Genotyping of Pseudomonas aeruginosa strains isolated from burn patients by RAPD-PCR

Background

Pseudomonas aeruginosa is one of the important causes of nosocomial infections that easily gains resistance to many antibiotics. This opportunistic pathogen is a major health hazard particularly in immunodeficient patients, patients in intensive care units (ICU) and burn units with life threatening outcome. The bacterium may be originated from different or common sources, and comprises a high colonization and transmission capacity.

Objective

The aim of present study was to investigate the genotypic variation of Pseudomonas aeroginosa strains isolated from burn patients by using Random Amplified Polymorphic DNA (RAPD) method.

Methods

Totally 70 clinical samples were collected from burn patients in Taleghani Burn Hospital of Ahvaz. Fifty out of total samples were positive for P. aeruginosa by application of conventional culture and biochemical identification tests. DNA was extracted from the isolates and the RAPD-PCR method was applied to the DNA extracts according to standard method using a short single primer of 272. The technique created repetitive electrophoresis patterns which was used for genotypic differentiation.

Results

RAPD-PCR, created 9 genotypic profiles designated as I–IX with base pair length ranging from 180 to 2700. Each genotype showed between 3 and 6 different weight DNA bands. Genotype I was the most prevalent, identified in 10 bacterial isolates (20%). Genotypes I, II and VI were mostly common in patients with more severe burn, and were mainly isolated from wound and blood samples obtained from the same patients.

Conclusion

In present study, we found RAPD-PCR technique as a useful tool for investigation of the genetic variation among P. aeruginosa strains. This is a rapid, low cost, genotypic method with high discriminatory power. The results could assist to screen for the original of infection caused by this organism with subsequent control of colonization and transmission.     

Risk of type III secretion systems in burn patients with Pseudomonas aeruginosa wound infection: A systematic review and meta-analysis

PurposeThe pathogenesis of Pseudomonas aeruginosa is multifactorial and attributed to the production of several cell-associated and extracellular virulence factors including those implicated in adherence, iron uptake, exoenzymes (Exo) and exotoxins. The present study aimed to determine the prevalence of type III secretion systems (T3SS) effectors in Iranian burn patients with P. aeruginosa wound infection.MethodsA systematic search was conducted to identify papers published by Iranian authors in the Web of Science, PubMed, Scopus, Embase, and Google Scholar electronic databases during the period of January, 2000 to December, 2018. Publications which met our inclusion criteria were selected for data extraction and analysis by Comprehensive Meta-Analysis Software. The inclusion criteria were articles that include burn patients with a wound infection caused by P. aeruginosa, and reported the prevalence of aimed exoenzymes.ResultsTen publications were selected out of 15 full-text reviewed articles with the inclusion criteria. Of ten studies, the pooled prevalence of ExoS producing isolates was estimated at 57.1% (95% CI: 40.3–72.5%). Five studies reported the prevalence of ExoU and ExoT, from which, the pooled prevalence of ExoU and ExoT producing isolates was estimated at 51.4% (95% CI: 31.4–70.9%) and 86.4% (95% CI: 48.1–97.8%), respectively. Four studies reported the prevalence of ExoY, from which, the pooled prevalence of ExoY producing isolates was estimated at 79.0% (95% CI: 48.6–93.8%).ConclusionOur results showed a remarkable prevalence of T3SS-positive genotype in patients with burn injuries. These findings provided attractive targets for new therapeutic strategies for burn patients who were infected with cytotoxin-producing P. aeruginosa.     

