Risk factors for mortality in patients with bloodstream infections caused by carbapenem-resistant Pseudomonas aeruginosa: clinical impact of bacterial virulence and strains on outcome

The incidence of carbapenem-resistant Pseudomonas aeruginosa (CRPA) bacteremia has increased in recent years, and infections caused by CRPA result in higher mortality than those caused by susceptible strains. This study was performed to evaluate the risk factors for mortality and to study the impact of virulence factors and bacterial strains on clinical outcomes in patients with CRPA bacteremia. Data on 63 episodes of CRPA bacteremia that have occurred between January 1, 2007, and December 31, 2009, in a teaching hospital (2000 beds) in Seoul, Korea, were analyzed. The Acute Physiology and Chronic Health Evaluation II (APACHE II) score at the time of CRPA bacteremia and the capacity of CRPA to form biofilm were independent predictive factors for mortality in patients with CRPA bacteremia. In addition, the biofilm-forming ability and elastase activity of strains were correlated with APACHE II scores to measure the severity of disease and estimate predicted mortality in the patients.     

密度感知系统对铜绿假单胞菌感染的免疫作用

目的研究密度感知信号（QS）系统在铜绿假单胞（PA）菌致大鼠肺部感染中的免疫调节作用,探讨其作用机制。方法（1）300只健康清洁级SD大鼠随机分为3组,应用锐孔喷射装置,制成两株铜绿假单孢菌（野生型铜绿假单孢菌PAO1及密度感知基因缺失的变异株PAO1-JP2）藻酸盐包裹体凝胶小珠,接种至大鼠肺部,建立两组慢性肺部感染模型,以无菌生理盐水,藻酸盐包裹体接种组作为对照组。（2）在接种后3、7、14、28d,取每组大鼠肺组织匀浆和血清检测,比较各组大鼠肺组织中免疫学指标IFN-γ、IL-4及血清中IgG、IgM、IgG1、IgG2a的不同,评价两株菌的致病差异性。结果（1）PAO1感染组大鼠死亡率（29．7％）明显高于PAO1-JP2感染组（11．0％）。（2）与PAO—JP2组相比,在感染早期（第3天）,PAO1组肺组织中IFN-γ明显升高;在感染的中期（第7天）,PAO1组IFN-γ、IL-4均显著升高,感染的后期（第14～28天）,PAO1组IFN-γ、IgG2a持续降低,IL-4、IgG、IgG1则持续升高。结论QS系统通过干预机体免疫系统和调控致病因子,在PA菌致病及免疫调节中起重要作用。     

Alternative approaches to treat bacterial infections: targeting quorum-sensing

ABSTRACT

Introduction

The emergence of multi- and pan-drug-resistant bacteria represents a global crisis that calls for the development of alternative anti-infective strategies. These comprise anti-virulence approaches, which target pathogenicity without exerting a bacteriostatic or bactericidal effect and are claimed to reduce the development of resistance. Because in many pathogens, quorum-sensing (QS) systems control the expression of virulence factors, interference with QS, or quorum-quenching, is often proposed as a strategy with a broad anti-virulence effect.     

Morbidity associated with Pseudomonas aeruginosa bloodstream infections

We sought to quantify patient morbidity throughout Pseudomonas aeruginosa bloodstream infection (PABSI) as a function of patient covariates. Individuals with PABSI were included in a retrospective, observational, cohort study. Morbidity was quantified by serial Sequential Organ Failure Assessment (SOFA) scores. Impact of active antimicrobial treatment was assessed as a function of changes in SOFA scores as the dependent variable. A total of 95 patients with PABSI were analyzed. Relative to baseline SOFA scores (day −2), scores after PABSI were increased by 37% on day 0 and 22% on day +2 but returned to baseline on day +7. Overall mortality was 37%, and mean length of hospital stay (postculture) was 16 days. Most patients were appropriately treated, with n = 83 (87%) receiving an active agent and n = 61 (64%) receiving >1 agent. As a result, an effect of therapy on morbidity was not observed. Advanced age and elevated baseline SOFA scores predicted increased in-hospital mortality (P = 0.01 and P < 0.001, respectively) and morbidity at day +2 (P < 0.05 and P < 0.05, respectively) and day +7 (P < 0.05 and P < 0.001, respectively). Neutropenia was also associated with increased morbidity at day +2 (P < 0.05). In treated PABSI, morbidity is highest the day of the diagnostic blood cultures and slowly returns to baseline over the subsequent 7 days. Age and baseline severity of illness are the strongest predictors of morbidity and mortality. Because neither of these factors are modifiable, efforts to minimize the negative impact of PABSI should focus on appropriate prevention and infection control efforts.     

