Emergence of vancomycin resistance during therapy against methicillin-resistant Staphylococcus aureus in a burn patient--importance of low-level resistance to vancomycin

Evaluation of Burn Wound Infection in a Referral Center in Colombia

Introduction  Burn wound infection (BWI) is the second most important cause of death in burn patients. There is currently limited data about the incidence and clinical presentation of BWI using quantitative techniques as quantitative biopsy culture (QBC) to prevent progress to burn wound sepsis (BWS).

Methods  This is a prospective cohort study of patients diagnosed with BWI, confirmed by QBC, from February 2018 to July 2019 at University Hospital of Santander (HUS). The primary outcome was to determine clinical, microbiological, and histopathological characteristics of patients diagnosed with BWI along with a positive QBC and their relationship with early diagnosis and progression to BWS.

Results  525 patients were admitted to HUS Burn Center. Of those, 44/525 (8.23%) presented a clinical diagnosis of BWI (median age, 20.5 years [1–67 years]; 25/44 [56.8%] male). QBC was positive in 26/44 (59%), Staphylococcus aureus 14/44 (31.8%), and Pseudomonas aeruginosa 7/44 (15.9%) were the mainly etiological agents isolated. Bacterial resistance to antibiotics was mostly to beta-lactams in 14/44 (31.8%), corresponding to methicillin-resistant Staphylococcus aureus (MRSA). Clinical signs more related to infection were erythema in 33/44 (61.3%). As many as 10/44 (22.7%) progressed to sepsis and 2/44 (6%) died.

Conclusion  BWI increases hospitalization time and number of surgeries, increasing the risk of sepsis and death. The QBC allows an accurate diagnosis with lesser false-positive cases that impact antibiotic resistance and mortality. Protocols targeting this problem are needed to decrease the impact of this.

MSI-1 combats drug-resistant S. aureus by affecting bacterial viability and inhibiting carotenoid pigment production

Development of novel therapeutic strategies and antibacterial agents against antibiotic-resistant Staphylococcus aureus (S. aureus) is urgent. In this study, antibacterial activities and possible mechanisms of peptide MSI-1 against multiple drug-resistant S. aureus were investigated. Results demonstrated that MSI-1 had potent bacteriostatic activity and bactericidal efficiency against S. aureus, including methicillin-resistant S. aureus (MRSA), vancomycin-intermediate S. aureus (VISA) and vancomycin-resistant S. aureus (VRSA), with minimum inhibitory concentrations (MICs) ranging from 4 to 16 μg/mL and bactericidal times from 2-12 h. MSI-1 exhibited a low incidence of developing resistance and additive effects with vancomycin to overcome MRSA and VRSA. Moreover, MSI-1, even at sub-MIC concentrations, inhibited staphyloxanthin (STX) production of S. aureus. This inhibitory effect was unique and effectively sensitized S. aureus to host immune defense. In terms of its modes of action, MSI-1 disrupted the cell membrane of S. aureus by binding to negatively-charged lipoteichoic acid to exert a direct bactericidal effect. Interestingly, MSI-1 interacted with 4,4'-diapophytoene desaturase (CrtN) of S. aureus via ionic bonds, hydrogen bonds, and Pi-Pi or Pi-alkyl interactions, and alanine substitution of the key amino acids contributed to these interactions weakened this STX production inhibition. Thus, in a MRSA-induced skin infection in mice and MRSA/VRSA-induced systemic infection in Galleria mellonella,MSI-1 alleviated staphylococcal scalded skin syndrome to promote mouse skin wound repair and mitigated staphylococcus infection-induced immune melanization to enhance G. mellonella survival. Collectively, MSI-1 has potent antibacterial activity against drug-resistant S. aureus by affecting bacterial viability and exerting its anti-virulence effects. It can be developed as a new antibacterial agent to resist refractory S. aureus infection.

