Hospital-acquired pneumonia: risk factors, microbiology, and treatment

Cefepime

Cefepime (Maxipime), Maxcef, Cepimax, Cepimex, Axepim, a parenteral fourth-generation cephalosporin, is active against many organisms causative in pneumonia. Cefepime has in vitro activity against Gram-positive organisms including Staphylococcus aureus and penicillin-sensitive, -intermediate and -resistant Streptococcus pneumoniae similar to that of cefotaxime and ceftriaxone. Cefepime also has good activity against Gram-negative organisms, including Pseudomonas aeruginosa, similar to that of ceftazidime. Importantly, cefepime is stable against many of the common plasmid- and chromosome-mediated beta-lactamases and is a poor inducer of AmpC beta-lactamases. As a result, it retains activity against Enterobacteriaceae that are resistant to third-generation cephalosporins, such as derepressed mutants of Enterobacter spp. Cefepime may be hydrolyzed by the extended-spectrum beta-lactamases produced by some members of the Enterobacteriaceae, but to a lesser extent than the third-generation cephalosporins. Monotherapy with cefepime 1 or 2g, usually administered intravenously twice daily, was as effective for clinical and bacteriological response as ceftazidime, ceftriaxone or cefotaxime monotherapy (1 or 2g two or three times daily) in a number of randomized, clinical trials in hospitalized adult, or less commonly, pediatric, patients with generally moderate to severe community-acquired or nosocomial pneumonia. More limited data indicated that monotherapy with cefepime 2g three times daily was also as effective in treating patients with nosocomial pneumonia as imipenem/cilostatin 0.5g four times daily, and when combined with amikacin, cefepime was as effective as ceftazidime plus amikacin. Patients with pneumonia who failed to respond to previous antibacterial therapy with penicillins or other cephalosporins responded to treatment with cefepime. Cefepime is generally well tolerated, with a tolerability profile similar to those of other parenteral cephalosporins. In clinical trials, the majority of adverse events experienced by cefepime recipients were mild to moderate and reversible. The most common adverse events with a causal relationship to cefepime reported in clinical trials included rash and diarrhea. Other, less common, adverse events included pruritus, urticaria, nausea, vomiting oral candidiasis, colitis, headache, fever, erythema and vaginitis.

CONCLUSION

Cefepime is an established and generally well tolerated parenteral drug with a broad spectrum of antibacterial activity which, when administered twice daily, provides coverage of most of the pathogens that may be causative in pneumonia. In randomized clinical trials in hospitalized patients with generally moderate to severe community-acquired or nosocomial pneumonia, cefepime monotherapy exhibited good clinical and bacteriological efficacy. Cefepime may become a preferred antibacterial agent for infections caused by Enterobacter spp. With prudent use in order to prevent the emergence of resistant organisms, cefepime will continue to be a suitable option for the empiric treatment of pneumonia.

Impact of oral simvastatin therapy on acute lung injury in mice during pneumococcal pneumonia

Background

Recent studies suggest that the reported protective effects of statins (HMG-CoA reductase inhibitors) against community-acquired pneumonia (CAP) and sepsis in humans may be due to confounders and a healthy user-effect. To directly test whether statins are protective against Streptococcus pneumoniae, the leading cause of CAP, we examined the impact of prolonged oral simvastatin therapy at physiologically relevant doses in a mouse model of pneumococcal pneumonia. BALB/c mice were placed on rodent chow containing 0 mg/kg (control), 12 mg/kg (low simvastatin diet [LSD]; corresponds to 1.0 mg/kg/day), or 120 mg/kg (high simvastatin diet [HSD]; corresponds to 10 mg/kg/day) simvastatin for four weeks, infected intratracheally with S. pneumoniae serotype 4 strain TIGR4, and sacrificed at 24, 36, or 42 h post-infection for assessment of lung histology, cytokine production, vascular leakage and edema, bacterial burden and bloodstream dissemination. Some mice received ampicillin at 12-h intervals beginning at 48 h post-infection and were monitored for survival. Immunoblots of homogenized lung samples was used to assess ICAM-1 production.

Results

Mice receiving HSD had reduced lung consolidation characterized by less macrophage and neutrophil infiltration and a significant reduction in the chemokines MCP-1 (P = 0.03) and KC (P = 0.02) and ICAM-1 in the lungs compared to control mice. HSD mice also had significantly lower bacterial titers in the blood at 36 (P = 0.007) and 42 (P = 0.03) hours post-infection versus controls. LSD had a more modest effect against S. pneumoniae but also resulted in reduced bacterial titers in the lungs and blood of mice after 42 h and a reduced number of infiltrated neutrophils. Neither LSD nor HSD mice had reduced mortality in a pneumonia model where mice received ampicillin 48 h after challenge.

Conclusions

Prolonged oral simvastatin therapy had a strong dose-dependent effect on protection against S. pneumoniae as evidenced by reduced neutrophil infiltration, maintenance of vascular integrity, and lowered chemokine production in the lungs of mice on HSD. Statin therapy also protected through reduced bacterial burden in the lungs. Despite these protective correlates, mortality in the simvastatin-receiving cohorts was equivalent to controls. Thus, oral simvastatin at physiologically relevant doses only modestly protects against pneumococcal pneumonia.

Prevalence of major infections and adverse outcomes among hospitalized. ST-elevation myocardial infarction patients in Florida, 2006

Background

ST-elevation myocardial infarction (STEMI) patients have risk factors and co-morbidities and require procedures predisposing to healthcare acquired infections (HAIs). As few data exist on the extent and consequences of infections among these patients, the prevalence, predictors, and potential complications of major infections among hospitalized STEMI patients at all Florida acute care hospitals during 2006 were analyzed.

Methods

Sociodemographic characteristics, risk factors, co-morbidities, procedures, complications, and mortality were analyzed from hospital discharge data for 11, 879 STEMI patients age ≥18 years. We used multivariable logistic regression modeling to examine and adjust for multiple potential predictors of any infection, bloodstream infection (BSI), pneumonia, surgical site infection (SSI), and urinary tract infection (UTI).

Results

There were 2, 562 infections among 16.6% of STEMI patients; 6.2% of patients had ≥2 infections. The most prevalent HAIs were UTIs (6.0%), pneumonia (4.6%), SSIs (4.1%), and BSIs (2.6%). Women were at 29% greater risk, Blacks had 23% greater risk, and HAI risk increased 11% with each 5 year increase in age. PCI was the only protective major procedure (OR 0.81, 95% CI, 0.69-0.95, p < .05). HAI lengthened hospital stays. STEMI patients with a BSI were almost 5 times more likely (31.3% vs. 6.5%, p < .0001), and those with pneumonia were 3 times more likely (19.6% vs. 6.5%, p < .0001) to die before discharge.

