Impact of multidrug resistance on the virulence and fitness of Pseudomonas aeruginosa: a microbiological and clinical perspective

Pseudomonas aeruginosa is one of the most common nosocomial pathogens and part of the top emergent species associated with antimicrobial resistance that has become one of the greatest threat to public health in the twenty-first century. This bacterium is provided with a wide set of virulence factors that contribute to pathogenesis in acute and chronic infections. This review aims to summarize the impact of multidrug resistance on the virulence and fitness of P. aeruginosa. Although it is generally assumed that acquisition of resistant determinants is associated with a fitness cost, several studies support that resistance mutations may not be associated with a decrease in virulence and/or that certain compensatory mutations may allow multidrug resistance strains to recover their initial fitness. We discuss the interplay between resistance profiles and virulence from a microbiological perspective but also the clinical consequences in outcomes and the economic impact.

Create artilysins from a recombinant library to serve as bactericidal and antibiofilm agents targeting Pseudomonas aeruginosa

Pseudomonas aeruginosa is a critical pathogen and novel treatments are urgently needed. The out membrane of P. aeruginosa facilitates biofilm formation and antibiotic resistance, and hinders the exogenous application against Gram-negative bacteria of endolysins. Engineered endolysins are investigated for enhancing antimicrobial activity, exemplified by artilysins. Nevertheless, existing research predominantly relies on laborious and time-consuming approaches of individually artilysin identification. This study proposes a novel strategy for expedited artilysin discovery using a recombinant artilysin library comprising proteins derived from 38 antimicrobial peptides and 8 endolysins. In this library, 19 colonies exhibited growth inhibition against P. aeruginosa exceeding 50 %, and three colonies were designated as dutarlysin-1, dutarlysin-2 and dutarlysin-3. Remarkably, dutarlysin-1, dutarlysin-2 and dutarlysin-3 demonstrated rapid and enhanced antibacterial activity, even minimum inhibitory concentration of them killed approximately 4.93 lg units, 6.75 lg units and 5.36 lg units P. aeruginosa, respectively. Dutarlysins were highly refractory to P. aeruginosa resistance development. Furthermore, 2 μmol/L dutarlysin-1 and dutarlysin-3 effectively eradicated over 76 % of the mature biofilm. These dutarlysins exhibited potential broad-spectrum activity against hospital susceptible Gram-negative bacteria. These results supported the effectiveness of this artilysins discovery strategy and suggested dutarlysin-1 and dutarlysin-3 could be promising antimicrobial agents for combating P. aeruginosa.

Factors associated with non-carbapenemase mediated carbapenem resistance of Gram-negative bacteria: a retrospective case-control study

Infections with carbapenemase-producing Gram-negative bacteria are related to increased morbidity and mortality, yet little is known regarding infections caused by non-beta-lactamase mediated carbapenem-resistant bacteria. Our objective was to identify risk factors for, and the clinical impact of infections caused by carbapenem-resistant carbapenemase-negative Enterobacterales and Pseudomonas aeruginosa. This retrospective matched case-control study was performed at the University Hospital of Basel, Switzerland, in 2016. We focused on other resistance mechanisms by excluding laboratory-confirmed carbapenemase-positive cases. Carbapenem resistance was set as the primary endpoint, and important risk factors were investigated by conditional logistic regression. The clinical impact of carbapenem resistance was estimated using regression models containing the resistance indicator as explanatory factor and adjusting for potential confounders. Seventy-five cases of infections with carbapenem-resistant, carbapenemase-negative bacteria were identified and matched with 75 controls with carbapenem-susceptible infections. The matched data set was well-balanced regarding age, gender, and comorbidity. Duration of prior carbapenem treatment (OR 1.15, [1.01, 1.31]) correlated with resistance to carbapenems. Our study showed that patients with carbapenem-resistant bacteria stayed 1.59 times (CI [0.81, 3.14]) longer in an ICU. The analyzed dataset did not provide evidence for strong clinical implications of resistance to carbapenems or increased mortality. The duration of prior carbapenem treatment seems to be a strong risk factor for the development of carbapenem resistance. The higher risk for a longer ICU stay could be a consequence of a carbapenem resistance. In contrast to carbapenemase-producers, the clinical impact of carbapenamase-negative, carbapenem-resistant strains may be limited. Trial registration: The study design was prospectively approved by the local Ethics Commission on 10.08.2017 (EKNZ BASEC 2017-00222).

A novel antibiotic combination of linezolid and polymyxin B octapeptide PBOP against clinical Pseudomonas aeruginosa strains

Background

Antibiotic-resistant Gram-negative bacteria are becoming a major public health threat such as the important opportunistic pathogen Pseudomonas aeruginosa (P. aeruginosa). The present study investigated enhancement of the linezolid spectrum, which is normally used to treat Gram-positive bacteria, at inhibiting P. aeruginosa growth.

Methods

The checkerboard test or time-kill assay were carried out to determine the antibacterial effects of linezolid in cooperation with polymyxin B octapeptide PBOP (LP) against P. aeruginosa based on in vitro model. The protective effect of LP against P. aeruginosa infection was assessed based on a Caenorhabditis elegans (C. elegans) model.

Results

The synergistic activity and antibacterial effects were significantly increased against P. aeruginosa by LP treatment, while linezolid and PBOP as monotherapies exhibited no remarkably bactericidal activity against the clinical strains. Additionally, LP treatment modified biofilm production, morphology, swimming motility of P. aeruginosa, and protected C. elegans from P. aeruginosa infection.

Conclusions

This research demonstrates that LP combination has significant synergistic activity against P. aeruginosa, and PBOP is potential to be an activity enhancer. Notably, this strategy improved the antibacterial activity spectrum of linezolid and other anti-Gram-positive agents and represents an effective choice to surmount the antibiotic resistance of bacteria in the long term.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12941-022-00531-5.

Survey on Carbapenem-Resistant Bacteria in Pigs at Slaughter and Comparison with Human Clinical Isolates in Italy

This study is focused on resistance to carbapenems and third-generation cephalosporins in Gram-negative microorganisms isolated from swine, whose transmission to humans via pork consumption cannot be excluded. In addition, the common carriage of carbapenem-resistant (CR) bacteria between humans and pigs was evaluated. Sampling involved 300 faecal samples collected from slaughtered pigs and 300 urine samples collected from 187 hospitalised patients in Parma Province (Italy). In swine, MIC testing confirmed resistance to meropenem for isolates of Pseudomonas aeruginosa and Pseudomonas oryzihabitans and resistance to cefotaxime and ceftazidime for Escherichia coli, Ewingella americana, Enterobacter agglomerans, and Citrobacter freundii. For Acinetobacter lwoffii, Aeromonas hydrofila, Burkolderia cepacia, Corynebacterium indologenes, Flavobacterium odoratum, and Stenotrophomonas maltophilia, no EUCAST MIC breakpoints were available. However, ESBL genes (blaCTXM-1, blaCTX-M-2, blaTEM-1, and blaSHV) and AmpC genes (blaCIT, blaACC, and blaEBC) were found in 38 and 16 isolates, respectively. P. aeruginosa was the only CR species shared by pigs (4/300 pigs; 1.3%) and patients (2/187; 1.1%). P. aeruginosa ST938 carrying blaPAO and blaOXA396 was detected in one pig as well as an 83-year-old patient. Although no direct epidemiological link was demonstrable, SNP calling and cgMLST showed a genetic relationship of the isolates (86 SNPs and 661 allele difference), thus suggesting possible circulation of CR bacteria between swine and humans.

Inhibition of the Quorum Sensing System, Elastase Production and Biofilm Formation in Pseudomonas aeruginosa by Psammaplin A and Bisaprasin

Natural products derived from marine sponges have exhibited bioactivity and, in some cases, serve as potent quorum sensing inhibitory agents that prevent biofilm formation and attenuate virulence factor expression by pathogenic microorganisms. In this study, the inhibitory activity of the psammaplin-type compounds, psammaplin A (1) and bisaprasin (2), isolated from the marine sponge, Aplysinellarhax, are evaluated in quorum sensing inhibitory assays based on the Pseudomonas aeruginosa PAO1 lasB-gfp(ASV) and rhlA-gfp(ASV) biosensor strains. The results indicate that psammaplin A (1) showed moderate inhibition on lasB-gfp expression, but significantly inhibited the QS-gene promoter, rhlA-gfp, with IC50 values at 14.02 μM and 4.99 μM, respectively. In contrast, bisaprasin (2) displayed significant florescence inhibition in both biosensors, PAO1 lasB-gfp and rhlA-gfp, with IC50 values at 3.53 μM and 2.41 μM, respectively. Preliminary analysis suggested the importance of the bromotyrosine and oxime functionalities for QSI activity in these molecules. In addition, psammaplin A and bisaprasin downregulated elastase expression as determined by the standard enzymatic elastase assay, although greater reduction in elastase production was observed with 1 at 50 μM and 100 μM. Furthermore, the study revealed that bisaprasin (2) reduced biofilm formation in P. aeruginosa.

