Antibiotic susceptibility and resistance of Staphylococcus aureus isolated from fresh porcine skin xenografts: Risk to recipients with thermal injury

The previous use of fresh porcine xenografts at the Prague Burn Centre had raised concerns over the transmission of zoonotic pathogens. This study examines the risk of zoonotic Staphylococcus aureus colonisation of burn patients from fresh porcine skin xenografts.     

Characterisation of SCCmec elements in methicillin-resistant Staphylococcus aureus isolated from burn patients

Staphylococcus aureus is an important pathogen, especially in burn units all around the world. Because of the emergence of the β-lactam antibiotic-resistant strains since 1961, concern about the prevalence of methicillin-resistant S. aureus (MRSA) has increased in these units. Resistance to methicillin is mediated by penicillin-binding proteins (PBPs) that have enough affinity for binding to the β-lactam ring, but another kind of protein (PBP2α), which is encoded by the mecA gene, has a lower affinity for binding to these antibiotics. The mecA gene is transferred by SCCmec (staphylococcal cassette chromosome mec) as a mobile genetic element, exclusively found in the Staphylococcus genus. Identification of the frequency of the mecA gene, different SCCmec types and also its incidence may have benefit in surveillance prevention and control of MRSA strains in burn units. In this study, 40 S. aureus isolates were collected from patients hospitalised in Motahari burn center of Tehran, during 2012–2013. Conventional microbiological methods were applied and the confirmed isolates were stored at −20 °C for molecular polymerase chain reaction (PCR) tests. The antibiotic resistance pattern was performed by disc diffusion method and finally the different SCCmec types were determined by specific primers. During this research, 40 isolates of S. aureus were collected from burn patients, of which (37.5%) of the specimens belonged to female patients and 62.5% to male patients. The aetiology of the burn was classified as follows: open flame (35%), liquid (32.5%), chemical (5%) and other (27.5%). By a disc diffusion method, no resistance pattern was observed to vancomycin and fosfomycin. Based on a multiplex PCR assay, the five different SCCmec types were detected as: 47.5% type III, 25% type IV, 10% type V, 10% type II and 7.5% type I.     

Risk factors for acquisition of Methicillin-resistant Staphylococcus aureus among patients from a burn unit in Brazil

Methicillin-resistant Staphylococcus aureus (MRSA) is an important agent of colonization and infection in burn units. In order to identify risk factors for MRSA acquisition in a Brazilian burn unit, we performed two retrospective studies. In the first (“cohort” study), 175 patients who were not colonized with MRSA on admission were followed to assess risk factors for MRSA acquisition. In the second (“case–case–control” study), 143 individuals from the previous study who were negative for both MRSA and Methicillin-susceptible S. aureus (MSSA) on admission were followed. Case–control studies were performed to investigate risk factors for MRSA and MSSA acquisition. MRSA and MSSA were recovered from 75 and 23 patients, respectively. In the “cohort” study, only the number of wound excisions (Odds Ratio [OR] = 1.55, 95% Confidence Interval [CI] = 1.21–1.98, P = 0.001) was associated with MRSA acquisition. In the “case–case–control” study, burns involving head (OR = 3.43, 95%CI = 1.50–7.81, P = 0.003) and the number of wound excisions (OR = 1.83, 95%CI = 1.27–2.63, P = 0.001) were significant risk factors for MRSA. Burns involving perineum were negatively associated with MSSA acquisition (OR = 0.16, 95%CI = 0.03–0.75, P = 0.02). In conclusion, the acquisition of MRSA was related to the site of the burn and to the surgical manipulation of tissues, but not to the use of antimicrobials.     

