Anaerobic infections in the surgical patient: microbial etiology and therapy

A pilot study: intraoperative 16S rRNA sequencing versus culture in predicting colorectal incisional surgical site infection

BACKGROUND

Surgical Site Infection (SSI) of the abdominal incision is a dreaded complication following colorectal surgery. Identifying the intraoperative surgical site microbes may provide clarity in the pathogenesis of SSIs. Genomic sequencing has revolutionized the ability to identify microbes from clinical samples. Utilization of 16S rRNA amplicon sequencing to characterize the intraoperative surgical site may provide the critical information required to predict and prevent infection in colorectal surgery.

METHODS

This is a pilot, prospective observational study of 50 patients undergoing elective colorectal resection. At completion of surgery, prior to skin closure, swabs were taken from the subcutaneous tissue of the abdominal incision to investigate the microbial profile. Dual swabs were taken to compare standard culture technique and 16S rRNA sequencing to establish if a microbial profile was associated with postoperative SSI.

RESULTS

8/50 patients developed an SSI, which was more likely in those undergoing open surgery (5/15 33.3% versus 3/35, 8.6%; P = 0.029). 16S rRNA amplicon sequencing was more sensitive in microbial detection compared to traditional culture. Both culture and 16S rRNA demonstrated contamination of the surgical site, predominantly with anaerobes. Culture was not statistically predictive of infection. 16S rRNA amplicon sequencing was not statistically predictive of infection, however, it demonstrated patients with an SSI had an increased biodiversity (not significant) and a greater relative abundance (not significant) of pathogens such as Bacteroidacaea and Enterobacteriaceae within the intraoperative site.

CONCLUSIONS

16S rRNA amplicon sequencing has demonstrated a potential difference in the intraoperative microbial profile of those that develop an infection. These findings require validation through powered experiments to determine the overall clinical significance.

The Influence of Bifidobacterium bifidum and Bacteroides fragilis on Enteric Glial Cell-Derived Neurotrophic Factors and Inflammasome

Enteric glial cells (EGCs) and enteric glial-derived neurotrophic factor (GDNF) are directly involved in intestinal inflammation. In this study, we sought to examine the possible mechanisms for how Bifidobacterium bifidum (B.b.) and Bacteroides fragilis (B.f.) influence EGC regulation. In this study, lipopolysaccharide (LPS) and interferon-γ (IFN-γ) were used as exogenous stimuli of EGCs to establish an intestinal inflammation model. After stimulation with LPS and IFN-γ, B.b. and B.f. supernatants were used to activate EGCs and to examine EGC immune mechanisms. For this purpose, qRT-PCR, western blotting, and laser scanning confocal microscopy (LSCM) were used to detect the expression of NLRP3, NLRP6, NGF, NT-3, IL-18, IL-1β, and caspase-1. We found that EGCs, after stimulation with LPS and IFN-γ, could express NLRP3, NLRP6, NT-3, NGF, IL-18, IL-1β, and caspase-1 through LSCM. In intestinal inflammation, B.b. and B.f. could trigger an increase in NGF and NT-3 expression in EGCs in order to protect the intestine. Furthermore, B.b. and B.f. could upregulate NLRP3 expression in EGCs and promote an inflammatory response. B.b. had a dual regulatory role in EGC NLRP6 expression, while B.f. inhibited NLRP6 protein expression. Moreover, B.b. could decrease the expression of IL-18, IL-1β, and caspase-1 in EGCs in order to inhibit the inflammatory response. Contrary to this, B.f. could upregulate IL-18, IL-1β, and caspase-1 expression in EGCs in order to promote the inflammatory response. B.b. and B.f. can influence the expression of NGF, NT-3, NLRP3, NLRP6, IL-18, IL-1β, and caspase-1 in EGCs in order to inhibit or promote intestinal inflammation.

