Impact of Antibiotic-Resistant Bacteria on the Outcome of Ventilator-Associated Pneumonia

Risk factors for slowly resolving pneumonia in the intensive care unit

BACKGROUND

Slowly resolving pneumonia (SRP) poses early challenges for identification and medical expense for clinicians in intensive care units (ICUs); to date, the literature has been very limited in this regard.

METHODS

This was a retrospective and cohort-based study in the ICU of a university-affiliated hospital in Shanghai. Medical records of pneumonia patients in the ICU between April 2008 and February 2011were reviewed retrospectively to evaluate the risk factors for SRP.

RESULTS

In all, 106 pneumonia patients in the ICU were identified as immune-competent with a diagnosis of bacterial pneumonia. There were 62 (58.49%) patients who showed SRP and their radiographic infiltrations were completely resolved between 5 weeks and 8 weeks. Multivariate logistic regression analysis demonstrated that initial treatment with an inappropriate antibiotic, multilobar infiltration, and a high CURB-65 score were independent risk factors for SRP, with odds ratio (OR) values of 8.338 [95% confidence interval (CI) 2.117-32.848], 11.184 (95% CI 2.526-49.514), and 2.329 (95% CI 1.172-4.626), respectively. The length of the ICU stay in the SRP group was twice as long as that of the normally resolving pneumonia (NRP) group (62.27 ± 73.73 vs. 32.25 ± 23, p = 0.002). The 28-day and 60-day mortality rates in the SRP group were 17.74% and 25.81%, respectively. In addition, the 60-day mortality rate was significantly higher in the SRP group than the NRP group (25.81% vs. 6.82%, respectively; p = 0.012). Moreover, SRP was an independent risk factor for 60-day mortality (OR 5.687, 95% CI 1.334-24.240).

CONCLUSION

Treatment with an inappropriate antibiotic, multilobar infiltration, and a high CURB-65 score were independent risk factors for SRP.

Drug-resistant ventilator associated pneumonia in a tertiary care hospital in Saudi Arabia

BACKGROUND:

There is a wide geographic and temporal variability of bacterial resistance among microbial causes of ventilator-associated pneumonia (VAP). The contribution of multi-drug resistant (MDR) pathogens to the VAP etiology in Saudi Arabia was never studied. We sought to examine the extent of multiple-drug resistance among common microbial causes of VAP.

MATERIALS AND METHODS:

We conducted a retrospective susceptibility study in the adult intensive care unit (ICU) of King Abdulaziz Medical City, Riyadh, Saudi Arabia. Susceptibility results of isolates from patients diagnosed with VAP between October 2004 and June 2009 were examined. The US National Healthcare Safety Network definition of MDR was adopted.

RESULTS:

A total of 248 isolates including 9 different pathogens were included. Acinetobacter spp. was highly (60-89%) resistant to all tested antimicrobials, including carbapenems (three- and four-class MDR prevalence were 86% and 69%, respectively). Pseudomonas aeruginosa was moderately (13-31%) resistant to all tested antimicrobials, including antipseudomonal penicillins (three- and four-class MDR prevalence were 13% and 10%, respectively). With an exception of ampicillin (fully resistant), Klebsiella spp. had low (0-13%) resistance to other tested antimicrobials with no detected MDR. Staphylococcus aureus was fully susceptible to vancomycin with 42% resistance to oxacillin. There were significant increasing trends of MDR Acinetobacter spp. however not P. aeruginosa during the study. Resistant pathogens were associated with worse profile of ICU patients but not patients’ outcomes.

CONCLUSION:

Acinetobacter in the current study was an increasingly resistant VAP-associated pathogen more than seen in many parts of the world. The current finding may impact local choice of initial empiric antibiotics.

