Therapeutic efficacy of 29 antimicrobial regimens in experimental intraabdominal sepsis

Contributions of animal studies to the understanding of infectious diseases

Experiments in animals have played an integral role in furthering basic understanding of the pathophysiology, host immune response, diagnosis, and treatment of infectious diseases. However, competing demands of modern-day clinical training and increasingly stringent requirements to perform animal research have reduced the exposure of infectious disease physicians to animal studies. For practitioners of infectious diseases and, especially, for contemporary trainees in infectious diseases, it is important to appreciate this historical body of work and its impact on current clinical practice. In this article, we provide an overview of some major contributions of animal studies to the field of infectious diseases. Areas covered include transmission of infection, elucidation of innate and adaptive host immune responses, testing of antimicrobials, pathogenesis and treatment of endocarditis, osteomyelitis, intraabdominal and urinary tract infection, treatment of infection associated with a foreign body or in the presence of neutropenia, and toxin-mediated disease.

Broad-spectrum Antibiotic Plus Metronidazole May Not Prevent the Deterioration of Necrotizing Enterocolitis From Stage II to III in Full-term and Near-term Infants: A Propensity Score-matched Cohort Study

Necrotizing enterocolitis (NEC) is the most common and frequently dangerous neonatal gastrointestinal disease. Studies have shown broad-spectrum antibiotics plus anaerobic antimicrobial therapy did not prevent the deterioration of NEC among very low birth preterm infants. However, few studies about this therapy which focused on full-term and near-term infant with NEC has been reported. The aim of this study was to evaluate the effect of broad-spectrum antibiotic plus metronidazole in preventing the deterioration of NEC from stage II to III in full-term and near-term infants.A retrospective cohort study based on the propensity score (PS) 1:1 matching was performed among the full-term and near-term infants with NEC (Bell stage ≥II). All infants who received broad-spectrum antibiotics were divided into 2 groups: group with metronidazole treatment (metronidazole was used ≥4 days continuously, 15 mg/kg/day) and group without metronidazole treatment. The depraved rates of stage II NEC between the 2 groups were compared. Meanwhile, the risk factors associated with the deterioration of stage II NEC were analyzed by case-control study in the PS-matched cases.A total of 229 infants met the inclusion criteria. Before PS-matching, we found the deterioration of NEC rate in the group with metronidazole treatment was higher than that in the group without metronidazole treatment (18.1% [28/155] vs 8.1% [6/74]; P = 0.048). After PS-matching, 73 pairs were matched, and the depraved rate of NEC in the group with metronidazole treatment was not lower than that in the group without metronidazole treatment (15.1% vs 8.2%; P = 0.2). Binary logistic regression analysis showed that sepsis after NEC (odds ratio [OR] 3.748, 95% confidence interval [CI] 1.171-11.998, P = 0.03), the need to use transfusion of blood products after diagnosis of NEC (OR 8.003, 95% CI 2.365-27.087, P = 0.00), and the need of longer time for nasogastric suction were risk factors for stage II NEC progressing to stage III (OR 1.102, 95% CI 1.004-1.21, P = 0.04).Broad-spectrum antibiotic plus metronidazole may not prevent the deterioration of NEC in full-term and near-term infants. Those infants who had sepsis required transfusion of blood products, and needed longer time for nasogastric suction after stage II NEC was more likely to progress to stage III.

Is a single positive blood culture for Enterococcus species representative of infection or contamination?

Data on the clinical outcomes of patients with a single compared with multiple positive blood cultures for Enterococcus species is limited. We undertook a retrospective cohort study in adults with at least one positive blood culture for Enterococcus species in a single institution. Clinical outcomes included death and elimination of infection. We included 471 positive blood cultures from 206 enterococcal positive blood culture episodes in 189 patients. Multiple positive blood cultures for Enterococcus species occurred in 110/206 (53.4 %) episodes; 31.6 % of patients had diabetes mellitus; 42.9 % of patients had solid or hematologic malignancy; 26.5 % of patients were solid organ transplant recipients; hospital-acquired and healthcare-associated acquisition represented 55.3 % and 33.0 % of episodes, respectively. Thirty-five patients died and 110 episodes of enterococcal bloodstream infection were successfully treated. In the multivariable analysis, multiple positive blood cultures were not statistically significantly associated with an increased likelihood of in-hospital death [odds ratio (OR) 1.00, 95 % confidence interval (CI) 0.42-2.40] or elimination (OR 1.41, 95 % CI 0.76-2.64) compared with single positive blood cultures. Hematologic malignancy and diabetes mellitus were independently associated with in-hospital death (OR 2.83, 95 % Cl 1.02-7.82; OR 2.79, 95 % Cl 1.16-6.70, respectively). Infectious disease consultation was associated with a greater likelihood of elimination (OR 2.50, 95 % Cl 1.32-4.72). The clinical outcomes of patients with single versus multiple positive blood cultures with Enterococcus species were similar in our institution. Further studies should examine efficient methods to detect contamination versus true infection.

Efficacy of moxifloxacin monotherapy versusgatifloxacin monotherapy, piperacillin-tazobactam combination therapy, and lindamycin plus gentamicin combination therapy: An experimental study in a rat model of intra-abdominal sepsis induced by fluoroquinolone-resistant Bacteroides fragilis

BACKGROUND

In intra-abdominal infections, the activity of antimicrobial agents against Bacteroides fragilis and phenotypically related organisms, and the increasing resistance of these organisms, are of particular importance and concern to surgeons. In vitro data suggest that moxifloxacin is more active than other quinolones against obligately anaerobic organisms, including Bacteroides spp.