Anaerobic infections in patients admitted in various surgical units of a tertiary care hospital of north India: neglected but important

Background and Objectives:

Anaerobic infections are usually caused by the host’s endogenous flora due to a breach in the anatomical barriers and Bacteroides spp. are the most notorious organisms associated with anaerobic infections. The identification of anaerobes has been a challenge since times. MALDI-TOF-MS is a boon for aiding the rapid detection of anaerobic organisms and has helped us to enlist the distribution of various anaerobic pathogens.

Materials and Methods:

This retrospective analysis (January 2018 to December 2019) was carried out in a tertiary care hospital in North India, in which the anaerobic microbiological profile of all patients admitted to surgical wards, ICU, and OPD of various departments (Orthopedics, Surgery, Gynecology, and Obstetrics) was reviewed. Samples received were immediately processed aerobically (5% sheep blood agar and Mac Conkeyagar) as well as anaerobically (RCM and freshly prepared sheep blood agar) as per the laboratory protocols.

Results:

Bacteroides fragilis (19.12%) was the most common anaerobe whereas among aerobes Escherichia coli (30.2%) followed by Klebsiella pneumoniae (10.34%) were most commonly isolated. The majority of patients were males (56%) and the most common presentation was with abscesses (21.4%). Polymicrobial infections (69.51%) outnumbered monomicrobial ones (30.48%).

Conclusion:

There is a paucity of literature on anaerobe isolation from surgical infections from our country which motivated us to study anaerobic infections and the high sample size in our institute enabled us to study surgical infections from an anaerobic perspective. This will add to the knowledge of microbiologists and clinicians. MALDI-TOF MS helped in rapid and accurate identification and hence we could report a wider spectrum of organisms in our study.

Identification of population of bacteria from culture negative surgical site infection patients using molecular tool

BACKGROUND

Managing surgical site infections, with negative culture report in routine diagnosis is a common dilemma in microbiology accounting more than 30% worldwide. The present study attempted to identify the presence of bacterial spp. if any in wound aspirates/swabs of culture negative surgical site infections of hospitalised patients using molecular tools.

METHODS

Ninety-seven patients with post-operative SSI whose wound swabs/aspirate were negative in the conventional aerobic culture after 72 h of incubation were analysed by 16S rRNA gene specific broad range PCR. The amplified DNA fragments were sequenced by Sanger DNA sequencing method and homology of the sequence were matched using NCBI BLAST (NCBI, USA) RESULTS: Of the 97 patients, 16S rRNA based broad range PCR assay could identify the presence of bacterial pathogen in 53(54.63%) cases, of which 29 isolates were supposed to be of viable but non-culturable bacteria (VBNC), 07 were of obligatory anaerobes and 13 were of unculturable bacteria, 04 were with poly bacterial infections.

CONCLUSIONS

Our study highlights the usefulness of PCR assay in detecting the presence of any VBNC, anaerobes and unculturable bacteria in SSI patients regardless of how well the bacteria may or may not grow in culture. Measures should be taken to use anaerobic culture system and PCR diagnosis along with conventional culture to detect the VBNC and unculturable bacteria where Gram stain is positive for better patient care.

Acute wound infections management: the 'Don'ts' from a multidisciplinary expert panel

Introduction: The management of acute wounds may be affected by malpractices leading to poor outcome, prolonged hospital stay and inappropriate use of antibiotic therapy.Areas covered: Acute wound infections are represented by surgical site and post-traumatic infections. The aim of this expert opinion is to identify a list of inadvisable actions and to provide a guide for an optimal management of acute wound infections. A literature search using Pubmed/MEDLINE database was performed. Articles pertaining to areas covered published until December 2019 were selected. We identified the most common malpractices in this setting and, using the Choosing Wisely methodology, we proposed a list of "Don'ts" for an easy use in clinical practice.Expert opinion: Malpractices may occur from the surgical prophylaxis to the discharge of patient. A prolonged surgical prophylaxis, the underestimation of signs and symptoms, the omission of source control, the inappropriate collection of wound swab, the improper use of clinical microbiology and pharmacology, the lack of hygiene measures and the delay of discharge are all factors that may lead to unfavorable outcome. A multidisciplinary approach is needed to optimally manage these patients. The "Don'ts" refer to all professional figures involved in the management of patients with acute wound infections.