Genetic mutations in adaptive evolution of growth-independent vancomycin-tolerant Staphylococcus aureus

BACKGROUND

Antibiotic tolerance allows bacteria to overcome antibiotic treatment transiently and potentially accelerates the emergence of resistance. However, our understanding of antibiotic tolerance at the genetic level during adaptive evolution of Staphylococcus aureus remains incomplete. We sought to identify the mutated genes and verify the role of these genes in the formation of vancomycin tolerance in S. aureus.

METHODS

Vancomycin-susceptible S. aureus strain Newman was used to induce vancomycin-tolerant isolates in vitro by cyclic exposure under a high concentration of vancomycin (20× MIC). WGS and Sanger sequencing were performed to identify the genetic mutations. The function of mutated genes in vancomycin-tolerant isolates were verified by gene complementation. Other phenotypes of vancomycin-tolerant isolates were also determined, including mutation frequency, autolysis, lysostaphin susceptibility, cell wall thickness and cross-tolerance.

RESULTS

A series of vancomycin-tolerant S. aureus (VTSA) strains were isolated and 18 mutated genes were identified by WGS. Among these genes, pbp4, htrA, stp1, pth and NWMN_1068 were confirmed to play roles in VTSA formation. Mutation of mutL promoted the emergence of VTSA. All VTSA showed no changes in growth phenotype. Instead, they exhibited reduced autolysis, decreased lysostaphin susceptibility and thickened cell walls. In addition, all VTSA strains were cross-tolerant to antibiotics targeting cell wall synthesis but not to quinolones and lipopeptides.

CONCLUSIONS

Our results demonstrate that genetic mutations are responsible for emergence of phenotypic tolerance and formation of vancomycin tolerance may lie in cell wall changes in S. aureus.

Eco-Friendly Preparation of Epoxy-Rich Graphene Oxide for Wound Healing

Despite the ever-growing endangerment caused by the multidrug resistance (MDR) of bacteria, the development of effective antibacterial materials still remains a global challenge. Current antibiotic therapies cannot simultaneously inactivate bacteria and accelerate wound healing. This study aimed to originally separate the intercalation of MnO₃⁺ and the oxidation processes to synthesize epoxy-rich graphene oxide (erGO) nanofilms via an eco-friendly synthetic route, which possessed low density and large lamellar distribution and was rich in epoxide. Importantly, the MnO₃⁺ could be separated from the product and recycled for preparing the next generation of erGO nanofilms, which was quite economical and eco-friendly. The erGO nanofilm was capable of successfully inhibiting Gram-negative bacteria and even had excellent growth-inhibitory effects on Gram-positive bacteria including multidrug resistance (MDR) bacteria, as evidenced by antibacterial phenomena. Additionally, the erGO nanofilm with high ^•C density formed from epoxide exerted excellent antibacterial effects through tight membrane wrapping and induction of lipid peroxidation. The wound-healing property of the erGO nanofilm was evaluated via treatments of wounds infected by Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli), which not only killed bacteria but also accelerated wound healing in mice with a skin infection. The novel erGO nanofilm with dual antimicrobial mechanisms might serve as a promising multifunctional antimicrobial agent for medical wound dressing with high biocompatibility.

Single nucleotide polymorphism leads to daptomycin resistance causing amino acid substitution-T345I in MprF of clinically isolated MRSA strains