OBJECTIVE

The aim of this study was to compare the efficacy of moxifloxacin monotherapy versus gatifloxacin monotherapy and 2 combination therapies (piperacillin-tazobactam and clindamycin plus gentamicin) in a rat model of intra-abdominal sepsis. The end point was marked by the incidence of mortality and intra-abdominal abscesses at necropsy 7 days after bacterial challenge.

METHODS

Three different strains of B fragilis with different degrees of resistanceto moxifloxacin (minimum inhibitory concentrations [MICs]: 4, 8, and 16 pg/mL) were added to the challenge inoculum in 3 separate experiments. Groups of 20 animals were used in each experiment. Group 1 served as saline-treated controls; group 2 received moxifloxacin 15 mg QD; group 3 received gatifloxacin 25 mg QD; group 4 received piperacillin-tazobactam 93 mg (-83 mg of piperacillin) QD; and group 5 received a combination of clindamycin 15 mg TID plus gentamicin 2 mg TID. All treatments were given intramuscularly. For all antimicrobials, dose was based on peak and trough serum drug concentrations determined by prior testing, with animal doses adjusted based on the ratio of body surface area to body weight, and comparing these doses and levels with studies in humans.

RESULTS

In all 3 experiments, the mortality rate with moxifloxacin was significantlylower or statistically similar compared with antibiotic active comparators (P ≤ 0.024). In addition, there were no significant differences in the incidence of abscess with moxifloxacin versus its comparators or between the 3 moxifloxacin groups across experiments. The best results for moxifloxacin were found in the experiment in which the B fragilis strain with MIC 16 μg/mL was added to the inoculum.

CONCLUSION

The results of this study in an animal model of intra-abdominalsepsis induced by fluoroquinolone-resistant B fragilis suggest that moxifloxacin monotherapy performs as well as combination regimens such as piperacillin-tazobactam and clindamycin plus gentamicin, and is as effective as other fluoroquinolones with antianaerobic activity, such as gatifloxacin.

How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy

Anaerobic bacteria are infrequent pulmonary pathogens, and, even then they are, they are almost never recovered due to the need for specimens uncontaminated by the upper airway flora and failure to do adequate anaerobic bacteriology. These bacteria are relatively common in selected types of lung infections including aspiration pneumonia, lung abscess, necrotizing pneumonia and emphyema. Preferred antibiotics for these infections based on clinical experience are clindamycin and any betalactam-betalactamase inhibitor.

Sepsis-induced leukocyte adhesion in the pulmonary microvasculature in vivo is mediated by CD11a and CD11b

Leukocyte accumulation is a rate-limiting step in inflammatory lung injury. The aim of this study was to define the role of CD11a/CD18 and CD11b/CD18 in sepsis-induced leukocyte rolling and adhesion in lung arterioles, capillaries and venules in male C57BL/6 mice using intravital fluorescence microscopy. Cecal ligation and puncture (CLP) markedly increased leukocyte rolling in arterioles and venules but not in capillaries in the lung. Immunoneutralization of CD11a, but not CD11b, decreased CLP-provoked leukocyte rolling in lung arterioles. Inhibition of CD11a or CD11b abolished CLP-induced arteriolar and venular leukocyte adhesion. Immunoneutralization of CD11a and CD11b reduced sepsis-induced leukocyte sequestration in pulmonary capillaries. Moreover, blocking CD11a or CD11b function improved microvascular blood flow in the lung of CLP animals. Considered together, our novel findings show that CD11a and CD11b mediate leukocyte adhesion in both arterioles and venules as well as trapping in capillaries in the lung. In addition, our data demonstrate that CD11a but not CD11b supports leukocyte rolling in pulmonary arterioles. Thus, these findings elucidate the molecular mechanisms behind leukocyte-endothelium interactions in the lung during systemic inflammation.

Animal models simulating anaerobic infections

Animal models simulating human disease have played an important role in our understanding of the pathogenesis and treatment of infections caused by obligately anaerobic bacteria. These models helped document the primary source of such infections as the host's own normal microflora. In addition, the polymicrobial nature of anaerobic infections was documented by using animal models for intraabdominal sepsis. Subsequent studies using animal models have led to an understanding of the nature of the host immune response to abscess causing agents and have been instrumental in defining the molecular basis for the virulence and protection provided by the polysaccharide capsule of Bacteroides fragilis. Animal models have also been important components for studies of toxigenic clostridial diseases, such as antibiotic associated colitis and ulcerative colitis. A discussion of some of these models is provided in this review.

Lactobacilli attenuate bacteremia and endotoxemia associated with severe intra-abdominal infection

BACKGROUND

Systemic administration of antibiotics or selective decontamination is frequently used in the prophylaxis and treatment of infections originating from the gastrointestinal flora. In this study, we wanted to compare the protective effect of enteral administration of lactobacilli to gentamicin against severe intra-abdominal infection.

METHODS

Male Sprague-Dawley rats underwent cecal ligation and puncture (CLP). Rats were pretreated with saline, Lactobacillus R2LC, and gentamicin. Bacterial growth and endotoxin levels in the blood, reticuloendothelial system (RES)-function, and intestinal transit were determined up to 24 hours after CLP.