Pseudomonas aeruginosa and the host pulmonary immune response

Pseudomonas aeruginosa is a highly adaptable, opportunistic pathogen that is commonly found in the environment. It can infect a number of sites in the body and disseminate. It can cause both acute and chronic pulmonary infection and the acuity of infection and accompanying inflammatory phenotype is determined, for the most part, by the host. Although P. aeruginosa has been a successful opportunist in the context of a number of different disease states, it has been best studied in the context of cystic fibrosis (CF). The adaptability of P. aeruginosa has enabled it to adjust quickly to the CF airway, transitioning from initial colonization to chronic infection. The organism quickly expresses virulence factors that allow it to circumvent some elements of the host immune response and, even more importantly, quickly develops antimicrobial resistance. In the case of CF, chronic infection resulting in progressive lung damage, coupled with antimicrobial resistance, becomes an increasingly important issue as individuals with CF live longer. It is for these reasons that both organism- and host-targeted immunotherapies are being increasingly explored.

Hyperoxia exaggerates bacterial dissemination and lethality in Pseudomonas aeruginosa pneumonia

Effects of hyperoxia on lethality in mice with Pseudomonas aeruginosa pneumonia were defined, and protective roles of macrolides were examined both in vitro and in vivo. Sub-lethal hyperoxia accelerated lethality of mice with P. aeruginosa pneumonia. Bacterial number was not different in the lungs, but higher in the liver of mice in hyperoxic conditions. Filter-sterilized culture supernatants of bacteria induced loss of viability of alveolar epithelial cells, which was exaggerated in hyperoxia. Metalloprotease blocking by inhibitor or gene-disruption in bacteria resulted in partial reduction of cytotoxic activity in culture supernatants. Co-culture of bacteria with sub-inhibitory concentrations of macrolides, such as azithromycin, reduced cytotoxic activity in the culture supernatants. Azithromycin provided significant survival benefit in hyperoxia-pneumonia model, which was associated with suppression of bacterial dissemination to extra-pulmonary organs. These results suggest that hyperoxia serves as an important cofactor for bacterial dissemination and lethality of P. aeruginosa pneumonia. Our data identify the potential of macrolides to protect individuals with P. aeruginosa pneumonia in the setting of hyperoxia.

Impact of multiresistance of gram-negative bacteria in bloodstream infection on mortality rates and length of stay

BACKGROUND

Bloodstream infections (BSI) with gram-negative bacteria (GNB) are one of the most serious infections in the hospital setting, a situation compounded by the increasing antibiotic resistance of gram-negative bacteria causing BSI. The aim of the study was to assess the impact of antibiotic multiresistance of GNB in BSI on mortality rates and length of stay (LOS).

MATERIALS AND METHODS

The setting was the University Hospital Aachen, a 1,500-bed tertiary-care hospital with over 100 ICU beds providing maximal medical care in all disciplines. We performed a 5-year hospital-wide matched cohort study (January 1996 to February 2001) in which 71 cases and 99 controls were enrolled. Matching criteria were sex, age and GNB isolated in blood cultures. Multiresistance was defined as resistance against at least two different classes of antibiotics such as penicillins (+beta-lactamase-inhibitor), third-generation cephalosporins, fluoroquinolones or carbapenems.

RESULTS

BSI were mainly nosocomially acquired, and cases of BSI with multiresistant bacteria were associated with a higher mortality (p=0.0418) and a prolonged LOS in the intensive care unit (ICU) (p=0.0049). Risk factors for BSI with multiresistant GNB were antibiotic treatment (p=0.0191) and mechanical ventilation (p=0.0283).

CONCLUSION

Multiresistance of GNB causing BSI was associated with higher mortality rates and longer LOS in ICU. The initial antibiotic therapy was significantly more often inadequate and might have had an impact on overall mortality. Thus, an effective strategy to administer an appropriate initial empirical antibiotic therapy, especially in patients with risk factors, must be sought. Moreover, the overall usage of antimicrobials must be limited and infection control guidelines should be followed to reduce the emergence and transmission of multiresistant GNB.

