Pathogenesis and management of polymicrobial infections due to aerobic and anaerobic bacteria

Treatment of anaerobic infection

Anaerobic bacteria are the predominant flora in the normal human skin and mucous membranes and are, therefore, a common cause of endogenous infections. Since anaerobic infections are generally polymicrobial, where anaerobes are mixed with aerobic organisms, therapy should provide coverage of both types of pathogens. The isolation of anaerobes requires appropriate methods of collection, transportation and cultivation of specimens. The lack of use of any of these methods can lead to inadequate recovery of anaerobes and inappropriate therapy. Treatment of anaerobic infection is complicated by the slow growth of these organisms and the growing resistance of anaerobic bacteria to antimicrobials. The primary role of antimicrobials is to limit the local and systemic spread of infection. Surgical drainage is of primary importance. This includes debriding of necrotic tissue, draining the pus, improving circulation, alleviating obstruction and increasing tissue oxygenation. The most effective antimicrobials against anaerobic organisms are metronidazole, the carbapenems (imipenem, meropenem and ertapenem), chloramphenicol, the combinations of a penicillin and a beta-lactamase inhibitor (ampicillin or ticarcillin plus clavulanate, amoxicillin plus sulbactam, and piperacillin plus tazobactam), tigecycline and clindamycin.

Antimicrobial profiles of Prevotella spp. and Fusobacterium nucleatum isolated from periodontal infections in a selected area of southern Italy

In view of the increasing antibiotic resistance of anaerobic Gram-negative bacteria, we determined the antimicrobial profile of 55 periodontal anaerobic Gram-negative bacteria correlated with human infections, comprising 16 strains of Fusobacterium nucleatum and 39 strains of Prevotella spp. isolated from periodontal pockets of 26 adults suffering from chronic periodontitis. All the strains of F. nucleatum were susceptible to amoxicillin/clavulanic acid, doxycycline, metronidazole, moxifloxacin and levofloxacin, whilst 2/16 strains were both resistant to amoxicillin and beta-lactamase-positive and 11/16 were resistant to clarithromycin. All of the Prevotella strains were susceptible to amoxicillin/clavulanic acid, doxycycline and metronidazole, whereas 7/39 strains were beta-lactamase-positive and resistant to amoxicillin, 5/39 were resistant to clarithromycin and 3/39 were resistant to both moxifloxacin and levofloxacin. Our findings confirm that there is an increasing need to encourage practitioners to use laboratory investigations to limit the risk of an incorrect therapeutic approach and to avoid the overuse of antimicrobial agents.

Antimicrobial resistance and beta-lactamase production of clinical isolates of prevotella and porphyromonas species

BACKGROUND

This study determined the beta-lactamase production and the antimicrobial resistance of 72 Prevotella species and 48 Porphyromonas species isolated from different clinical specimens.

METHODS

All strains were identified using API 32 ID. The beta-lactamase production was determined by nitrocefin disks. E test strips of benzylpenicillin, ampicillin + sulbactam, cefoxitin, clindamycin, metronidazole and imipenem were tested for each strain.

RESULTS

Nineteen Prevotella melaninogenica, 18 Prevotella intermedia, 16 Prevotella denticola, 11 Prevotella loescheii and 8 Prevotella bivia strains were identified. Four were clindamycin resistant. The highest beta-lactamase production was found at a rate of 68.4% in P. melaninogenica species. Additionally, 33 Porphyromonas asaccharolytica and 15 Porphyromonas gingivalis strains were identified. None of them produced beta-lactamase.

CONCLUSION

In view of the emerging antibiotic resistance among anaerobes, the current local susceptibility profile of our Prevotella and Porphyromonas species will establish the basis for additional surveys tracing significant changes in the antimicrobial resistance of our clinical isolates.

Pharmacokinetics of ceftiofur in plasma and uterine secretions and tissues after subcutaneous postpartum administration in lactating dairy cows

A study was conducted to measure concentrations of potentially active ceftiofur derivatives, in plasma, in uterine tissues (endometrium and caruncles) and in uterine secretions at different time points after a single subcutaneous administration of ceftiofur hydrochloride (Excenel RTU Sterile Suspension) at the dose of 1 mg/kg body weight in Holstein-Friesian dairy cows. The animals (n=4) were injected within 24 h of calving, after expulsion of the foetal membranes. Plasma, lochial fluid, caruncles and endometrium were collected before ceftiofur hydrochloride administration and at 1, 2, 4, 8, 12 and 24 h after treatment. For each cow the concentrations of ceftiofur in the biological matrices were quantified using an high-performance liquid chromatography (HPLC) assay. The limit of quantification of the method was 0.1 microg/mL for plasma and 0.1 microg/g for lochial fluid, caruncles and endometrium. The concentrations of potentially active ceftiofur derivatives detected in plasma reached a maximum of 2.85 +/- 1.11 microg/mL at 2 h and decreased to 0.64 +/- 0.14 microg/mL at 24 h after administration. In lochial fluid, these concentrations reached a maximum of 0.97 +/- 0.25 microg/g at 4 h and decreased to 0.22 +/- 0.21 microg/g at 24 h after administration. In endometrium, these concentrations reached a maximum of 2.23 +/- 0.82 microg/g at 4 h and decreased to 0.56 +/- 0.14 microg/g at 24 h following the injection, whereas these levels in caruncles were 0.96 +/- 0.45 and 0.60 +/- 0.39 microg/g obtained at 8 and 24 h, respectively. At the dose of 1 mg/kg body weight in healthy dairy cows, subcutaneous administration of ceftiofur (as ceftiofur hydrochloride) after parturition results in concentrations of ceftiofur derivatives in uterine tissues and in lochial fluid that exceed the reported minimal inhibitory concentrations (MICs) for the common pathogens (Escherichia coli, Fusobacterium necrophorum, Bacteroides spp., and Arcanobacterium pyogenes) associated with acute puerperal metritis.

Escherichia coli hemoglobin protease autotransporter contributes to synergistic abscess formation and heme-dependent growth of Bacteroides fragilis

Intra-abdominal infections (IAI) continue to be a serious clinical problem. Bacterial synergism is an important factor that influences the shift from contamination to IAI, leading to the development of lesions and abscess formation. Escherichia coli and Bacteroides fragilis are particularly abundant in IAI. The underlying molecular mechanisms of this pathogenic synergy are still unclear. The role of the hemoglobin protease (Hbp) autotransporter protein from E. coli in the synergy of IAI was investigated. Hbp is identical to Tsh, a temperature-sensitive hemagglutinin associated with avian pathogenic E. coli. Clinical isolates from miscellaneous extraintestinal infections were phenotypically and genotypically screened for Hbp. The presence of Hbp was significantly associated with E. coli isolated from IAI and other extraintestinal infections. In a murine infection model, Hbp was shown to contribute to the pathogenic synergy of abscess development. Mice immunized with Hbp were protected against mixed infections and did not develop abscess lesions. Furthermore, an E. coli wild-type strain that did not induce abscess formation in the synergy model was transformed with a plasmid encoding the hbp gene, and mixed infections with this strain lead to increased growth of B. fragilis and induction of abscess lesions. Growth-promoting studies showed that purified Hbp is able to deliver heme to B. fragilis strain BE1. In conclusion, results suggest the synergy of abscess formation by E. coli and B. fragilis can be partly explained by the capacity of B. fragilis to intercept Hbp and iron from heme to overcome the iron restrictions imposed by the host.