Treatment of Acinetobacter spp infections

A 2000 patient retrospective assessment of a new strategy for burn wound management in view of infection prevention and treatment

Infections in burn patients are still the principal cause of complications in burn injuries. The aim of this study is to assess a new strategy for burn wound management in view of infection prevention and treatment in the experience of the Burn Treatment Center in Siemianowice Śląskie. The applied methodology involved the analysis of patient records describing the hospital's epidemiological situation between 2014 and 2016. The analysis also included the use and cost of antibiotics, silver-containing dressings, and other antiseptics relative to the number of sepsis cases, including those caused by Pseudomonas aeruginosa, as well as the mortality ratio. The total costs of prevention and treatment of infections were reduced, while the use of silver-containing dressings and antiseptics increased. The number of patients with sepsis decreased, including cases caused by P. aeruginosa, and the mortality ratio was reduced. Introducing a strategy for burn wound-oriented infection prevention and treatment in burn patients provides a number of benefits. It is also cost-effective. Using locally applied active dressings and antiseptics can be a welcome choice for often-unnecessary antibiotic therapy of a suspected or existing burn wound infection.

Polymyxin B and Doxycycline Use in Patients with Multidrug-Resistant Acinetobacter baumannii Infections in the Intensive Care Unit

Background:

Multidrug-resistant Acinetobacter baumannii (MDR-Ab) has emerged as an increasingly problematic cause of hospital-acquired infections in the intensive care unit (ICU). MDR-Ab is resistant to most standard antimicrobials but often retains susceptibility to polymyxin B and doxycycline.

Objective:

To evaluate the efficacy and toxicity of polymyxin B and doxycycline in the treatment of MDR-Ab infections.

Methods:

A retrospective chart review was conducted between March 2002 and May 2005 in patients who received doxycycline or polymyxin B for treatment of MDR-Ab infections in ICUs within Grady Memorial Hospital, Atlanta, GA.

Results:

Thirty-seven patients with MDR-Ab infections were treated with polymyxin B or doxycycline. Median age was 41 years and median ICU length of stay was 18 days prior to acquisition of MDR-Ab. Clinical cure was observed in 22 of 29 (76%) evaluable patients treated with polymyxin B and 2 of 4 (50%) patients treated with doxycycline. In patients with follow-up cultures, microbiological cure was observed in 17 of 21 (81%) patients treated with polymyxin B and 2 of 3 (67%) patients treated with doxycycline. Nephrotoxicity developed in 21% (7 of 33) of patients who received polymyxin B. Neurotoxicity was observed in 2 (6%) patients who received polymyxin B. No adverse reactions were observed with doxycycline. Overall, crude mortality was 27% (9 of 33) and 75% (3 of 4) among those who received polymyxin B and doxycycline, respectively. Three (9%) deaths were attributed to polymyxin B treatment failure, and no deaths were attributed to doxycycline treatment failure.

Conclusions:

Polymyxin B was effectively used to treat a substantial proportion of critically ill patients with MDR-Ab infection and was associated with a similar rate of nephrotoxicity as previously reported. Doxycycline monotherapy was used in a limited number of patients for the treatment of MDR-Ab; further evaluation of its efficacy in larger numbers of patients is warranted.

Inhaled colistin for treatment of pneumonia due to colistin-only-susceptible Acinetobacter baumannii

PURPOSE

Colistin is used for the treatment of pneumonia associated with multidrug- resistant Acinetobacter baumannii and Pseudomonas aeruginosa. However, the best route of administration and dosage is not known. We report our experience with aerosolized colistin in twelve patients with pneumonia caused by colistin-only-susceptible (COS) A. baumannii.

MATERIALS AND METHODS

We retrospectively reviewed patients' medical records who were treated with aerosolized colistin for the treatment of pneumonia.

RESULTS

Ten patients were treated only with aerosolized colistin inhalation and two patients received a 3-day course intravenous colistin, and then switched to colistin inhalation therapy. The median duration of aerosolized colistin therapy was 17 days (5-31 days). Four patients were treated only with aerosolized colistin, whereas 4 patients received concomitant glycopeptides, and 4 received concomitant levofloxacin or cefoperazone/sulbactam. At the end of the therapy, the clinical response rate and bacteriological clearance rate was 83% and 50%, respectively. Colistin-resistant strains were isolated from 3 patients after aerosolized colistin therapy; however, all of them showed favorable clinical response. The median interval between inhalation therapy and resistance was 7 days (range 5-19 days). Acute kidney injury developed in 3 patients. Two patients experienced Clostridium difficile associated diarrhea. One patient developed fever and skin rash after aerosolized colistin therapy. No patient developed neurotoxicity or bronchospasm.