Daptomycin (DAP) is one of the most potent antibiotics used for the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infections. Due to an increase in its administration for combating MRSA infections, DAP non-susceptible (DAP-NS) MRSA strains have recently been reported in clinical settings. The presence of single nucleotide polymorphisms (SNPs) in the multiple peptide resistance factor (mprF) gene is the most frequently reported cause for the evolution of DAP-NS MRSA strains; however, there are some variations of SNPs that could lead to DAP-NS. In this study, we used two clinical MRSA strains, including DAP susceptible (DAP-S) and DAP-NS, isolated from the same patient at different time points. We introduced T345I SNP to mprF of the DAP-S MRSA strain using the gene exchange method with pIMAY vector. Further, we investigated the phenotype of the mutant strain, including drug susceptibility, cell surface positive charge, and growth speed. The mutant strain exhibited (i) resistance to DAP, (ii) up-regulation of positive surface charge, (iii) slower growth speed, and (iv) thickened cell walls. Hence, the SNP in mprF may have caused an up-regulation in MprF function, with a subsequent increase in positive surface charge. Cumulatively, these results demonstrated that the T345I amino acid substitution in mprF represents one of the primary causes of DAP-NS in MRSA strains.

Bacterial contamination upon the opening of injection needles

Introduction

Two opening methods are used for injection needle products: the “peel-apart method” where the adhesive surface of the packaging mount is peeled off, and the “push-off top method,” where the needle hub is pressed against the mount to break it. However, the risks of bacterial contamination as a result of opening method remain unknown. The aim of our study was to evaluate the bacterial contamination of needle hubs upon the opening of injection needles by the peel-apart or push-off top method under various conditions.

Methods

Bacterial contamination upon the opening of injection needles was examined in two materials, paper and plastic. Various concentrations of Staphylococcus aureus were applied to the mount and were maintained under wet or dry conditions. Injection needles were opened using the peel-apart or push-off top method. Needle hub contamination was examined using agar medium colony counting. Clinically assumed conditions (the hands and saliva of anesthesiologists) were also evaluated. Data were statistically examined using the Cochran-Mantel-Haenszel, Jonckheere, and Fisher’s exact tests.

Results

The lateral surfaces of needle hubs were contaminated using the push-off top method, but not by the peel-apart method, in a manner that was dependent on S. aureus concentrations. No significant differences were observed between mount materials. Needle hub contamination was significantly more severe for the wet than for the dry opening portion. The clinically assumed condition study revealed that the lateral and bottom surfaces of the needle hub were contaminated significantly more in the saliva contamination group than in the dry and wet hand groups.

Conclusions

The bacterial contamination of needle hubs may occur upon the opening of injection needles when the push-off top method is used and may be affected by hands contaminated with saliva under clinical conditions.

Antibiotic tolerance facilitates the evolution of resistance

Controlled experimental evolution during antibiotic treatment can help to explain the processes leading to antibiotic resistance in bacteria. Recently, intermittent antibiotic exposures have been shown to lead rapidly to the evolution of tolerance—that is, the ability to survive under treatment without developing resistance. However, whether tolerance delays or promotes the eventual emergence of resistance is unclear. Here we used in vitro evolution experiments to explore this question. We found that in all cases, tolerance preceded resistance. A mathematical population-genetics model showed how tolerance boosts the chances for resistance mutations to spread in the population. Thus, tolerance mutations pave the way for the rapid subsequent evolution of resistance. Preventing the evolution of tolerance may offer a new strategy for delaying the emergence of resistance.

Increased biofilm formation ability and accelerated transport of Staphylococcus aureus along a catheter during reciprocal movements

Staphylococcus spp. is a major cause of device-related infections. However, the mechanisms of deep-tissue infection by staphylococci from the skin surface remain unclear. We performed in vitro experiments to determine how staphylococci are transferred from the surface to the deeper layers of agar along the catheter for different strains of Staphylococcus aureus with respect to bacterial concentrations, catheter movements, and biofilm formation. We found that when 5-mm reciprocal movements of the catheter were repeated every 8h, all catheter samples of S. aureus penetrated the typical distance of 50mm from the skin to the epidural space. The number of reciprocal catheter movements and the depth of bacterial growth were correlated. A greater regression coefficient for different strains implied faster bacterial growth. Enhanced biofilm formation by different strains implied larger regression coefficients. Increased biofilm formation ability may accelerate S. aureus transport along a catheter due to physical movements by patients.

