Factors associated with methicillin resistance in diabetic foot infections

Virulence Factor Genes and Antimicrobial Susceptibility of Staphylococcus aureus Strains Isolated from Blood and Chronic Wounds

Staphylococcus aureus is one of the predominant bacteria isolated from skin and soft tissue infections and a common cause of bloodstream infections. The aim of this study was to compare the rate of resistance to various antimicrobial agents and virulence patterns in a total of 200 S. aureus strains isolated from patients with bacteremia and chronic wounds. Disk diffusion assay and in the case of vancomycin and teicoplanin-microdilution assay, were performed to study the antimicrobial susceptibility of the isolates. The prevalence of genes encoding six enterotoxins, two exfoliative toxins, the Panton–Valentine leukocidin and the toxic shock syndrome toxin was determined by PCR. Of the 100 blood strains tested, the highest percentage (85.0%, 31.0%, and 29.0%) were resistant to benzylpenicillin, erythromycin and clindamycin, respectively. Out of the 100 chronic wound strains, the highest percentage (86.0%, 32.0%, 31.0%, 31.0%, 30.0%, and 29.0%) were confirmed as resistant to benzylpenicillin, tobramycin, amikacin, norfloxacin, erythromycin, and clindamycin, respectively. A significantly higher prevalence of resistance to amikacin, gentamicin, and tobramycin was noted in strains obtained from chronic wounds. Moreover, a significant difference in the distribution of sea and sei genes was found. These genes were detected in 6.0%, 46.0% of blood strains and in 19.0%, and 61.0% of wound strains, respectively. Our results suggest that S. aureus strains obtained from chronic wounds seem to be more often resistant to antibiotics and harbor more virulence genes compared to strains isolated from blood.

Quorum-sensing-regulated virulence factors in Pseudomonas aeruginosa are toxic to Lucilia sericata maggots

Maggot debridement therapy (MDT) is widely used for debridement of chronic infected wounds; however, for wounds harbouring specific bacteria limited effect or failure of the treatment has been described. Here we studied the survival of Lucilia sericata maggots encountering Pseudomonas aeruginosa PAO1 in a simple assay with emphasis on the quorum-sensing (QS)-regulated virulence. The maggots were challenged with GFP-tagged P. aeruginosa wild-type (WT) PAO1 and a GFP-tagged P. aeruginosa ΔlasRrhlR (ΔRR) QS-deficient mutant in different concentrations. Maggots were killed in the presence of WT PAO1 whereas the challenge with the QS mutant showed a survival reduction of ∼25 % compared to negative controls. Furthermore, bacterial intake by the maggots was lower in the presence of WT PAO1 compared to the PAO1 ΔRR mutant. Maggot excretions/secretions (ES) were assayed for the presence of QS inhibitors; only high doses of ES showed inhibition of QS in P. aeruginosa. Thus P. aeruginosa was shown to be toxic to L. sericata maggots. This, coupled to the preferential feeding by the maggots and reduced ingestion of P. aeruginosa, could explain MDT failure in wounds colonized by P. aeruginosa. Wounds heavily colonized with P. aeruginosa should be a counterindication for MDT unless used in combination with a pre-treatment with other topical therapeutics targeting P. aeruginosa.

Bacterial profiling using skin grafting, standard culture and molecular bacteriological methods

OBJECTIVE

Wound healing can be delayed by the presence of colonising bacteria, and in polymicrobial wounds they may act synergistically to the further detriment of wound healing. In this pilot investigation, biopsy and swab samples were obtained as part of skin-graft operations performed on a chronic venous leg ulcer in order to study the spatial microbial diversity and to compare standard bacteriological and molecular biological techniques.

METHOD

The wound was sampled before excision, and sampling was undertaken at multiple locations across the wound. Swab samples and biopsies were subjected to culture analysis and 16S rRNA polymerase chain reaction (PCR), and to denaturing gradient gel electrophoresis (DGGE).

RESULTS

Within the wound samples, DGGE identified the major wound microflora components and established the extent of local differences in bacterial diversity.

CONCLUSION

This ongoing investigation has verified DGGE as a powerful tool for elucidating the clinical microbiology of a chronic disease state. It also suggests that skin graft operations are a novel way of obtaining multiple samples for in vivo bacteriology and for establishing the spatial distribution of bacteria in the complex micro-environment of chronic wounds.

A review of the microbiology, antibiotic usage and resistance in chronic skin wounds

Chronic leg and foot wounds represent an increasing burden to healthcare systems as the age of the population increases. The deep dermal tissues of all chronic wounds harbour microorganisms, however, the precise interaction between microbes in the wounds and impaired healing is unknown. With regard to antibiotic therapy, there is a lack of evidence concerning its effectiveness, optimal regimens or clinical indications for treatment. Despite this lack of evidence, antibiotics are frequently a feature of the management of chronic wounds and these patients receive significantly more antibiotic prescriptions (both systemic and topical) than age and sex-matched patients. Current guidelines for antibiotic prescribing for such wounds are often based on expert opinion rather than scientific fact and may present difficulties in interpretation and implementation to the clinician. Although the increasing prevalence of antibiotic resistance is widely recognized, the relationships between antibiotic resistance, chronic wound microbiology and rationales for antibiotic therapy have yet to be determined. This review discusses the role of microbes in chronic wounds from a clinical perspective with particular focus on the occurrence of bacteria and their impact on such wounds. The evidence and role of antibiotics in the treatment of such wounds are outlined and current practice of antibiotic usage for chronic wounds in the primary care setting described. The implications of antibiotic usage with regard to antibiotic resistance are also considered.