RESULTS

CLP-provoked bacteremia was significantly reduced by 48% and 55% in lactobacilli- and gentamicin-treated rats, respectively. Notably, CLP-induced endotoxemia was abolished at 12 hours, and reduced by 47% at 24 hours, in rats pretreated with lactobacilli. Gentamicin reduced endotoxin levels provoked by CLP by 86% at 12 hours, but had no effect at 24 hours. Lactobacilli had no effect on the clearance of Escherichia coli (E coli) from the blood, whereas intestinal transit was increased in lactobacilli-treated animals, suggesting that the beneficial effect of Lactobacillus R2LC is not related to an increase of phagocytic capacity but may rather be partly attributable to an enhanced intestinal motility.

CONCLUSION

Enteral administration of Lactobacillus R2LC attenuates bacteremia and endotoxemia associated with intra-abdominal infection in rats.

Microbiology and management of intra-abdominal infections in children

The present review describes the microbiology, diagnosis, and management of intra-abdominal infections in children. Infection generally occurs due to the entry of enteric micro-organisms into the peritoneal cavity through a defect in the wall of the intestine or other viscus as a result of obstruction, infarction, or direct trauma. Mixed aerobic and anaerobic flora can be recovered from the peritoneal cavity of these patients. The predominant aerobic isolates are Escherichia coli, and enterococci; the main anaerobic bacteria are Bacteroides fragilis group, Peptostreptococcus spp. and Clostridium spp. The treatment of abdominal infection includes surgical correction and drainage, and administration of antimicrobials that are effective against both aerobic and anaerobic micro-organisms.

Effect of prolonged selective intramesenteric arterial vasodilator therapy on intestinal viability after acute segmental mesenteric vascular occlusion

OBJECTIVE

To evaluate the effect of selective intramesenteric artery vasodilator infusion on intestinal viability in a rat model of acute segmental mesenteric vascular occlusion.

SUMMARY BACKGROUND DATA

Although intramesenteric arterial vasodilator infusion may be an effective treatment for nonocclusive mesenteric ischemia, it has also been advocated to increase collateral blood flow after mesenteric vascular occlusion. However, the authors have previously found that intraarterial vasodilators actually reduce collateral blood flow acutely, by preferentially dilating the vasculature of adjacent, nonischemic mesenteric vascular beds, a phenomenon well established in other organs.

METHODS

A segment of rat ileum was acutely devascularized, with blood flow provided only by collateral arterial vessels from adjacent, nonischemic bowel. Papaverine (30 or 40 microg/kg/min), isoproterenol (0.06 microg/kg/min), norepinephrine (0.1 or 0.2 microg/kg/min), or vehicle saline was continuously infused into the cranial (superior) mesenteric artery for 48 hours. Viability was then assessed using previously established, objective gross and microscopic criteria.

RESULTS

Although papaverine increased total mesenteric blood flow in normally vascularized rats, it not only failed to improve but actually significantly reduced the length of the devascularized segment maintained viable by collateral blood flow after 48 hours. Isoproterenol had a similar effect. Norepinephrine infusion decreased both normal mesenteric blood flow and viable segment length.

CONCLUSIONS

These findings suggest that intraarterial vasodilator therapy fails to improve intestinal viability after segmental mesenteric vascular occlusion.

Surgical management of severe secondary peritonitis

BACKGROUND

Despite advances in diagnosis, surgery, antimicrobial therapy and intensive care support, the mortality rate associated with severe secondary peritonitis remains unacceptably high. This article presents various surgical treatment strategies for severe secondary peritonitis, emphasizing the role of open management of the abdomen and planned relaparotomies.

METHODS

Material was identified from previous review articles, references cited in original papers and a Medline search of the literature.

RESULTS AND CONCLUSION

Surgical treatment of severe secondary peritonitis is highly demanding and very complex. The combination of improved surgical techniques, antimicrobial therapy and intensive care support has improved the outcome of such peritonitis following perforation or anastomotic disruption of the digestive tract, or infected necrotizing pancreatitis. However, aggressive surgical treatment strategies, such as open management of the abdomen and planned relaparotomies, may have reached their limits.

Pharmacokinetics and pharmacodynamics of the nitroimidazole antimicrobials

Metronidazole, the prototype nitroimidazole antimicrobial, was originally introduced to treat Trichomonas vaginalis, but is now used for the treatment of anaerobic and protozoal infections. The nitroimidazoles are bactericidal through toxic metabolites which cause DNA strand breakage. Resistance, both clinical and microbiological, has been described only rarely. Metronidazole given orally is absorbed almost completely, with bioavailability > 90% for tablets; absorption is unaffected by infection. Rectal and intravaginal absorption are 67 to 82%, and 20 to 56%, of the dose, respectively. Metronidazole is distributed widely and has low protein binding (< 20%). The volume of distribution at steady state in adults is 0.51 to 1.1 L/kg. Metronidazole reaches 60 to 100% of plasma concentrations in most tissues studied, including the central nervous system, but does not reach high concentrations in placental tissue. Metronidazole is extensively metabolised by the liver to 5 metabolites. The hydroxy metabolite has biological activity of 30 to 65% and a longer elimination half-life than the parent compound. The majority of metronidazole and its metabolites are excreted in urine and faeces, with less than 12% excreted unchanged in urine. The pharmacokinetics of metronidazole are unaffected by acute or chronic renal failure, haemodialysis, continuous ambulatory peritoneal dialysis, age, pregnancy or enteric disease. Renal dysfunction reduces the elimination of metronidazole metabolites; however, no toxicity has been documented and dosage alterations are unnecessary. Liver disease leads to a decreased clearance of metronidazole and dosage reduction is recommended. Recent pharmacodynamic studies of metronidazole have demonstrated activity for 12 to 24 hours after administration of metronidazole 1 g. The post-antibiotic effect of metronidazole extends beyond 3 hours after the concentration falls below the minimum inhibitory concentration (MIC). The concentration-dependent bactericidal activity, prolonged half-life and sustained activity in plasma support the clinical evaluation of higher doses of metronidazole given less frequently. Metronidazole-containing regimens for Helicobacter pylori in combination with proton pump inhibitors demonstrate higher success rates than antimicrobial regimens alone. The pharmacokinetics of metronidazole in gastric fluid appear contradictory to these results, since omeprazole reduces peak drug concentration and area under the concentration-time curve for metronidazole and its hydroxy metabolite; however, concentrations remain above the MIC. Other members of this class include tinidazole, ornidazole and secnidazole. They are also well absorbed and distributed after oral administration. Their only distinguishing features are prolonged half-lives compared with metronidazole. The choice of nitroimidazole may be influenced by the longer administration intervals possible with other members of this class; however, metronidazole remains the predominant antimicrobial for anaerobic and protozoal infections.