An Outbreak of Heterogeneous Glycopeptide-IntermediateStaphylococcus aureusRelated to a Device Source in an Intensive Care Unit

Objective.

The emergence ofStaphylococcus aureuswith reduced susceptibility to glycopeptides (glycopeptide-intermediateS. aureus[GISA] and heterogeneous GISA [h-GISA]) leads to intensive care unit (ICU) outbreaks that frequently result in ward closure. We investigated the role of hospital hygiene in the transmission and eradication of an h-GISA outbreak.

Design.

The study is a description of an original environmental investigation around a series of 12 cases.

Setting and Patients.

The outbreak occurred in a 20-bed polyvalent/trauma ICU in a 2,800-bed tertiary care university hospital in France.

Interventions.

Specimens were obtained for surveillance and diagnostic cultures from all patients in the unit. Surface sampling was also performed. Geographic cohorting, contact isolation, emphasis on adherence to infection control practices, and environmental cleaning were implemented.

Results.

Twelve patients with h-GISA infection (n= 5) or colonization (n= 7) were identified. The mean interval between admission and h-GISA detection was 23.6 days (range, 10–89 days), with a median of 16.5 days. Environmental investigation identified an unexpected reservoir, namely, SpO2sensors. The outbreak was controlled by a combination of measures, including eradication of this reservoir, avoiding total ward closure.

Conclusions.

Targeted surface sampling helps to secure the environment through active investigation of various reservoirs while maintaining normal activity on the ward. In our study, this method led to the detection of an unsuspected reservoir, the eradication of which helped control the h-GISA epidemic. Further applications of this original investigative procedure should allow confirmation of its relevance and efficiency.

Infect Control Hosp Epidemiol2012;33(2):167-174

Presence of both heterogeneous vancomycin-intermediate resistance and β-lactam antibiotic-induced vancomycin resistance phenotypes is associated with the outcome in methicillin-resistant Staphylococcus aureus bloodstream infection

BACKGROUND

Although the individual expression of heterogeneous vancomycin-intermediate resistance (hVISA) and β-lactam antibiotic-induced vancomycin resistance (BIVR) phenotypes has been associated with treatment failure and recurrence in methicillin-resistant Staphylococcus aureus (MRSA) infections, the effect of the co-expression of these phenotypic profiles on clinical outcome has not been fully elucidated. The aim of this study was to determine the impact of the combination of hVISA and BIVR phenotypes on the clinical outcome in MRSA bacteremia.

METHODS

One hundred and sixty-two MRSA blood isolates from a 21-y period, 1987-2007, were randomly selected. Screening for hVISA was done by the macromethod Etest and confirmed by population analysis profiles. BIVR was identified using Mu3 agar containing 4 μg/ml of vancomycin.

RESULTS

Thirty (18.5%) and 39 (24.1%) of the 162 MRSA blood isolates were positive for the hVISA and BIVR phenotypes, respectively. Eighteen (11.1%) isolates possessed both hVISA and BIVR phenotypes (hVISA(+)/BIVR(+)). In a subset of patients who received initial treatment with glycopeptides, only the patients whose isolates were hVISA(+)/BIVR(+) displayed a significantly higher mortality rate in comparison to those with non-hVISA(+)/BIVR(+) (80.0% vs 31.3%, p = 0.004). The presence of both hVISA and BIVR phenotypes was a predictor of mortality using a logistic regression analysis (p = 0.025).

CONCLUSIONS

The combined phenotype of hVISA and BIVR was associated with a higher probability of mortality in patients with MRSA bacteremia. Further prospective studies are warranted to delineate the clinical significance of the combined phenotype of hVISA and BIVR.

New therapy options for MRSA with respiratory infection/pneumonia

PURPOSE OF REVIEW

Methicillin-resistant Staphylococcus aureus (MRSA) is a frequent causative agent of nosocomial pneumonia. Because of important clinical consequences of inappropriate treatment, a current review of the potential modifications undergone by S. aureus and adaptation to new treatment options is necessary.