Conclusions

The protective effect of PCI on risk of infection is likely mediated by its many benefits, including reduced length of hospitalizations.

Structural characterization of the tobramycin-piperacillin reaction product formed at pH 6.0

Tobramycin is an aminoglycoside antibiotic that loses a significant amount of activity in the presence of Zosyn at pH 6. As part of our investigation into ways to improve the compatibility of tobramycin with Zosyn (which contains piperacillin and tazobactam in an 8:1 ratio buffered at pH 6 by sodium citrate) by lowering the pH, we identified the reaction product of tobramycin and piperacillin at pH 6.0 and the order of the pK(a) values of tobramycin. The structure of the main reaction product of tobramycin and piperacillin at pH 6.0 was determined by 2D NMR to be the product of 3″-NH(2) reacting with the β-lactam of piperacillin. The order of the pK(a) values of the nitrogens of tobramycin was determined by (1)H and (15)N NMR titrations to be 6'-NH(2)>2'-NH(2)>1-NH(2)≈3″-NH(2)>3-NH(2). At pH 4.0, the reaction between tobramycin and Zosyn was almost negligible for a period of up to 2 h. The pH can be lowered by adding an acid such as HCl or citric acid to Zosyn to make a pH 4.0 buffer.

Clinical practice guidelines for hospital-acquired pneumonia and ventilator-associated pneumonia in adults

Hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are important causes of morbidity and mortality, with mortality rates approaching 62%. HAP and VAP are the second most common cause of nosocomial infection overall, but are the most common cause documented in the intensive care unit setting. In addition, HAP and VAP produce the highest mortality associated with nosocomial infection. As a result, evidence-based guidelines were prepared detailing the epidemiology, microbial etiology, risk factors and clinical manifestations of HAP and VAP. Furthermore, an approach based on the available data, expert opinion and current practice for the provision of care within the Canadian health care system was used to determine risk stratification schemas to enable appropriate diagnosis, antimicrobial management and nonantimicrobial management of HAP and VAP. Finally, prevention and risk-reduction strategies to reduce the risk of acquiring these infections were collated. Future initiatives to enhance more rapid diagnosis and to effect better treatment for resistant pathogens are necessary to reduce morbidity and improve survival.

Ophthalmic antibiotics and antimicrobial resistance a randomized, controlled study of patients undergoing intravitreal injections

PURPOSE

To determine whether repeated exposure of ocular and nasopharyngeal flora to ophthalmic antibiotics promotes antimicrobial resistance in patients undergoing intravitreal injections for choroidal neovascularization (CNV).

DESIGN

Prospective, randomized, controlled, clinical trial.

PARTICIPANTS

Forty-eight eyes of 24 patients undergoing unilateral intravitreal injections for CNV.

METHODS

Patients were assigned randomly to 1 of 4 ophthalmic antibiotics (azithromycin 1%, ofloxacin 0.3%, gatifloxacin 0.3%, moxifloxacin 0.5%) to be used after each injection in the treatment eye only. Bilateral conjunctival and unilateral nasopharyngeal cultures on the treatment side were obtained at baseline and were repeated at each subsequent visit for 1 year. All bacterial isolates were tested for antibiotic susceptibility to 16 different antibiotics using the Kirby-Bauer disc diffusion technique. Genetic analysis of bacteria strains was performed using pulse-field gel electrophoresis.

MAIN OUTCOME MEASURES

Changes in antibiotic susceptibility patterns of conjunctival and nasopharyngeal flora over time and emergence of resistant strains.

RESULTS

Eight subjects (33%) grew Staphylococcus aureus from the nasopharynx and 1 subject (13%) showed emergence of a resistant strain. Coagulase-negative staphylococci (CNS) cultured from eyes repeatedly exposed to fluoroquinolone antibiotics demonstrated significantly increased rates of resistance to third- and fourth-generation fluoroquinolones compared with untreated eyes. Resistance to ofloxacin and levofloxacin was roughly 85% (P = 0.003), and resistance to gatifloxacin and moxifloxacin approached 67% (P = 0.009) and 77% (P<0.001), respectively. In contrast, CNS isolated from eyes repeatedly exposed to azithromycin demonstrated significantly increased resistance (94%) to erythromycin and azithromycin when compared with control eyes (P = 0.009) and decreased resistance to third-generation (P<0.03) and fourth-generation (P<0.001) fluoroquinolones when compared with eyes exposed to fluoroquinolones.

CONCLUSIONS

Repeated exposure of ocular and nasopharyngeal flora to ophthalmic antibiotics selects for resistant strains.

Sepsis induces early alterations in innate immunity that impact mortality to secondary infection

Sepsis, the systemic inflammatory response to microbial infection, induces changes in both innate and adaptive immunity that presumably lead to increased susceptibility to secondary infections, multiorgan failure, and death. Using a model of murine polymicrobial sepsis whose severity approximates human sepsis, we examined outcomes and defined requirements for survival after secondary Pseudomonas aeruginosa pneumonia or disseminated Listeria monocytogenes infection. We demonstrate that early after sepsis neutrophil numbers and function are decreased, whereas monocyte recruitment through the CCR2/MCP-1 pathway and function are enhanced. Consequently, lethality to Pseudomonas pneumonia is increased early but not late after induction of sepsis. In contrast, lethality to listeriosis, whose eradication is dependent upon monocyte/macrophage phagocytosis, is actually decreased both early and late after sepsis. Adaptive immunity plays little role in these secondary infectious responses. This study demonstrates that sepsis promotes selective early, impaired innate immune responses, primarily in neutrophils, that lead to a pathogen-specific, increased susceptibility to secondary infections.