Inhibitors and antagonists of bacterial quorum sensing

Bacteria can regulate community-wide behaviors including biofilm formation, virulence, conjugation, sporulation, and swarming motility through a process called quorum sensing. Inhibitors and antagonists of bacterial quorum sensing are important research tools and potential therapeutic agents. In this review, we have summarized recent developments in this area.     

Five-year report of national surveillance of antimicrobial resistance in Pseudomonas aeruginosa isolated from non-tertiary care hospitals in Korea (2002-2006)

A nationwide surveillance of the antimicrobial resistance of Pseudomonas aeruginosa isolates from non-tertiary care hospitals was conducted in Korea from 2002 to 2006. Resistance to almost all antimicrobial agents decreased significantly from 2003 (P < 0.01). Resistance rates to the major antipseudomonal agents, ceftazidime, imipenem, meropenem, and aztreonam, were 18.8%, 20.5%, 18.7%, and 19.7%, respectively, in 2003. However, they had all decreased to below 10% in 2006. The proportion of multidrug-resistant isolates that were resistant to at least 3 of 5 major antipseudomonal agent decreased from 33.5% in 2003 to 23.1% in 2006 (P < 0.05). In this study, we found a decreasing trend in resistance rates and low resistance rates in P. aeruginosa from non-tertiary care hospitals compared with those from general hospitals, including tertiary care hospitals, in Korea. Our data provide valuable information for the selection of reliable empiric therapies for P. aeruginosa infections in non-tertiary care hospital patients, including outpatients.     

Genetic characterization of Staphylococcus aureus isolates causing bloodstream infections in Austria

A total of 112 Staphylococcus aureus bloodstream isolates were genetically characterized. Spa typing and DNA microanalysis exhibited high diversity, resulting in 64 different spa types and 9 different SplitsTree clusters. Methicillin-resistant S. aureus (MRSA) were found in 6 cases only, including the first case of life-stock–associated MRSA (MRSA ST398) in bloodstream infection in Austria.     

Evidence of Multiple Virulence Subtypes in Nosocomial and Community-Associated MRSA Genotypes in Companion Animals from the Upper Midwestern and Northeastern United States

Objective: Not much is known about the zoonotic transmission of methicillin-resistant Staphylococcus aureus (MRSA) in companion animals in the United States. We report the rate of prevalence of S. aureus and MRSA recovered from clinical samples of animals requiring treatment at veterinary clinics throughout the upper midwestern and northeastern United States.Design: We compared phenotypes, genotypes, and virulence profiles of the MRSA isolates identified in companion animals, such as cats, dogs, horses, and pigs, with typical human nosocomial and community-associated MRSA (CA-MRSA) genotypes to assess implied zoonotic transmission or zooanthroponosis. Five hundred thirty-three coagulase-positive staphylococci (CPS) isolates recovered between 2006 and 2008 from a variety of animal-source samples were screened for S. aureus by S. aureus-specific 16S rDNA primers and were screened for methicillin-resistance. All MRSA isolates were genotyped by pulsed-field gel electrophoresis (PFGE), multilocus sequence typing (MLST), and spa typing. They were also screened for common staphylococcal enterotoxin and adhesion genes by multiplex and singleplex PCR.Results: Among the 533 CPS isolates recovered, 66 (12.4%) were determined to be S. aureus and 24 (4.5%) were MRSA. The percent of animals that were positive for S. aureus were as follows: 6.6% (32 of 487) dogs, 39.6% (19 of 48) cats, 83.3% (10 of 12) horses, and 100% of pigs, rabbits, hamsters and rats. Notably, 36.4% of all S. aureus identified were MRSA. Methicillin-resistant S. aureus was present in clinical samples from 12 of 487 dogs (2.5%), 6 of 48 cats (12.5%), 5 of 12 horses (42%), and 1 of 2 pigs (50%). The 24 MRSA isolates resolved into 4 PFGE clones: USA100 (50%), USA300 (16.7%), USA500 (20.8%) and USA800 (12.5%) and 6 sequence types (ST5, ST8, ST105, ST830, and ST986) or 2 clonal complexes, CC5 and CC8. Five major virulence profiles (clusters A to E) were observed in these MRSA isolates. Genotypic and virulence profiles of cats and dogs were more similar to each other than to those of horses. A Panton-Valentine leukocidin positive isolate with ST8:USA300 background was identified in a pig causing skin and soft infection.Conclusion: The presence of human MRSA clones in these animals suggests possible reverse zoonotic transmission. This study reports the first case of a USA300 genotype in a pig. Presence of multiple virulence profiles within a MRSA genotype in these animals suggests the potential of emergence of new MRSA clones by gaining or losing additional virulence genes.     