Association of bacterial isolates and antimicrobial susceptibility between prostatic fluid and urine samples in canine prostatitis with concurrent cystitis

Most old, intact male dogs usually have prostate disorders, especially benign prostatic hypertrophy and prostatitis with or without abscesses, and concurrent cystitis. The successful treatment of dogs with prostatitis concurrent with cystitis has relied on choosing an appropriate antimicrobial drug based on a bacterial culture and drug sensitivity testing. The objective of the study was to compare the prevalence of bacterial species and results of drug susceptibility testing of bacteria that were isolated from the prostatic fluids and urine samples that were collected from dogs with both prostatitis and cystitis. One hundred and sixty intact male dogs, who presented with both diseases, were recruited for the study. The disease diagnoses were based on clinical history notes, physical examinations, abdominal ultrasonography, prostatic fluid cytology, urinalysis and bacterial cultures from both prostatic fluid and urine samples. The bacterial culture results demonstrated that the major species that were detected in either the prostatic fluid or urine samples were Staphylococcus spp., Escherichia coli, Pseudomonas spp., Streptococcus spp., Proteus mirabilis and Klebsiella pneumoniae. Staphylococcus spp. (26.5 %, 43/162) and Escherichia coli (26.1 %, 12/46) were the most prevalent species from the prostatic fluid and urine samples, respectively. Statistical tests revealed that there were no significantly different prevalence levels among the isolated bacteria between the prostatic fluid and urine samples. Imipenem and gentamicin were the most potent antimicrobial drugs tested against the bacterial isolates in the present study. However, the administration of imipenem to treat prostatitis and cystitis in dogs was of concern. Interestingly, there were no significant differences in the antimicrobial drug susceptibility trends between the prostatic fluid and urine samples. Based on these results, a urine sample might be considered as an optional sample for bacterial cultures and antimicrobial drug susceptibility testing when it is not possible to collect a prostatic fluid sample.

An Application of Imipenem Discs or P. aeruginosa ATCC 27853 Reference Strain Increases Sensitivity of Carbapenem Inactivation Method for Non-Fermenting Gram-Negative Bacteria

Non-fermenting Gram-negative rods are one of the most commonly isolated bacteria from human infections. These microorganisms are typically opportunistic pathogens that pose a serious threat to public health due to possibility of transmission in the human population. Resistance to beta-lactams, due to carbapenemases synthesis, is one of the most important antimicrobial resistance mechanisms amongst them. The aim of this study was to evaluate the usefulness of the Carbapenem Inactivation Method (CIM), and its modifications, for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. This research involved 81 strains of Gram-negative rods. Of the tested strains, 55 (67.9%) synthesized carbapenemases. For non-fermenting rods, 100% sensitivity and specificity was obtained in the version of the CIM test using imipenem discs and E. coli ATCC 25922 strain. The CIM test allows for differentiation of carbapenems resistance mechanisms resulting from carbapenemase synthesis from other resistance types. It is a reliable diagnostic method for the detection of carbapenemase activity amongst non-fermenting Gram-negative rods. Application of imipenem discs and P. aeruginosa ATCC 27853 reference strain increases CIM results sensitivity, while imipenem discs and E. coli ATCC 25922 strain use maintains full precision of the test for non-fermenting rods.

Socioeconomic burden of bloodstream infections caused by carbapenem-resistant and carbapenem-susceptible Pseudomonas aeruginosa in China

OBJECTIVES

Drug resistance in Pseudomonas aeruginosa (PAE) is a serious health threat. Additionally, it is important to understand the associated socioeconomic burden.

METHODS

Clinical information and hospital cost data for patients with PAE bloodstream infections (BSIs) in a tertiary teaching hospital (2011-2016) were collected retrospectively to estimate the direct economic burden. Socioeconomic loss incurred by patients was calculated using the human capital approach combined with estimating disability-adjusted life years (DALYs). Differences in socioeconomic burden between BSIs caused by carbapenem-resistant (CR) and carbapenem-susceptible (CS) PAE were compared.

RESULTS

This study included data for 220 patients, of which were 29.5% (65/220) CR-PAE BSIs. The median direct economic burden of patients following CR-PAE BSI was significantly higher than following CS-PAE BSI ($5005.94 vs. $1462.86; P < 0.001). The median DALY loss was significantly higher in the CR-PAE group compared with CS-PAE group (0.024 vs. 0.008; P = 0.001). The median indirect socioeconomic loss of patients in the CR-PAE group tended to be significantly higher than in the CS-PAE group ($64.06 vs. $29.71; P = 0.011). The annual economic burden of CR-PAE is higher (up to >1.5 times) than the Chinese annual per capita GDP.

CONCLUSION

The economic burden of PAE BSIs is significant, irrespective of carbapenem resistance. The direct economic burden of CR-PAE BSI was at least three-fold that of CS-PAE BSI. The DALY loss caused by CR-PAE BSI is three-fold that caused by CS-PAE BSI. The indirect socioeconomic loss caused by CR-PAE BSI is more than twice that of CS-PAE BSI.

Clinical and Economic Burden of Carbapenem-Resistant Infection or Colonization Caused by Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii: A Multicenter Study in China

Background: Carbapenem resistant Klebsiella pneumoniae (CRKP), Pseudomonas aeruginosa (CRPA), and Acinetobacter baumannii (CRAB) pose significant threats to public health. However, the clinical and economic impacts of CRKP, CRPA, and CRAB remain largely uninvestigated in China. This study aimed to examine the clinical and economic burden of CRKP, CRPA, and CRAB compared with carbapenem susceptible cases in China. Method: We conducted a retrospective and multicenter study among inpatients hospitalized at four tertiary hospitals between 2013 and 2015 who had K. pneumoniae, P. aeruginosa, and A. baumannii positive clinical samples. Propensity score matching (PSM) was used to balance the impact of potential confounding variables, including age, sex, insurance, number of diagnosis, comorbidities (disease diagnosis, and Charlson comorbidity index), admission to intensive care unit, and surgeries. The main indicators included economic costs, length of stay (LOS), and mortality rate. Results: We included 12,022 inpatients infected or colonized with K. pneumoniae, P. aeruginosa, and A. baumannii between 2013 and 2015, including 831 with CRKP and 4328 with carbapenem susceptible K. pneumoniae (CSKP), 1244 with CRPA and 2674 with carbapenem susceptible P. aeruginosa (CSPA), 1665 with CRAB and 1280 with carbapenem susceptible A. baumannii (CSAB). After PSM, 822 pairs, 1155 pairs, and 682 pairs, respectively were generated. Compared with carbapenem-susceptible cases, those with CRKP, CRPA, and CRAB were associated with statistically significantly increased total hospital cost ($14,252, p < 0.0001; $4605, p < 0.0001; $7277, p < 0.0001) and excess LOS (13.2 days, p < 0.0001; 5.4 days, p = 0.0003; 15.8 days, p = 0.0004). In addition, there were statistically significantly differences in hospital mortality rate between CRKP and CSKP, and CRAB and CSAB group (2.94%, p = 0.024; 4.03%, p = 0.03); however, the difference between CRPA and CSPA group was marginal significant (2.03%, p = 0.052). Conclusion: It highlights the clinical and economic impact of CRKP, CRPA, and CRAB to justify more resources for implementing antibiotic stewardship practices to improve clinical outcomes and to reduce economic costs.

Impact of renal impairment and human organic anion transporter inhibition on pharmacokinetics, safety and tolerability of relebactam combined with imipenem and cilastatin

AIMS

Two phase 1, open-label studies were conducted to investigate the effect of renal impairment (RI) and organic anion transporter (OAT) inhibition on pharmacokinetics (PK) and safety of relebactam (REL) plus imipenem/cilastatin (IMI).

METHODS

Study PN005 evaluated the PK of REL (125 mg) plus IMI (250 mg) in participants with RI vs healthy controls. Study PN019 evaluated the PK of REL (250 mg) and imipenem (500 mg; dosed as IMI) with/without probenecid (1 g; OAT inhibitor) in healthy adults.