Comparative efficacies of human simulated exposures of telavancin and vancomycin against methicillin-resistant Staphylococcus aureus with a range of vancomycin MICs in a murine pneumonia model

Telavancin displays potent in vitro and in vivo activity against methicillin-resistant Staphylococcus aureus (MRSA), including strains with reduced susceptibility to vancomycin. We compared the efficacies of telavancin and vancomycin against MRSA strains with vancomycin MICs of ≥1 μg/ml in a neutropenic murine lung infection model. Thirteen clinical MRSA isolates (7 vancomycin-susceptible, 2 vancomycin-heteroresistant [hVISA], and 4 vancomycin-intermediate [VISA] isolates) were tested after 24 h, and 7 isolates (1 hVISA and 4 VISA isolates) were tested after 48 h of exposure. Mice were administered subcutaneous doses of telavancin at 40 mg/kg of body weight every 12 h (q12h) or of vancomycin at 110 mg/kg q12h; doses were designed to simulate the area under the concentration-time curve for the free, unbound fraction of drug (fAUC) observed for humans given telavancin at 10 mg/kg q24h or vancomycin at 1 g q12h. Efficacy was expressed as the 24- or 48-h change in lung bacterial density from pretreatment counts. At dose initiation, the mean bacterial load was 6.16 ± 0.26 log(10) CFU/ml, which increased by averages of 1.26 ± 0.55 and 1.74 ± 0.68 log in untreated mice after 24 and 48 h, respectively. At both time points, similar CFU reductions were noted for telavancin and vancomycin against MRSA, with vancomycin MICs of ≤2 μg/ml. Both drugs were similarly efficacious after 24 and 48 h of treatment against the hVISA strains tested. Against VISA isolates, telavancin reduced bacterial burdens significantly more than vancomycin for 1 of 4 isolates after 24 h and for 3 of 4 isolates after 48 h. These data support the potential utility of telavancin for the treatment of MRSA pneumonia caused by pathogens with reduced susceptibility to vancomycin.

Reduction in the incidence of poststroke nosocomial pneumonia by using the "turn-mob" program

BACKGROUND

One of the most common complications in patients with acute ischemic stroke (AIS) is pneumonia, a complication that has an impact on the patient's survival. The purpose of this study was to establish whether the implementation of a passive turning and mobilization program can prevent the occurrence of nosocomial pneumonia (NP) in patients with AIS.

METHODS

We conducted a randomized clinical trial. Patients diagnosed with AIS within the last 48 hours and without mechanical ventilation were included. Group A was the "turn-mob" program: turning and passive mobilization carried out by a previously trained relative. Group B was the control group: standard treatment characterized by turning carried out by the nursing staff. The purpose was to demonstrate whether the implementation of a manual turning and passive mobilization program could reduce the incidence of NP in patients with AIS during their stay at the hospital and up to 14 days after discharge.

RESULTS

In all, 223 patients were included (group A, n = 111; group B, n = 112). Fourteen (12.6%) patients in group A and 30 (26.8%) in group B developed NP. The implementation of the turn-mob program was associated with a decrease in NP, with a relative risk of 0.39 (95% confidence interval .19-.79; P = .008).

CONCLUSION

The turn-mob program applied on patients during the acute phase of an ischemic stroke decreases the incidence of NP.

Influenza infection leads to increased susceptibility to subsequent bacterial superinfection by impairing NK cell responses in the lung

Influenza viral infection is well-known to predispose to subsequent bacterial superinfection in the lung but the mechanisms have remained poorly defined. We have established a murine model of heterologous infections by an H1N1 influenza virus and Staphylococcus aureus. We found that indeed prior influenza infection markedly increased the susceptibility of mice to secondary S. aureus superinfection. Severe sickness and heightened bacterial infection in flu and S. aureus dual-infected animals were associated with severe immunopathology in the lung. We further found that flu-experienced lungs had an impaired NK cell response in the airway to subsequent S. aureus bacterial infection. Thus, adoptive transfer of naive NK cells to the airway of prior flu-infected mice restored flu-impaired antibacterial host defense. We identified that TNF-alpha production of NK cells played an important role in NK cell-mediated antibacterial host defense as NK cells in flu-experienced lungs had reduced TNF-alpha expression and adoptive transfer of TNF-alpha-deficient NK cells to the airway of flu-infected mice failed to restore flu-impaired antibacterial host defense. Defected NK cell function was found to be an upstream mechanism of depressed antibacterial activities by alveolar macrophages as contrast to naive wild-type NK cells, the NK cells from flu-infected or TNF-alpha-deficient mice failed to enhance S. aureus phagocytosis by alveolar macrophages. Together, our study identifies the weakened NK cell response in the lung to be a novel critical mechanism for flu-mediated susceptibility to bacterial superinfection.

Hospital-acquired thoracic empyema in adults: a 5-year study

BACKGROUND

The objective of this study was to assess the etiology, microbiology and outcome of hospital-acquired thoracic empyema (HATE) in adults.

METHODS

From December 2001 to December 2006, 459 adult patients with a diagnosis of thoracic empyema in a tertiary hospital were screened for HATE. HATE was defined as a new pleural empyema which developed after 48 hours of hospitalization.

RESULTS

In total, 56 adult (>or=18 years) patients who were diagnosed with HATE were enrolled in our series, including 35 men (62.5%) and 21 women (37.5%), with ages ranging from 22 to 87 years old (mean = 59). Causes of HATE were classified into two categories: hospital-acquired pneumonia (HAP) related (n = 25) and non-HAP related (n = 31). Causes of non-HAP related empyema were comprised of catheter-related infections (n = 20), hepatobiliary tract infections (n = 6), septic emboli (n = 4), and postpneumonectomy (n = 1). Comparing the bacteriology between the two categories, HAP-related empyema had a significantly higher incidence of aerobic Gram-negative organisms (76% vs. 38.7%, P = 0.005), polymicrobial pathogens (40% vs. 9.7%, P = 0.008), and anaerobic pathogens (20% vs. 0%, P = 0.009) than non-HAP related empyema. However, there was no significant difference in mortality rate (60% vs. 52%, P = 0.52) between the two categories.

CONCLUSIONS

Choice of antibiotic treatment for HATE should be based on the etiology of the pleural infection. In treating HAP-related empyema, antibiotics should cover aerobic Gram-negative, polymicrobial, and anaerobic pathogens.

C5a mediates peripheral blood neutrophil dysfunction in critically ill patients

RATIONALE

Critically ill patients are highly susceptible to hospital-acquired infection. Neutrophil function in critical illness remains poorly understood.

OBJECTIVES

To characterize and define mechanisms of peripheral blood neutrophil (PBN) dysfunction in critically ill patients. To determine whether the inflamed lung contributes additional phagocytic impairment.

METHODS

Prospective collection of blood and bronchoalveolar lavage fluid from patients with suspected ventilator-associated pneumonia and from age- and sex-matched volunteers; laboratory analysis of neutrophil functions.