Antimicrobial susceptibility of Pseudomonas aeruginosa isolates obtained from patients in Canadian hospitals: CANWARD 2008-2011

Broth microdilution (Clinical and Laboratory Standards Institute) was used to evaluate the antimicrobial susceptibility of 1549 Pseudomonas aeruginosa clinical isolates collected in Canada between January 2008 and October 2011. The percentage of isolates susceptible was as follows: amikacin 92.0%, ceftazidime 83.5%, ciprofloxacin 74.3%, colistin 93.4%, gentamicin 76.8%, meropenem 82.7%, and piperacillin-tazobactam 83.6%. Antimicrobial susceptibility did not change significantly between 2008 and 2011, with the exception of increasing susceptibility to gentamicin (P < 0.0001).     

Exogenous or endogenous reservoirs of nosocomialPseudomonas aeruginosa andStaphylococcus aureus infections in a surgical intensive care unit

Objective A 4 month prospective study was performed to assess the incidence and routes of endogenous or exogenous colonization and nosocomial infection caused byStaphylococcus aureus andPseudomonas aeruginosa in surgical critically ill patients.Design A total of 4634 specimens ware obtained. Patient's nasal, scalp, and rectal swabs as well as tracheal secretion (TS) were cultured every second day beginning on the day of admission. Nasal swabs and hand cultures of the personnel as well as cultures from gowns were also taken. all isolates ofS. aureus were phage typed and 116 of these isolates were also plasmid typed.P. aeruginosa isolates were sero-and pyocin typed. Resistance patterns were determined in all isolates.Setting The suty was carried out in the surgical intensive care unit (SICU) of an teaching hospital.Patients During the study period each patient (a total of 153 patients) admitted to the SICU entered the study.Results P. aeruginosa andS. aureus colonisation rate on admission were 5% and 36.5% respectively. Only 10 patients (6.5%) were colonized withP. aeruginosa during hospitalization, and only 7 patients (4.5%) acquiredS. aureus in the surgical intensive care unit (SICU). The most common primary colonisation site ofP. aeruginosa was the rectum, whereasS. aureus was predominantly found in nasal cultures. Horizontal transmission ofS. aureus occured in only 2 patients.Conclusion The study suggests that colonisation withP. aeruginosa andS. aureus occurs from endogenous rather than from exogenous sources and that the endogenous acquisition of both bacteria play a more important role in development of nosocomial infections than the exogenous route of transmission.     

Antimicrobial activity of ceftaroline and comparator agents tested against bacterial isolates causing skin and soft tissue infections and community-acquired respiratory tract infections isolated from the Asia-Pacific region and South Africa (2010)

Ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, is a cephalosporin with in vitro bactericidal activity against resistant Gram-positive organisms including methicillin-resistant Staphylococcus aureus (MRSA) and multidrug-resistant strains of Streptococcus pneumoniae, and common Gram-negative organisms, including wild-type Enterobacteriaceae. We evaluated the in vitro activity of ceftaroline and selected comparator agents against bacterial isolates collected from patients with skin and soft tissue infections (SSTI) and community-acquired respiratory tract infections (CARTI) in the Asia-Pacific region and South Africa. A total of 2351 isolates, 1100 from SSTI and 1251 from CARTI, were collected from 25 medical centers distributed across 8 countries as part of the 2010 AWARE ceftaroline surveillance program and tested for susceptibility by reference broth microdilution methods. Ceftaroline was very active against S. aureus (MIC_50/90, 0.25/1 μg/mL; 93.4% susceptible), including MRSA (MIC_50/90, 1/2 μg/mL; 80.6% susceptible). Against β-hemolytic streptococci, ceftaroline demonstrated greater activity (MIC₉₀, 0.015 μg/mL) than penicillin (MIC₉₀, 0.06 μg/mL). Ceftaroline was also highly active against viridans group streptococci (MIC₉₀, 0.12 μg/mL). Similarly to ceftriaxone, ceftaroline activity against Escherichia coli (MIC_50/90, >32/>32 μg/mL) and Klebsiella spp. (MIC_50/90, 0.12/>32 μg/mL) was compromised by the high prevalence of isolates with an ESBL phenotype in the region, particularly in China. Ceftaroline was the most potent β-lactam tested against S. pneumoniae (MIC_50/90 of 0.015/0.25 μg/mL; 99.8% susceptible by Clinical and Laboratory Standards Institute [CLSI] criteria), and it was also highly potent against Haemophilus influenzae (MIC_50/90, ≤0.008/0.03 μg/mL; 100% susceptible by CLSI criteria). Ceftaroline was also active against H. parainfluenzae (MIC_50/90, ≤0.008/0.015 μg/mL) and Moraxella catarrhalis (MIC_50/90, 0.06/0.12 μg/mL). In summary, ceftaroline showed potent in vitro activity against a large collection of bacterial isolates (2351) associated with SSTI and CARTI from the Asia-Pacific region and South Africa.     

