Infections caused by anaerobic bacteria are common, and may be serious and life-threatening. Anaerobes predominant in the bacterial flora of normal human skin and mucous membranes, and are a common cause of bacterial infections of endogenous origin. Infections due to anaerobes can evolve all body systems and sites. The predominate ones include: abdominal, pelvic, respiratory, and skin and soft tissues infections. Because of their fastidious nature, they are difficult to isolate and are often overlooked. Failure to direct therapy against these organisms often leads to clinical failures. Their isolation requires appropriate methods of collection, transportation and cultivation of specimens. Treatment of anaerobic bacterial infection is complicated by the slow growth of these organisms, which makes diagnosis in the laboratory only possible after several days, by their often polymicrobial nature and by the growing resistance of anaerobic bacteria to antimicrobial agents.

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Sunday, December 22, 2013

Multidrug-Resistant Bacteroides fragilis isolated in the US

B. fragilis strains, especially in the US, are virtually always susceptible to metronidazole, carbapenems, and beta-lactam antibiotics. Although isolated cases of resistance to single agents have been reported, multidrug-resistant (MDR) B. fragilis strains are exceptionally rare. In May 2013, an MDR B. fragilis strain was isolated from the bloodstream and intra-abdominal abscesses of a patient who had recently received health care in India. The organism was resistant to metronidazole, imipenem, piperacillin/tazobactam, clindamycin, tcefotetan, ampicillin/sulbactam, and moxifloxacin. It was susceptible to minocycline, linezolid, and tigecycline. He was successfully treated with linezolid and ertapenem. This is only the second published case of MDR B. fragilis in the US.

Although B. fragilis has long been considered reliably susceptible to a number of broad-spectrum anti-anaerobic drugs, this case and others like it suggest clinicians should no longer rely on cumulative susceptibility data from surveys alone to direct treatment and should consider requesting susceptibility testing when treating serious infections caused by B. fraglis. They also underscore the need for improved antibiotic stewardship. 

Wednesday, May 29, 2013

American Surgical Society and American Society of Infectious Diseases guidelines for the treatment of abdominal infection.

In 2010 the American Surgical Society and American Society of Infectious Diseases have updated their guidelines for the treatment of abdominal infection.

The recommendations suggest the following:
For mild-to-moderate community-acquired infections in adults, the agents recommended for empiric regimens are: ticarcillin- clavulanate, cefoxitin, ertapenem, moxifloxacin, or tigecycline as single-agent therapy or combinations of metronidazole with cefazolin, cefuroxime, ceftriaxone, cefotaxime, levofloxacin, or ciprofloxacin. Agents no longer recommended are: cefotetan and clindamycin ( Bacteroides fragilis group resistance) and ampicillin-sulbactam (E. coli resistance) and aminoglycosides (toxicity).

 For high risk community-acquired infections in adults, the agents recommended for empiric regimens are: meropenem, imipenem-cilastatin, doripenem, piperacillin-tazobactam, ciprofloxacin or levofloxacin in combination with metronidazole, or ceftazidime or cefepime in combination with metronidazole. Quinolones should not be used unless hospital surveys indicate >90% susceptibility of E. coli to quinolones.

Aztreonam plus metronidazole is an alternative, but addition of an agent effective against gram-positive cocci is recommended. The routine use of an aminoglycoside or another second agent effective against gram-negative facultative and aerobic bacilli is not recommended in the absence of evidence that the infection is caused by resistant organisms that require such therapy.

Empiric use of agents effective against enterococci is recommended and agents effective against methicillin-resistant S. aureus (MRSA) or yeast is not recommended in the absence of evidence of infection due to such organisms.

Empiric antibiotic therapy for health care-associated intra-abdominal infection should be driven by local microbiologic results. Empiric coverage of likely pathogens may require multidrug regimens that include agents with expanded spectra of activity against gram-negative aerobic and facultative bacilli. These include meropenem, imipenem-cilastatin, doripenem, piperacillin-tazobactam, or ceftazidime or cefepime in combination with metronidazole. Aminoglycosides or colistin may be required.

Antimicrobial regimens for children include an aminoglycoside-based regimen, a carbapenem (imipenem, meropenem, or ertapenem), a beta-lactam/beta-lactamase-inhibitor combination (piperacillin-tazobactam or ticarcillin-clavulanate), or an advanced-generation cephalosporin (cefotaxime, ceftriaxone, ceftazidime, or cefepime) with metronidazole.

Tuesday, January 29, 2013

Infectious Diseases Society of America guideline for the diagnosis and treatment of diabetic foot infections.

Foot infections are a frequent and serious problem in individuals with diabetes. The Infectious Diseases Society of America recently published clinical practice guideline for the diagnosis and treatment of diabetic foot infections.  Diabetic foot infections (DFIs) usually starts as a wound, most often a neuropathic ulceration. While all wounds are colonized with microorganisms, the presence of infection is defined by ≥2 classic findings of inflammation or purulence.
Infections are then classified into:

·       Mild (superficial and limited in size and depth).
·       Moderate (deeper or more extensive).
·       Severe (accompanied by systemic signs or metabolic perturbations).

This classification system, along with a vascular assessment, helps determine which patients should be hospitalized, which may require special imaging procedures or surgical interventions, and which will require amputation.
Most DFIs are polymicrobial infections caused by aerobic gram-positive cocci (GPC), and especially staphylococci, the most common causative organisms. Aerobic gram-negative bacilli are frequently copathogens in infections that are chronic or follow antibiotic treatment, and obligate anaerobes may be copathogens in ischemic or necrotic wounds.
The Guidelines stat that wounds without evidence of soft tissue or bone infection do not require antibiotic therapy. For infected wounds, they suggest obtaining a post-debridement specimen (preferably of tissue) for aerobic and anaerobic culture. Empiric antibiotic therapy can be narrowly targeted at GPC in many acutely infected patients, but those at risk for infection with antibiotic-resistant organisms or with chronic, previously treated, or severe infections usually require broader spectrum regimens.
According to the Guidelines imaging is helpful in most DFIs; plain radiographs may be sufficient, but magnetic resonance imaging is far more sensitive and specific. Osteomyelitis occurs in many diabetic patients with a foot wound and can be difficult to diagnose (optimally defined by bone culture and histology) and treat (often requiring surgical debridement or resection, and/or prolonged antibiotic therapy).
It is recommended that in most DFIs some surgical intervention, ranging from minor (debridement) to major (resection, amputation) is performed. Wounds must also be properly dressed and off-loaded of pressure, and patients need regular follow-up. An ischemic foot may require revascularization, and some nonresponding patients may benefit from selected adjunctive measures. Employing multidisciplinary foot teams improves outcomes. The guidelines encouraged clinicians and healthcare organizations to monitor, and thereby improve, the outcomes and processes in caring for DFIs.

Diabetic foot ulcer