MEASUREMENTS AND MAIN RESULTS

Seventy-two patients and 21 volunteers were included. Phagocytic capacity of PBNs was 36% lower in patients than in volunteers (P < 0.0001). From several biologically plausible candidates only activated complement was significantly associated with impaired PBN phagocytosis (P < 0.0001). Phagocytosis was negatively correlated with serum C3a and positively correlated with expression of C5a receptor type 1 (CD88) on PBNs. C5a recapitulated impaired PBN phagocytosis and significantly down-regulated CD88 expression in vitro. C5a-mediated phagocytic impairment was prevented by blocking either CD88 or phosphoinositide 3-kinase, and completely reversed by granulocyte-macrophage colony-stimulating factor. C5a also impaired killing of Pseudomonas aeruginosa by, and migration of, PBNs, indicating that effects were not restricted to phagocytosis. Bronchoalveolar lavage fluid leukocytes from patients also demonstrated significantly impaired function, and lavage supernatant reduced phagocytosis in healthy neutrophils by 43% (P = 0.0001). However, lavage fluid did not affect CD88 expression and lavage-mediated impairment of phagocytosis was not blocked by anti-CD88 antibody.

CONCLUSIONS

Critically ill patients have significant dysfunction of PBNs, which is mediated predominantly by activated complement. Further, profound complement-independent neutrophil dysfunction occurs in the inflamed lung.

Hospital acquired pneumonia with high-risk bacteria is associated with increased pulmonary matrix metalloproteinase activity

Background

Neutrophil products like matrix metalloproteinases (MMP), involved in bacterial defence mechanisms, possibly induce lung damage and are elevated locally during hospital- acquired pneumonia (HAP). In HAP the virulence of bacterial species is known to be different. The aim of this study was to investigate the influence of high-risk bacteria like S. aureus and pseudomonas species on pulmonary MMPconcentration in human pneumonia.

Methods

In 37 patients with HAP and 16 controls, MMP-8, MMP-9 and tissue inhibitors of MMP (TIMP) were analysed by ELISA and MMP-9 activity using zymography in bronchoalveolar lavage (BAL).

Results

MMP-9 activity in mini-BAL was increased in HAP patients versus controls (149 ± 41 vs. 34 ± 11, p < 0.0001). In subgroup analysis, the highest MMP concentrations and activity were seen in patients with high-risk bacteria: patients with high-risk bacteria MMP-9 1168 ± 266 vs. patients with low-risk bacteria 224 ± 119 ng/ml p < 0.0001, MMP-9 gelatinolytic activity 325 ± 106 vs. 67 ± 14, p < 0.0002. In addition, the MMP-8 and MMP-9 concentration was associated with the state of ventilation and systemic inflammatory marker like CRP.

Conclusion

Pulmonary MMP concentrations and MMP activity are elevated in patients with HAP. This effect is most pronounced in patients with high-risk bacteria. Artificial ventilation may play an additional role in protease activation.

Differentiated S100A7 expression in infected tonsils and tonsils from allergic individuals

Palatine tonsils are continuously exposed to microorganisms and antigens and secrete antimicrobial peptides as a first line of defense. S100A7 is a protein with antimicrobial and chemotactic properties. Our aim was to investigate how the expression of S100A7 in human palatine tonsils is affected by inflammatory processes. Tonsils obtained from 109 patients undergoing tonsillectomy were divided into groups of infected and noninfected as well as allergic and nonallergic, based on the results from tonsillar core culture tests and Phadiatop analysis, respectively. Western blot and immunohistochemistry were used to assess protein expression and real-time PCR was used to quantify mRNA levels. To explore the induction of S100A7, tonsils were stimulated with lipopolysaccharide in vitro. The immunohistochemical staining for S100A7 was most intense in the tonsillar epithelium, but the protein was also detected in B- and T-cell regions, which was confirmed with Western blot on isolated B and T cells. The S100A7 expression appeared to be the highest in CD8+ T cells. Reduced mRNA levels of S100A7 were detected in infected tonsils as well as in tonsils from allergic individuals. In vitro stimulation of tonsils with lipopolysaccharide did not have any effect on the expression. The results suggest a role for S100A7 in recurrent tonsillitis and allergic disease.

The role of carbapenems in the treatment of severe nosocomial respiratory tract infections

The prevalence of antibiotic-resistant bacteria continues to increase, particularly in patients in the intensive care unit with nosocomial pneumonia. The intention of this review is to provide an overview of severe nosocomial pneumonia, carbapenems and the problem of bacterial resistance to antimicrobial agents. Attention was focused on the efficacy, safety and pharmacodynamics of imipenem, meropenem, ertapenem and doripenem. Issues on the impact of appropriate empiric antibiotic therapy for nosocomial pneumonia patients considered at risk for resistant pathogens are discussed. Critical decision making regarding the use of carbapenems for treating severe nosocomial pneumonia requires careful consideration of the four Ds of optimal antimicrobial therapy: right Drug, right Dose, De-escalated to pathogen-directed therapy and right Duration of therapy.

Capsule and O-antigen from an extraintestinal isolate of Escherichia coli modulate cytokine levels in rat macrophages in vitro and in a rat model of pneumonia

Gram-negative pneumonia results in significant morbidity, mortality, and cost to the healthcare system. Previously the authors demonstrated that capsule and O-antigen, virulence factors of the extraintestinal Escherichia coli isolate CP9, modulate pulmonary neutrophil influx in a rat pneumonia model. In this report, the authors utilized CP9 and mutants deficient in O-antigen (CP921), capsule (CP9.137), or both (CP923) to test the hypothesis that modulation of cytokine levels by capsule and/or O-antigen may be a contributory mechanism. Effects of capsule and O-antigen on cytokine levels in rats in vivo and in isolated pulmonary macrophages in vitro were assessed. In vivo, capsule and O-antigen had no significant effect on tumor necrosis factor (TNF)-alpha levels in bronchoalveolar lavage fluid (BALF), but both were associated with significant increases in the levels of interleukin (IL)-1beta and Cytokine-induced neutrophil Chemoattractant-1 (CINC-1). However, potential difficulties in interpreting data occurred because challenge bacterial strains exhibited differential growth, and clearance characteristics and mixed cell populations were present. Therefore, added mechanistic studies investigated specific interactions of capsule and O-antigen with pulmonary macrophages purified from normal rats and exposed to CP9, CP921, CP9.137, or CP923 in vitro. Results indicated that the presence of capsule led to significantly increased levels of TNF-alpha, IL-1beta, and CINC-1, whereas O-antigen significantly decreased macrophage-associated levels of these mediators. These findings support the hypothesis that CP9 capsule is proinflammatory for macrophage-induced neutrophil recruitment, whereas O-antigen attenuates macrophage production of proinflammatory mediators in pneumonia. These results expand our understanding on the mechanisms by which these virulence traits may contribute to the inflammatory pathogenesis of pneumonia.