In vitro Evaluation of the Antiviral Activity of an Extract of Date Palm (Phoenix dactylifera L.) Pits on a Pseudomonas Phage

A crude acetone extract of the pit of date palm (Phoenix dactylifera L.) was prepared and its antiviral activity evaluated against lytic Pseudomonas phage ATCC 14209-B1, using Pseudomonas aeruginosa ATCC 25668 as the host cell. The antiviral activity of date pits was found to be mediated by binding to the phage, with minimum inhibitory concentration (MIC) of <10 μg ml(-1). The decimal reduction time (D-values), the concentration exponent (η) and the phage inactivation kinetics were determined. The date pit extracts show a strong ability to inhibit the infectivity of Pseudomonas phage ATCC 14209-B1 and completely prevented bacterial lysis, which it is hoped will promote research into its potential as a novel antiviral agent against pathogenic human viruses.     

Impact of AmpC overexpression on outcomes of patients with Pseudomonas aeruginosa bacteremia

AmpC overexpression (AmpC++) is a significant mechanism of β-lactam resistance in Pseudomonas aeruginosa, but its impact on clinical outcomes is not well established. To examine the influence of AmpC++ on clinical outcomes of patients with P. aeruginosa bacteremia, we screened all bloodstream P. aeruginosa isolates obtained from 2003 to 2006 for AmpC++. Demographics and outcomes were retrospectively compared between patients with P. aeruginosa bacteremia caused by AmpC++ and pan-susceptible strains (wild-type controls). Of the 263 isolates screened, 63 (24.0%) were nonsusceptible to ceftazidime. Clinical data of 42 AmpC++ isolates from 21 patients were compared with 33 control patients. The 2 groups were similar in sex and race. Patients in the AmpC++ group was more likely to receive inappropriate empiric antibiotics (odds ratio [OR] = 67.5; 95% confidence interval [CI], 6.3–720.0) and experience microbiologic persistence (OR = 12.2; 95% CI, 1.7–87.7). In institutions with a high prevalence of AmpC++, empiric therapy with agents with activity against AmpC++ strains may be warranted.     

Emergence of plasmid-mediated quinolone resistance genes in clinical isolates of Acinetobacter baumannii and Pseudomonas aeruginosa in Henan,China

A total of 216 clinical isolates of Acinetobacter baumannii and Pseudomonas aeruginosa were collected from a general hospital in Henan, China, and screened for the plasmid-mediated quinolone resistance (PMQR) determinants. The presence of β-lactamase genes and mutations in quinolone resistance–determining regions were investigated among the PMQR-positive isolates.     

Regulation of Staphylococcal Superantigen-Like Gene,ssl8, Expression in Staphylococcus aureus strain,RN6390

Staphylococcal superantigen-like (SSL) proteins, which are encoded by a cluster of eleven ssl genes, contribute to the Staphylococcus aureus virulence. Recently we reported ssl8 expression profiles in seven clinically important strains—MW2, USA300FPR3757, MSSA476, Newman, RN6390, Mu50, and N315—and showed the differential expression of ssl8 in Newman, RN6390, and USA300FPR3757 strains, despite harboring identical allelic forms of ssl8, suggesting the roles for different regulatory elements for this gene in different S. aureus strains. In this communication, using RN6390, a common laboratory S. aureus strain and its isogenic knockout mutant strains of agr, sae, sarA, sigB, rot, and the agr-_/sigB⁻ double mutant, we showed that SarA and Rot are inducer and repressor, respectively, for ssl8 expression in RN6390. This is in contrast to the Newman strain, where ssl8 is positively regulated by Sae but negatively by Agr, indicating the variable expression of ssl8 in clinical strains is more likely due to strain-specific regulatory elements.     