Prevalence of multidrug-resistant organisms recovered at a military burn center

Infections caused by multidrug-resistant (MDR) pathogens are associated with significant morbidity and mortality in patients with burn injuries. We performed a 6-year antibiotic susceptibility records review from January 2003 to December 2008 to assess the prevalence of MDR isolates by pathogen at the US Army Institute of Surgical Research Burn Center. During the study period Acinetobacter baumannii (780 isolates [22%]) was the most prevalent organism recovered, followed by Pseudomonas aeruginosa (703 isolates [20%]), Klebsiella pneumoniae (695 isolates [20%]), and Staphylococcus aureus (469 isolates [13%]). MDR prevalence rates among these isolates were A. baumannii 53%, methicillin-resistant S. aureus (MRSA) 34%, K. pneumoniae 17% and P. aeruginosa 15%. Two isolates, 1 A. baumannii and 1 P. aeruginosa, were identified as resistant to all 4 classes of antibiotics tested plus colistin. A. baumannii isolates recovered from patients with burns greater than 30% of total body surface area (TBSA) were more likely to be MDR (61%) with no significant difference for P. aeruginosa and K. pneumoniae. A higher proportion of MDR P. aeruginosa isolates were recovered from respiratory specimens compared to blood specimens (24% vs. 9%) while the opposite was true for MRSA (35% vs. 54%). A comparison of A. baumannii recovered during hospitalization days 1–5 and 15–30 revealed higher MDR levels as length of stay increased (48% vs. 75%) while no significant trends were observed for P. aeruginosa and K. pneumoniae. A similar pattern was observed for MDR A. baumannii levels for the facility between 2003 and 2005 and 2006–2008 (39% vs. 70%), with no significant increase in MDR P. aeruginosa and MDR K. pneumoniae. Increasing antibiotic resistance patterns of the most prevalent isolates recovered during extended hospitalization, impact of % TBSA and other clinical parameters may affect empirical antimicrobial therapy and patient management decisions during treatment.     

Imipenem-resistant Pseudomonas aeruginosa strains carry metallo-β-lactamase gene blaVIM in a level I Iranian burn hospital

Introduction

In this study, we aimed to determine the distribution of bla_VIM and bla_IMP transferable genes in Pseudomonas aeruginosa isolates from infected burn wounds in an Iranian level I burn care center. These genes confer imipenem resistance and increase the mortality rate of burn patients.

Methods

P. aeruginosa isolates from burn patients were tested for antibiotic susceptibility with Kirby-Bauer disk diffusion method and for production of metallo-β-lactamase (MBL) by EDTA disk method. DNA was purified from isolates with positive MBL results and underwent PCR for detection of bla_VIM and bla_IMP genes.

Results

MBL was produced by 23 imipenem-resistant isolates and bla_VIM gene was detected in all of these isolates. None of the isolates carried bla_IMP gene. Mortality rate of infection with MBL-producing Pseudomonas strains was 82.6% in this hospital while the mortality rate for non-MBL-producing Pseudomonas was 22.7%.

Conclusion

We found that all MBL-producing isolates in this hospital carry bla_VIM gene. This result is similar to the previous Iranian study and emphasizes the importance of VIM family of MBLs in Iran. Timely identification of these strains and strict isolation methods can prevent spread of this transferable gene to other Gram-negative bacteria and prevent the subsequent outbreak of high mortality.     

Spread of extended-spectrum β-lactamase genes of bla OXA-10, bla PER-1 and bla CTX-M in Pseudomonas aeruginosa strains isolated from burn patients

BackgroundPseudomonas aeruginosa is resistant to many antibiotics due to production of different classes of extended spectrum β-lactamases (ESBLs). Prevalence of ESBLs among P. aeruginosa has been increased in recent years, demonstrate a serious health problem especially in burn units worldwide.ObjectivePresent study was designed to determine the ESBL producing strains and identify the genes encoding three different ESBLs of bla PER-1, bla OXA-10 and bla CTX-M genes in P. aeruginosa isolates from burn patients.MethodsIn total 185 clinical isolates of P. aeruginosa were collected from infectious wounds of hospitalized burn patients. Antimicrobial susceptibility testing and phenotypic detection of ESBL were performed by disk diffusion method and Double disk Synergy Test (DDST). Polymerase Chain Reaction (PCR) was done for detection of bla OXA-10, bla PER-1 and bla CTX-M ESBL encoding genes.ResultsIn total, 176 (95.13%) isolates were multidrug resistant. The DDST demonstrated 96 (51.9%) isolates as putative ESBL producers with 100% or highly resistance to ofloxacin, cephalexin, aztreonam (97.57%) and ceftriaxone (91.6%). By PCR amplification, bla PER-1, bla OXA-10 and bla CTX-M genes were detected in 52 (54.16%), 66 (68.75%) and 1 (1.04%) isolates of ESBL producers respectively. Forty-three isolates (44.79%) were simultaneously positive for both bla OXA-10 and bla PER-1 related genes.ConclusionThe rate of ESBL producing P. aeruginosa was notable in present study. Since there are only limited effective antibiotics against the bacterium, therefore all isolates must be investigated by antimicrobial susceptibility testing, which limits resistance development in burn units and helps the management of treatment strategy.     