Carbapenem resistance in clinical isolates of Pseudomonas aeruginosa

The objectives of this study were to identify the carbapenem resistance mechanisms of clinical Pseudomonas aeruginosa isolates. The strains resistant to imipenem had lost only the OprD protein, the isolates resistant to imipenem and meropenem had both loss of the OprD porin and reduced minimum inhibitory concentrations (MICs) in the presence of efflux pump inhibitors. In the isolates in which efflux had been identified (n=2) only 1 isolate had a mutation in the mexR gene corresponding to a glutamine to a stop codon change at amino acid 106. This has not been previously identified. There were no significant changes in the mexT genes. No mutations previously associated with the upregulation of the carbapenem efflux pumps in in vitro generated resistant isolates were identified in any of the clinical isolates. Therefore, the resistance mechanisms identified by development of carbapenem resistance in vitro are not sufficient to understand carbapenem resistance development in clinical isolates.

Prolonged use of carbapenems and colistin predisposes to ventilator-associated pneumonia by pandrug-resistant Pseudomonas aeruginosa

OBJECTIVE

We present our experience with five cases of pandrug-resistant Pseudomonas aeruginosa ventilator-associated pneumonia (VAP) and analysis of risk factors.

DESIGN AND SETTING

Case-control study in a 15-bed intensive care unit (ICU).

PATIENTS AND PARTICIPANTS

The study included 5 cases and 20 controls. Each case patient was matched to four contemporary controls according to gender, prior hospital admissions, hospitalization duration, ICU admission cause, Acute Physiology and Chronic Health Evaluation (APACHE) II and Sequential Organ Function Assessment (SOFA) scores on ICU admission, and length of ICU stay, and mechanical ventilation duration until first VAP episode by a multidrug-resistant bacterium.

MEASUREMENTS AND RESULTS

Recorded variables included age, gender, daily APACHE II and SOFA scores, patient medication, treatment interventions, positive cultures and corresponding antibiograms, occurrence of infection, sepsis, and septic shock, other ICU-associated morbidity, length of ICU stay and mechanical ventilation, and patient outcome. Healthcare worker and environmental cultures, and a hand-disinfection survey were performed. Pandrug-resistant P. aeruginosa isolates belonged to the same genotype and were bla (VIM-1)-like gene positive. The outbreak resolved following reinforcement of infection-control measures (September 27). The sole independent predictor for pandrug-resistant P. aeruginosa VAP was combined use of carbapenem for more than 20 days and colistin use for and more than 13 days (odds ratio 76.0; 95% confidence interval 3.7-1487.6). An additional risk factor was more than 78 open suctioning procedures during 6-26 September (odds ratio 16.0; 95% confidence interval 1.4-185.4).

CONCLUSIONS

Prolonged carbapenem-colistin use predisposes to VAP by pandrug-resistant P. aeruginosa. Cross-transmission may be facilitated by open suctioning.

Enterobacteriaceae

This review summarises the changing epidemiology of resistance to cephalosporins and fluoroquinolones among the Enterobacteriaceae since the 1980s and its potential impact on prescribing choices now and in the immediate future. Whilst multiresistant Enterobacteriaceae are not a novel problem for high-risk hospital units, such as intensive care, the emergence of Escherichia coli co-expressing extended-spectrum beta-lactamases, such as CTX-M types, along with fluoroquinolone resistance in the community is starting to impact in situations where cephalosporins and ciprofloxacin were seen as reliable first-line choices. The reduction in effective options to treat these infections, particularly of the urinary tract and bacteraemia, is likely to result in increased prescribing of carbapenems, thus generating further selective pressure for carbapenemases and other mechanisms of carbapenem resistance in the future.

Surfactant dysfunction and lung injury due to the E. coli virulence factor hemolysin in a rat pneumonia model

This study tests the hypothesis that the virulence factor hemolysin (Hly) expressed by extraintestinal pathogenic Escherichia coli contributes to surfactant dysfunction and lung injury in a rat model of gram-negative pneumonia. Rats were instilled intratracheally with CP9 (wild type, Hly-positive), CP9hlyA (Hly-minus), CP9/pEK50 (supraphysiological Hly), or purified LPS. At 6 h postinfection, rats given CP9 had a decreased percentage content of large surfactant aggregates in cell-free bronchoalveolar lavage (BAL), decreased large aggregate surface activity, decreased Pa(O2)/FiO2) ratio, increased BAL albumin/protein levels, and increased histological evidence of lung injury compared with rats given CP9hlyA or LPS. In addition, rats given CP9/pEK50 or CP9 had decreased large aggregate surface activity, decreased Pa(O2)/FiO2) ratios, and increased BAL albumin/protein levels at 2 h postinfection compared with rats given CP9hlyA. The severity of permeability lung injury based on albumin/protein levels in BAL at 2 h was ordered as CP9/pEK50 > CP9 > CP9hlyA > normal saline controls. Total lung titers of bacteria were increased at 6 h in rats given CP9 vs. CP9hlyA, but bacterial titers were not significantly different at 2 h, indicating that increased surfactant dysfunction and lung injury were associated with Hly as opposed to bacterial numbers per se. Further studies in vitro showed that CP9 could directly lyse transformed pulmonary epithelial cells (H441 cells) but that indirect lysis of H441 cells secondary to Hly-induced neutrophil lysis did not occur. Together, these data demonstrate that Hly is an important direct mediator of surfactant dysfunction and lung injury in gram-negative pneumonia.

Epidemiology and economic impact of meticillin-resistant Staphylococcus aureus: review and analysis of the literature

In the past 2 decades, meticillin-resistant Staphylococcus aureus (MRSA) has become an increasingly prevalent problem in healthcare, both in acute care institutions and in the community. MRSA is associated with worse outcomes and higher costs for care than meticillin sensitive S. aureus (MSSA). MRSA is a particular problem in several conditions, including hospital-acquired pneumonia (including ventilator-associated pneumonia), skin and soft tissue infections, and diabetic foot infections. Hospitalisation costs associated with MRSA infection are substantially greater than those associated with MSSA infection, and MRSA has wider economic effects that involve indirect costs to the patient and to society. In several countries, infection control programmes have shown potential economic benefits, as savings accruing from strict and effective control have been shown to outweigh the cost of policy implementation. Standard therapy is based on glycopeptide treatment, usually with vancomycin, although resistance to this agent has emerged. Alternative available treatments for MRSA include teicoplanin, tigecycline, daptomycin, quinupristin-dalfopristin and the oxazolidinone, linezolid, which has a higher acquisition cost than vancomycin but is available as intravenous and oral formulations. Despite some limitations of analyses to date, linezolid has been shown to be cost effective in the treatment of MRSA and appears to be related, in part, to the drug's potential for facilitating earlier discharge from hospital. Current opinion favours rational prescribing to maximise therapeutic benefit and minimise the risk of further antibacterial resistance.