异质性万古霉素中介金黄色葡萄球菌对临床细菌感染治疗的影响

以往认为细菌不易对万古霉素产生耐药,但近年来国际上许多国家和地区报道了万古霉索的耐药性现象,其中异质性万古霉素中介金黄色葡萄球菌(hVISA)受到了关注,因其发生率上升而又不易被检测,影响了细菌感染的治疗.本期刊登了王辉教授课题组以可靠的检测方法 时分离自我国14个城市的甲氧西林耐药金黄色葡萄球菌进行了hVISA检测,首次发现hVISA在我国的发生率高,应引起临床医师的重视.     

Chemotaxis inhibitory protein of Staphylococcus aureus, a bacterial antiinflammatory agent

Leukocyte migration is a key event both in host defense against invading pathogens as well as in inflammation. Bacteria generate chemoattractants primarily by excretion (formylated peptides), complement activation (C5a), and subsequently through activation of leukocytes (e.g., leukotriene B4, platelet-activating factor, and interleukin 8). Here we describe a new protein secreted by Staphylococcus aureus that specifically impairs the response of neutrophils and monocytes to formylated peptides and C5a. This chemotaxis inhibitory protein of S. aureus (CHIPS) is a 14.1-kD protein encoded on a bacteriophage and is found in >60% of clinical isolates. CHIPS reduces the neutrophil recruitment toward C5a in a mouse peritonitis model, even though its activity is much more potent on human than on mouse cells. These findings suggest a new immune escape mechanism of S. aureus and put forward CHIPS as a potential new antiinflammatory therapeutic compound.     

An increase of blood squamous cell carcinoma antigen in Pseudomonas aeruginosa spondylitis

Squamous cell carcinoma antigen (SCCA) is traditionally engaged for detecting and following up malignancy from a squamous cell origin. We encountered an unusual increase of blood SCCA but no other cancer markers in a patient associated with an infective lumbar spondylitis due to Pseudomonas aeruginosa. An overshooting of Th1 expression, such as tumor necrosis factor alpha, bumped up by his uremia as a result of P. aeruginosa infection may hasten SCCA. Therefore, SCCA might additionally serve as a serological marker for infection besides squamous cell cancer, and its false-positive increase also highlights the appropriateness of tumor marker screening.     

Development of a single-tube polymerase chain reaction assay for the simultaneous detection of Haemophilus influenzae, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus spp. directly in clinical samples

This study describes the development and evaluation of a multiplex single-tube polymerase chain reaction assay for the simultaneous detection of Haemophilus influenzae, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus spp. used as target species-specific or genus-specific genes. The assay enables the detection of 5 to 50 pg of bacterial DNA. The sensitivity of the assay was evaluated as 100% for P. aeruginosa, S. aureus, and Streptococcus spp., and 94.3% for H. influenzae; the specificity was 100% for all 4 microorganisms (positive predictive value, 100%; negative predictive value, 98.2%). The assay permits rapid and accurate detection of these 4 microorganisms in a wide range of clinical samples such as whole blood, cerebrospinal, ear, pleural and ophthalmic fluids, as well as bronchoalveolar lavage and bronchial secretions.     

Determination of the critical concentration of neutrophils required to block bacterial growth in tissues

We showed previously that the competition between bacterial killing by neutrophils and bacterial growth in stirred serum-containing suspensions could be modeled as the competition between a first-order reaction (bacterial growth) and a second-order reaction (bacterial killing by neutrophils). The model provided a useful parameter, the critical neutrophil concentration (CNC), below which bacterial concentration increased and above which it decreased, independent of the initial bacterial concentration. We report here that this model applies to neutrophil killing of bacteria in three-dimensional fibrin matrices and in rabbit dermis. We measured killing of 10(3)-10(8) colony forming units/ml Staphylococcus epidermidis by 10(5)-10(8) human neutrophils/ml in fibrin gels. The CNC was approximately 4 x 10(6) neutrophils/ml gel in the presence of normal serum and approximately 1.6 x 10(7) neutrophils/ml gel in the presence of C5-deficient serum. Application of our model to published data of others on killing of approximately 5 x 10(7) to 2 x 10(8) E. coli/ml rabbit dermis yielded CNCs from approximately 4 x 10(6) to approximately 8 x 10(6) neutrophils/ml dermis. Thus, in disparate tissues and tissuelike environments, our model fits the kinetics of bacterial killing and gives similar lower limits (CNCs) to the neutrophil concentration required to control bacterial growth.