Molecular epidemiology of methicillin-resistant Staphylococcus aureus in a burn unit from Brazil

Methicillin-resistant Staphylococcus aureus (MRSA) poses a threat for patients in burn units. Studies that mix epidemiological designs with molecular typing may contribute to the development of strategies for MRSA control. We conducted a study including: molecular characterization of Staphylococcal Chromosome Cassette mecA (SCCmec), strain typing with pulsed field gel electrophoresis (PFGE) and detection of virulence genes, altogether with a case–case–control study that assessed risk factors for MRSA and for methicillin-susceptible S. aureus (MSSA), using S. aureus negative patients as controls. Strains were collected from clinical and surveillance cultures from October 2006 through March 2009. MRSA was isolated from 96 patients. Most isolates (94.8%) harbored SCCmec type III. SCCmec type IV was identified in isolates from four patients. In only one case it could be epidemiologically characterized as “community-associated”. PFGE typing identified 36 coexisting MRSA clones. When compared to MSSA (38 isolates), MRSA isolates were more likely to harbor two virulence genes: tst and lukPV. Previous stay in other hospital and admission to Intensive Care Unit were independent risk factors for both MRSA and MSSA, while the number of burn wound excisions was significantly related with the former (OR = 6.80, 95%CI = 3.54–13.07). In conclusion, our study found polyclonal endemicity of MRSA in a burn unit, possibly related to importing of strains from other hospitals. Also, it pointed out to a role of surgical procedures in the dissemination of MRSA strains.     

An in vitro biofilm model to examine the effect of antibiotic ointments on biofilms produced by burn wound bacterial isolates

Purpose

Topical treatment of burn wounds is essential as reduced blood supply in the burned tissues restricts the effect of systemic antibiotics. On the burn surface, microorganisms exist within a complex structure termed a biofilm, which enhances bacterial resistance to antimicrobial agents significantly. Since bacteria differ in their ability to develop biofilms, the susceptibility of these biofilms to topically applied antibiotics varies, making it essential to identify which topical antibiotics efficiently disrupt or prevent biofilms produced by these pathogens. Yet, a simple in vitro assay to compare the susceptibility of biofilms produced by burn wound isolates to different topical antibiotics has not been reported.

Methods

Biofilms were developed by inoculating cellulose disks on agar plates with burn wound isolates and incubating for 24 h. The biofilms were then covered for 24 h with untreated gauze or gauze coated with antibiotic ointment and remaining microorganisms were quantified and visualized microscopically.

Results

Mupirocin and triple antibiotic ointments significantly reduced biofilms produced by the Staphylococcus aureus and Pseudomonas aeruginosa burn wound isolates tested, as did gentamicin ointment, with the exception of one P. aeruginosa clinical isolate.

Conclusions

The described assay is a practical and reproducible approach to identify topical antibiotics most effective in eliminating biofilms produced by burn wound isolates.     

Telavancin versus vancomycin for the treatment of complicated skin and skin-structure infections associated with surgical procedures

Background

We compared telavancin with vancomycin for the treatment of complicated skin and skin-structure infections (cSSSI) caused by Gram-positive bacteria.

Methods

This was a retrospective analysis of clinical and microbiologic efficacy assessed at test-of-cure (7 to 14 days after completing therapy) in 194 patients from 2 randomized, double-blind clinical trials comparing telavancin (10 mg/kg intravenous [IV] every 24 hours; n = 101) with vancomycin (1 g IV every 12 hours; n = 93) for the treatment of cSSSI.

Results

Baseline characteristics were similar for both treatment groups. Clinical cure and microbiologic eradication rates demonstrated consistent trends favoring telavancin over vancomycin; however, the differences were not statistically significant. The incidence of adverse events was mostly similar between groups.

Conclusions

The efficacy of telavancin was at least equivalent to that of vancomycin for the treatment of cSSSI. These data suggest that telavancin may be a useful alternative for treatment of cSSSI caused by S. aureus, particularly MRSA.     

A selected screening programme was less effective in the detection of methicillin-resistant Staphylococcus aureus colonisation in an orthopaedic unit

Purpose

Our unit has used a selective screening policy for methicillin-resistant Staphylococcus aureus (MRSA) colonisation using standard chromogenic growth media, based upon risk stratification. The aim of this study was to examine the effectiveness of this selective screening policy.