RECENT FINDINGS

Vancomycin has been considered the treatment of choice for pneumonia due to MRSA. However, detection of a progressive increase in the minimum inhibitory concentration for this antibiotic, its limited access to the lung parenchyma, and its considerable adverse effects have called into question its position. Linezolid has been shown to have a better pharmacokinetic and safety profiles. The prior uncertainty regarding the clinical superiority of linezolid appears to have been resolved with the publication of a recent trial. Linezolid achieved a higher clinical and microbiological response rate (the latter was not statistically significant), together with a lower incidence of all types of renal adverse effects in patients with nosocomial pneumonia, compared with vancomycin. Tigecycline, teicoplanin and quinupristin/dalfopristin were inferior to the compared drug in their respective clinical trials. The clinical efficacy of telavancin was similar to that of vancomycin. The renal adverse effects of telavancin have to be clarified. Other drugs are efficacious against MRSA but their profile should be evaluated in nosocomial pneumonia.

SUMMARY

Current therapeutic alternatives for nosocomial pneumonia due to MRSA appear to be limited to vancomycin and linezolid. However, vancomycin pitfalls, together with the apparent clinical superiority of linezolid, appear to restrict its indication. Telavancin could be a good alternative in patients without basal renal failure.

Identification of the active component that induces vancomycin resistance in MRSA

A fraction of methicillin-resistant Staphylococcus aureus (MRSA) shows resistance to vancomycin (VCM) in the presence of β-lactam antibiotics (BIVR) at low concentrations. We hypothesized that the BIVR phenomenon might be exerted by a peptidoglycan derivative(s) generated as a consequence of β-lactam antibiotic action. To verify this hypothesis, we isolated the fraction that mimicked the effect of β-lactam antibiotics by the enzymatic treatment of the crude cell wall. The active components were purified by a combination of reverse phase chromatographies, mass spectrum and amino-acid analyses, and were identified to be a muropeptide with the following formula: N-acetyglucosamyl-N-acetylmuramyl--Ala-D-isoGln-L-Lys-(ɛ-NH-4Gly)-D-Ala-2Gly. This is the very first identification of the active component, which induces VCM resistance in MRSA. We found that the BIVR cells are highly sensitive to this compound rendering the cells resistant to VCM compared with non-BIVR MRSA.

Rapid depletion of free vancomycin in medium in the presence of beta-lactam antibiotics and growth restoration in Staphylococcus aureus strains with beta-lactam-induced vancomycin resistance

A class of methicillin-resistant Staphylococcus aureus strains shows vancomycin resistance in the presence of beta-lactam antibiotics (beta-lactam-induced VAN-resistant methicillin-resistant S. aureus [BIVR]). Two possible explanations may be offered: (i) vancomycin in culture medium is depleted, and (ii) the D-Ala-D-Ala terminal of the peptidoglycan network is replaced with D-Ala-D-lactate. We tested these hypotheses by quantifying free vancomycin in the medium through the course of cell growth and by PCR amplification of the van genes. Growth of the BIVR cells to an absorption level of approximately 0.3 at 578 nm required about 24 h in the presence of vancomycin alone at the MIC (4.0 microg/ml). However, growth was achieved in only about 10 h when 1/1,000 to 1/2,000 the MIC of beta-lactam antibiotic was added 2 h prior to the addition of vancomycin, suggesting that the beta-lactams shortened the time to recovery from vancomycin-mediated growth inhibition. Free vancomycin in the culture medium decreased to 2.3 microg/ml in the first 8 h in the culture containing vancomycin alone, yet cell growth was undetectable. When the vancomycin concentration dropped below approximately 1.5 microg/ml at 24 h, the cells began to grow. In the culture supplemented with the beta-lactam 2 h prior to the addition of vancomycin, the drug concentration continuously dropped from 4 to 0.5 microg/ml in the first 8 h, and the cells began to grow at a vancomycin concentration of approximately 1.7 microg/ml or at 4 h of incubation. The gene encoding the enzyme involved in D-Ala-D-lactate synthesis was undetectable. Based on these results, we concluded that BIVR is attributable mainly to a rapid depletion of vancomycin in the medium triggered or promoted by beta-lactam antibiotics.