RESULTS

Geometric mean ratios (RI/healthy matched controls) of area under the concentration-time curve from time 0 to infinity (AUC0-∞ ; 90% confidence interval) for REL, imipenem and cilastatin increased as RI increased from mild (1.6 [1.1, 2.4], 1.4 [1.1, 1.8] and 1.6 [1.0, 2.5], respectively) to severe (4.9 [3.4, 7.0], 2.5 [1.9, 3.3] and 5.6 [3.6, 8.6], respectively). For all 3 analytes, plasma and renal clearance decreased and corresponding plasma apparent terminal half-life increased with increasing RI. Geometric mean ratios ([probenecid+IMI/REL]/[IMI/REL]) of plasma exposure for REL and imipenem were 1.24 (1.19, 1.28) and 1.16 (1.13, 1.20), respectively. The dose fraction excreted (fe) in the urine decreased progressively from mild to severe RI. Probenecid reduced renal clearance of REL and imipenem by 25 and 31%, respectively. Compared with IMI/REL, coadministration of IMI/REL with probenecid yielded lower fe for REL and imipenem. In both studies, treatment was well tolerated; there were no serious adverse events or discontinuations due to adverse events.

CONCLUSION

RI increased plasma exposure and similarly decreased clearance of REL, imipenem and cilastatin; IMI/REL dose adjustment (fixed-ratio) will be required for patients with RI. Probenecid had no clinically meaningful impact on the PK of REL or imipenem.

In-hospital Medical Costs of Infections Caused by Carbapenem-resistant Klebsiella pneumoniae

Background

Carbapenem-resistant Klebsiella pneumoniae (CRKP) is a major health threat, but the economic impact of carbapenem resistance in K. pneumoniae infections remains largely uninvestigated.

Methods

We constructed a retrospective cohort of all patients hospitalized at West China Hospital in 2017 who had CRKP- or carbapenem-susceptible K. pneumoniae (CSKP)-positive clinical samples. Propensity score matching (PSM) was used to control the impact of potential confounding variables, including demographics, comorbidities, and treatment, and to observe the impact of factors other than length of stay (LOS). Patients who survived were subjected to subgroup analyses stratified by infection type.

Results

There were 267 patients with CRKP and 1328 with CSKP. Patients with CRKP had a higher crude in-hospital mortality rate (14.61% vs 5.65%, P < .05) and longer LOS (median, 31 vs 19 days; P < .05). PSM for demographics, comorbidities, and treatment generated 237 pairs. Patients with CRKP had higher medical costs than those with CSKP during the entire hospitalization (median, in US dollars, $22962 vs $11755, respectively; P < .05) and during the period after infection (median, $9215 vs $6904, respectively; P < .05). When LOS was matched, patients with CRKP still had high excess costs compared to those with CSKP (median, $22917 vs $13851, respectively, for the entire hospitalization, P < .05; $9101 vs $7001, respectively, after infection, P < .05). For infection type, the sample size generated sufficient power to compare only the patients with pneumonia. For surviving patients, high excess costs were observed in those with pneumonia caused by CRKP as compared to CSKP ($21890 vs $11698, respectively, for the entire hospitalization, P < .05; $9773 vs $5298, respectively, after infection, P < .05). Medicines other than antibacterial agents and nonmedicinal therapies contributed most (57.8%) of the excess costs associated with CRKP.

Conclusions

Carbapenem resistance in K. pneumoniae was associated with increased medical costs not accounted for by the cost of antimicrobial therapy.

In vitro activity of ceftolozane-tazobactam and ceftazidime-avibactam against clinical isolates of meropenem-non-susceptible Pseudomonas aeruginosa: A two-centre study

OBJECTIVES

This study aimed to compare the activity of ceftazidime-avibactam (C/A), ceftolozane-tazobactam (C/T) and three anti-pseudomonal β-lactams (piperacillin-tazobactam, ceftazidime and cefepime) against a collection of meropenem-non-susceptible Pseudomonas aeruginosa (P. aeruginosa) clinical isolates recovered from two centres in Turkey.

METHODS

A total of 102 unique patient isolates of meropenem-non-susceptible P. aeruginosa were included in the study. MICs of antimicrobials were determined by the gradient diffusion method.

RESULTS

Overall susceptibility rates for C/A and C/T were 83.3% and 82.4%, respectively. Both C/A and C/T had better activity than any one of the three anti-pseudomonal β-lactams. According to the MIC₅₀ values, C/T was the most potent agent against isolates. Although the susceptibility rates of isolates to C/T and C/A were similar, C/T (MIC₅₀, 1 μg/mL) was four-fold more potent than C/A (MIC₅₀, 4 μg/mL). The MIC₅₀ values of C/A and C/T for the isolates that were non-susceptible to three β-lactams were significantly higher than those for isolates that were non-susceptible to zero, one or two β-lactams. Also, the C/A MIC₅₀ value for the isolates that were non-susceptible to two β-lactams was higher than that for isolates which were non-susceptible to one β-lactam.

CONCLUSIONS

C/A and C/T showed good activity against meropenem-non-susceptible P. aeruginosa isolates. However, resistance to these agents was not uncommon among these isolates. The overall β-lactam susceptibility profile of isolates seems to have an effect on the probability of susceptibility to C/A and C/T. Antimicrobial susceptibility testing should be performed for C/A and C/T if these agents are considered for treatment of infections caused by meropenem-non-susceptible P. aeruginosa.

Economic burden of antibiotic resistance in ESKAPE organisms: a systematic review

Background

Antibiotic resistance (ABR) is one of the biggest threats to global health. Infections by ESKAPE (Enterococcus, S. aureus, K. pneumoniae, A. baumannii, P. aeruginosa, and E. coli) organisms are the leading cause of healthcare-acquired infections worldwide. ABR in ESKAPE organisms is usually associated with significant higher morbidity, mortality, as well as economic burden. Directing attention towards the ESKAPE organisms can help us to better combat the wide challenge of ABR, especially multi-drug resistance (MDR).

Objective

This study aims to systematically review and evaluate the evidence of the economic consequences of ABR or MDR ESKAPE organisms compared with susceptible cases or control patients without infection/colonization in order to determine the impact of ABR on economic burden.

Methods

Both English-language databases and Chinese-language databases up to 16 January, 2019 were searched to identify relevant studies assessing the economic burden of ABR. Studies reported hospital costs (charges) or antibiotic cost during the entire hospitalization and during the period before/after culture among patients with ABR or MDR ESKAPE organisms were included. The costs were converted into 2015 United States Dollars. Disagreements were resolved by a third reviewer.

Results

Of 13,693 studies identified, 83 eligible studies were included in our review. The most studied organism was S. aureus, followed by Enterococcus, A. baumannii, E. coli, E. coli or/and K. pneumoniae, P. aeruginosa, and K. pneumoniae. There were 71 studies on total hospital cost or charge, 12 on antibiotic cost, 11 on hospital cost or charge after culture, 4 on ICU cost, 2 on hospital cost or charge before culture, and 2 on total direct and indirect cost. In general, ABR or MDR ESKAPE organisms are significantly associated with higher economic burden than those with susceptible organisms or those without infection or colonization. Nonetheless, there were no differences in a few studies between the two groups on total hospital cost or charge (16 studies), antibiotic cost (one study), hospital cost before culture (one study), hospital cost after culture (one study). Even, one reported that costs associated with MSSA infection were higher than the costs for similar MRSA cases.

Conclusions

ABR in ESKAPE organisms is not always, but usually, associated with significantly higher economic burden. The results without significant differences may lack statistical power to detect a significant association. In addition, study design which controls for severity of illness and same empirical antibiotic therapy in the two groups would be expected to bias the study towards a similar, even negative result. The review also highlights key areas where further research is needed.

Carbapenem-resistant Pseudomonas aeruginosa and carbapenem use in Japan: an ecological study

Objective

This study focused on carbapenem resistance in Pseudomonas aeruginosa and examined potential ecological correlations with carbapenem use in Japan.

Methods

The proportion of carbapenem-resistant P. aeruginosa isolates from 2015 and 2016 by prefecture was obtained from the Japan Nosocomial Infections Surveillance system. Data on carbapenem use was obtained from the National Database of Health Insurance Claims. The correlation between the proportion of carbapenem-resistant isolates and carbapenem consumption was assessed in a cross-sectional manner. The study also collected information on other variables including the numbers of physicians, nurses and medical facilities per 100 000 individuals by prefecture.

Results

Both the proportion of carbapenem-resistant P. aeruginosa isolates and levels of carbapenem use were higher in western Japan. Using a multivariate model, only carbapenem use remained significantly associated with the proportion of carbapenem-resistant isolates.

Conclusions

Carbapenem use and the proportion of carbapenem-resistant P. aeruginosa isolates were positively correlated. By longitudinal data collection, this approach offers an avenue to establish causal links as the frequency of carbapenem-resistant P. aeruginosa isolates starts to change in the future.