Lung epithelium as a sentinel and effector system in pneumonia--molecular mechanisms of pathogen recognition and signal transduction

Pneumonia, a common disease caused by a great diversity of infectious agents is responsible for enormous morbidity and mortality worldwide. The bronchial and lung epithelium comprises a large surface between host and environment and is attacked as a primary target during lung infection. Besides acting as a mechanical barrier, recent evidence suggests that the lung epithelium functions as an important sentinel system against pathogens. Equipped with transmembranous and cytosolic pathogen-sensing pattern recognition receptors the epithelium detects invading pathogens. A complex signalling results in epithelial cell activation, which essentially participates in initiation and orchestration of the subsequent innate and adaptive immune response. In this review we summarize recent progress in research focussing on molecular mechanisms of pathogen detection, host cell signal transduction, and subsequent activation of lung epithelial cells by pathogens and their virulence factors and point to open questions. The analysis of lung epithelial function in the host response in pneumonia may pave the way to the development of innovative highly needed therapeutics in pneumonia in addition to antibiotics.

Toward a zero VAP rate: personal and team approaches in the ICU

In a fast-paced setting like the intensive care unit (ICU), nurses must have appropriate tools and resources in order to implement appropriate and timely interventions. Ventilator-associated pneumonia (VAP) is a costly and potentially fatal outcome for ICU patients that requires timely interventions. Even with established guidelines and care protocols, nurses do not always incorporate best practice interventions into their daily plan of care. Despite the plethora of information and guidelines about how to apply interventions in order to save lives, managers of ICUs are challenged to involve the bedside nurse and other ICU team members to apply these bundles of interventions in a proactive, rather than reactive, manner in order to prevent complications of care. The purpose of this article is to illustrate the success of 2 different methods utilized to improve patient care in the ICU. The first method is a personal process improvement model, and the second method is a team approach model. Both methods were utilized in order to implement interventions in a timely and complete manner to prevent VAP and its related problem, hospital-associated pneumonia, in the ICU setting. Success with these 2 methods has spurred an interest in other patient care initiatives.

Methicillin-resistant Staphylococcus aureus: a new community-acquired pathogen?

PURPOSE OF REVIEW

The main goal of this review is to describe the emergence of methicillin-resistant Staphylococcus aureus (MRSA) as a community pathogen.

RECENT FINDINGS

Community-acquired MRSA has emerged as an important infection in the community setting. It has primarily been associated with skin and soft-tissue infections, but can also cause severe pulmonary infections, including pneumonia and empyema. Community-acquired MRSA is typically more susceptible to a wider class of antibiotics than healthcare-associated MRSA. Community-acquired MRSA is also more virulent compared with healthcare-associated MRSA isolates. Community-acquired MRSA usually contains the gene encoding Panton-Valentive leukocidin, which is a toxin that creates lytic pores in the cell membranes of neutrophils and induces the release of neutrophil chemotactic factors that promote inflammation and tissue destruction. The optimal antibiotic treatment for Panton-Valentive leukocidin-positive community-acquired MRSA is unknown; however, antibiotics with activity against MRSA and the ability to inhibit toxin production may be optimal (linezolid or clindamycin for susceptible isolates).

SUMMARY

Clinicians should be aware of the emergence of community-acquired MRSA as an important cause of serious infections arising in the community setting. Appropriate antibiotic therapy should be initiated as soon as infection with this pathogen is suspected.

Molecular mechanisms of beta-lactam resistance mediated by AmpC hyperproduction in Pseudomonas aeruginosa clinical strains

The molecular mechanisms of beta-lactam resistance mediated by AmpC hyperproduction in natural strains of Pseudomonas aeruginosa were investigated in a collection of 10 isogenic, ceftazidime-susceptible and -resistant pairs of isolates, each sequentially recovered from a different intensive care unit patient treated with beta-lactams. All 10 ceftazidime-resistant mutants hyper-produced AmpC (beta-lactamase activities were 12- to 657-fold higher than those of the parent strains), but none of them harbored mutations in ampR or the ampC-ampR intergenic region. On the other hand, six of them harbored inactivating mutations in ampD: four contained frameshift mutations, one had a C-->T mutation, creating a premature stop codon, and finally, one had a large deletion, including the complete ampDE region. Complementation studies revealed that only three of the six ampD mutants could be fully trans-complemented with either ampD- or ampDE-harboring plasmids, whereas one of them could be trans-complemented only with ampDE and two of them (including the mutant with the deletion of the ampDE region and one with an ampD frameshift mutation leading to an ampDE-fused open reading frame) could not be fully trans-complemented with any of the plasmids. Finally, one of the four mutants with no mutations in ampD could be trans-complemented, but only with ampDE. Although the inactivation of AmpD is found to be the most frequent mechanism of AmpC hyperproduction in clinical strains, our findings suggest that for certain types of mutations, AmpE plays an indirect role in resistance and that there are other unknown genes involved in AmpC hyperproduction, with at least one of them apparently located close to the ampDE operon.

Polmoniti

Non è semplice ordinare una materia così articolata come la patologia infettiva respiratoria. La gestione delle polmoniti si presenta complessa per le problematiche ad esse connesse (aspetti epidemiologici, microbiologici, farmacoeconomici, ecc.) per cui è necessario confrontare costantemente le conoscenze di quanti hanno dimestichezza in questo settore per proporre e condividere linee strategiche che tengano in considerazione da un lato i suggerimenti contenuti nelle linee guida più accreditate e dall’altro le esperienze prodotte dalla pratica quotidiana al fine di migliorare potenzialità e metodi di cura e razionalizzare i percorsi diagnostico-terapeutici più idonei a fronteggiarle. L’incremento costante delle infezioni respiratorie sostenute dai patogeni emergenti e interessate dal fenomeno delle resistenze batteriche è oggi un elemento preoccupante che rischia, tra l’altro, di vanificare, in carenza di un adeguamento costante, tutti gli schemi, le linee guida e i protocolli diagnostico-terapeutici elaborati in questi ultimi anni per un razionale trattamento delle patologie pneumoinfettivologiche. Il trattamento delle polmoniti acquisite in comunità (CAP) rappresenta uno degli argomenti più dibattuti in pneumologia negli ultimi anni, sottoposto a continue revisioni, aggiornamenti, precisazioni dottrinarie.