Systematic review of international guidelines for perioperative antibiotic prophylaxis in Head & Neck Surgery. A YO-IFOS Head & Neck Study Group Position Paper

BACKGROUND

Surgical site infection (SSI) is defined as an infection that occurs after a surgical incision or organ manipulation during surgery. The frequency reported for clean head and neck surgical procedures without antimicrobial prophylaxis is <1%. In contrast, infection rates in patients undergoing complicated cancer surgery are high, ranging from 24% to 87% of patients without antimicrobial prophylaxis.

METHODS

Guidelines and recommendations about the use of antibiotics in head and neck surgery from 2004 to 2019 were reviewed.

RESULTS

Four guidelines from Oceania, 5 from South America, 5 from North America, 2 from the United Kingdom, 11 from Europe, 1 from Africa, 1 from the Middle East, and 3 from Asia were included. A total of 118 papers were included for analysis and recommendation.

CONCLUSION

Antibiotic prophylaxis can decrease the incidence of SSI. However, the risks associated with antibiotic exposure and the risk of antibiotic resistance need to be taken into consideration.

Continuous venovenous hemodiafiltration using cytokine-adsorbing hemofilters as adjuvant therapy for anaerobic descending necrotizing mediastinitis: a case report

Background

We describe a combinatorial intensive care approach and discuss the critical factors that allowed us to successfully manage a life-threatening case of acute anaerobic septic shock triggered by descending necrotizing mediastinitis.

Case presentation

We admitted a 38-year-old critically ill Kosovar Albanian man to our intensive care unit because of clinical manifestations of severe sepsis. His condition had worsened in the previous 2 weeks following unsuccessful antibiotic therapy for tonsillitis complicated by retropharyngeal abscesses. Computed tomography and intraoperative observations identified abscesses in the anterior and middle mediastinum regions and the distal part of the neck, directly on the border with the left lobe of the thyroid gland. Cultures indicated infections with α-hemolytic Streptococcus and Clostridium species: High procalcitonin and lactate levels, blood gas analysis, poor peripheral capillary oxygen saturation, and severe hemodynamic instability pointed to a case of acute septic shock. The entire treatment consisted of an aggressive antibiotic regimen, transthoracic and mediastinal surgical evacuation of the abscess, vacuum sealing drainage with a pleural chest tube, continuous venovenous hemodiafiltration using cytokine-adsorbing hemofilters, and extracorporeal blood hyperoxygenation.

Conclusions

Efficient treatment of severe anaerobic sepsis resulting from descending necrotizing mediastinitis should build on a multidisciplinary approach. In support of first-line therapies with targeted antibiotics and surgical debridement, clinicians should consider alternative therapies such as continuous venovenous hemodiafiltration with cytokine-adsorbing hemofilters and hyperoxygenation.

Electronic supplementary material

The online version of this article (10.1186/s13256-019-2123-7) contains supplementary material, which is available to authorized users.

Bacteroides fragilis requires the ferrous-iron transporter FeoAB and the CobN-like proteins BtuS1 and BtuS2 for assimilation of iron released from heme