Incremental clinical and economic burden of suspected respiratory infections due to multi-drug-resistant Pseudomonas aeruginosa in the United States

BACKGROUND

Multi-drug resistant (MDR) Pseudomonas aeruginosa can negatively affect patients and hospitals.

AIM

To evaluate excess mortality and cost burden among patients hospitalized with suspected respiratory infections due to MDR P. aeruginosa vs patients with non-MDR P. aeruginosa in 78 United States (US) hospitals.

METHODS

This study analyzed electronically captured microbiological and outcomes data of patients hospitalized with non-duplicate P. aeruginosa isolates from respiratory sources collected ≥3 days after admission to identify hospital-onset MDR or non-MDR P. aeruginosa per the Centers for Disease Control and Prevention definition. The risk of multi-drug resistance was estimated on mortality, length of stay (LOS), cost, operation gain/loss, and 30-day readmission. A sensitivity analysis was conducted utilizing a cohort with pharmacy data available.

FINDINGS

Of 523 MDR and 1381 non-MDR P. aeruginosa cases, unadjusted mortality was 23.7% vs 18.0% and multi-variable-adjusted mortality was 20.0% (95% confidence interval (CI): 14.3-27.2%) vs 15.5% (95% CI: 11.2-20.9%; P=0.026), the average adjusted excess LOS was 6.7 days (P<0.001); excess cost per case was US$22,370 higher (P=0.002) and operational loss per case was US$10,661 (P=0.024) greater, and the multi-variable adjusted readmission rate was 16.2% (95% CI: 11.2-22.9%) vs 11.1% (95% CI: 7.8-15.6%; P=0.006). The sensitivity analysis yielded similar results.

CONCLUSIONS

Compared with suspected infections due to non-MDR P. aeruginosa, patients with MDR P. aeruginosa had higher risk of mortality, readmission, and longer LOS, as well as US$20,000 incremental cost and >US$10,000 incremental net loss per case after controlling for patient and hospital characteristics.

The impact of carbapenem-resistant Pseudomonas aeruginosa on clinical and economic outcomes in a Chinese tertiary care hospital: A propensity score-matched analysis

BACKGROUND

This study aimed to estimate the impact of carbapenem-resistant Pseudomonas aeruginosa (CRPA) on clinical and economic outcomes in a Chinese tertiary care hospital.

METHODS

Patients were assigned to a carbapenem-susceptible P aeruginosa group or to a CRPA group and matched using propensity score matching. In-hospital mortality, length of stay (LOS), LOS after culture, total hospital costs, daily hospital cost, and 30-day readmission were comparatively analyzed. Subgroup analysis was performed to determine the associations between the subgrouping factors and in-hospital mortality in patients with CRPA isolates.

RESULTS

Within the propensity-matched cohort, in-hospital mortality (12.6% vs 7.8%; P   =   .044), LOS (median 29.0 vs 25.5 days; P   =   .026), LOS after culture (median 18.5 vs 14.0 days; P   =   .029), total hospital costs (median $6,082.0 vs $4,954.2; P  =  .015), and daily hospital cost (median $236.1 vs $223.6; P  =  .045) were significantly higher in CRPA patients than in carbapenem-susceptible P aeruginosa patients. Subgroup analysis revealed a significant interaction between CRPA and age (P  =  .009).

CONCLUSION

Prevention and control of CRPA among hospitalized patients, especially among those over the age of 65 years, is a good measurement for the reduction of mortality and medical costs derived from CRPA infection or colonization.

Epidemiology and antibiotic resistance trends in clinical isolates of Pseudomonas aeruginosa from Rio de janeiro - Brazil: Importance of mutational mechanisms over the years (1995-2015)

Pseudomonas aeruginosa is a major health concern globally and treating infections caused by MDR-isolates unarguably a humongous challenge that remains an unmet need in modern medicine. To determine patterns and mechanisms of antimicrobial resistance and its spread over the years in Rio de Janeiro, Brazil, 88 P. aeruginosa isolates were selected from 1995 to 2015. Phenotypic and genotypic characterization of antimicrobial resistance was evaluated and isolates were submitted to clonality by PFGE and MLST. PFGE analysis showed a great variability of clonal groups mainly over the past 10 years of this study. STs predominant in the early years (ST804, ST1860, ST487 and ST1602) associated to multidrug resistance (MDR) phenotype were replaced by ST277, ST244, ST1945, ST1791 with extensive drug resistance (XDR) in last years, with significant increase in resistance to carbapenems, fluoroquinolones and aminoglycosides. Colistin resistance was detected in 3.5%. The main mechanisms of antimicrobial resistance were mutational mechanisms (mutations in oprD, mexT and gyrA genes). We found the ESBL genes bla_TEM (n = 2), bla_SHV (n = 3) and bla_CTX (n = 1).The carbapenemases genes was present in ST277 (bla_SPM, n = 3), ST1560 (bla_KPC, n = 3) and ST1944 (bla_KPC, n = 2). The 16S RNA methylase gene (rmtD) was found in five isolates belonged to ST277. In conclusion, molecular epidemiological investigation reveals an increase of antimicrobial resistance in P. aeruginosa over 21 years in Rio de Janeiro with higher population structure and occurrence of high risk clone in the last years. The mutational mechanisms of resistance were present in all XDR isolates.

Study of Antibiotic Sensitivity and Resistance Pattern of Bacterial Isolates in Intensive Care Unit Setup of a Tertiary Care Hospital

Objective

To evaluate the antibiotic sensitivity and resistance pattern in an intensive care unit (ICU) setting of a tertiary care hospital.

Materials and methods

A cross-sectional, retrospective study was conducted for a period of 1 month in October 2017 on a total of 195 patients who were admitted to ICU of tertiary care hospital. The culture and sensitivity pattern of clinical isolates from blood, urine, sputum, endotracheal tube (ET) aspirate, catheter sites, and wound swabs were analyzed. Positive cultures were segregated and their antibiotic sensitivity testing was performed under the guidelines of clinical and laboratory standard institute (CLSI).

Results

Of the total 195 ICU admissions, cultures were sent for 167 cases. Of which 127 patients were culture positive and 40 cases were culture negative. Isolated bacteria were mostly gram-negative bacilli, of which Escherichia coli was (18.6%), Acinetobacter (14.5%), Klebsiella (11.6%), Pseudomonas (9.8%), and Proteus (1.74%). Among the gram-positive organisms, coagulase negative staphylococcus (CoNS) (15.6%) was most commonly isolated followed by Streptococcus (2.32%). Fungal growth was also seen in 26 (15.11%) samples. Samples that grew organisms were blood (n = 48), sputum (n = 17), urine (n = 39), ET aspirate (n = 40), pus (n = 11), catheter (n = 4), ear swab (n = 2), and stool (n = 1).

Conclusion

Gram-negative bacterial infections are increasing in ICUs, leading to inappropriate selection of antibiotics. Hence, antibiotic sensitivity and resistance pattern in a hospital setup has to be studied so as to guide the treating consultant to initiate empirical antibiotics in critical cases.

How to cite this article

Savanur SS, Gururaj H. Study of Antibiotic Sensitivity and Resistance Pattern of Bacterial Isolates in Intensive Care Unit Setup of a Tertiary Care Hospital. Indian J Crit Care Med 2019;23(12):547–555.

Outcomes of empiric aminoglycoside monotherapy for Pseudomonas aeruginosa bacteremia

We evaluated 30-day mortality in patients with Pseudomonas aeruginosa bacteremia. There was no significant difference in mortality among patients who received functional aminoglycoside monotherapy versus inappropriate empiric therapy. Among patients given appropriate empiric therapy, functional aminoglycoside monotherapy was associated with less favorable outcomes compared to beta-lactam monotherapy.

Development and Assessment of Risk Scores for Carbapenem and Extensive β-Lactam Resistance Among Adult Hospitalized Patients With Pseudomonas aeruginosa Infection

IMPORTANCE

Treatment of patients with infections due to Pseudomonas aeruginosa has been complicated by increased antibiotic resistance rates, which contribute to delayed appropriate treatment and deleterious outcomes.

OBJECTIVE

To develop 2 clinical risk scores based on variables available at clinical presentation to estimate the risk of carbapenem resistance (CR) or extensive β-lactam resistance (EBR) among hospitalized, adult patients with P aeruginosa infections.

DESIGN, SETTING, AND PARTICIPANTS

This retrospective cohort study included adult (age, ≥18 years) members of Kaiser Permanente Southern California (KPSC) with a P aeruginosa infection during hospitalization from September 1, 2011, through August 31, 2016, who received antibiotic therapy within 2 days of the culture date. Data were analyzed from July 2, 2017, through August 15, 2018.

EXPOSURES

Demographic, clinical, and laboratory covariates 1 year before the index culture date were evaluated.