Persistent bacteraemia due to methicillin-resistant Staphylococcus aureus with reduced susceptibility to vancomycin in a patient with erythrodermic psoriasis

A 49-y-old male with erythrodermic psoriasis developed persistent bacteraemia for 3 months due to methicillin-resistant Staphylococcus aureus despite antimicrobial therapy. The skin was the likely focus. Three consecutive isolates from the blood and 1 from the nose were identical and had vancomycin MIC of 4 mg/l.

Community-associated methicillin-resistant Staphylococcus aureus in the patient with HIV infection

The prevalence of community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA) has increased alarmingly in both the general population and the HIV-infected community. We look at the background of MRSA including the mechanisms of resistance, genetics, and trends in the individual with HIV infection. Numerous studies have investigated the risk factors for CA-MRSA. Other studies have further characterized the incidence of and risk factors for MRSA infections in the HIV community. Although one might not readily associate advanced HIV infection with increased susceptibility to bacterial pathogens, a number of studies have explained the mechanisms of this B-cell-mediated susceptibility. Invasive MRSA infections have spread into communities, are increasingly prevalent, and pose a public health challenge for their containment, prevention, and treatment.

Nosocomial infection of beta-lactam antibiotic-induced vancomycin-resistant Staphylococcus aureus (BIVR)

We report here an outbreak of beta-lactam-induced vancomycin-resistant methicillin-resistant Staphylococcus aureus (MRSA; BIVR) at one of the Cancer-Institute-affiliated hospitals in Tokyo. We examined a total of 500 strains (100 per year) of clinically isolated MRSA from 1998 to 2002. The detection rates of BIVR in the years 1998, 1999, 2000, 2001, and 2002 were 10%, 9%, 49%, 15%, and 19%, respectively. To investigate the cause of the high incidence of BIVR detection in the year 2000, we carried out pulsed-field gel electrophoresis (PFGE) of the SmaI-digested chromosomal DNA of BIVR and MRSA. The results showed that 96% of the BIVR strains isolated in 2000 were classified as an identical DNA type "A", while only 47% of the MRSA strains were classified as this type. We concluded, based on these results, that this hospital had a nosocomial infection of BIVR in the year 2000. An important message given by this study would be that nosocomial BIVR infection could occur in any hospital where MRSA infection is treated with vancomycin and beta-lactam antibiotics.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Burn wound infections

Burns are one of the most common and devastating forms of trauma. Patients with serious thermal injury require immediate specialized care in order to minimize morbidity and mortality. Significant thermal injuries induce a state of immunosuppression that predisposes burn patients to infectious complications. A current summary of the classifications of burn wound infections, including their diagnosis, treatment, and prevention, is given. Early excision of the eschar has substantially decreased the incidence of invasive burn wound infection and secondary sepsis, but most deaths in severely burn-injured patients are still due to burn wound sepsis or complications due to inhalation injury. Burn patients are also at risk for developing sepsis secondary to pneumonia, catheter-related infections, and suppurative thrombophlebitis. The introduction of silver-impregnated devices (e.g., central lines and Foley urinary catheters) may reduce the incidence of nosocomial infections due to prolonged placement of these devices. Improved outcomes for severely burned patients have been attributed to medical advances in fluid resuscitation, nutritional support, pulmonary and burn wound care, and infection control practices.

Antimicrobial resistance among gram-positive organisms in the intensive care unit

PURPOSE OF REVIEW

The epidemiology of gram-positive pathogens in the intensive care unit are reviewed, recent trends in antimicrobial resistance among these organisms are discussed, and the significance of these data with respect to treatment are considered.