Determination of extended spectrum beta-lactamases,metallo-beta-lactamases and AmpC-beta-lactamases among carbapenem resistant Pseudomonas aeruginosa isolated from burn patients

BackgroundPseudomonas aeruginosa is an important cause of morbidity and mortality in patients with burns.MethodA total of 214 nonduplicated burn wound isolates of P. aeruginosa were recovered from burn patients. Identification of carbapenem resistant isolates and their antimicrobial susceptibility pattern was carried out using the phenotypic methods. The presence of genes encoding extended spectrum beta-lactamases (ESBLs) and metallo-beta-lactamases (MBLs) enzymes were determined by PCR. The genetic relationships between carbapenem resistant isolates were determined by Random Amplified Polymorphic DNA (RAPD)-PCR.ResultsOf 214 investigated P. aeruginosa isolates, 100 (46.7%) were carbapenem resistant. All carbapenem resistant P. aeruginosa were resistant to imipenem, meropenem, ertapenem, carbenicillin, aztreonam, gentamicin and ciprofloxacin but susceptible to polymyxin B. Among 100 carbapenem resistant P. aeruginosa isolates, 3%, 65% and 52% were identified as ESBLs, carbapenemase and AmpC overproduction positive isolates respectively. The most prevalent ESBLs and MBLs genes included bla_OXA-10 (97%), bla_TEM (61%), bla_VIM (55%), bla_PER (13%), bla_IMP (3%) and bla_AIM (1%). RAPD analysis yielded 13 distinct profiles among 92 isolates. A dominant RAPD type was designated as A that consisting of 80 isolates.ConclusionThis is the first report of Adelaide IMipenmase (AIM) MBLs producing P. aeruginosa from Iran and also of the high prevalence of AmpC overproduction isolates. According to the results of current study, P. aeruginosa isolates producing OXA-10, TEM, VIM, PER and IMP beta-lactamases are frequent and the population structures of these isolates are highly similar.     

Incidence and bacteriology of burn infections at a military burn center

Considerable advancements in shock resuscitation and wound management have extended the survival of burned patients, increasing the risk of serious infection. We performed a 6-year review of bacteria identification and antibiotic susceptibility records at the US Army Institute of Surgical Research Burn Center between January 2003 and December 2008. The primary goal was to identify the bacteria recovered from patients with severe burns and determine how the bacteriology changes during extended hospitalization as influenced by population and burn severity. A total of 460 patients were admitted to the burn ICU with 3507 bacteria recovered from 13,727 bacteriology cultures performed. The most prevalent organisms recovered were Acinetobacter baumannii (780), Pseudomonas aeruginosa (703), Klebsiella pneumoniae (695) and Staphylococcus aureus (469). A. baumannii was most often recovered from combat-injured (58%) and S. aureus the most frequent isolate from local (46%) burn patients. Culture recovery rate of A. baumannii and S. aureus was highest during the first 15 hospital days (73% and 71%); while a majority of P. aeruginosa and K. pneumoniae were recovered after day 15 (63% and 53%). All 4 pathogens were recovered throughout the course of hospitalization. A. baumannii was the most prevalent pathogen recovered from patients with total body surface area (TBSA) burns less than 30% (203) and 30–60% (338) while P. aeruginosa was most prevalent in patients with burns greater than 60% TBSA (292). Shifting epidemiology of bacteria recovered during extended hospitalization, bacteriology differences between combat-injured and local burn patients, and impact of % TBSA may affect patient management decisions during the course of therapy.     