The intestinal commensal and opportunistic anaerobic pathogen Bacteroides fragilis has an essential requirement for both heme and free iron to support growth in extraintestinal infections. In the absence of free iron, B. fragilis can utilize heme as the sole source of iron. However, the mechanisms to remove iron from heme are not completely understood. In this study, we show that the inner membrane ferrous iron transporter ∆feoAB mutant strain is no longer able to grow with heme as the sole source of iron. Genetic complementation with the feoAB gene operon completely restored growth. Our data indicate that iron is removed from heme in the periplasmic space, and the released iron is transported by the FeoAB system. Interestingly, when B. fragilis utilizes iron from heme, it releases heme-derived porphyrins by a dechelatase activity which is upregulated under low iron conditions. This is supported by the findings showing that formation of heme-derived porphyrins in the ∆feoAB mutant and the parent strain increased 30-fold and fivefold (respectively) under low iron conditions compared to iron replete conditions. Moreover, the btuS1 btuS2 double-mutant strain (lacking the predicted periplasmic, membrane anchored CobN-like proteins) also showed growth defect with heme as the sole source of iron, suggesting that BtuS1 and BtuS2 are involved in heme-iron assimilation. Though the dechelatase mechanism remains uncharacterized, assays performed in bacterial crude extracts show that BtuS1 and BtuS2 affect the regulation of the dechelatase-specific activities in an iron-dependent manner. These findings suggest that the mechanism to extract iron from heme in Bacteroides requires a group of proteins, which spans the periplasmic space to make iron available for cellular functions.

Considerations for antibiotic prophylaxis in head and neck cancer surgery

Peri/post-operative antibiotic prophylaxis (POABP) has become standard practice for preventing surgical site infections (SSI) in head and neck cancer patients undergoing microvascular reconstruction, but few data exist on optimal POABP regimens. Current surgical prophylaxis guideline recommendations fail to account for the complexity of microvascular reconstruction relative to other head and neck procedures, specifically regarding wound classification and antibiotic duration. Selection of POABP spectrum is also controversial, and must balance the choice between too narrow, risking subsequent infection, or too broad, and possible unwanted effects (e.g. antibiotic resistance, Clostridium difficile-associated diarrhea). POABP regimens should retain activity against bacteria expected to colonize the upper respiratory/salivary tracts, which include Gram-positive organisms and facultative anaerobes. However, Gram-negative bacilli also contribute to SSI in this setting. POABP doses should be optimized in order to achieve therapeutic tissue concentrations at the surgical site. Antibiotics targeted towards methicillin-resistant Staphylococcus aureus or Pseudomonas aeruginosa are not warranted for all patients. Prolonged POABP durations have shown no differences in SSI when compared to short POABP durations, but prolonged durations provide unnecessarily antibiotic exposure and risk for adverse effects. Given the lack of standardization behind antibiotic POABP in this setting and the potential for poor patient outcomes, this practice necessitates an additional focus of surgeons and antimicrobial stewardship programs. The purpose of this review is to provide an overview of POABP evidence and discuss pertinent clinical implications of appropriate use.

nim gene-independent metronidazole-resistant Bacteroides fragilis in surgical site infections

Background:Bacteroides fragilis is the most common anaerobic pathogen isolated from surgical site infections (SSIs). Metronidazole resistance is increasing and the mechanisms of resistance are not clear in some isolates. The aim of the present study was to investigate the metronidazole susceptibility prevalence, and detect nim genes in B. fragilis isolates from SSIs. Methods: This study included 100 surgery patients with signs and symptoms indicative of SSIs. Syringe aspiration of the infected site was used to collect specimens. All specimens were cultured on BBA (Brucella blood agar), KVLB (kanamycin-vancomycin laked blood), and BBE (Bacteroides bile esculin) agar. The MIC (minimum inhibitory concentration) of metronidazole was determined by the agar dilution method according to the Clinical and Laboratory Standard Institute (CLSI). Then the PCR method was used to determine the presence of the nim gene. Results: In the present study, 26 B. fragilis were isolated from 100 SSIs specimens. Eight isolates were metronidazole resistant; the metronidazole MIC was 32 µg/mL for 7 isolates and 64 µg/mL for one isolate. All isolates were nim gene negative. Conclusion: The emergence of metronidazole-resistant B. fragilis limits the application of this drug for treatment and prophylaxis of SSIs. Thus, rapid identification of metronidazole-resistant B. fragilis is essential to restrict inappropriate, superfluous administration. In spite of various metronidazole resistance mechanisms other than that depending on the nim gene, detection of nim by PCR is unsuitable for identifying resistant isolates. Therefore, phenotypic methods are better to screen for and identify metronidazole-resistant B. fragilis.