CONCLUSION

Colistin inhalation therapy is deemed tolerable and safe, and could be beneficial as an adjuctive therapy for the management of pneumonia due to COS A. baumannii. However, the potential development of colistin resistance cannot be overlooked.

Epidemiology of bloodstream infections caused by Acinetobacter baumannii and impact of drug resistance to both carbapenems and ampicillin-sulbactam on clinical outcomes

Acinetobacter baumannii has become a leading cause of bloodstream infections (BSI) in health care settings. Although the incidence of infection with carbapenem- and ampicillin-sulbactam-resistant (CASR) A. baumannii has increased, there is a scarcity of studies which investigate BSI caused by CASR A. baumannii. A retrospective cohort study was conducted on adult patients with BSI caused by A. baumannii and who were admitted to the Detroit Medical Center between January 2006 and April 2009. Medical records were queried for patients' demographics, antimicrobial exposures, comorbidities, hospital stay, and clinical outcomes. Bivariate analyses and logistic regression were employed in the study. Two hundred seventy-four patients with BSI caused by A. baumannii were included in the study: 68 (25%) caused by CASR A. baumannii and 206 (75%) caused by non-CASR A. baumannii. In multivariate analysis, factors associated with BSI caused by CASR A. baumannii included admission with a rapidly fatal condition (odds ratio [OR] = 2.83, 95% confidence interval [CI] = 1.27 to 6.32, P value = 0.01) and prior use of antimicrobials (OR = 2.83, 95% CI = 1.18 to 6.78, P value = 0.02). In-hospital mortality rates for BSI caused by CASR A. baumannii were significantly higher than those for non-CASR A. baumannii-induced BSI (43% versus 20%; OR = 3.0, 95% CI = 1.60 to 5.23, P value < 0.001). However, after adjusting for potential confounders, the association between BSI caused by CASR A. baumannii and increased risk of in-hospital mortality was not significant (OR = 1.15, 95% CI = 0.51 to 2.63, P value = 0.74). This study demonstrated that CASR A. baumannii had a distinct epidemiology compared to more susceptible A. baumannii strains; however, clinical outcomes were similar for the two groups. Admission with a rapidly fatal condition was an independent predictor for both CASR A. baumannii and in-hospital mortality.

Trends in antimicrobial resistance of Acinetobacter baumannii isolates from a metropolitan Detroit health system

A phenotypic and genotypic analysis of Acinetobacter baumannii was conducted from 2003 to 2008 in Detroit, MI. The incidence of A. baumannii increased from 1.7 to 3.7/1,000 patient days during the study period. Susceptibility to ampicillin-sulbactam and imipenem decreased from approximately 90% to approximately 40%. Genotyping revealed polyclonality, suggesting either emergence of multiple resistant strains or spread of a common genetic element. The sharp rise mandates major multidisciplinary interventions to optimize management of this multidrug-resistant pathogen.

Inhibition of the class C beta-lactamase from Acinetobacter spp.: insights into effective inhibitor design

The need to develop beta-lactamase inhibitors against class C cephalosporinases of Gram-negative pathogens represents an urgent clinical priority. To respond to this challenge, five boronic acid derivatives, including a new cefoperazone analogue, were synthesized and tested against the class C cephalosporinase of Acinetobacter baumannii [Acinetobacter-derived cephalosporinase (ADC)]. The commercially available carbapenem antibiotics were also assayed. In the boronic acid series, a chiral cephalothin analogue with a meta-carboxyphenyl moiety corresponding to the C(3)/C(4) carboxylate of beta-lactams showed the lowest K(i) (11 +/- 1 nM). In antimicrobial susceptibility tests, this cephalothin analogue lowered the ceftazidime and cefotaxime minimum inhibitory concentrations (MICs) of Escherichia coli DH10B cells carrying bla(ADC) from 16 to 4 microg/mL and from 8 to 1 microg/mL, respectively. On the other hand, each carbapenem exhibited a K(i) of <20 microM, and timed electrospray ionization mass spectrometry (ESI-MS) demonstrated the formation of adducts corresponding to acyl-enzyme intermediates with both intact carbapenem and carbapenem lacking the C(6) hydroxyethyl group. To improve our understanding of the interactions between the beta-lactamase and the inhibitors, we constructed models of ADC as an acyl-enzyme intermediate with (i) the meta-carboxyphenyl cephalothin analogue and (ii) the carbapenems, imipenem and meropenem. Our first model suggests that this chiral cephalothin analogue adopts a novel conformation in the beta-lactamase active site. Further, the addition of the substituent mimicking the cephalosporin dihydrothiazine ring may significantly improve affinity for the ADC beta-lactamase. In contrast, the ADC-carbapenem models offer a novel role for the R(2) side group and also suggest that elimination of the C(6) hydroxyethyl group by retroaldolic reaction leads to a significant conformational change in the acyl-enzyme intermediate. Lessons from the diverse mechanisms and structures of the boronic acid derivatives and carbapenems provide insights for the development of new beta-lactamase inhibitors against these critical drug resistance targets.