Systematic surveillance cultures as a tool to predict involvement of multidrug antibiotic resistant bacteria in ventilator-associated pneumonia

OBJECTIVE

To assess prediction of multidrug resistant (MDR) pathogens in ventilator-associated pneumonia (VAP) by systematic surveillance cultures (SC) and to assess the contribution of SC to initial antibiotic therapy.

DESIGN

Prospective cohort study of patients with microbiologically confirmed VAP. Comparison of actual early antibiotic coverage with three hypothetical empirical schemes.

SETTING

A 50-bed university hospital ICU. SC consisted of oral, nasal, urinary and rectal samples upon admission, 3-weekly urinary and 1-weekly oral, nasal, and rectal samples in all patients, 3-weekly tracheal aspirates in intubated patients.

RESULTS

MDR pathogens were found in 86 of 199 VAP episodes. Sensitivity of SC to predict MDR pathogens was 69% (tracheal SC) and 82% (all SC); specificity was 96% (tracheal) and 91% (all), respectively. Appropriate antibiotic coverage within 24 h and 48 h following MDR VAP was 77% and 89%, respectively. A carbapenem-based empirical scheme would have been equally appropriate (83% vs. 77% at 24 h; 83% vs. 89% at 48 h), but a beta-lactam-fluoroquinolone empirical therapy would have been less (59% vs. 77% at 24 h; 59% vs. 89% at 48 h) as would have been beta-lactam-aminoglycoside therapy (68% vs. 77% at 24 h; 68% vs. 89% at 48 h). Empirical comparators would have resulted in significantly more prescription of broad-spectrum antibiotics within the first 48 h.

CONCLUSIONS

With MDR pathogens highly prevalent, systematic SC predicted MDR pathogens causing VAP in 69% to 82% and may have contributed to high rates of early appropriate antibiotic therapy with limited use of broad-spectrum antimicrobials.

Antibacterial Activity of Allicin Alone and in Combination with β-Lactams against Staphylococcus spp. and Pseudomonas aeruginosa

Allicin is one of the most effective compounds isolated from garlic showing antibacterial activity. Determination of MIC alone or in combination with cefazolin/oxacillin against Staphylococcus spp. or with cefoperazone against Pseudomonas aeruginosa showed that allicin alone did not have good antibacterial activity (MIC90>512 microg/ml) but it facilitated antibacterial activity of all three beta-lactams tested at subinhibitory concentrations. In the presence of 1/8 to 1/2 the MIC of allicin, the MIC90 values of cefazolin, oxicillin, and cefoperazone were reduced by 4 approximately 128, 32 approximately 64, and 8 approximately 16 fold, respectively. Thus, allicin-beta-lactam combinations offer promise of clinical utility especially if synergism is demonstrated by in vivo experimental studies.

Management of ventilator-associated pneumonia caused by multiresistant bacteria

PURPOSE OF REVIEW

The inappropriate choice of antibiotics (in nearly one third of episodes) is the most important risk factor for death. Traditionally, a narrow-spectrum drug was used first, and the most potent drugs were reserved for subsequent use.

RECENT FINDINGS

As multidrug resistance increases in the intensive care unit in patients treated for nosocomial pneumonia, costs, mortality, and morbidity are rising. Although methicillin-resistant Staphylococcus aureus, Pseudomonas aeruginosa and Acinetobacter baumannii are frequently considered together, they have different virulence, risk factors and susceptibilities, requiring different antimicrobial choices. Assessment of clinical resolution should be differentiated in the presence of acute lung injury. In the absence of biochemical markers, oxygenation and core temperature should guide therapeutic decisions.

SUMMARY

As ventilator-associated pneumonia increases, empiric therapy should be based on local pathogen etiology and antibiotic resistant patterns. A new approach to consider is to start with a high-dose, broad-spectrum antibiotic and then tailor the individual therapy based on microbiological results and clinical resolution. With the use of broad-spectrum antibiotics available in empiric therapy tailored after reassessment of the patient, there is hope for reducing costs, length of stay and mortality whereas the emergence of resistance will be minimized.