Antibiotic Susceptibility Pattern of Aerobic and Anaerobic Bacteria Isolated From Surgical Site Infection of Hospitalized Patients

BACKGROUND

Surgical Site Infections (SSIs) are infections of incision or deep tissue at operation sites. These infections prolong hospitalization, delay wound healing, and increase the overall cost and morbidity.

OBJECTIVES

This study aimed to investigate anaerobic and aerobic bacteria prevalence in surgical site infections and determinate antibiotic susceptibility pattern in these isolates.

MATERIALS AND METHODS

One hundred SSIs specimens were obtained by needle aspiration from purulent material in depth of infected site. These specimens were cultured and incubated in both aerobic and anaerobic condition. For detection of antibiotic susceptibility pattern in aerobic and anaerobic bacteria, we used disk diffusion, agar dilution, and E-test methods.

RESULTS

A total of 194 bacterial strains were isolated from 100 samples of surgical sites. Predominant aerobic and facultative anaerobic bacteria isolated from these specimens were the members of Enterobacteriaceae family (66, 34.03%) followed by Pseudomonas aeruginosa (26, 13.4%), Staphylococcus aureus (24, 12.37%), Acinetobacter spp. (18, 9.28%), Enterococcus spp. (16, 8.24%), coagulase negative Staphylococcus spp. (14, 7.22%) and nonhemolytic streptococci (2, 1.03%). Bacteroides fragilis (26, 13.4%), and Clostridium perfringens (2, 1.03%) were isolated as anaerobic bacteria. The most resistant bacteria among anaerobic isolates were B. fragilis. All Gram-positive isolates were susceptible to vancomycin and linezolid while most of Enterobacteriaceae showed sensitivity to imipenem.

CONCLUSIONS

Most SSIs specimens were polymicrobial and predominant anaerobic isolate was B. fragilis. Isolated aerobic and anaerobic strains showed high level of resistance to antibiotics.

Expression of Bacteroides fragilis hemolysins in vivo and role of HlyBA in an intra-abdominal infection model

Bacteroides fragilis is the most frequent opportunistic pathogen isolated from anaerobic infections. However, there is a paucity of information regarding the genetic and molecular aspects of gene expression of its virulence factors during extra-intestinal infections. A potential virulence factor that has received little attention is the ability of B. fragilis to produce hemolysins. In this study, an implanted perforated table tennis "ping-pong" ball was used as an intra-abdominal artificial abscess model in the rat. This procedure provided sufficient infected exudate for gene expression studies in vivo. Real-time reverse transcription polymerase chain reaction (RT-PCR) was used to quantify the relative expression of hlyA, hlyB, hlyC, hlyD, hlyE, hlyF, hlyG, and hlyIII mRNAs. The hlyA mRNA was induced approximately sixfold after 4 days postinfection compared with the mRNA levels in the inoculum culture prior to infection. The hlyB mRNA increased approximately sixfold after 4 days and 12-fold after 8 days postinfection. Expression of hlyC mRNA increased sixfold after 1 day, 45-fold after 4 days, and 16-fold after 8 days postinfection, respectively. The hlyD and hlyE mRNAs were induced approximately 40-fold and 30-fold, respectively, after 4-days postinfection. The hlyF expression increased approximately threefold after 4-days postinfection. hlyG was induced approximately fivefold after 4 and 8 days postinfection. The hlyIII mRNA levels had a steady increase of approximately four-, eight-, and 12-fold following 1, 4, and 8 days postinfection, respectively. These findings suggest that B. fragilis hemolysins are induced and differentially regulated in vivo. Both parent and hlyBA mutant strains reached levels of approximately 3-8 × 10(9) cfu/mL after 1 day postinfection. However, the hlyBA mutant strain lost 2 logs in viable cell counts compared with the parent strain after 8 days postinfection. This is the first study showing HlyBA is a virulence factor which plays a role in B. fragilis survival in an intra-abdominal abscess model.