Pseudomonas aeruginosa infections in burns

Observations were carried out on 32 patients with burns. In 20 cases of extensive and severe burns Pseudomonas aeruginosa infections were found.Twenty-eight strains of Ps. aeruginosa were isolated from burn wounds and blood of the burn patients.These strains were typed by pyocine method. Among investigated strains of Ps. aeruginosa, the pyocine type A (39·2 per cent) dominated. When Ps. aeruginosa type A was present in burn wounds, the level of antibodies in blood sera of patients was distinctly increased.In 3 cases of septicaemia, low level of antibodies in blood sera of patients was found. Two patients died.All isolated strains of Ps. aeruginosa were sensitive to gentamycin and colimycin.     

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.     

Antimicrobial susceptibility and ESBL prevalence in Pseudomonas aeruginosa isolated from burn patients in the North West of Pakistan

Pseudomonas aeruginosa is one of the most prevalent pathogen in burn infections. Infections with P. aeruginosa are associated with higher mortality rate and antibiotic costs in hospitalized patients. These bacteria also produce enzymes called Expanded Spectrum Beta-Lactamases (ESBL) which render penicillins and cephalosporins inactive. The aim of this study was to assess the antimicrobial susceptibility pattern and prevalence of ESBL in P. aeruginosa in Peshawar, North West of Pakistan. During 2005–2006, one hundred and six P. aeruginosa isolates were collected from burn patients at a tertiary care hospital. Antibiotic susceptibility testing and ESBL detection were carried out according to Clinical Laboratory and Standards Institute (CLSI) criteria. Eighteen antibiotics were tested in this study. A total of 38 (35.85%) isolates were found to be ESBL producers. Thirty one (29.24%) isolates were resistant to 3 or more antibiotics (multidrug resistance). Meropenem and imipenem showed high potency with 99% and 96% isolates being susceptible respectively. Susceptibility to amikacin was 70%; gentamicin 25%; ciprofloxacin 49%; enoxacin 47%; gatifloxacin 42%; doxycycline 21% and to co-trimoxazole only 16%. This study reveals that P. aeruginosa isolated from burns in this region are multidrug resistant and produce ESBL in large proportions.     

Comparison of pathogens and antibiotic resistance of burn patients in the burn ICU or in the common burn ward

Background

This study aims to compare pathogens and their antibiotic resistances of burn patients from burn intensive care unit (ICU) or common burn ward. Of 2395 clinical samples from 63 patients in burn ICU, pathogens were detected in 1621 samples, in which 1203 strains (74.2%) were Gram negative bacteria, 248 strains (15.3%) were Gram positive bacteria, 170 strains (10.5%) were fungi. Top-4 microorganisms isolated from patients in burn ICU were Bauman's Acinetobacter (557, 34.4%), Pseudomonas aeruginosa (287.17.7%), Staphylococcus aureus (199, 12.3%) and Klebsiella pneumoniae (171, 10.5%). Of 512 clinical samples from 235 patients in common burn units, pathogens were detected in 373 samples, in which 189 (50.6%) strains were Gram negative bacteria, 150 strains (40.2%) were Gram positive bacteria, 34 strains (9.2%) were fungi. Top-4 microorganisms isolated from patients in common burn units were S. aureus (103, 27.6%), P. aeruginosa (46, 12.3%), K. pneumoniae (38, 10.2%) and Escherichia coli (32, 8.6%). Antibiotic resistance rates of pathogens isolated from clinical samples of burn patients from ICU was significantly higher than those from common units.

Conclusions

Pathogens and their antibiotic resistances are significantly different between burn ICU and common burn units. This finding has great implication for infection control in burn patients.     