RECENT FINDINGS

Results of surveillance studies published in 2001 and 2002 have demonstrated that gram-positive organisms such as Staphylococcus aureus, coagulase-negative staphylococci, and enterococci are among the most common bacteria infecting patients in intensive care units. Furthermore, these organisms are becoming increasingly resistant to available antimicrobial agents, and 2002 has ushered in worrisome developments such as the appearance of vancomycin-resistant S. aureus. Community-acquired methicillin-resistant S. aureus and the rise in incidence of vancomycin-resistant enterococci are other problems of great concern. Novel antibiotics such as quinupristin/dalfopristin and linezolid have activity against these agents, but resistance may develop to these agents as well. Studies have shown that infections caused by antibiotic-resistant organisms may be associated with increased morbidity, mortality, and costs. Exposure to antibiotics is a major risk factor for producing antibiotic resistance in patients, and methods to limit the spread of these organisms include restriction of antibiotic use, infection control, surveillance programs, and isolation procedures.

SUMMARY

An awareness of the prevalence and patterns of resistance among gram-positive nosocomial pathogens is vital for the appropriate treatment of hospitalized patients. In addition, efforts must be made to minimize the selection and spread of these organisms.

New Developments in Antibacterial Choice for Lower Respiratory Tract Infections in Elderly Patients

Elderly patients are at increased risk of developing lower respiratory tract infections compared with younger patients. In this population, pneumonia is a serious illness with high rates of hospitalisation and mortality, especially in patients requiring admission to intensive care units (ICUs). A wide range of pathogens may be involved depending on different settings of acquisition and patient's health status. Streptococcus pneumoniae is the most common bacterial isolate in community-acquired pneumonia, followed by Haemophilus influenzae, Moraxella catarrhalis and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae. However, elderly patients with comorbid illness, who have been recently hospitalised or are residing in a nursing home, may develop severe pneumonia caused by multidrug resistant staphylococci or pneumococci, and enteric Gram-negative bacilli, including Pseudomonas aeruginosa. Moreover, anaerobes may be involved in aspiration pneumonia. Timely and appropriate empiric treatment is required in order to enhance the likelihood of a good clinical outcome, prevent the spread of antibacterial resistance and reduce the economic impact of pneumonia. International guidelines recommend that elderly outpatients and inpatients (not in ICU) should be treated for the most common bacterial pathogens and the possibility of atypical pathogens. The algorithm for therapy is to use either a selected beta-lactam combined with a macrolide (azithromycin or clarithromycin), or to use monotherapy with a new anti-pneumococcal quinolone, such as levofloxacin, gatifloxacin or moxifloxacin. Oral (amoxicillin, amoxicillin/clavulanic acid, cefuroxime axetil) and intravenous (sulbactam/ampicillin, ceftriaxone, cefotaxime) beta-lactams are agents of choice in outpatients and inpatients, respectively. For patients with severe pneumonia or aspiration pneumonia, the specific algorithm is to use either a macrolide or a quinolone in combination with other agents; the nature and the number of which depends on the presence of risk factors for specific pathogens. Despite these recommendations, clinical resolution of pneumonia in the elderly is often delayed with respect to younger patients, suggesting that optimisation of antibacterial therapy is needed. Recently, some new classes of antibacterials, such as ketolides, oxazolidinones and streptogramins, have been developed for the treatment of multidrug resistant Gram-positive infections. However, the efficacy and safety of these agents in the elderly is yet to be clarified. Treatment guidelines should be modified on the basis of local bacteriology and resistance patterns, while dosage and/or administration route of each antibacterial should be optimised on the basis of new insights on pharmacokinetic/pharmacodynamic parameters and drug interactions. These strategies should be able to reduce the occurrence of risk factors for a poor clinical outcome, hospitalisation and death.