First Korean case of Robinsoniella peoriensis bacteremia in a patient with aspiration pneumonia

Robinsoniella peoriensis has recently been identified as a Gram-positive, spore-forming, anaerobic rod originally recovered from swine manure storage pits. To date, 6 cases of R. peoriensis infection have been reported, including 2 cases of bacteremia, 1 of abdominal fluid collection, and 3 of wound infection. In the present study, we report a 76-yr-old man with R. peoriensis bacteremia who developed aspiration pneumonia. Gram staining of a purified colony revealed Gram-positive, rod-shaped bacteria. Biochemical identification using API 20 A (bioMérieux, France) indicated presence of Clostridium spp. We performed both 500-bp and full-gene sequencing of 16S rRNA of the isolate. The sequence was analyzed with MicroSeq ID 16S rRNA Library v2.0 (Applied Biosystems, USA), GenBank Basic Local Alignment Search Tool (BLAST) (http://www.ncbi.nlm.nih.gov/genbank), and EzTaxon database v2.1 (http://www.eztaxon.org). The 500-bp 16S rRNA sequence of the blood culture isolate showed 99.16-99.79% similarity with R. peoriensis and the full-gene 16S rRNA sequence showed 98.87-99.50% similarity with R. peoriensis. The organism was confirmed as R. peoriensis by using all of the mentioned databases except for MicroSeq, which did not include the RNA sequence of this bacterium. This case suggests that identification of R. peoriensis might be challenging in clinical laboratories with no access to molecular methods, as certain commercial identification systems may not identify, or may misidentify, this organism. To the best of our knowledge, this is the first report of the isolation of R. peoriensis in Korea.

Robinsoniella peoriensis infection following surgery for scoliosis: a case report

INTRODUCTION

Robinsoniella peoriensis was recently identified as a Gram-positive, spore-forming, anaerobic bacillus originally isolated from swine manure storage pits. Seven isolates have been subsequently reported from human sources.

CASE PRESENTATION

We report the case of an infection caused by R. peoriensis in a 45-year-old Caucasian woman after posterior instrumentation correction of idiopathic thoracolumbar scoliosis. The identification was made by culture of samples inoculated onto blood agar and chocolate agar and was confirmed by 16 S ribosomal ribonucleic acid gene sequencing.

CONCLUSIONS

We discuss similar cases suggesting that R. peoriensis is responsible for health care-associated infections with the colonic flora as a potential source of infection.

Epidemiological characteristics of infections caused by Bacteroides, Prevotella and Fusobacterium species: a prospective observational study

In order to investigate differences among infections due to Gram-negative anaerobic bacteria (Bacteroides, Prevotella and Fusobacterium spp.), clinical, epidemiological, and microbiological data were collected and evaluated from 206 anaerobic infections. The most frequently isolated species was Bacteroides fragilis. The majority of the cases were intra-abdominal infections (49%) followed by skin and soft tissue infections (24.7%). Logistic regression analysis showed that Bacteroides spp. strains were more often isolated from intra-abdominal infections (p = 0.002), whereas Prevotella spp. were isolated more frequently from cases with shorter duration of hospitalization (p = 0.026), and less frequently from bloodstream infections (p = 0.049). In addition, Bacteroides spp. were associated with coinfection due to Enterobacteriaceae species (p = 0.007), whereas Prevotella spp. were associated with coinfection due to Staphylococcus spp. (p = 0.002). Patients with an infection due to B. fragilis, were more frequently admitted in a general surgical ward (p = 0.017), or have been treated with a 2nd generation cephalosporin before anaerobic infection onset (p = 0.05). Total mortality was 10.9% and was associated with bacteremia (p = 0.026), and hematological (p = 0.028), or solid organ malignancy (p = 0.007). Metronidazole resistance was detected only among Prevotella spp. (16.2%) and B. fragilis group (0.8%) isolates. In conclusion, this study indicated differences between infections due to the most frequently isolated Gram-negative anaerobic species, differences that may affect the design and implementation of empirical antimicrobial chemotherapy guidelines.