Methods

A cohort of 429 patients was assessed for their risk status for MRSA colonisation using both rapid polymerase chain reaction (PCR) swabs and traditional culture and sensitivity analysis. The sensitivity, specificity, positive predictive values and negative predictive values of the traditional selective approach were calculated compared to universal rapid screening.

Results

One hundred eighteen patients were considered high risk and would traditionally be further screened with standard culture of swabs. The prevalence of MRSA was 15/429 (3.5 %). The sensitivity of selective screening was 53 % identifying eight of 15 cases. The false-negative rate was therefore 47 % and seven would have been missed. PCR results were available within four to six hours, whereas culture results were only available at 24 hours for the media showing no growth and not until 72 hours for positive MRSA cases.

Conclusions

We now advocate universal screening prior to, or on admission, using this rapid PCR test, as we consider this identifies MRSA colonisation more effectively and facilitates “ring-fencing” of orthopaedic beds.     

Albumin reduces the antibacterial activity of polyhexanide-biguanide-based antiseptics against Staphylococcus aureus and MRSA

Background

Wound infection is one of the major complications in acute and chronic wound healing. Antiseptic solutions and wound irrigating agents are routinely used for therapy and prevention in healthcare today. Even if wound exudate contains total protein concentrations up to 9.3% and albumin concentrations up to 2.7% its influence to the antibacterial efficacy of these agents is barely investigated.

Materials and methods

This study analyzed the antibacterial effect of polyhexanide biguanide (PHMB) agents (PHMB-concentration 0.005–0.1%) against Staphylococcus aureus and methicillin-resistant-S. aureus (MRSA) after 2 min incubation in presents of albumin in different concentrations (0–3%) in a standardized quantitative suspension assay.

Results

A significant decrease of the antibacterial activity against S. aureus was shown for a PHMB-concentration of 0.005% from 0.3% albumin (p < 0.05), respectively highly significant from 0.75% (p < 0.01) on. Thereby the loss of antimicrobial effect was presented as a linear correlation to the rising concentration of albumin. Furthermore a reduction of the antibacterial activity against MRSA in comparison to S. aureus was presented, for albumin concentrations from 3% on highly significant (p < 0.01).

Conclusion

The study showed that albumin causes a significant decrease of the antibacterial potency of PHMB-based antiseptics. Furthermore a diminished potency of the investigated substances for MRSA-contaminated wounds must be taken in consideration. If in vitro experiments show a significant decrease of antibacterial efficacy in the presence of albumin a sufficient activity of PHMB-based agents in clinical practice, especially in cases of exuding wounds or dried-up exudates, cannot be expected.     

An outbreak of a multiresistant methicillin-susceptible Staphylococcus aureus (MR-MSSA) strain in a burn centre: the importance of routine molecular typing

Here we report an outbreak among 17 patients caused by a single strain of a Multiresistant Methicillin-Susceptible Staphylococcus aureus (MR-MSSA) in a burn centre. The MR-MSSA strains were resistant to penicillin, ciprofloxacin, erythromycin, clindamycin and co-trimoxazole. Further analysis showed an increased prevalence of MR-MSSA carriership in S. aureus colonized patients admitted to the burn centre, from 0% in 2005 (0/118), 3.3% in 2006 (4/121), 6.1% in 2007 (6/99), to 7.8% in 2008 (7/90). Molecular typing with Amplified Fragment Length Polymorphism showed that all MR-MSSA isolates derived from burn centre patients had a unique genotype, and was different compared to isolates derived from other hospital patients. All healthcare workers (HCWs) who worked in the burn centre during the outbreak were screened for nasal carriage with MR-MSSA. One HCW tested positive for a genotype of MR-MSSA that was indistinguishable from the genotype found in samples of the burned patients. No new cases of MR-MSSA colonization or infection were identified after the colonized HCW stopped working at the burn centre. The routine practice of molecular typing of collected S. aureus strains from both patients and HCWs will help to detect nosocomial spread in a burn centre, and opens the possibility of a rapid, almost pre-emptive response.     