Early bacterial and inflammatory responses to antibiotic therapy in a model of polymicrobial peritonitis in rats

OBJECTIVE: To assess the consequences of different more or less selective treatments on the microbiological and inflammatory responses within the peritoneum. METHODS: The early effects of various antibiotic regimens were evaluated in a model of polymicrobial peritonitis with specifically prepared organisms. Six regimens (amoxycillin plus gentamicin, pefloxacin, ornidazole, pefloxacin plus ornidazole, imipenem and imipenem plus gentamicin) were evaluated at 24 h and 3 days in a non-fatal model of peritonitis in rats achieved by implantation of a capsule containing Escherichia coli, Bacteroides fragilis and Enterococcus faecalis. RESULTS: Therapies that disregarded several organisms were associated with persistence of the strains and an increased peritoneal inflammatory response within the peritoneum. In contrast, therapies active against Enterobacteriaceae and anaerobes were associated with decreases of all the inoculated organisms and a smaller inflammatory response. CONCLUSION: Therapies that disregarded the microorganisms implicated in peritoneal infection are associated with delayed bacterial eradication. The persistence of these organisms within the peritoneal fluid might be involved in prolonged peritoneal inflammation. Although it disregards enterococci, the standard therapy, represented by therapy against Enterobacteriaceae and anaerobes, demonstrates satisfactory effects towards all the inoculated organisms. This apparent contradiction could be related to mechanisms of bacterial synergy.

Studies on the pathogenicity of anaerobes, especially Prevotella bivia, in a rat pyometra model

OBJECTIVE

Prevotella bivia is one of the anaerobic bacteria that resides in the flora of the female genital tract. We studied the pathogenicity of P. bivia in a rat pyometra model.

METHODS

The experimental animal (rat) model of pyometra was developed to investigate the pathogenicity of P. bivia in a rat pyometra model.

RESULTS

In the groups inoculated with aerobes alone, the infection rate was 10% (1/10) in the Staphylococcus aureus- or Staphylococcus agalactiae-inoculated group and 20% (2/10) in the Escherichia coli-inoculated group. Infection was not established in the groups inoculated with anaerobes alone. High infection rates were observed in all the mixed-infection groups. In the S. agalactiae- and Bacteroides fragilis-, S. agalactiae- and P. bivia-, F. coli- and B. fragilis-, and E. coli- and P. bivia-inoculated groups, an infection rate of 100% (10/10) was demonstrated. The efficacy of antibiotics such as flomoxef (FMOX) could be determined using a rat pyometra model. In relation to the alteration of vaginal microbial flora during the menstrual cycle, estrogen increased the growth of P. bivia.

CONCLUSION

Mixture of aerobic bacteria and P. bivia increased the pathogenicity of P. bivia. Estrogen would be useful for raising up the inflammatory change of the uterus in experimental models of genital tract infection due to P. bivia.

Definition of the role of enterococcus in intraabdominal infection: analysis of a prospective randomized trial

BACKGROUND

The role of enterococcus in intraabdominal infection is controversial. This study examines the contribution of enterococcus to adverse outcome in a large intraabdominal infection trial.

METHODS

A randomized prospective double-blind trial was performed to compare two different antimicrobial regimens in combination with surgical or percutaneous drainage in the treatment of complicated intraabdominal infections. A total of 330 valid patients was enrolled from 22 centers in North America.

RESULTS

In 330 valid patients, 71 had enterococcus isolated from the initial drainage of an intraabdominal focus of infection. This finding was associated with a significantly higher treatment failure rate than that of patients without enterococcus (28% versus 14%, p < 0.01). In addition, only Acute Physiology and Chronic Health Evaluation II score and presence of enterococcus were significant independent predictors of treatment failure when stepwise logistic regression was performed (p < 0.01 and < 0.03). Risk factors for the presence of enterococcus include age, Acute Physiology and Chronic Health Evaluation II, preinfection hospital length of stay, postoperative infections, and anatomic source of infection. There was no difference between the clinical trial treatment regimens with regard to overall failure, failure associated with enterococcus, or frequency of enterococcal isolation.

CONCLUSIONS

This study is the first to report enterococcus as a predictor of treatment failure in complicated intraabdominal infections. This trial also identifies several significant risk factors for the presence of enterococcus in such infections.