Isolation of Robinsoniella peoriensis from four human specimens

Robinsoniella peoriensis is a recently described anaerobic, spore-forming, Gram-positive bacillus originally recovered from swine manure. We report four human cases in which R. peoriensis was isolated from clinical samples.

Do antimicrobial susceptibility patterns of colonic isolates of Bacteroides species change after antibiotic prophylaxis with cefoxitine during elective abdominal surgery?

The objectives of the study were to investigate and compare the susceptibility profiles of preoperative and postoperative intestinal Bacteroides fragilis and Bacteroides thetaiotaomicron strains against antimicrobials to evaluate their resistance development patterns due to prophylactic antibiotic administration. Preoperative and postoperative stool samples were obtained from patients undergoing elective abdominal surgery with a "clean-contaminated" wound categorization. All patients received cefoxitin 2 g as prophylaxis. Isolates of Bacteroides species were identified. Susceptibility tests against ampicillin, piperacillin, cefoxitin, clindamycin, chloramphenicol, metronidazole, imipenem, and amoxicillin-clavulanate were performed. Stool samples were collected from 40 patients at two settings: before and after the operation. Most of the patients (53%) were operated on because of colorectal carcinoma and underwent surgery that included colectomy or anterior resection. Bacteroides fragilis and Bacteroides thetaiotaomicron were isolated in both samples obtained from 22 and 34 patients, respectively. In the present study 95% to 100%, 50% to 74%, 46% to 64%, and 18% to 35% of preoperatively isolated Bacteroides species were resistant to ampicillin, cefoxitin, clindamycin, and piperacillin, respectively. Although there were no statistically significant difference, postoperative strains were more resistant than preoperative isolates, and the resistance rates were found to be 95% to 100%, 55% to 82%, 46% to 86%, and 37% to 41%, respectively. Both Bacteroides species isolated from all specimens before and after the surgery were uniformly susceptible to amoxicillin-clavulanate, imipenem, metronidazole, and chloramphenicol.Our data revealed that Bacteroides strains revealed high resistance to ampicillin, cefoxitin, piperacillin, and clindamycin. Metronidazole, imipenem, and amoxicillin-clavulanate seem highly effective against both Bacteroides species. Cefoxitin prophylaxis did not significantly increase the resistance patterns against antimicrobial agents.

Bacteroides fragilis-derived lipopolysaccharide produces cell activation and lethal toxicity via toll-like receptor 4