A high prevalence of mupirocin and macrolide resistance determinant among Staphylococcus aureus strains isolated from burnt patients

Infections due to Staphylococcus aureus have become increasingly common among burn patients. The antibiotic resistance profile of S. aureus isolates and inducible resistance against clindamycin were investigated in this study. The presence of mecA gene, mupA gene and macrolide resistance genes were detected using PCR and multiplex-PCR. The resistance rate to methicillin, erythromycin and mupirocin were 58.5%, 58% and 40%, respectively. The prevalence of constitutive and inducible resistance among macrolide resistant isolates was 75% and 25%, respectively. Ninety five percent of the isolates were positive for one or more erm genes. The most common genes were ermA (75%), ermC (72%) and ermB (69%), respectively. The ermA gene predominated in the strains with the inducible phenotype, while ermC was more common in the isolates with the constitutive phenotype. The msrA gene was only found in one MRSA isolate with the constitutive phenotype. A total of 27 isolates (25%) carried the mupA gene. All the mupirocin resistant isolates and almost all the erythromycin resistant isolates were also resistant against methicillin which may indicate an outbreak of MRSA isolates with high-level mupirocin and erythromycin resistance in the burn unit assessed.     

Efficacy and safety of linezolid versus vancomycin for the treatment of complicated skin and soft-tissue infections proven to be caused by methicillin-resistant Staphylococcus aureus

Background

This open-label study compared oral or intravenous linezolid with intravenous vancomycin for treatment of complicated skin and soft-tissue infections (cSSTIs) caused by methicillin-resistant Staphylococcus aureus (MRSA).

Methods

Patients with proven MRSA cSSTI were randomized to receive linezolid or vancomycin. Clinical and microbiologic outcomes, duration of antimicrobial therapy, length of hospital stay, and safety were assessed.

Results

In the per-protocol population, the rate of clinical success was similar in linezolid- and vancomycin-treated patients (P = .249). The rate of success was significantly higher in linezolid-treated patients in the modified intent-to-treat population (P = .048). The microbiologic success rate was higher for linezolid at the end of treatment (P < .001) and was similar at the end of the study (P = .127). Patients receiving linezolid had a significantly shorter length of stay and duration of intravenous therapy than patients receiving vancomycin. Both agents were well tolerated. Adverse events were similar to each drug's established safety profile.

Conclusions

Linezolid is an effective alternative to vancomycin for the treatment of cSSTI caused by MRSA.     

Factors associated with duration of hospitalization and outcome in burns patients: A cross sectional study from Government Tertiary Care Hospital in Karachi,Pakistan

Objective

Burns are important contributors toward mortality in trauma related injuries in Karachi, Pakistan. The aim of the present study was to delineate the factors contributing to the duration of hospitalization and mortality in such patients.

Methods

We performed a single center retrospective study of patients admitted during a 2 year period (January 2009 till December 2010) in Burns Center, Karachi. Patients with incomplete record were excluded. Variables included were age and gender of the patient, the percent total body surface area (%TBSA) burn, the cause of the burn and the body parts affected along with the micro-organisms isolated from the burn wounds. The relationship of these variables with the duration of hospitalization and the outcome of patients was assessed by means of Pearson Chi Square test in SPSS version 14.

Results

Mean age of patients was 26.64 years (±13.430). More males (56.6%) were admitted than females (43.4%), giving a male to female ratio of 1.3:1. Mean percent total body surface area (%TBSA) burnt and mortality were 24.69% and 26.38% respectively with both having higher values in females (p < 0.001). Males had a mean longer duration of hospitalization compared to females (35.94 days vs. 27.63 days). The most common micro-organism colonizing the wounds was found to be Staphylococcus aureus. Factors significantly (p < 0.05) associated with increased duration of hospitalization and mortality include the age and gender of the patient, the cause of burn, inhalation injury, the region affected and %TBSA burnt.