Intra-abdominal sepsis

This article addresses controversial issues in the field of intra-abdominal sepsis with particular attention to major changes in management that have evolved during the past decade. In the area of diagnostics, scanning techniques have revolutionized the ability to detect loculated collections, although many of these techniques are of limited value in the early stages of inflammation. The greatest debate concerns the relative merits of scanning techniques; the author's choice is CT scans with contrast, although ultrasonography is preferred in patients who cannot be transported and is probably preferred for pelvic infections. In the area of therapeutics, virtually all studies seem to show that single-drug treatment is as effective as dual combinations or triple-combination therapy that has been standard practice in the past with the proviso that the drug used has activity versus Enterobacteriaceae and B. fragilis. The role of enterococcus remains enigmatic; this organism was readily discounted as an important pathogen in the great majority of cases 10 years ago, but it has subsequently become a major nosocomial pathogen that now commands newfound respect. P. aeruginosa is also controversial, but most studies show that antipseudomonad treatment is not necessary in the empiric selection of drugs and may not be necessary even when P. aeruginosa is found at infected sites; the corollary to this is that aminoglycosides may no longer be required in the dual drug treatment regimens. There is increasing resistance by B. fragilis and some other species of Bacteroides to some of the drugs considered "standard" in the past, including clindamycin, cefoxitin, and cefotetan; nevertheless, it has been difficult to demonstrate that resistance of these organisms correlates with antibiotic failure. It was demonstrated 20 years ago that elective colon surgery must be accompanied by preoperative antibiotics, and erythromycin plus neomycin has evolved as the regimen of choice according to recommendations of authoritative sources for the past 20 years. Nevertheless, surveys of practicing surgeons indicate that most actually combine this oral preparation with parenteral agents as well. The final controversy concerns percutaneous drainage, which has now become a standard technique for dealing with intra-abdominal abscesses in 50% to 90% of cases. This controversy has sometimes been seen as a territorial battle between surgeons and radiologists, and most cases are clearly the prerogative of one discipline or the other, but many are in a gray zone in which clearly defined indications are not readily available.

Activity of fleroxacin alone and in combination with clindamycin or metronidazole in experimental intra-abdominal abscesses

To assess the potential efficacy of fleroxacin in combination with clindamycin or metronidazole in mixed aerobic and anaerobic infections, we used a rat model of intra-abdominal abscesses in which the inoculum consisted of pooled rat feces mixed with BaSO4. Two hours after bacterial challenge, antimicrobial therapy was begun intravenously with regimens designed to stimulate human pharmacokinetics. A combination of clindamycin and gentamicin was included as an established treatment regimen. After 8.5 days of therapy, final bacterial counts in abscesses showed that fleroxacin alone or combined with metronidazole or clindamycin effectively eradicated Escherichia coli, with bacterial densities of < or = 2.84 +/- 0.1, < or = 2.9 +/- 0.1, and < or = 2.9 +/- 0.1 (mean +/- standard error of the mean) log10 CFU/g, respectively. The addition of either clindamycin or metronidazole to fleroxacin substantially enhanced the effectiveness of the regimens against Bacteroides fragilis, with bacterial counts of < or = 3.0 +/- 0.1 or < or = 2.9 +/- 0.1 log10 CFU/g, respectively, versus 9.2 +/- 0.2 log10 CFU/g for fleroxacin alone. The combination of metronidazole and fleroxacin also resulted in a significantly greater reduction of peptostreptococci and Bacteroides thetaiotaomicron than fleroxacin alone (< or = 2.9 +/- 0.1 versus 6.1 +/- 0.9 log10 CFU/g and 3.3 +/- 0.4 versus 8.3 +/- 0.1 log10 CFU/g, respectively). Except for those of B. fragilis, counts of other anaerobes were reduced to a greater extent by metronidazole plus fleroxacin than by clindamycin plus fleroxacin, although differences were not always significant. Metronidazole plus fleroxacin was at least as active a clindamycin plus gentamicin against all species and was significantly more active against Clostridium spp. No regimen effectively eradicated enterococci from the abscesses. These results suggest that the addition of either metronidazole or clindamycin would effectively enhance the spectrum of fleroxacin for treatment of mixed aerobic and anaerobic infections.

Empiric antibiotic therapy of abdominal sepsis and serious perioperative infections

This article discusses empiric therapy for several serious infections in surgical patients. The accepted antibiotic treatment for purulent peritonitis, the empiric treatment of postsurgical wound infection, and the empiric treatment of postsurgical pneumonia are discussed. The cost of the various regimens is listed. Recommendation of the various regimens is based on the seriousness of the infection, peculiarities of the hospital flora, effectiveness of the regimens, and cost.

Current perspectives on antibiotic use in the treatment of surgical infections

Infections that involve the attention of the surgeon include those that require operations for cure as well as those that complicate emergency and elective surgical procedures. Mechanical correction is of paramount importance in the eradication of such infections with antibiotics serving an adjuvant role, primarily to clear lymphatics and prevent bacteremia and seeding of distant sites. Review of the current hospital antibiotic susceptibility profile is important to determine likely sensitivity to expected pathogens. Infection of the urinary tract remains the most common nosocomial infection, but in surgical patients the severe infections are pneumonia, fasciitis, and peritonitis. Often caused by the gram-negative Enterobacteriaceae, empiric broad spectrum antibiotic therapy is initiated after cultures are obtained. Bacterial infection of the respiratory tract is often difficult to diagnose in severely ill patients because the underlying fever, leukocytosis, and chest X-ray changes are often nonspecific. Reliance on sputum gram stain and culture is important to guide antibiotic therapy. Empiric treatment of peritonitis requires knowledge of the normal enteric flora and the likely pathogenic organisms. The most lethal agent against obligate anaerobic organisms is atmospheric oxygen, yet antibiotic coverage against these organisms appears wise, particularly when debridement or resection will be delayed or not performed. Staphylococcus aureus is still the most commonly cultured organism from our Surgical Intensive Care Unit and Burn Unit and S. aureus is often responsible for central line and burn wound infection. For patients in septic shock, we favor administration of a broad-spectrum penicillin or cephalosporin combined with an aminoglycoside, with subsequent narrowing of the antibiotic spectrum based on culture results. Antibiotic efficacy, toxicity, efficiency, and cost all must be weighed in the decision-making process.