Diabetic foot ulcer and multidrug-resistant organisms: risk factors and impact

AIMS

The primary objective was to characterize factors allowing the colonization of diabetic foot wounds by multidrug-resistant organisms (MDRO), and the secondary objective was to evaluate the influence of MDRO colonization/infection on wound healing.

METHODS

In 180 patients admitted to a specialized diabetic foot unit, microbiological specimens were taken on admission. Potential risk factors for MDRO-positive specimens were examined using univariate and multivariate analyses. Prospective follow-up data from 75 patients were used to evaluate the influence of MDRO colonization/infection on time to healing.

RESULTS

Eighteen per cent of admission specimens were positive for MDRO. MDRO-positive status was not associated with patient characteristics (age, sex, type of diabetes, complications of diabetes), wound duration, or wound type (neuropathic or ischaemic). In the multivariate analysis, the only factors significantly associated with positive MDRO status on admission were a history of previous hospitalization for the same wound (21/32 compared with 48/148; P = 0.0008) or the presence of osteomyelitis (22/32 compared with 71/148; P = 0.025). In the longitudinal study of 75 wounds, MDRO-positive status on admission or during follow-up (6 months at least or until healing, mean 9 +/- 7 months) was not associated with time to healing (P = 0.71).

CONCLUSION

MDROs are often present in severe diabetic foot wounds. About one-third of patients with a history of previous hospitalization for the same wound, and 25% of patients with osteomyelitis, had MDRO-positive specimens. This suggests that hygiene measures, or isolation precautions in the case of admission of patients presenting with these characteristics, should be aggressively implemented to prevent cross-transmission. Positive MDRO status is not associated with a longer time to healing.

Comparison of microbial findings and resistance to antibiotics between transplant patients, patients on hemodialysis, and other patients with the diabetic foot

Infectious complications of the diabetic foot may be influenced by impaired renal function and by immunosuppression therapy.

AIMS

To assess differences in microbial findings and resistance to antibiotics between transplant recipients, hemodialysis patients, and other patients with the diabetic foot.

METHODS

207 patients treated in the foot clinic for diabetic ulcers from 12/1998 to 12/1999 were included into this retrospective study. Patients were divided into three groups (transplant, dialysis, and other patients). Occurrence of individual bacterial species and resistance to antibiotics was compared between study groups.

RESULTS

Study groups did not differ significantly in ulcer grades defined by the Wagner classification or in the mean number of pathogens per patient. The prevalence of individual microorganisms did not differ between the study groups. However, the study groups differed significantly in the occurrence of microbial resistance to antibiotics. Transplant patients had more frequently Staphylococcus aureus resistant to oxacillin (P<.01), imipenem (P<.01), co-trimoxazole (P<.01), Enterococcus species resistant to ampicillin (P<.01), piperacillin (P<.01), and dialysis patients had more frequently Pseudomonas species resistant to piperacillin (P<.05) and cefpirom (P<.05) in comparison with the other two groups.

CONCLUSIONS

Transplant patients had significantly more resistant microorganisms in comparison with dialysis and other patients with the diabetic foot. Empiric antibiotic selection based on general population data should be modified in transplant patients with diabetic foot according to actual susceptibility to antibacterial drugs.

Antibiotic selection for diabetic foot infections: a review

Foot infections account for about 20% of all hospitalizations in people with diabetes and at least 50% of all nontraumatic lower-limb amputations performed annually in the United States. As many as 25% of all diabetics are expected to develop severe foot problems at some point in their lifetimes. Diabetic foot infections are generally more severe and more difficult to treat than infections in nondiabetics. This is due to impaired microvascular circulation, neuropathy, anatomical alterations, and impaired immune capacity in diabetic patients. Most moderate-to-severe soft-tissue diabetic foot infections are polymicrobial (i.e., due to gram-positive, gram-negative, aerobic, and anaerobic pathogens). Empiric antibiotic therapy should include broad-spectrum antibiotics capable of covering the most common pathogens found in diabetic infections. Other factors to consider in antibiotic selection include the severity of the infection, the presence of peripheral vascular disease, and the possibility of drug-resistant organisms in the infection. This review summarizes the clinical presentation and antimicrobial therapy of diabetic foot infections.

Evidence-based antibiotic therapy of diabetic foot infections

In addition to proper cleansing, debridement and local wound care, foot infections in diabetic patients require carefully selected antibiotic therapy. Serious infections necessitate hospitalization for initial parenteral broad-spectrum antibiotic therapy. Appropriately selected patients with mild infections can be treated as outpatients with oral (or even topical) therapy. Initial antibiotic selection is usually empirical, but definitive therapy may be modified based on culture results and the clinical response. Therapy should nearly always be active against staphylococci and streptococci, with broader-spectrum agents indicated if Gram-negative or anaerobic organisms are likely. In infected foot tissues levels of most antibiotics, except fluoroquinolones, are often subtherapeutic. The duration of therapy ranges from a week (for mild soft tissue infections) to over 6 weeks (for osteomyelitis). Recent antibiotic trials have shown that several intravenously or orally administered agents are effective in treating these infections, with no one agent or combination emerging as optimal. Suggested regimens based on the severity of infection are provided.