Detection of VEB-1, OXA-10 and PER-1 genotypes in extended-spectrum β-lactamase-producing Pseudomonas aeruginosa strains isolated from burn patients

Resistance of Pseudomonas aeruginosa strains to the broad-spectrum cephalosporins may be mediated by the extended-spectrum β-lactamases (ESBLs). These enzymes are encoded by different genes located on either chromosomes or plasmids. This study aimed to investigate the prevalence of ESBLs and antimicrobial susceptibilities of P. aeruginosa isolated from burn patients in Tehran, Iran. Antimicrobial susceptibility of 170 isolates to cefpodoxime, aztreonam, ciprofloxacin, ofloxacin, ceftazidime, cefepime, imipenem, meropenem, cefotaxime, levofloxacin, piperacillin–tazobactam and ceftriaxone was determined by disc agar diffusion test. Polymerase chain reaction (PCR) amplification of the genes encoding OXA-10, PER-1 and VEB-1 was also performed. All isolates (100%) were resistant to ceftazidime, cefotaxime, cefepime and aztreonam. Imipenem and meropenem were the most effective anti-pseudomonal agents. The results revealed that 148 (87.05%) of the isolates were multidrug resistant and 67 (39.41%) of the isolates were ESBL positive. Fifty (74.62%), 33 (49.25%) and 21 (31.34%) strains among 67 ESBL-producing strains amplified bla_OXA-10, bla_PER-1 and bla_VEB-1 respectively.     

Antimicrobial susceptibility of bacterial isolates from burn units in Gaza

Background

Bacterial infections continue to be a leading cause of morbidity and mortality among burn patients despite intensive prophylaxis and treatment. Often treatment is complicated by the emergence of antimicrobial resistance pathogens. There are no reports or published data on the susceptibility profiles of bacteria isolated from burn patients in the Gaza strip.

Patients and methods

A cross sectional study was performed in the two burn units of Al-Shifa and Naser hospitals for 6 months from October 2010 to March 2011. A total of 118 wound samples from burn patients, 97 environmental samples and 28 samples from health care workers (HCWs) were collected and cultured according to the standard microbiological procedures. The bacterial isolates were identified by conventional methods and the antibiotic susceptibility profiles were determined by the standard disc diffusion method according to CLSI guidelines.

Results

The overall percentage of positive cultures from both hospitals was 45.8%, where Nasser burn unit revealed higher positive cultures than Al-Shifa burn unit. Pseudomonas aeruginosa was the most common pathogen isolated (50%) followed by Enterobacter cloacae (28.3%). Meanwhile, fingers and nasal samples that collected from HCWs showed 78.6% and 32.3% positive cultures respectively, where P. aeruginosa was the highest pathogen isolated (32.3%), followed by Coagulase Negative Staphylococci (CoNS) (29%). Environmental samples also showed higher isolation rate of Pseudomonas and CoNS. Pseudomonas isolates from patients samples were found to be resistant to most of antimicrobials used except for piperacillin–tazobactam. The family Enterobacteriaceae isolated from patients and environmental samples were resistant to most of the tested antimicrobials. However, the Enterobacteriaceae isolates from HCWs samples were sensitive to the most of the tested antimicrobials. The incidence of methicillin-resistant Staphylococci according to oxacillin sensitivity test was 60% in patient's samples, 77.8% in HCWs samples and 90% in environmental samples.

Conclusion

High percentage of resistance was found among clinical isolates in general to the commonly used antibiotics with a notable increase in MRSA incidence among both patients and environmental samples as well as HCWs.     

Pseudomonas aeruginosa bacteraemia in burns patients: Risk factors and outcomes

Introduction

We aimed to identify the risk factors for, and outcomes of Pseudomonas aeruginosa bacteraemia in adult burns patients.

Method

All adult burns patients who developed a Gram-negative bacteraemia over a period of 7 years were included. Retrospective data analysed included patient demographics, organisms cultured, antibiotic susceptibility patterns, isolation of P. aeruginosa in non-blood isolates, treatment, length of stay and mortality.