Polymyxin B and colistimethate are comparable as to efficacy and renal toxicity

We compared 41 patients who received colistimethate with 41 who received polymyxin B for the treatment of serious infections caused by carbapenem-resistant Acinetobacter spp. and found both polymyxins have similar efficacy and toxicity.

Drug treatment for multidrug-resistant Acinetobacter baumannii infections

Acinetobacter baumannii has emerged in the last decades as a major cause of healthcare-associated infections and nosocomial outbreaks. Multidrug-resistant (MDR) A. baumannii is a rapidly emerging pathogen in healthcare settings, where it causes infections that include bacteremia, pneumonia, meningitis, and urinary tract and wound infections. Antimicrobial resistance poses great limits for therapeutic options in infected patients, especially if the isolates are resistant to the carbapenems. Other therapeutic options include sulbactam, aminoglycosides, polymixyns and tigecycline. The discovery of new therapies coupled with the development of controlled clinical trial antibiotic testing combinations and the prevention of transmission of MDR Acinetobacter infection are essential to face this important hospital problem.

Tigecycline for the treatment of multidrug-resistant (including carbapenem-resistant) Acinetobacter infections: a review of the scientific evidence

OBJECTIVES

New antibacterial agents are required for the treatment of infections caused by multidrug-resistant (MDR) Acinetobacter spp. Whether tigecycline constitutes an effective treatment option or not, is not well established. We sought to evaluate the available evidence regarding the microbiological activity and clinical effectiveness of tigecycline for MDR (including the subset of carbapenem-resistant) Acinetobacter spp.

METHODS

We searched PubMed for relevant articles and extracted/evaluated the available evidence.

RESULTS

We identified 22 microbiological studies reporting data for 2384 Acinetobacter spp. (1906 Acinetobacter baumannii). Susceptibility of at least 90% of the Acinetobacter isolates to tigecycline (with an MIC breakpoint of susceptibility < or =2 mg/L) was noted in 9/18 studies reporting data on MDR Acinetobacter and in 7/15 studies reporting specific data on carbapenem-resistant Acinetobacter. In an additional study reporting data for both resistance categories, adequate susceptibility of Acinetobacter spp. was observed by one (broth microdilution) of the methods employed. The effectiveness of tigecycline for MDR Acinetobacter infections was evaluated in eight identified clinical studies, reporting retrospective data regarding 42 severely ill patients, among whom 31 had respiratory tract infection (in 4 cases with secondary bacteraemia) and 4 had bacteraemia. Tigecycline therapy (in combination with other antibiotics in 28 patients) was effective in 32/42 cases. In three cases, resistance to tigecycline developed during treatment.

CONCLUSIONS

Tigecycline showed considerable, though not consistent, antimicrobial activity against MDR (including carbapenem-resistant) Acinetobacter spp. However, data to support its clinical use, particularly for ventilator-associated pneumonia or bacteraemia, caused by these pathogens, are still limited.

Molecular and epidemiologic study of polyclonal outbreaks of multidrug-resistant Acinetobacter baumannii infection in an Israeli hospital

OBJECTIVES

To perform a molecular and epidemiologic investigation of multidrug-resistant (MDR) Acinetobacter baumannii in an institution were polyclonal outbreaks have been observed and determine whether these polyclonal outbreaks had an endogenous origin or were caused by in-hospital patient-to-patient transmission.

DESIGN

Retrospective analysis of prospectively collected data.

SETTING

An epidemiologic and genotypic investigation of incident cases of MDR A. baumannii infection in an Israeli university tertiary care center.

PATIENTS

Hospitalized patients with MDR A. baumannii isolated from clinical samples during a 13-week period, from April 15, 2003, through July 15, 2003.