MAIN OUTCOMES AND MEASURES

Pseudomonas aeruginosa was categorized as antibiotic susceptible, CR, or EBR (nonsusceptibility to carbapenems, ceftazidime, and combined piperacillin sodium and tazobactam sodium). Patients were randomly split (1:1) into training and validation data sets. The training data set was used to develop 2 prediction models using high-performance logistic regression with variable selection by Schwarz-Bayesian criterion. The models were translated into risk scores, with risk score points equaling the weighted sums of regression coefficients from the prediction model. The patient's risk was estimated as the inverse logit of the risk score.

RESULTS

Of the 7775 patients with 11 502 P aeruginosa infections included in the analysis, most were male (4308 [55.4%]) and non-Hispanic white (3927 [50.5%]). The mean (SD) age was 70.3 (15.5) years. Among 11 502 P aeruginosa infections, 2324 (20.2%) were CR, 9178 (79.8%) were non-CR, 1033 (9.0%) were EBR, and 10 469 were non-EBR (91.0%). The strongest predictors of resistance in the CR and EBR models were history of CR P aeruginosa infection (odds ratios [ORs], 8.80 [95% CI, 6.74-11.49] and 5.04 [95% CI, 3.88-6.54], respectively), tracheostomy (ORs, 3.49 [95% CI, 2.92-4.16] and 3.13 [95% CI, 2.50-3.91], respectively), and carbapenem use in the prior 30 days (ORs, 4.18 [95% CI, 3.29-5.31] and 2.26 [95% CI, 1.74-2.93], respectively). The models for CR and EBR performed well, with areas under the receiver operating characteristics curve of 0.81 or greater for the training and validation data sets.

CONCLUSIONS AND RELEVANCE

The findings of this study suggest that parsimonious risk scores can aid physicians in appropriate treatment selection during the critical period when P aeruginosa infection is suspected but antibiotic susceptibility results are not yet available.

Rose Bengal-Mediated Photoinactivation of Multidrug Resistant Pseudomonas aeruginosa Is Enhanced in the Presence of Antimicrobial Peptides

Due to the overuse of antibiotics in medicine and food production, and their targeted mechanism of action, an increasing rate in spreading of antibiotic resistance genes has been noticed. This results in inefficient therapy outcomes and higher mortality all over the world. Pseudomonas aeruginosa (carbapenem-resistant) is considered one of the top three critical species according to the World Health Organization’s priority pathogens list. This means that new drugs and/or treatments are needed to tackle infections caused by this bacterium. In this context search for new/alternative approaches that would overcome resistance to classical antimicrobials is of prime importance. The use of antimicrobial photodynamic inactivation (aPDI) and antimicrobial peptides (AMPs) is an efficient strategy to treat localized infections caused by multidrug-resistant P. aeruginosa. In this study, we have treated P. aeruginosa cells photodynamically in the presence and in the absence of AMP (CAMEL or pexiganan). The conditions for aPDI were as follows: rose bengal (RB) as a photosensitizing agent at 1–10 μM concentration, and subsequent irradiation with 514 nm-LED at 23 mW/cm² irradiance. The analysis of cell number after the treatment has shown that the combined action of RB-mediated aPDI and cationic AMPs reduced the number of viable cells below the limit of detection (<1log₁₀ CFU/ml). This was in contrast to no reduction or partial reduction after aPDI or AMP applied separately. Students t-test was applied to test the statistical significance of the results. Noteworthy, our treatment proved to be effective against all 35 clinical isolates of P. aeruginosa tested within this study, including those characterized as multiresistant. Moreover, we demonstrated that such treatment is safe and does not violate the growth dynamics of human keratinocytes (77.3–97.64% survival depending on the concentration of the studied compounds or their mixtures).

Risk factors for hospitalized patients with resistant or multidrug-resistant Pseudomonas aeruginosa infections: a systematic review and meta-analysis

Background

Identifying risk factors predicting acquisition of resistant Pseudomonas aeruginosa will aid surveillance and diagnostic initiatives and can be crucial in early and appropriate antibiotic therapy. We conducted a systematic review examining risk factors of acquisition of resistant P. aeruginosa among hospitalized patients.

Methods

MEDLINE®, EMBASE®, and Cochrane Central were searched between 2000 and 2016 for studies examining independent risk factors associated with acquisition of resistant P. aeruginosa, among hospitalized patients. Random effects model meta-analysis was conducted when at least three or more studies were sufficiently similar.

Results

Of the 54 eligible articles, 28 publications (31studies) examined multi-drug resistant (MDR) or extensively drug resistant (XDR) P. aeruginosa and 26 publications (29 studies) examined resistant P. aeruginosa. The acquisition of MDR P. aeruginosa, as compared with non-MDR P. aeruginosa, was significantly associated with intensive care unit (ICU) admission (3 studies: summary adjusted odds ratio [OR] 2.2) or use of quinolones (4 studies: summary adjusted OR 3.59). Acquisition of MDR or XDR compared with susceptible P. aeruginosa was significantly associated with prior hospital stay (4 studies: summary adjusted OR 1.90), use of quinolones (3 studies: summary adjusted OR 4.34), or use of carbapenems (3 studies: summary adjusted OR 13.68). The acquisition of MDR P. aeruginosa compared with non-P. aeruginosa was significantly associated with prior use of cephalosporins (3 studies: summary adjusted OR 3.96), quinolones (4 studies: summary adjusted OR 2.96), carbapenems (6 studies: summary adjusted OR 2.61), and prior hospital stay (4 studies: summary adjusted OR 1.74). The acquisition of carbapenem-resistant P. aeruginosa compared with susceptible P. aeruginosa, was statistically significantly associated with prior use of piperacillin-tazobactam (3 studies: summary adjusted OR 2.64), vancomycin (3 studies: summary adjusted OR 1.76), and carbapenems (7 studies: summary adjusted OR 4.36).

Conclusions

Prior use of antibiotics and prior hospital or ICU stay was the most significant risk factors for acquisition of resistant P. aeruginosa. These findings provide guidance in identifying patients that may be at an elevated risk for a resistant infection and emphasize the importance of antimicrobial stewardship and infection control in hospitals.

Importance of control groups when delineating antibiotic use as a risk factor for carbapenem resistance, extreme-drug resistance, and pan-drug resistance in Acinetobacter baumannii and Pseudomonas aeruginosa: A systematic review and meta-analysis

BACKGROUND

Carbapenem-resistant (CR), extremely drug-resistant (XDR), and pan-drug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa pose a huge clinical threat. This study reviews the impact of control groups on the association of antecedent antibiotic use and the acquisition of CR/XDR/PDR A. baumannii and P. aeruginosa.

METHODS

Studies investigating the role of antibiotics as a risk factor for CR/XDR/PDR A. baumannii and P. aeruginosa acquisition in adult hospitalized patients from 1950 to 2016 were identified in the databases. These were divided into two groups: antibiotic-resistant versus antibiotic-sensitive pathogens (group I); antibiotic-resistant versus no infection (group II). A random-effects model was performed.

RESULTS

Eighty-five studies (46 A. baumannii, 38 P. aeruginosa, and one of both) involving 22 396 patients were included. CR was investigated in 60 studies, XDR in 20 studies, and PDR in two studies. Prior antibiotic exposure was associated with significant acquisition of CR/XDR/PDR A. baumannii and P. aeruginosa in both groups I and II (p<0.05). Antibiotic classes implicated in both groups included aminoglycosides, carbapenems, glycopeptides, and penicillins. Cephalosporin use was not associated with resistance in either group. Fluoroquinolone exposure was only associated with resistance in group I but not group II.

CONCLUSIONS

Control groups play an important role in determining the magnitudes of risk estimates for risk factor studies, hence careful selection is necessary. Antibiotic exposure increases the acquisition of highly resistant A. baumannii and P. aeruginosa, thus appropriate antibiotic use is imperative.

Comparative Study of Drainage and Antibiotics versus Drainage Only in the Management of Primary Subcutaneous Abscesses

BACKGROUND

Skin and soft tissue infections are common problems dealt with in emergency departments and medical offices. It is routine practice to prescribe antibiotic agents after incision and drainage of cutaneous abscesses. However, current evidence does not support prescribing oral antibiotic agents after surgical debridement. The aim of the present study was to determine the actual role of antibiotic agents after drainage of cutaneous abscesses.

PATIENTS AND METHODS

This was a prospective study of patients undergoing incision and drainage (I&D) of a subcutaneous abscess. Patients were randomly assigned either to receive antibiotic agents (group 1) or placebo (group 2) after I&D. The primary end point was resolution rate of the abscess at the seventh day. Secondary end points were pain at the seventh day and total time to full healing of the wound. P value <0.05 was considered statistically significant.