Comparison of the efficacy of three different treatments with imipenem versus the classical clindamycin plus tobramycin in experimental peritonitis

This study compares the efficacy of three different treatment modalities of imipenem/cilastatin and the conventional clindamycin plus tobramycin in an experimental model of intra-abdominal sepsis. 145 Wistar rats were used. 40 served as control and 105 as study groups. A capsule with 0.5 ml of inoculum was surgically implanted in the peritoneal cavity. The inoculum was prepared from human feces of healthy volunteers, with a composition of E. coli 10(6), E. faecalis 10(6), B. fragilis, Clostridium sp 10(5) to 10(6) and anaerobic streptococci 10(5) to 10(6). Eighty animals were treated with imipenem/cilastatin and divided in 3 subgroups: "short pretreatment"--29 animals treated 1 hour prior to surgery and 3 days after; "short"--26 animals starting treatment 2 hours post-surgery and continuing it for 3 days; and "long"--25 animals treated for 10 days, starting 2 hours post-surgery. 25 animals received clindamycin plus tobramycin for 10 days. Mortality and the presence of visceral and peritoneal abscesses were the endpoints of the study. The control group had 100% mortality. There were no statistically significant differences among the treated groups although lower mortality was obtained with "short pretreatment" and "long" treatment with imipenem. The presence of abscesses were statistically significant between the imipenem and the combination group. In the imipenem groups, the "short pretreatment" and the long treatment had fewer abscesses than the short one. We conclude that imipenem may be a good alternative monotherapy to conventional therapy with clindamycin plus tobramycin. The "short pretreatment" seemed as good as the long one and better than the short treatment.

Pathogenicity of the enterococcus in surgical infections

The enterococcus has been relegated to a position of unimportance in the pathogenesis of surgical infections. However the increasing prevalence and virulence of these bacteria prompt reconsideration of this view, particularly because the surgical patient has become increasingly vulnerable to infectious morbidity due to debility, immunosuppression, and therapy with increasingly potent antibiotics. The enterococcus is a versatile opportunistic nosocomial pathogen, causing such diverse infections as wound, intra-abdominal, and urinary tract infections; catheter-associated infection; suppurative thrombophlebitis; endocarditis; and pneumonia. Although surgical drainage remains the cornerstone of therapy for enterococcal infections involving a discrete focus, in the circumstances typified by the compromised surgical patient, specific antibacterial therapy directed against the enterococcus is warranted. Recent evidence indicates that parenteral antibiotic therapy for enterococcal bacteremia is mandatory and that appropriate therapy clearly reduces the number of deaths.

Comparison of parenteral ciprofloxacin with clindamycin-gentamicin in the treatment of pelvic infection

A prospective, randomized study of intravenous followed by oral ciprofloxacin compared with the combination of intravenous clindamycin and gentamicin was conducted in 122 women hospitalized with pelvic infections. Clinical diagnoses included endometritis (97 patients) and uncomplicated pelvic inflammatory disease (25 patients). Treatment successes for endometritis included 42 of 50 (84 percent) patients treated with ciprofloxacin compared with 35 of 47 (75 percent) treated with the clindamycin-gentamicin combination. Treatment successes for acute salpingitis included 10 of 10 (100 percent) treated with ciprofloxacin and 13 of 15 (87 percent) treated with clindamycin-gentamicin. Ciprofloxacin successfully eradicated Chlamydia trachomatis in 11 of 12 patients as did clindamycin-gentamicin in six of seven patients. In this study of pelvic infection, ciprofloxacin demonstrated efficacy comparable with the combination of clindamycin and gentamicin, and is effective against C. trachomatis.

Phagocytic activity of polymorphonuclear leukocytes on Escherichia coli previously exposed to metronidazole

A study was made of the action of different concentrations of metronidazole of the viability of Escherichia coli under aerobic and anaerobic conditions. The viability of E. coli was reduced by 60 to 99% after 24 hours of anaerobic incubation, according to the concentration of metronidazole tested. In addition, there were significant morphological changes in the bacteria. Exposure of antibiotic-induced filaments of E. coli LP 136 to phagocytosis caused the cfu/ml value to drop by 60% after 120 minutes. Under identical conditions, using the mutant strain E. coli RYC 819, which did not become filamented by metronidazole although it did present similar ultrastructural changes, this reduction reached 83%. These results may explain the therapeutic success of metronidazole in polymicrobial infections.

Sulbactam/ampicillin versus metronidazole/gentamicin in the treatment of post-cesarean section endometritis

Sixty-seven patients diagnosed with post-cesarean-section endometritis were studied in a prospective comparative randomized trial of sulbactam/ampicillin, a new beta-lactamase inhibitor drug combination, versus treatment with metronidazole/gentamicin. The success rate was 91% for each antibiotic regimen. Mycoplasma spp. or Ureaplasma spp. were isolated from all treatment failures. Endometrial cultures revealed 2.3 aerobes as well as anaerobes per patient, with Enterococcus faecalis, Bacteroides bivius, and Escherichia coli the most frequently reported bacterial isolates in 64, 40, and 28% of all patients, respectively. Positive blood cultures were noted in 11 (15%) patients with Mycoplasma sp. the most commonly found isolate (45.5%). Sulbactam/ampicillin appears to be safe and equally effective as a metronidazole/aminoglycoside drug regimen in the treatment of postpartum endometritis.