Nosocomial pneumonia : rationalizing the approach to empirical therapy

Nosocomial pneumonia or hospital-acquired pneumonia (HAP) causes considerable morbidity and mortality. It is the second most common nosocomial infection and the leading cause of death from hospital-acquired infections. In 1996 the American Thoracic Society (ATS) published guidelines for empirical therapy of HAP. This review focuses on the literature that has appeared since the ATS statement. Early diagnosis of HAP and its etiology is crucial in guiding empirical therapy. Since 1996, it has become clear that differentiating mere colonization from etiologic pathogens infecting the lower respiratory tract is best achieved by employing bronchoalveolar lavage (BAL) or protected specimen brush (PSB) in combination with quantitative culture and detection of intracellular microorganisms. Endotracheal aspirate and non-bronchoscopic BAL/PSB in combination with quantitative culture provide a good alternative in patients suspected of ventilator-associated pneumonia. Since culture results take 2-3 days, initial therapy of HAP is by definition empirical. Epidemiologic studies have identified the most frequently involved pathogens: Enterobacteriaceae, Haemophilus influenzae, Streptococcus pneumoniae and Staphylococcus aureus ('core pathogens'). Empirical therapy covering only the 'core pathogens' will suffice in patients without risk factors for resistant microorganisms. Studies that have appeared since the ATS statement issued in 1996, demonstrate several new risk factors for HAP with multiresistant pathogens. In patients with risk factors, empirical therapy should consist of antibacterials with a broader spectrum. The most important risk factors for resistant microorganisms are late onset of HAP (>/=5 days after admission), recent use of antibacterial therapy, and mechanical ventilation. Multiresistant bacteria of specific interest are methicillin-resistant S. aureus (MRSA), Pseudomonas aeruginosa, Acinetobacter calcoaceticus-baumannii, Stenotrophomonas maltophilia and extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae. Each of these organisms has its specific susceptibility pattern, demanding appropriate antibacterial treatment. To further improve outcomes, specific therapeutic options for multiresistant pathogens and pharmacological factors are discussed. Antibacterials developed since 1996 or antibacterials with renewed interest (linezolid, quinupristin/dalfopristin, teicoplanin, meropenem, new fluoroquinolones, and fourth-generation cephalosporins) are discussed in the light of developing resistance.Since the ATS statement, many reports have shown increasing incidences of resistant microorganisms. Therefore, one of the most important conclusions from this review is that empirical therapy for HAP should not be based on general guidelines alone, but that local epidemiology should be taken into account and used in the formulation of local guidelines.

Contribution of clonal dissemination and selection of mutants during therapy to Pseudomonas aeruginosa antimicrobial resistance in an intensive care unit setting

Rates of antibiotic resistance in Pseudomonas aeruginosa isolates from intensive care unit (ICU) patients are expected to be dependent on the selection of resistance mutations during therapy, the availability of exogenous resistance determinants and their dissemination potential, and the efficiency of transmission of the resistant strains. The relative contributions of these three factors were studied in an ICU with no apparent outbreak in 216 sequential P. aeruginosa isolates recovered from 102 patients between September 2002 and November 2003. Analysis of pulsed-field gel electrophoresis patterns revealed the presence of 82 different clones. Thus, the dissemination of particular resistant clones had a minimal effect on the relatively high overall resistance frequencies found for imipenem (32%), cefepime (25%), ceftazidime (24%), meropenem (22%), ciprofloxacin (18%) and tobramycin (2%). Rates of primary resistance were relatively low, and resistance development during treatment (secondary resistance) was the main factor contributing to the overall high resistance rates. In ICU settings with a low prevalence of epidemic resistant strains, the main strategy for resistance control should focus on the design of targeted regimens to avoid the development of resistance.

Antibiotic management of ventilator-associated pneumonia due to antibiotic-resistant gram-positive bacterial infection

Gram-positive cocci, in particular Staphylococcus aureus, account for as much as one-third of all cases of hospital-acquired pneumonia, and treatment has become increasingly complex as the proportion of resistant isolates has increased. Methicillin-resistant S. aureus is of particular concern because this pathogen is now associated with hospital-acquired, ventilator-associated, community-acquired, and healthcare-associated pneumonia. Antibiotic therapy for ventilator-associated pneumonia is challenging because it can be caused by multiple pathogens, which can be resistant to multiple drugs. This article reviews the epidemiology of ventilator-associated pneumonia and describes options for antibiotic treatment. Particular attention is paid to pneumonia due to methicillin-resistant S. aureus. Studies suggest that vancomycin, the traditional treatment for ventilator-associated pneumonia, may not be the best option for this type of pneumonia and that other antibiotics, such as linezolid and clindamycin, might be better choices. New antibiotics with activity against methicillin-resistant S. aureus are under investigation and may soon become available for clinical use. Studies are needed to define the optimal choice of antibiotic for pneumonias caused by this organism, and these choices will need to be balanced with the need to minimize the emergence of resistance.

Neumonía nosocomial en el enfermo no intubado

Hospital-acquired pneumonia is one of the main causes of nosocomial infection. Although its incidence is higher in intubated patients, around half of all cases occur outside the intensive care unit (ICU). However, few studies have been performed in this setting and consequently most data come from hospitalized series that include patients undergoing mechanical ventilation. The epidemiological differences between intubated patients and non-ICU patients suggest that the etiology and therapeutic approach differ between these two groups. The present article reviews the epidemiology, diagnosis, treatment and prevention of nosocomial pneumonia in general wards.

Pleuropulmonary complications of Panton-Valentine leukocidin-positive community-acquired methicillin-resistant Staphylococcus aureus: importance of treatment with antimicrobials inhibiting exotoxin production

Four patients with pleuropulmonary complications attributed to community-acquired methicillin-resistant Staphylococcus aureus (CAMRSA) positive for Panton-Valentine leukocidin (PVL) are described. These patients presented to Barnes-Jewish Hospital with severe necrotizing pneumonia, empyema, ARDS-complicating pneumonia, and ventilator-associated pneumonia-complicating acute pancreatitis, respectively. The first three patients had influenza-like illnesses preceding their PVL-positive CAMRSA infections. In all four cases, PVL-positive CAMRSA was isolated from respiratory secretions, and from blood cultures in three of the individuals. Antimicrobial therapy was inappropriate initially in all four patients. Three patients failed to respond to subsequent treatment with vancomycin, including two patients with persistent bacteremia despite at least 48 h of treatment with vancomycin. These patients were subsequently treated with antimicrobials inhibiting exotoxin production (linezolid or clindamycin) with good clinical results. Clinicians should be aware of PVL-positive CAMRSA due to the rapid and severe progression of pleuropulmonary complications associated with this infection. Additionally, specific antimicrobial therapy directed against CAMRSA differs from the traditional antimicrobial agents prescribed for community-acquired pneumonia. Antimicrobial agents that specifically inhibit exotoxin production appear to be the preferred treatment agents.