RESULTS

One hundred sixty-five patients were included for analysis. Age, gender, body mass index (BMI), and comorbidities did not differ substantially between groups. Chest and peri-anal abscesses were statistically more frequent in group 2, whereas neck abscesses were more frequent in group 1 (p = 0.02). Leukocyte count was also statistically higher in group 1 (p = 0.005). Resolution rate was 96% in group 1 and 93% in group 2, with no statistical difference between both (p = 0.28). Neither pain at seventh day nor time to full healing differed statistically between groups.

CONCLUSIONS

Antibiotic agents are not necessary for uncomplicated subcutaneous abscesses after I&D. These cases can be managed safely on an outpatient basis without any increase in morbidity.

High excess costs of infections caused by carbapenem-resistant Gram-negative bacilli in an endemic region

The financial burden of antibiotic resistance is a serious concern worldwide. The aim of this study was to describe the excess costs associated with pneumonia, bacteraemia, surgical site infections and intra-abdominal infections (IAIs) caused by carbapenem-resistant Gram-negative bacilli in Medellín, Colombia, an endemic region for carbapenem resistance. A cohort study was conducted in a third-level hospital from 2014-2015. All patients with carbapenem-resistant and carbapenem-susceptible Gram-negative bacterial infections were included. Pharmaceutical, medical and surgical direct costs were described from the health system perspective. Excess costs were estimated from generalised linear models with gamma distribution and adjusted for variables that could affect the cost difference. A total of 218 patients were enrolled, 48 (22.0%) of whom were infected with carbapenem-resistant bacteria. IAIs were the most frequent. The adjusted total excess cost was US$3966 [95% confidence interval (CI) US$1684-6249], with a significantly higher cost for antibiotics, followed by hospital stay, laboratory tests and interconsultation. The highest excess cost was attributed mainly to the use of broad-spectrum antibiotics (US$1827, 95% CI US$1005-2648), followed by length of hospital stay (US$1015, 95% CI US$163-1867). The results of this study highlight the importance of designing antimicrobial stewardship programmes and infection control strategies in endemic regions to reduce the financial threat of antimicrobial resistance to health systems.

The impact of carbapenem resistance on clinical deterioration and mortality in patients with liver disease

BACKGROUND & AIMS

Infections with multidrug-resistant gram-negative bacteria are significantly impairing the prognosis of patients with liver disease. In particular, carbapenem resistance further narrows therapeutic options. This study investigates the impact of carbapenem-resistant gram-negative bacteria on the outcome of patients with liver disease and cirrhosis.

METHODS

Between January 2011 and July 2015, 132 patients treated at the tertiary liver transplant centre at University Hospital Frankfurt, Germany, were tested positive for carbapenem-resistant gram-negative bacteria and retrospectively analysed in this study. Risk factors for fatal outcome were evaluated using multivariate regression analysis. Competing-risk analysis was performed on patients tested positive for Enterobacteriaceae or non-fermenting species, for example, Pseudomonas aeruginosa, Acinetobacter baumannii, Stenotrophomonas maltophilia. Subgroup analysis of cirrhotic patients was performed on a matched cohort of cirrhotic patients, comparable model for end-stage liver disease and tested negative for carbapenem-resistant gram-negative bacteria.

RESULTS

97 (73.5%) and 35 (26.5%) patients were infected or colonised with carbapenem-resistant gram-negative bacteria respectively. Within the observation period, 61/132 (46.2%) patients died, with sepsis being the leading cause (38/61, 62.3%). Decompensated liver disease, sepsis and admission to intensive care unit were independent risk factors for fatal outcome. Lethal sepsis in patients positive for non-fermenting bacteria was significantly more frequent than in those positive for Enterobacteriaceae, independently from liver function. Subgroup analysis of cirrhotic patients showed that sepsis (54.9% vs 13%) and lethal sepsis were significantly more frequent after detection of carbapenem-resistant gram-negative bacteria, independently from localisation of pathogen detection.

CONCLUSIONS

Patients with advanced liver disease are prone to fatal infections caused by carbapenem-resistant gram-negative bacteria.

Isolation and characterization of a bacteriophage and its utilization against multi-drug resistant Pseudomonas aeruginosa-2995

AIMS

To identify, isolate, and characterize a lytic bacteriophage against the multiple-drug resistant clinical strain of Pseudomonas aeruginosa-2995 and to determine the phage efficacy against the bacterial planktonic cells and the biofilm.

MAIN METHODS

Wastewater was used to isolate a bacteriophage. The phage was characterized with Transmission electron microscopy (TEM). Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) was used to identify the expressed proteins. Bacteria were cultured in both suspension and biofilm to check and compare their susceptibility to phage lytic action. The activity of the phage (determined as AZ1) was determined against P. aeruginosa-2995 in both planktonic cells and the biofilm.

KEY FINDINGS

A bacteriophage, designated as AZ1, was isolated from waste water showing a narrow host range. AZ1 was characterized by TEM and could be identified as an isolate in the family Siphoviridae [order Caudovirals]. Seventeen structural proteins ranging from about 12 to 110kDa were found through SDS-PAGE analysis. Its genome was confirmed as dsDNA with a length of approx. 50kb. The log-phase growth of P. aeruginosa-2995 was significantly reduced after treatment with AZ1 (4.50×10⁸ to 2.1×10³CFU/ml) as compared to control. Furthermore, phage AZ1 significantly reduced 48h old biofilm biomass about 3-fold as compared to control.

SIGNIFICANCE

Pseudomonas aeruginosa is a ubiquitous free-living opportunistic human pathogen characterized by high antibiotic tolerance and tendency for biofilm formation. The phage, identified in this study, AZ1, showed promising activity in the destruction of both planktonic cells and biofilm of P. aeruginosa-2995. However, complete eradication may require a combination of phages.

Systematic review and meta-analysis of imipenem-resistant Pseudomonas aeruginosa prevalence in Iran

INTRODUCTION

Imipenem-resistant Pseudomonas aeruginosa (IRPA), due to resistance to different classes of antibiotics and its remarkable capacity to survive in harsh and adverse conditions such as those in the hospital environment, is considered a serious threat to the healthcare system. Given the great impact of IRPA on patients' outcome and in order to possibly improve antibiotic prescription, this study was conducted to determine the prevalence of clinical isolates of IRPA in different parts of Iran.

METHODS

A systematic literature search was performed in PubMed, Web of Science, Google Scholar and Scopus, as well as in two Iranian domestic search engines, i.e., Iranian Scientific Information Database and Magiran. Finally, after applying exclusion and inclusion criteria 37 articles with full-texts describing the prevalence of imipenem-resistant P. aeruginosa were selected for meta-analysis and systematic review.

RESULTS

The pooled estimation of 5227 P. aeruginosa isolates in this analysis showed that the percentage of imipenem-resistant P. aeruginosa is about 54% in the Iranian population (95%CI: 0.47-0.62, logit event rate=0.19, 95%CI: -0.12,0.49).

CONCLUSION

The findings of this analysis show that in the majority of Iranian hospitals the relative frequency of IRPA is high, therefore, in order to prevent further dissemination of IRPA, more appropriate antibiotic prescription and infection control policies must be implemented by decision-makers.

Increased Costs Associated with Bloodstream Infections Caused by Multidrug-Resistant Gram-Negative Bacteria Are Due Primarily to Patients with Hospital-Acquired Infections

The clinical and economic impacts of bloodstream infections (BSI) due to multidrug-resistant (MDR) Gram-negative bacteria are incompletely understood. From 2009 to 2015, all adult inpatients with Gram-negative BSI at our institution were prospectively enrolled. MDR status was defined as resistance to ≥3 antibiotic classes. Clinical outcomes and inpatient costs associated with the MDR phenotype were identified. Among 891 unique patients with Gram-negative BSI, 292 (33%) were infected with MDR bacteria. In an adjusted analysis, only history of Gram-negative infection was associated with MDR BSI versus non-MDR BSI (odds ratio, 1.60; 95% confidence interval [CI], 1.19 to 2.16; P = 0.002). Patients with MDR BSI had increased BSI recurrence (1.7% [5/292] versus 0.2% [1/599]; P = 0.02) and longer hospital stay (median, 10.0 versus 8.0 days; P = 0.0005). Unadjusted rates of in-hospital mortality did not significantly differ between MDR (26.4% [77/292]) and non-MDR (21.7% [130/599]) groups (P = 0.12). Unadjusted mean costs were 1.62 times higher in MDR than in non-MDR BSI ($59,266 versus $36,452; P = 0.003). This finding persisted after adjustment for patient factors and appropriate empirical antibiotic therapy (means ratio, 1.18; 95% CI, 1.03 to 1.36; P = 0.01). Adjusted analysis of patient subpopulations revealed that the increased cost of MDR BSI occurred primarily among patients with hospital-acquired infections (MDR means ratio, 1.41; 95% CI, 1.10 to 1.82; P = 0.008). MDR Gram-negative BSI are associated with recurrent BSI, longer hospital stays, and increased mean inpatient costs. MDR BSI in patients with hospital-acquired infections primarily account for the increased cost.