Conclusion

The relationship of age and gender of the patient, the cause of burn, inhalation injury, the region affected and %TBSA burnt are important factors in determining the duration of hospitalization of the patients and whether the patients will survive or succumb to injuries.     

Susceptibility patterns and cross-resistance of antibiotics against Pseudomonas aeruginosa isolated from burn patients in the South of Iran

Pseudomonas aeruginosa plays a prominent role in serious infections in burn patients. Rapid acquisition of multi-drug resistance leads to high morbidity and mortality, especially in burn centers. Ten antibiotics, which were widely used in our burn patients were selected. MICs for imipenem, mropenem, cefepime, ceftazidime, cafoparazone/sulbactam, ticarcillin/clavulanate, piperacillin/tazobactam, ciprofloxacin, tobramycin and amikacin to 70 strains of P. aeruginosa, which were isolated from burn patients were determined by the E-test method (AB Biodisk, Sweden). Extended-spectrum beta-lactamase, group I inducible beta-lactamases and metallo-beta-lactamase activities were also determined. Imipenem and meropenum were the most active in vitro antibacterial agents followed by ciprofloxacin (p<0.05), whereas, ticarcillin/clavulanate was the least active. Almost all (98-100%) of the resistant isolates also showed cross-resistance to cefepime. The majority of imipenem and meropenem resistant isolates (85-100% and 76-100%) demonstrated cross-resistance to all the other antibiotics. ESBLs were detected in only three (4.3%) isolates, whereas, inducible beta-lactamase was observed in eight (11.4%) isolates. Metallo-beta-lactamase was detected in none of the isolates. Almost all of the antibiotic resistant isolates also showed cross-resistance to the majority of penicillins and cephalosporins with or without beta-lactamase inhibitors, from which ticarcillin/clavulanate demonstrated this phenomenon at the highest level.     

Prophylactic antibiotics alter the bacteriology of infected necrosis in severe acute pancreatitis

BACKGROUND: Use of appropriate prophylactic antibiotics has been shown to decrease infectious complications and mortality rate in patients with severe acute pancreatitis, but its influence on the bacteriology of secondary pancreatic infection is poorly defined. STUDY DESIGN: Operative cultures from 61 consecutive patients with pancreatic necrosis treated during routine prophylactic antibiotic use (1993-2001) were compared with 34 consecutive patients with necrosis treated before routine antibiotic use (1977-1992). RESULTS: The two groups of patients were similar in demographics, etiology of pancreatitis, and severity of illness. All patients in the antibiotic group received prophylactic antibiotics compared with only 38% (13 of 34) in the control group. Routine broad-spectrum prophylactic antibiotics altered the bacteriology of secondary pancreatic infection in severe acute pancreatitis from predominantly gram-negative coliforms (56% versus 26%, p = 0.005) to predominately gram-positive organisms (23% versus 52%, p = 0.009) without a significant increase in either the rate of beta-lactam resistance or fungal infections. The overall hospital stay in patients treated with prophylactic antibiotics was significantly reduced (61 +/- 24 days versus 41 +/- 28 days, p = 0.002), and there was a trend toward a decline in mortality rate in the antibiotic treatment group. CONCLUSION: Routine broad-spectrum prophylactic antibiotic use has altered the bacteriology of secondary pancreatic infection in severe acute pancreatitis from predominantly gram-negative coliforms to predominantly gram-positive organisms without altering the rate of beta-lactam resistance or fungal superinfection.     

Comparison of the antibacterial effect of silver sulfadiazine 1%, mupirocin 2%, Acticoat and octenidine dihydrochloride in a full-thickness rat burn model contaminated with multi drug resistant Acinetobacter baumannii

In this study, our aim is to compare the efficacy of different topical antibacterial agents in a rat model contaminated with a multi drug resistant (MDR) standard Acinetobacter baumannii strain.