offending organisms express overt virulence factors that enhance microbial adherence, tissue destruction, and, in the case of Bacteroides fragilis, facilitate abscess formation. The selection of an appropriate perioperative or therapeutic agent requires a fundamental knowledge of the microbial ecology of this microbial population. The failure to consider the anaerobic flora as a component in the etiology of mixed surgical infections is associated with a high rate of perioperative and therapeutic failures.