Multidrug-Resistant Gram-Negative Bacilli: Infection Control Implications

Antimicrobial resistance is a common iatrogenic complication of both modern life and medical care. Certain multidrug resistant and extensively drug resistant Gram-negative organisms pose the biggest challenges to health care today, predominantly owing to a lack of therapeutic options. Containing the spread of these organisms is challenging, and in reality, the application of multiple control measures during an evolving outbreak makes it difficult to measure the relative impact of each measure. This article reviews the usefulness of various infection control measures in containing the spread of multidrug-resistant Gram-negative bacilli.

Antimicrobial Resistance in the Intensive Care Unit

Bacterial infections are a frequent cause of hospitalization, and nosocomial infections are an increasingly common condition, particularly within the acute/critical care setting. Infection control practices and new antimicrobial development have primarily focused on gram-positive bacteria; however, in recent years, the incidence of infections caused by gram-negative bacteria has risen considerably in intensive care units. Infections caused by multidrug-resistant (MDR) gram-negative organisms are associated with high morbidity and mortality, with significant direct and indirect costs resulting from prolonged hospitalizations due to antibiotic treatment failures. Of particular concern is the increasing prevalence of antimicrobial resistance to β-lactam antibiotics (including carbapenems) among Pseudomonas aeruginosa and Acinetobacter baumannii and, recently, among pathogens of the Enterobacteriaceae family. Treatment options for infections caused by these pathogens are limited. Antimicrobial stewardship programs focus on optimizing the appropriate use of currently available antimicrobial agents with the goals of improving outcomes for patients with infections caused by MDR gram-negative organisms, slowing the progression of antimicrobial resistance, and reducing hospital costs. Newly approved treatment options are available, such as β-lactam/β-lactamase inhibitor combinations, which significantly extend the armamentarium against MDR gram-negative bacteria.

Cost Attributable to Nosocomial Bacteremia. Analysis According to Microorganism and Antimicrobial Sensitivity in a University Hospital in Barcelona

AIM

To calculate the incremental cost of nosocomial bacteremia caused by the most common organisms, classified by their antimicrobial susceptibility.

METHODS

We selected patients who developed nosocomial bacteremia caused by Staphylococcus aureus, Escherichia coli, Klebsiella pneumoniae, or Pseudomonas aeruginosa. These microorganisms were analyzed because of their high prevalence and they frequently present multidrug resistance. A control group consisted of patients classified within the same all-patient refined-diagnosis related group without bacteremia. Our hospital has an established cost accounting system (full-costing) that uses activity-based criteria to analyze cost distribution. A logistic regression model was fitted to estimate the probability of developing bacteremia for each admission (propensity score) and was used for propensity score matching adjustment. Subsequently, the propensity score was included in an econometric model to adjust the incremental cost of patients who developed bacteremia, as well as differences in this cost, depending on whether the microorganism was multidrug-resistant or multidrug-sensitive.

RESULTS

A total of 571 admissions with bacteremia matched the inclusion criteria and 82,022 were included in the control group. The mean cost was € 25,891 for admissions with bacteremia and € 6,750 for those without bacteremia. The mean incremental cost was estimated at € 15,151 (CI, € 11,570 to € 18,733). Multidrug-resistant P. aeruginosa bacteremia had the highest mean incremental cost, € 44,709 (CI, € 34,559 to € 54,859). Antimicrobial-susceptible E. coli nosocomial bacteremia had the lowest mean incremental cost, € 10,481 (CI, € 8,752 to € 12,210). Despite their lower cost, episodes of antimicrobial-susceptible E. coli nosocomial bacteremia had a major impact due to their high frequency.

CONCLUSIONS

Adjustment of hospital cost according to the organism causing bacteremia and antibiotic sensitivity could improve prevention strategies and allow their prioritization according to their overall impact and costs. Infection reduction is a strategy to reduce resistance.

Mortality attributable to carbapenem-resistant Pseudomonas aeruginosa bacteremia: a meta-analysis of cohort studies

Whether carbapenem resistance is associated with mortality in patients with Pseudomonas aeruginosa bacteremia is controversial. To address this issue, we conducted a systematic review and meta-analysis based on cohort studies. We searched PubMed and Embase databases to identify articles (up to April 2015). The DerSimonian and Laird random-effect model was used to generate a summary estimate of effect. Associations were evaluated in subgroups based on different patient characteristics and study quality criteria. Seven studies with a total of 1613 patients were finally included, of which 1 study had a prospective design, and the other 6 were retrospective. Our meta-analysis showed patients with carbapenem-resistant P. aeruginosa bacteremia were at a higher risk of death compared with those with carbapenem-susceptible P. aeruginosa bloodstream infections (pooled odds ratio (OR) from three studies reporting adjusted ORs: 3.07, 95% confidence interval (CI), 1.60-5.89; pooled OR from 4 studies only reporting crude ORs: 1.46, 95% CI, 1.10-1.94). The results were robust across a number of stratified analyses and a sensitivity analysis. We also calculated that 8%-18.4% of deaths were attributable to carbapenem resistance in four studies assessing the outcome with 30-day mortality, and these were 3% and 14.6%, respectively, in two studies using 7-day mortality or mortality during bacteremia as an outcome of interest. Carbapenem resistance had a deleterious impact on the mortality of P. aeruginosa bacteremia; however, the results should be interpreted cautiously because only three studies reporting adjusted ORs were included. More large-scale, well-designed prospective cohorts, as well as mechanistic studies, are urgently needed in the future.

Epidemiology and Characteristics of Metallo-β-Lactamase-Producing Pseudomonas aeruginosa

Metallo-β-lactamase-producing Pseudomonas aeruginosa (MPPA) is an important nosocomial pathogen that shows resistance to all β-lactam antibiotics except monobactams. There are various types of metallo-β-lactamases (MBLs) in carbapenem-resistant P. aeruginosa including Imipenemase (IMP), Verona integron-encoded metallo-β-lactamase (VIM), Sao Paulo metallo-β-lactamase (SPM), Germany imipenemase (GIM), New Delhi metallo-β-lactamase (NDM), Florence imipenemase (FIM). Each MBL gene is located on specific genetic elements including integrons, transposons, plasmids, or on the chromosome, in which they carry genes encoding determinants of resistance to carbapenems and other antibiotics, conferring multidrug resistance to P. aeruginosa. In addition, these genetic elements are transferable to other Gram-negative species, increasing the antimicrobial resistance rate and complicating the treatment of infected patients. Therefore, it is essential to understand the epidemiology, resistance mechanism, and molecular characteristics of MPPA for infection control and prevention of a possible global health crisis. Here, we highlight the characteristics of MPPA.

Risk factors and clinical significance of bacteremia caused by Pseudomonas aeruginosa resistant only to carbapenems

BACKGROUND/PURPOSE

Carbapenem-resistant Pseudomonas aeruginosa infections have been a challenge and issue in hospital settings. However, the clinical impact of P. aeruginosa blood isolates resistant only to carbapenems has never been discussed previously.

METHODS

To assess the risk factors and clinical significance of bacteremia caused by carbapenem resistance only P. aeruginosa (CROPA), a 6-year retrospective case-control study was conducted. The CROPA strains were defined as isolates susceptible to ciprofloxacin, antipseudomonal penicillins and cephalosporins, and aminoglycosides but resistant to one antipseudomonal carbapenem (imipenem or meropenem) or both. The controls were selected among patients with bacteremia due to P. aeruginosa susceptible to all above classes of antipseudomonal antibiotics, which was defined as all-susceptible P. aeruginosa.

RESULTS

Twenty-five patients had at least one blood culture positive for CROPA, and 50 controls had all-susceptible P. aeruginosa bacteremia. CROPA bacteremia had a high 30-day mortality rate (72.0%), as compared to 26.0% for the controls (p < 0.001). Through multivariate analysis, carbapenem exposure was the only risk factor for developing CROPA bacteremia (p = 0.002). A comparison between the surviving and deceased patients with CROPA bacteremia showed that nine (50%) of those who died, but none of the survivors, received carbapenems as the initial empirical therapy (p = 0.027).

CONCLUSION

Carbapenem exposure was associated with emergence of CROPA infections. Repeated carbapenem use in such patients might increase rates of inappropriate initial empirical treatment and mortality. Prudent carbapenem use is important to reduce the emergence of CROPA.