Results

Forty-three patients developed a Gram-negative bacteraemia over the study period, 12 of whom had Pseudomonas bacteraemia during the course of their admission. In eight patients (18.6%) P. aeruginosa was the first Gram-negative isolated. The only factor predicting P. aeruginosa bacteraemia as a first episode (compared to another Gram-negative) was prior isolation of Pseudomonas at other sites (wound sites, urine or sputum). Overall length of stay was less in patients who developed P. aeruginosa as a first episode, mainly because of increased mortality in this group. Prior non-blood isolates of P. aeruginosa could have correctly predicted the sensitivity pattern of the strain of P. aeruginosa organism in 75% of patients who did not receive appropriate initial antibiotics.

Conclusion

Prior colonisation with P. aeruginosa predicts P. aeruginosa in blood cultures, as opposed to other Gram-negative bacteria. Clinicians should have a high index of suspicion for P. aeruginosa bacteraemia where a septic burns patient has a prior history of non-blood P. aeruginosa cultures. Empirical antibiotic regimes based on the antibiotic-sensitivity patterns of previous non-blood P. aeruginosa isolates in each patient should be given at the time blood cultures are taken.     

Multiple-locus variable number of tandem repeats (VNTR) fingerprinting (MLVF) and antibacterial resistance profiles of extended spectrum beta lactamase (ESBL) producing Pseudomonas aeruginosa among burnt patients in Tehran

Extended spectrum β-lactamase (ESBL)-producing trait was present in 48 out of the 112 (42.8%) Pseudomonas aeruginosa isolates collected from burn wound infections during a 12-month period. The presence of oxa-10, per-1, veb-1 and ges genes and the multiple-locus variable number of tandem repeats (VNTR) fingerprinting (MLVF) of 112 P. aeruginosa strains were determined by PCR and multiplex PCR. Disk diffusion methods were used to determine the susceptibility of the isolates to antimicrobial agents as instructed by CLSI. All ESBL isolates were resistant to aztreonam, cefepime, cefotaxime, cefpodoxime, ceftazidime, ceftriaxone and ofloxacin. Fewer than 60% of ESBL isolates were resistant to imipenem, meropenem, and piperacillin-tazobactam but more than 90% were resistant to amikacin, ciprofloxacin, levofloxacin, ticarcillin and tobramycin. The most prevalent ESBL genes included oxa-10 (70%) and per-1 (50%) followed by veb-1 (31.3%). The gene encodes GES enzyme did not detect in any isolates. A total of 100 P. aeruginosa strains were typed by MLVF typing method. MLVF produced 42 different DNA banding patterns. These data indicate that different MLVF types infect burn wounds in patients at a hospital in Tehran and also suggest an alarming rate of ESBL-producing isolates in this test location.     

Description of Streptococcus pneumoniae infections in burn patients

Background

Longer survival in burn patients has resulted in more infectious complications, typically with Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, and Staphylococcus aureus. Although Streptococcus pneumoniae infections are common in the community and can cause nosocomial infections, the incidence and risk factors for pneumococcal infections in burn patients is unclear.

Methods

We performed an electronic retrospective chart review to collect rates of and risk factors for S. pneumoniae infections in patients with thermal burns from March 2003 through June 2008.

Results

Of the 1838 patients admitted to the burn center, 10 were infected (0.54% incidence). Patients presented with pneumonia (seven patients, 0.38% incidence) and bacteremia (three patients, 0.16% incidence) within a week of initial burn (median 1 day, range 0–8), often in the setting of bacterial co-infection (five patients). This group was mainly young males with median 28.8% total body surface area burns; 60% had concomitant inhalational injury. Most did not have traditional risk factors for pneumococcal infection but had objective signs of infection at time of positive culture and were treated with appropriate antibiotics. Two patients in this series died, although no mortality was attributed to S. pneumoniae.