Effects of enteral and intravenous antimicrobial treatment on survival following intestinal ischemia in rats

One hundred and twenty rats underwent transection of the superior mesenteric artery. The animals were randomly divided into eight groups of 15 animals. Control group 1 and groups 3, 5, and 7 received intravenous normal saline, gentamicin, metronidazole, and gentamicin plus metronidazole, respectively. Control group 2 and groups 4, 6, and 8 received the same compounds enterally. Small and large bowel sections were taken postmortem and a necrosis score was assigned in blinded fashion. Gentamicin did not prolong survival, indicating that gram-negative microbes were not important in this pathology. Longer survival times for animals given either metronidazole or gentamicin plus metronidazole (P less than 0.01) indicate that anaerobes were a causative factor in mortality. During the first 15 hr after ischemia, antibiotics did not change mortality. After 15 hr, enteral administration was superior to intravenous administration in any regimen including metronidazole (P less than 0.01).

Management of anaerobic infections

Successful management of anaerobic infection first requires an accurate diagnosis. Cytologic examination of wound exudates and inspection for characteristic clinical clues greatly facilitates an accurate initial diagnosis of anaerobic infection. Knowledge of antimicrobial activity against specific anaerobic pathogens is essential, since antibiotic susceptibility information is not routinely available. Whenever possible, antimicrobial and surgical therapy should be combined in managing anaerobic infections. Chloramphenicol, clindamycin, and metronidazole provide the most consistently reliable activity against pathogenic anaerobes, including Bacteroides. Penicillins are also generally effective, except for treatment of infections caused by penicillinase-producing strains of Bacteroides. Cephalosporins are not considered drugs of choice for anaerobic infections, although cefoxitin may in some instances be useful as monotherapy of mixed infections containing obligate anaerobes and coliform bacteria. Aminoglycosides and sulfonamides are ineffective and should be avoided for treatment of anaerobic infection.

Susceptibility testing today: myth, reality, and new direction

Recent concerns about the clinical relevance of susceptibility testing echo those expressed previously by a number of authors.’-” These concerns are well founded and are perhaps even more important today because of the proliferation of new antibiotics and the changes in reimbursement philosophy.” Ultimately, the question becomes that raised by David Greenwood: “In vitro veritas?” The following discussion will review the role of susceptibility testing in clinical medicine with emphasis on myth versus reality. In addition, new directions for susceptibility testing that promise increased clinical relevance will be covered.

A randomized, controlled trial of parenteral clindamycin in neonatal necrotizing enterocolitis

For an assessment of the efficacy of clindamycin in preventing bowel necrosis (intestinal gangrene or perforation), 42 premature infants with radiographically confirmed necrotizing enterocolitis (NEC) (pneumatosis, intraportal gas, or both) were randomly assigned to receive parenterally either ampicillin and gentamicin (control group, n = 22) or ampicillin, gentamicin, and clindamycin (n = 20), 20 mg/kg/d at 8-hour intervals for 10 to 14 days. Infants who had received antibiotics for greater than 24 hours before randomization and those developing intestinal gangrene or perforation less than 12 hours after randomization were excluded. Intestinal gangrene or perforation developed in four infants in the control group and six in the clindamycin group. Four in each group died of NEC. In the control group, one of 18 survivors developed a late stricture requiring surgical resection, whereas six of 15 survivors in the clindamycin group developed such strictures (P = 0.022). Routine inclusion of clindamycin in medical treatment of NEC does not reduce the frequency of intestinal gangrene or perforation and may be associated with an increase in late stricture formation.

Symposium on antimicrobial agents. Metronidazole

Metronidazole, a nitroimidazole derivative, is a unique antimicrobial agent that is active against both bacterial and parasitic organisms, although only the anaerobic members of these groups are susceptible. It has been used for the treatment of trichomoniasis for almost 30 years and is also effective in amebiasis and giardiasis. More recently, metronidazole has emerged as a principal agent for the treatment of anaerobic infections. It is highly effective against all species of anaerobes except certain non-spore-forming gram-positive bacilli and cocci and is the only agent rapidly bactericidal against the Bacteroides fragilis group. The hydroxy metabolite is 65% as effective as metronidazole and may play a major therapeutic role. Clinical studies have substantiated its efficacy for prophylaxis during elective colorectal surgical procedures and the treatment of deep abdominal sepsis (usually in combination with another agent such as an aminoglycoside). Metronidazole is the treatment of choice for bacterial vaginosis and seems to be as effective as vancomycin for treatment of Clostridium difficile-related diarrhea and colitis. Good blood levels are produced after both oral and intravenous administration, and side effects are infrequent and minimal. Metronidazole should not be taken during the first trimester of pregnancy because of concerns about mutagenicity. Tinidazole and ornidazole are recently developed nitroimidazole derivatives that have even greater antimicrobial activity than metronidazole.