Influence of carbapenem resistance on mortality of patients with Pseudomonas aeruginosa infection: a meta-analysis

Treatment of infectious diseases caused by the carbapenem-resistant Pseudomonas aeruginosa (CRPA) is becoming more challenging with each passing year. We conducted a meta-analysis to assess the impact of carbapenem resistance on mortality of patients with P. aeruginosa infection. We searched PUBMED, Web of science, EMBASE, Google Scholar and the Cochrane Library up to December 25, 2014, to identify published cohort or case-control studies. 17 studies, including 6660 patients carrying P. aeruginosa, were identified. The pooling analysis indicated that patients infected with CRPA had significantly higher mortality than those infected with carbapenem-susceptible P. aeruginosa (CSPA) (crude OR = 1.64; 95%CI = 1.40, 1.93; adjusted OR = 2.38; 95%CI = 1.53, 3.69). The elevated risk of mortality in patients with CRPA infection was not lessened when stratified by study design, sites of infection, or type of carbapenem, except that the estimate effect vanished in CRPA high-incidence region, South America (crude OR = 1.12; 95%CI = 0.64, 1.99). Begg's (z = 0.95, p = 0.34) and Egger's test (t = 1.23, p = 0.24) showed no evidence of publication bias. Our results suggest that carbapenem resistance may increase the mortality of patients with P. aeruginosa infection, whether under univariate or multivariate analysis.

Healthcare utilization and costs associated with S. aureus and P. aeruginosa pneumonia in the intensive care unit: a retrospective observational cohort study in a US claims database

BACKGROUND

Staphylococcus aureus and Pseudomonas aeruginosa are major causes of pneumonia in intensive care unit (ICU) patients. Limited data exist regarding the health economic impact of S. aureus and P. aeruginosa pneumonias in the ICU setting.

METHODS

We conducted a retrospective observational cohort study using a 29.6 million enrollee US medical and pharmacy administrative claims database. ICU patients with S. aureus or P. aeruginosa infection per International Classification of Diseases, 9th ed. coding between 01/01/2007-8/31/2012 were compared with ICU patients without any pneumonia or infections of interest. Primary outcomes were costs in 2012 US dollars, healthcare utilization and all-cause mortality associated with hospital-acquired S. aureus or P. aeruginosa pneumonia, and the relative odds of incurring higher costs due to a comorbid condition.

RESULTS

Patients with S. aureus or P. aeruginosa pneumonia had longer mean hospital (37.9 or 55.4 vs 7.2 days, P < .001) and ICU stays (6.9 or 14.8 vs 1.1 days, P < .001), a higher rate of mechanical ventilation (62.6 % or 62.3 % vs 7.4 %, P < .001), higher mortality (16.0 % or 20.2 % vs 3.1 %, P < .001), and higher total mean hospitalization costs ($146,978 or $213,104 vs $33,851, P < .001) vs controls. Pneumonia survivors had significantly increased risk of rehospitalization within 30 days (27.2 % or 31.1 % vs 15.3 %, P < .001). Comorbid conditions were not associated with increased cost in the pneumonia cohorts.

CONCLUSIONS

Healthcare costs and resource utilization were high among ICU patients with S. aureus or P. aeruginosa pneumonia. Reducing the incidence of these infections could lead to substantial cost savings in the United States.

Acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill medical patients: role of colonization pressure and antibiotic exposure

INTRODUCTION

The objective of this work was to investigate the risk factors for the acquisition of Pseudomonas aeruginosa and its resistance phenotypes in critically ill patients, taking into account colonization pressure.

METHODS

We conducted a prospective cohort study in an 8-bed medical intensive care unit during a 35-month period. Nasopharyngeal and rectal swabs and respiratory secretions were obtained within 48 hours of admission and thrice weekly thereafter. During the study, a policy of consecutive mixing and cycling periods of three classes of antipseudomonal antibiotics was followed in the unit.

RESULTS

Of 850 patients admitted for ≥ 3 days, 751 (88.3%) received an antibiotic, 562 of which (66.1%) were antipseudomonal antibiotics. A total of 68 patients (8%) carried P. aeruginosa upon admission, and among the remaining 782, 104 (13%) acquired at least one strain of P. aeruginosa during their stay. Multivariate analysis selected shock (odds ratio (OR) = 2.1; 95% confidence interval (CI), 1.2 to 3.7), intubation (OR = 3.6; 95% CI, 1.7 to 7.5), enteral nutrition (OR = 3.6; 95% CI, 1.8 to 7.6), parenteral nutrition (OR = 3.9; 95% CI, 1.6 to 9.6), tracheostomy (OR = 4.4; 95% CI, 2.3 to 8.3) and colonization pressure >0.43 (OR = 4; 95% CI, 1.2 to 5) as independently associated with the acquisition of P. aeruginosa, whereas exposure to fluoroquinolones for >3 days (OR = 0.4; 95% CI, 0.2 to 0.8) was protective. In the whole series, prior exposure to carbapenems was independently associated with carbapenem resistance, and prior amikacin use predicted piperacillin-tazobactam, fluoroquinolone and multiple-drug resistance.

CONCLUSIONS

In critical care settings with a high rate of antibiotic use, colonization pressure and non-antibiotic exposures may be the crucial factors for P. aeruginosa acquisition, whereas fluoroquinolones may actually decrease its likelihood. For the acquisition of strains resistant to piperacillin-tazobactam, fluoroquinolones and multiple drugs, exposure to amikacin may be more relevant than previously recognized.

Impact of combination antimicrobial therapy on mortality risk for critically ill patients with carbapenem-resistant bacteremia

There are limited treatment options for carbapenem-resistant Gram-negative infections. Currently, there are suggestions in the literature that combination therapy should be used, which frequently includes antibiotics to which the causative pathogen demonstrates in vitro resistance. This case-control study evaluated risk factors associated with all-cause mortality rates for critically ill patients with carbapenem-resistant Gram-negative bacteremia. Adult patients who were admitted to an intensive care unit with sepsis and a blood culture positive for Gram-negative bacteria resistant to a carbapenem were included. Patients with polymicrobial, recurrent, or breakthrough infections were excluded. Included patients were classified as survivors (controls) or nonsurvivors (cases) at 30 days after the positive blood culture. Of 302 patients screened, 168 patients were included, of whom 90 patients died (53.6% [cases]) and 78 survived (46.4% [controls]) at 30 days. More survivors received appropriate antibiotics (antibiotics with in vitro activity) than did nonsurvivors (93.6% versus 53.3%; P < 0.01). Combination therapy, defined as multiple appropriate agents given for 48 h or more, was more common among survivors than nonsurvivors (32.1% versus 7.8%; P < 0.01); however, there was no difference in multiple-agent use when in vitro activity was not considered (including combinations with carbapenems) (87.2% versus 80%; P = 0.21). After adjustment for baseline factors with multivariable logistic regression, combination therapy was independently associated with decreased risk of death (odds ratio, 0.19 [95% confidence interval, 0.06 to 0.56]; P < 0.01). These data suggest that combination therapy with multiple agents with in vitro activity is associated with improved survival rates for critically ill patients with carbapenem-resistant Gram-negative bacteremia. However, that association is lost if in vitro activity is not considered.

In vitro activity of fosfomycin in combination with colistin against clinical isolates of carbapenem-resistant Pseudomas aeruginosa

The shortage of effective antibiotics against carbapenem-resistant Pseudomonas aeruginosa (CRPA) poses a public health threat. Combination treatment may represent a good choice for treating infections caused by CRPA. The aim of this study was to evaluate the in vitro efficacy of fosfomycin in combination with colistin against clinical CRPA isolates. Eighty-seven isolates were collected from three hospitals in China. The checkerboard method and time-kill assay were used to assess the interactions between fosfomycin and colistin. The fosfomycin/colistin combination displayed synergistic and partial synergistic activity against 21.84% and 27.59% of the isolates, respectively. Antagonism was not observed. In combination, the colistin MIC values were ⩽0.5 μg ml(-1) for 91.95% of the isolates. This result differed significantly from those obtained using a single agent treatment (The colistin MIC values were ⩽0.5 μg ml(-1) for only 25.29% of the isolates). In addition, the time-kill assay demonstrated that the fosfomycin/colistin combination treatment exerted bactericidal effects against five isolates and that the regrowth observed after colistin monotherapy was prevented. In summary, the combination of fosfomycin and colistin demonstrated synergistic activity against the CRPA isolates tested in this study. Furthermore, fosfomycin may potentially widen the therapeutic window of colistin, suggesting that this combination could be applied clinically to control infections caused by CRPA.