Conclusions

Pneumococcal disease is not common in burn patients and generally occurs early on in hospitalization after burn making it more likely to be a community-acquired pathogen rather than nosocomial in the burn population. It should be considered in the setting of sepsis or new pulmonary infiltrates within a week after burn, but typical empiric antibiotics against the usual burn pathogens should be adequate to also treat for pneumococcal infection.     

Spectrum and drug resistance of pathogens from patients with burns

Microbial infection is an obstacle of burn treatment. However, little is known on what types of microbial infection dominate in the burn center and how the dynamic change of those microorganisms occurs during the past several years in China. We conducted a retrospective study of nosocomial infection (NI) in a large burn center to analyze the spectrum and antimicrobial resistance of microbial isolates from January 2003 to December 2010. We studied 989 isolates from 677 patients who had signs and symptoms of infection 48 h after admission. The number of NIs per 100 admissions was 10.9. The commonest isolates were Pseudomonas aeruginosa (23.1%), Staphylococcus aureus (18.7%), and Candida (11.4%). The result indicated that the numbers of patients with Acinetobacter sp. infection increased (P = 0.004), but with Proteus mirabilis infection decreased (P = 0.004). The isolated Acinetobacter sp. and P. aeruginosa were consistently highly resistant to almost all antibiotics tested. Notably, more frequent Acinetobacter sp. isolates appeared to be resistant to amikacin, gentamicin, tobramycin, ceftazidim, piperacillin, tazobactam, levofloxacin, and ciprofloxacin and more frequent Escherichia coli isolates were resistant to ceftazidime and aztreonam at the late time period although the P. aeruginosa and E. coli isolates were sensitive to less used ciprofloxacin and piperacillin/tazobactam. The increased rates of drug-resistant isolates in the later period might be associated with regular prophylactic therapy with antibiotics.     

Changes in the prevalence of causative pathogens isolated from severe burn patients from 2012 to 2017

Infection is the leading cause of mortality in severe burn patients, benefitting from periodic monitoring of changes in bacterial prevalence and antibiotic resistance trends. This single facility retrospective study evaluated blood culture results for patients hospitalized in the burn intensive care unit (BICU) from January 2012 to December 2017. A total of 969 samples from 420 patients were reviewed. Isolated pathogens were recorded by year and the number of days of hospitalization. Results showed that Acinetobacter baumanni was the most predominant isolated pathogen, followed closely by Pseudomonas aeruginosa, Klebsiella spp., and Enterococcus spp. Throughout this 6-year study, several significant trends were noted; Klebsiella species increased, while P. aeruginosa decreased. Staphylococcus aureus and Klebsiella species gradually increased, and P. aeruginosa doubled as the length of hospital stay increased to 22 days. Interestingly, as the length of the hospital stay increased, the proportion of Carbapenem-resistant Enterobacteriaceae (CRE) significantly increased up to 45.0% at 22 days (P = 0.003). Conversely, the proportion of Acinetobacter baumannii gradually decreased as the days hospitalized increased. Overall, the rate of multidrug-resistant (MDR) bacteremia found in burn patients was substantially higher than that in other patients and appeared from the earliest phase of hospitalization. Therefore, early use of antibiotics targeting MDR Gram-negative bacteria in burn patients admitted to the BICU might be warranted. Further, since CRE infections increase in abundance over time, significant effort should be made to manage the initial CRE infections of burn patients before they can multiply into a life-threatening situation.     

Extensive diversification is a common feature of Pseudomonas aeruginosa populations during respiratory infections in cystic fibrosis

BackgroundPopulations of the Liverpool Epidemic Strain (LES) of Pseudomonas aeruginosa undergo extensive diversification in the cystic fibrosis (CF) lung during long-term chronic infections.MethodsWe analyzed sets of 40 isolates from the sputa of five CF patients, each chronically infected with a different non-LES strain of P. aeruginosa. For each sample (two per patient), diversity was assessed by characterizing nine phenotypic traits.ResultsAll P. aeruginosa populations were highly diverse, with the majority of phenotypic variation being due to within-sample diversity.ConclusionsMaintenance of diverse populations in the CF lung is a common feature of P. aeruginosa infections.