Epidemiology, treatment, and outcomes of nosocomial bacteremic Staphylococcus aureus pneumonia

OBJECTIVE

To describe outcomes associated with nosocomial bacteremic Staphylococcus aureus pneumonia (NBSAP) and to determine whether delay in adequate antimicrobial treatment is a risk factor for negative clinical and microbiological outcomes.

DESIGN

Retrospective cohort analysis.

SETTING

This study was conducted at Detroit Receiving Hospital and University Health Center, which is a 279-bed, level 1 trauma center in Detroit, MI.

PATIENTS

All episodes of NBSAP identified from January 1, 1999, to April 30, 2004.

RESULTS

Of 206 patients identified over a 5-year period with positive blood and respiratory cultures for S aureus, 60 patients met strict clinical, radiographic, and microbiological criteria for NBSAP. The overall mean (+/- SD) characteristics include the following: age, 55.5 +/- 15.0 years; acute physiology and chronic health evaluation II score, 20 (range, 3 to 41); ICU at onset, 93.3%; mechanical ventilation, 83.3%; length of stay (LOS) prior to NBSAP, 9 days (range, 2 to 81 days); methicillin-resistant S aureus (MRSA) rate, 70%; and all-cause hospital and infection-related mortality (IRM), 55.5% and 40.0%, respectively. Overall, S aureus pneumonia developed late in the patient's hospital stay in ICU patients previously receiving mechanical ventilation and was associated with high crude mortality and IRM rates. No significant difference existed with respect to mortality or infection-related LOS between patients who had received early appropriate antibiotic therapy vs those who had received delayed appropriate antibiotic therapy at the onset of pneumonia or in patients with methicillin-sensitive S aureus pneumonia vs those with MRSA pneumonia.

CONCLUSION

IRM from NBSAP is high, and standard therapies evaluated at the time of this study resulted in poor clinical outcomes. Delayed therapy was not found to be a predictor of adverse outcomes; however, this lack of ability to detect a difference may be a product of small sample size. These findings suggest that newer agents with enhanced clinical activity in NBSAP are needed and that these should be evaluated in a real-world setting, where outcomes of the most ill patients can be assessed.

Synergistic potential of ceftazidime plus amikacin or levofloxacin against Pseudomonas aeruginosa as determined using a checkerboard and a disk diffusion technique

The synergistic potential of ceftazidime plus amikacin or levofloxacin was assessed against 61 Pseudomonas aeruginosa isolates with variable susceptibility patterns to the 3 antibiotics. A checkerboard broth method and a disk diffusion method were used and compared. The latter, also easy to perform as a triple-disk assay, could be a helpful laboratory screening tool for drug synergism to drive possible combination treatments.

Hypermutation is a key factor in development of multiple-antimicrobial resistance in Pseudomonas aeruginosa strains causing chronic lung infections

Pseudomonas aeruginosa is the most relevant pathogen producing chronic lung infections in patients with chronic underlying diseases such as cystic fibrosis (CF), bronchiectasis, and chronic obstructive pulmonary disease (COPD). Hypermutable (or mutator) P. aeruginosa strains, characterized by increased (up to 1,000-fold) spontaneous mutation rates due to alterations of the DNA mismatch repair (MMR) system have been found at high frequencies in the lungs of CF patients, but their role in other chronic processes is still unknown. Sixty-two P. aeruginosa isolates from 30 patients with underlying non-CF chronic respiratory diseases (22 with bronchiectasis and 8 with COPD) and documented chronic infection were studied. Antibiotic susceptibility profiles and mutation frequencies were determined, and complementation assays using the cloned wild-type mutS gene and molecular epidemiology studies (pulsed-field electrophoresis, [PFGE]) were performed with these strains. Thirty-three (53%) of the isolates were hypermutable, and 17 (57%) of the 30 patients were colonized by hypermutable strains. Strains from 11 of the 17 patients were found to be defective in the MMR mutS gene by complementation assays. Interpatient transmission of strains was ruled out by PFGE. Multiple-antimicrobial resistance was documented in 42% of the hypermutable strains in contrast to 0% resistance in the nonhypermutable strains (P < 0.0001). Hypermutable P. aeruginosa strains are extremely prevalent in chronic infections in contrast to what has been described in acute processes, suggesting a role of hypermutation in bacterial adaptation for long-term persistence. Furthermore, hypermutation is found to be a key factor for the development of multiple-antimicrobial resistance, and therefore these findings are expected to have important consequences for the treatment of chronic infections.

E. colivirulence factor hemolysin induces neutrophil apoptosis and necrosis/lysis in vitro and necrosis/lysis and lung injury in a rat pneumonia model

Enteric gram-negative bacilli, such as Escherichia coli are the most common cause of nosocomial pneumonia. In this study a wild-type extraintestinal pathogenic strain of E. coli (ExPEC)(CP9) and isogenic derivatives deficient in hemolysin (Hly) and cytotoxic necrotizing factor (CNF) were assessed in vitro and in a rat model of gram-negative pneumonia to test the hypothesis that these virulence factors induce neutrophil apoptosis and/or necrosis/lysis. As ascertained by in vitro caspase-3/7 and LDH activities and neutrophil morphology, Hly mediated neutrophil apoptosis at lower E. coli titers (1 × 105–6cfu) and necrosis/lysis at higher titers (≥1 × 107cfu). Data suggest that CNF promotes apoptosis but not necrosis or lysis. We also demonstrate that annexin V/7-amino-actinomycin D staining was an unreliable assessment of apoptosis using live E. coli. The use of caspase-3/7 and LDH activities and neutrophil morphology supported the notion that necrosis, not apoptosis, was the primary mechanism by which neutrophils were affected in our in vivo gram-negative pneumonia model using live E. coli. In addition, in vivo studies demonstrated that Hly mediates lung injury. Neutrophil necrosis was not observed when animals were challenged with purified lipopolysaccharide, demonstrating the importance of using live bacteria. These findings establish that Hly contributes to ExPEC virulence by mediating neutrophil toxicity, with necrosis/lysis being the dominant effect of Hly on neutrophils in vivo and by lung injury. Whether Hly-mediated lung injury is due to neutrophil necrosis, a direct effect of Hly, or both is unclear.