Bacteroides fragilis, which is part of the normal intestinal flora, is a frequent cause of serious disease, especially in diabetic and surgical patients. In these conditions, B. fragilis lipopolysaccharide (LPS) is likely to play a major pathophysiologic role. B. fragilis LPS is structurally different from classical enterobacterial LPS, whose biological activities are mediated by Toll-like receptor 4 (TLR4) activation. The ability of B. fragilis LPS to activate TLR4 and TLR2 was investigated here, since evidence on this issue is scarce and controversial. Each of four different protein-free B. fragilis LPS preparations could induce interleukin-8 responses in cells cotransfected with TLR4/CD14/MD2 but not TLR4/CD14 alone. Two of the preparations also induced cytokine production in cells cotransfected with TLR2/CD14 or in peritoneal macrophages from TLR4 mutant C3H/HeJ mice. Both of these activities, however, were lost after repurification with a modified phenol reextraction procedure. Importantly, all preparations could induce endotoxic shock in TLR2-deficient mice, but not in TLR4 mutant C3H/HeJ mice. Consistent with these findings, anti-TLR4 and anti-CD14, but not anti-TLR2, antibodies could inhibit B. fragilis LPS-induced cytokine production in human monocytes. Collectively, these results indicate that B. fragilis LPS signals via a TLR4/CD14/MD2-dependent pathway, and it is unable to activate TLR2. Moreover, our data document the occurrence of TLR2-activating contaminants even in highly purified B. fragilis LPS preparations. This may explain earlier contradictory findings on the ability of B. fragilis LPS to activate cells in the absence of functional TLR4. These data may be useful to devise strategies to prevent the pathophysiologic changes observed during B. fragilis sepsis and to better understand structure-activity relationships of LPS.

Comparative in vitro antimicrobial activity of a novel quinolone, garenoxacin, against aerobic and anaerobic microbial isolates recovered from general, vascular, cardiothoracic and otolaryngologic surgical patients

OBJECTIVES

The aim of the study was to analyse the susceptibility of unique and non-duplicate aerobic and anaerobic isolates from surgical patients to a novel des-F(6)-quinolone (garenoxacin) and other selected antimicrobial agents.

METHODS

Eleven hundred and eighty-five aerobic and anaerobic isolates from general, vascular, cardiothoracic and otolaryngologic surgical patients were tested for susceptibility to garenoxacin and seven other antibiotics (ciprofloxacin, moxifloxacin, levofloxacin, piperacillin/tazobactam, imipenem, clindamycin and metronidazole) using the referenced microbroth and agar-dilution method.

RESULTS

Garenoxacin exhibited greater antimicrobial activity than comparator quinolones such as ciprofloxacin, levofloxacin and other antimicrobials when tested against selected gram-positive organisms. The in vitro aerobic and anaerobic activity of garenoxacin was similar to that of moxifloxacin. All fluoroquinolones tested were effective against most gram-negative facultative anaerobes including Escherichia coli. Garenoxacin and moxifloxacin demonstrated similar in vitro antimicrobial activity against selected anaerobic gram-positive and gram-negative anaerobic bacteria such as members of the Bacteroides fragilis group. Overall, the in vitro activity of the advanced spectrum quinolones against anaerobic surgical isolates compared favourably with selected comparator agents, metronidazole, imipenem and piperacillin/tazobactam.

CONCLUSIONS

These findings suggest that 82.4% of aerobic surgical isolates were susceptible to a concentration of garenoxacin < or = 1.0 mg/L, whereas 84.5% of the anaerobic isolates were susceptible to a garenoxacin concentration < or = 1.0 mg/L. Garenoxacin may be a valuable surgical anti-infective for treatment of serious head and neck, soft tissue, intra-abdominal and diabetic foot infections.

Patterns of microbiology in intra-abdominal packing for trauma

INTRODUCTION

This study tracks the microbiology of packs and infections in damage-control trauma patients to determine whether the packs cause infections.

METHODS

The peritoneum and abdominal packs were cultured in patients who survived to re-operation. The study recorded all positive cultures, pack count, packing duration, number of operations, and infections.

RESULTS

Thirty-five patients were studied. Twenty-eight patients survived; seven died. Packs were cultured in 29 patients. Data for 291 cultures collected. Pack cultures were positive in 20 patients and negative in nine. Positive pack cultures grew skin and gut flora. Twenty-one patients had infections, 14 did not. Organisms from positive pack cultures did not contribute to subsequent infections or mortality. Microbes and sites of infections were consistent with SICU patients.

CONCLUSIONS

Intra-abdominal packs are contaminated with skin and gut flora. These contaminants, however, do not contribute to subsequent infections. Pathogens from subsequent infections were typical for ICU infections.