INTERVENTION

All patients with new MDR A. baumannii infections were recruited, and isolates were typed using pulsed-field gel electrophoresis. Data on in-hospital movements and consultations were extracted from computerized databases. Quantification of transmission opportunities (TOPs), defined as encounters between an established carrier and a future carrier of MDR A. baumannii, and analysis of ward clusters were performed.

RESULTS

We studied 96 MDR A. baumannii isolates, which belonged to 18 different pulsed-field gel electrophoresis clones. In 65% of cases, TOPs involving patients with the same clone were demonstrated, which is significantly greater than the number of TOPs involving patients with different clones (P=.01).

CONCLUSION

Although outbreaks of MDR A. baumannii infection may be polyclonal, we believe that patient-to-patient transmission explains most cases of transmission. Polyclonal local outbreaks reflect several clonal outbreaks occurring simultaneously. The cause of polyclonal outbreaks of A. baumannii infections clustered by ward and time remains to be explained.

Salvage treatment of pneumonia and initial treatment of tracheobronchitis caused by multidrug-resistant Gram-negative bacilli with inhaled polymyxin B

Systemic colistin has shown efficacy against multidrug-resistant Pseudomonas aeruginosa and Acinetobacter spp., but it has presented poor results in pneumonia. Aerosolized polymyxin in cystic fibrosis patients has had good results. In this study, inhaled polymyxin B was used to treat respiratory infections by multidrug-resistant Gram-negative bacilli (MR-GNBs). Nineteen patients were treated with inhaled polymyxin B: 14 pneumonia, most of which had previously failed treatment with intravenous polymyxin B, and 5 tracheobronchitis. Inhaled polymyxin B was given at the dose of 500,000 IU twice a day after an aerosolized beta(2)-agonist. In pneumonia, inhaled and intravenous polymyxin B was given together. Median age was 69 years; 89% were in the intensive care unit. Sixteen infections (84%) were caused by P. aeruginosa. Klebsiella pneumoniae, Alcaligenes xylosoxidans, and Burkholderia sp. caused one infection each. In the 14 pneumonia cases, median of previous use of intravenous polymyxin B was 20 days (range, 0-32). Inhaled polymyxin B was used for a mean of 14 days (range, 4-25). Cure occurred in 10 (53%) patients, improvement in 8 (42%), and failure in 1. Nine patients died during hospitalization (all with pneumonia). Adverse events occurred in 4 patients without interruption of inhalation. This is the largest report using inhaled polymyxin B to treat nosocomial pneumonia by MR-GNB that had failed intravenous polymyxin B. It was also effective alone in P. aeruginosa tracheobronchitis.

Surveillance cultures and duration of carriage of multidrug-resistant Acinetobacter baumannii

Isolating carriers of multidrug-resistant (MDR) Acinetobacter baumannii is the main measure to prevent its spread. Identification of carriers accompanied by contact precautions is essential. We aimed to determine the appropriate surveillance sampling sites and the duration of carriage of MDR A. baumannii. We studied prospectively two groups of patients from whom MDR A. baumannii was previously isolated: (i) those with recent clinical isolation (<or=10 days) and (ii) those with remote clinical isolation (>or=6 months). Screening for carriage was conducted from six sites: nostrils, pharynx, skin, rectum, wounds, and endotracheal aspirates. Strains recovered concurrently from different sites were genotyped using pulsed-field gel electrophoresis. Twelve of 22 with recent clinical isolation of MDR A. baumannii had >or=1 positive screening culture, resulting in a sensitivity of 55% when six body sites were sampled. Sensitivities of single sites ranged from 13.5% to 29%. Among 30 patients with remote clinical isolation, screening cultures were positive in 5 (17%), with a mean duration of 17.5 months from the last clinical culture. Remote carriers had positive screening cultures from the skin and pharynx but not from nose, rectum, wounds, or endotracheal aspirates. Eleven strains from five patients were genotyped. In all but one case, isolates from different sites in a given patient were clonal. Current methodology is suboptimal to detect MDR A. baumannii carriage. The sensitivity of surveillance cultures is low, even when six different body sites are sampled. The proportion of individuals with previous MDR A. baumannii isolation who remain carriers for prolonged periods is substantial. These data should be considered when designing measures to limit the spread of MDR A. baumannii.

Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp

Acinetobacter sp. isolates having multidrug resistance (MDR) patterns have become common in many medical centers worldwide, limiting therapeutic options. A five-center study tested 103 contemporary clinical Acinetobacter spp., including MDR strains, by reference broth microdilution and disk diffusion (15-mug disk content) methods against tigecycline. Applying U.S. Food and Drug Administration tigecycline breakpoint criteria for Enterobacteriaceae (susceptibility at < or =2 microg/ml [< or =1 microg/ml by the European Committee on Antimicrobial Susceptibility Testing]; disk diffusion breakpoints at > or =19 mm and < or =14 mm) to Acinetobacter spp. led to an unacceptable error rate (23.3%). However, an adjustment of tigecycline disk diffusion breakpoints (susceptible/resistant) to > or =16/ < or =12 mm reduced intermethod errors to an acceptable level (only 9.7%, all minor).

The epidemiology and control of Acinetobacter baumannii in health care facilities

Acinetobacter baumannii is a ubiquitous pathogen capable of causing both community and health care-associated infections (HAIs), although HAIs are the most common form. This organism has emerged recently as a major cause of HAI because of the extent of its antimicrobial resistance and its propensity to cause large, often multifacility, nosocomial outbreaks. The occurrence of outbreak is facilitated by both tolerance to desiccation and multidrug resistance, contributing to the maintenance of these organisms in the hospital environment. In addition, the epidemiology of A. baumannii infection is often complex, with the coexistence of epidemic and endemic infections, the latter of which often is favored by the selection pressure of antimicrobials. The only good news is that potentially severe A. baumannii infection, such as bacteremia or pneumonia in patients in the intensive care unit who are undergoing intubation, do not seem to be associated with a higher attributable mortality rate or an increased length of hospital stay.

Treatment of multidrug resistant Acinetobacter

PURPOSE OF REVIEW

Acinetobacter baumannii-calcoaceticus complex has become a serious nosocomial pathogen due to its persistence in the hospital environment and its broad antimicrobial resistance patterns. This review summarizes the most recent literature pertaining to the clinical management of infections with this bacteria emphasizing in-vitro antimicrobial resistance patterns and antimicrobial efficacy in animals and humans.

RECENT FINDINGS

Although this pathogen can be associated with an elevated crude mortality, it only contributes to this mortality in a subset of high-risk patients. Determining in-vitro activity of antimicrobial agents can be problematic due to conflicting results sometimes obtained through different testing methods. There is no simple answer as to the most appropriate antimicrobial therapy secondary to lack of adequate studies. Imipenem/cilastatin, amikacin, ampicillin/sulbactam, colistin, rifampin, and tetracyclines are typically active against these bacteria. It is also not clear if combination therapy is more effective than monotherapy. In cases in which A. baumannii-calcoaceticus complex bacteria are resistant to all available agents, we have prolonged infusion times, increased drug dose, and altered route of instillation, such as nebulized therapy for pulmonary infections with mixed results. A primary goal of A. baumannii-calcoaceticus complex management should be to prevent initial colonization and subsequent infection by adequate infection control.

SUMMARY

The A. baumannii-calcoaceticus complex continues to play a significant role in our healthcare systems. Prompt and adequate therapy with agents having in-vitro activity is required once it is established that the bacteria represents infection and not colonization. Aggressive infection control policies should be enforced when this pathogen is identified.

Identification of a new allelic variant of the Acinetobacter baumannii cephalosporinase, ADC-7 beta-lactamase: defining a unique family of class C enzymes

Acinetobacter spp. are emerging as opportunistic hospital pathogens that demonstrate resistance to many classes of antibiotics. In a metropolitan hospital in Cleveland, a clinical isolate of Acinetobacter baumannii that tested resistant to cefepime and ceftazidime (MIC = 32 microg/ml) was identified. Herein, we sought to determine the molecular basis for the extended-spectrum-cephalosporin resistance. Using analytical isoelectric focusing, a beta-lactamase with a pI of > or = 9.2 was detected. PCR amplification with specific A. baumannii cephalosporinase primers yielded a 1,152-bp product which, when sequenced, identified a novel 383-amino-acid class C enzyme. Expressed in Escherichia coli DH10B, this beta-lactamase demonstrated greater resistance against ceftazidime and cefotaxime than cefepime (4.0 microg/ml versus 0.06 microg/ml). The kinetic characteristics of this beta-lactamase were similar to other cephalosporinases found in Acinetobacter spp. In addition, this cephalosporinase was inhibited by meropenem, imipenem, ertapenem, and sulopenem (K(i) < 40 microM). The amino acid compositions of this novel enzyme and other class C beta-lactamases thus far described for A. baumannii, Acinetobacter genomic species 3, and Oligella urethralis in Europe and South Africa suggest that this cephalosporinase defines a unique family of class C enzymes. We propose a uniform designation for this family of cephalosporinases (Acinetobacter-derived cephalosporinases [ADC]) found in Acinetobacter spp. and identify this enzyme as ADC-7 beta-lactamase. The coalescence of Acinetobacter ampC beta-lactamases into a single common ancestor and the substantial phylogenetic distance separating them from other ampC genes support the logical value of developing a system of nomenclature for these Acinetobacter cephalosporinase genes.