Pseudomonas aeruginosa as a primary pathogen in children with bacterial peritonitis

This prospective study compared the efficacy of sulbactam/ampicillin and clindamycin/gentamicin in the treatment of children with bacterial peritonitis. Of the 29 children enrolled, 17 were evaluable; eight received sulbactam/ampicillin/gentamicin and nine clindamycin/gentamicin. Sixteen patients were previously healthy children with appendicitis. An average of 3.6 bacterial species were recovered from the peritoneal fluid of each patient. E coli and B fragilis were the most common aerobic and anaerobic isolates, recovered from 15 and ten patients, respectively. Pseudomonas aeruginosa was recovered from seven of 17 children; the three children with P aeruginosa infections randomized to the sulbactam/ampicillin group received gentamicin in addition to the investigational agents throughout the treatment course. Although the study groups were small, there was no difference in age, sex, number of pathogens per patient, duration of hospitalization, toxicity, or treatment failures between the two treatment groups or between children infected with P aeruginosa and controls. As a result of the high prevalence of P aeruginosa in the peritoneal exudate of otherwise healthy children with appendicitis, initial antimicrobial therapy in this patient population should include agents effective against this organism.

Comparison of kill-kinetic studies with agar and broth microdilution methods for determination of antimicrobial activity of selected agents against members of the Bacteroides fragilis group

Kill-kinetic studies often are used to determine the rate and degree of killing of aerobic bacteria by antimicrobial agents. Few studies, however, make use of this method for determining antimicrobial activity against anaerobic bacteria. To evaluate kill-kinetic studies for anaerobes, kill-kinetic studies were performed for selected antimicrobial agents against members of the Bacteroides fragilis group and compared with MICs obtained by using a reference agar dilution method and a broth microdilution method. Results of the kill-kinetic studies showed that the degree of killing over a 24-h test period was related to the MIC for the test organism. In general, the higher the MIC of an antimicrobial agent for a test organism, the less the killing observed. In addition, these studies demonstrate subtle differences in bactericidal activity at various concentrations of the antimicrobial agents, which cannot be determined by agar or broth dilution methods. Kill-kinetic studies are a useful addition to dilution methods for the evaluation of antimicrobial agents against anaerobes.

Metronidazole

Metronidazole was introduced to the market in 1959 as the only effective therapy for Trichomonas vaginalis. A nitroimidazole derivative, its success in the therapy of parasitic infections, including Entamoeba histolytica and Giardia lamblia, has been well documented. Metronidazole's activity against anaerobic bacteria was first described in 1962 by Shinn, and by Davies and associates in 1964. In both reports, metronidazole effectively treated patients with Vincent's angina (necrotizing ulcerative gingivitis). Metronidazole's excellent activity against anaerobes has been substantiated by numerous articles. It has the best bactericidal activity of all drugs active against anaerobic bacteria.

Bacteroides fragilis: current susceptibilities, mechanisms of drug resistance, and principles of antimicrobial therapy

The Bacteroides fragilis group of organisms includes the most clinically important anaerobic bacteria. Optimal therapy of infections in which these organisms are involved includes adequate and timely surgical drainage of all collections, debridement of necrotic tissue, optimal nutritional support, and administration of appropriate empiric antibiotics to cover both the aerobic and anaerobic bacterial components of these mixed infections. Special attention must be paid to the B. fragilis group because of its high rate of resistance to many of the commonly used antibiotics. Of the currently available beta-lactam antibiotics, piperacillin has the lowest rate of resistance. Successful antimicrobial agents include clindamycin, chloramphenicol, and metronidazole plus an aminoglycoside. Piperacillin, cefoxitin, and moxalactam can be used with an aminoglycoside or alone if no resistant organisms are revealed on culture and susceptibility testing. Beta-lactam-based regimens are potentially less toxic and may be less costly than those that contain one or more non-beta-lactam antibiotics.

Aminoglycosides in gynecologic infections

Aminoglycosides have always had a major role in the treatment of gynecologic infections. This therapeutic emphasis has been based upon the bactericidal activity of the aminoglycosides against gram-negative aerobes. This group of organisms is important to the gynecologist because of their frequent isolation from soft tissue, urinary sites, and the bloodstream in women with nosocomial or community-acquired pelvic infections. In the past decade, there has been increasing clinical awareness of the multi-bacterial nature of these soft tissue pelvic infections. A major therapeutic change directed against gram-negative anaerobes has been the substitution of more effective agents like clindamycin or metronidazole for the penicillin arm of the older penicillin-aminoglycoside combination. The majority of intra-abdominal and pelvic infections treated by gynecologists occur in patients who are younger and usually healthier than those with similar infections who are treated by general surgeons. Consequently, in many instances, single drug therapy with a cephalosporin (usually cefoxitin) is adequate, if combined with surgical drainage when indicated. However, there is an increasingly larger group of patients who are significantly older and who may also have pelvic malignancies. In addition, they may be immunocompromised. Infections in this group mandate the use of the most effective antimicrobial agents that will cover the broadest spectrum. When anaerobic bacteria are involved, either clindamycin or metronidazole are acceptable choices; for aerobic gram-negative organisms, an aminoglycoside should be used. Recent studies suggest that amikacin may be the best choice, since it is associated with a low level of bacterial resistance and has been shown to reduce levels of resistance to other aminoglycosides. Amikacin has become the "gold standard" for comparisons with any new cephalosporins or penicillins. New developments will modify the use of aminoglycosides in the future. The expansion of oncology care with immune-system-modifying chemotherapy and radiation will expose patients to the dangers of gram-negative sepsis. Aminoglycosides are a logical part of the initial therapeutic regimen for these septic patients. On the other hand, the majority of gynecologic patients with pelvic infections are young and healthy. Recent studies have demonstrated that as many as 40 percent of these women will be underdosed by standard treatment regimens based upon ideal body weight. This means that patients receiving aminoglycosides will require monitoring of peak and trough levels to insure therapeutic drug levels.(ABSTRACT TRUNCATED AT 400 WORDS)