Hospital outbreak caused by a carbapenem-resistant strain of Acinetobacter baumannii: patient prognosis and risk-factors for colonisation and infection

Between October 2001 and August 2002, 30 hospital patients became infected or colonised by a multiresistant (including to carbapenems) epidemic strain of Acinetobacter baumannii (AbMR) in a hospital outbreak. This study analysed the risk-factors associated with acquisition of this epidemic strain and investigated the prognosis of patients infected by AbMR, with the aim of elucidating factors which lead to mortality. A case-control study of the acquisition of AbMR in patients infected or colonised in the hospital outbreak was performed. Independent risk-factors leading to death were studied by logistic regression analysis. Multivariate analysis of the risk-factors for colonisation/infection with AbMR revealed an independent association with the presence of an arterial catheter (OR, 1.13; 95% CI, 1.03-1.25) and administration of imipenem as monotherapy (OR, 11.12; 95% CI, 2.33-53.09). Multivariate analysis of the prognostic features leading to mortality revealed a significant association with hypotension or shock (OR, 24.63; 95% CI, 1.56-387.56) at the time of bacterial isolation.

Comprehensive in vitro evaluation of cefepime combined with aztreonam or ampicillin/sulbactam against multi-drug resistant Pseudomonas aeruginosa and Acinetobacter spp

Pseudomonas aeruginosa and Acinetobacter spp. are becoming increasingly resistant to antimicrobial agents, and serious infections caused by these organisms often require combination therapy. Interactions of cefepime with either aztreonam (P. aeruginosa; n=46) or ampicillin/sulbactam (Acinetobacter spp.; n=34) were investigated by the chequerboard synergy method against isolates with various resistance phenotypes, including resistance to imipenem (36 P. aeruginosa and 19 Acinetobacter spp.). Synergy or partial synergy interactions occurred with 56.5% of P. aeruginosa and 88.2% of Acinetobacter spp. strains examined. Among the imipenem-resistant strains, synergy or partial synergy interactions were observed in 47.2% of P. aeruginosa and 84.2% of Acinetobacter spp. strains. In addition, the vast majority of impenem-resistant strains showed MIC values within achievable concentrations in plasma for at least one of the antimicrobials evaluated in the combination. The role of combination antimicrobial therapy in the treatment of severe infections caused by multidrug-resistant P. aeruginosa and Acinetobacter spp. should be further evaluated to maximize favourable clinical outcomes.

β-Lactamase inhibitors: evolving compounds for evolving resistance targets

The many and diverse beta-lactamases produced by bacteria, particularly by Gram-negative pathogens, are increasingly posing a serious threat to the clinical utility of beta-lactams. First-generation inhibitors (clavulanic acid, sulbactam, tazobactam) focus on Ambler class A enzymes. However, recent structural upgrades of class A beta-lactamases (e.g. TEM, SHV) have extended their spectrum (extended-spectrum beta-lactamases and carbapenemases [Sme, NMC-A, IMI-1]) and have brought about the possibility of beta-lactamase-inhibitor resistance. Furthermore, the mobilisation and spread of originally chromosomal class C enzymes (CMY, MIR), the growing clinical importance of class B enzymes (IMP, VIM), the emergence of inhibitor-resistant, broad spectrum class D (OXA) enzymes and the co-existence of different classes of beta-lactamases in the same pathogen have spurred research toward universal inhibitors. A complicating issue is target accessibility in Gram-negative bacteria, particularly in Enterobacter, Acinetobacter, Pseudomonas, Stenotrophomonas and other organisms, which is necessary in order for the inhibitor to synergise with vulnerable beta-lactam antibiotics. Several new, broad-spectrum inhibitors have emerged: cephem sulfones and oxapenems are upgrades of penam sulfones and oxapenams, respectively, with cephem sulfones possibly extending their inhibition to class B metallo-enzymes; and boronates and phosphonates are designed de novo, based on common structural and mechanistic features of serine beta-lactamases.