Ampicillin-resistant Haemophilus influenzae type B possessing a TEM-type beta-lactamase but little permeability barrier to ampicillin

Evolution of mutations in the ftsI gene leading to amino acid substitutions in PBP3 in Haemophilus influenzae strains under the selective pressure of ampicillin and cefuroxime

BACKGROUND

Aminopenicillins are recommended agents for non-invasive Haemophilus influenzae infections. One of the mechanisms of resistance to β-lactams is the alteration of the transpeptidase region of penicillin binding protein 3 (PBP3) which is caused by mutations in the ftsI gene. It was shown that exposure to beta-lactams has a stimulating effect on increase of prevalence of H. influenzae strains with the non-enzymatic mechanism of resistance.

OBJECTIVES

The aim of our study was to compare the mutational potential of ampicillin and cefuroxime in H. influenzae strains, determination of minimum inhibitory concentration and the evolution of mutations over time, focusing on amino acid substitutions in PBP3.

METHODS

30 days of serial passaging of strains in liquid broth containing increasing concentrations of ampicillin or cefuroxime was followed by whole-genome sequencing.

RESULTS

On average, cefuroxime increased the minimum inhibitory concentration more than ampicillin. The minimum inhibitory concentration was increased by a maximum of 32 fold. Substitutions in the PBP3 started to appear after 15 days of passaging. In PBP3, cefuroxime caused different substitutions than ampicillin.

CONCLUSIONS

Our experiment observed differences in mutation selection by ampicillin and cefuroxime. Selection pressure of antibiotics in vitro generated substitutions that do not occur in clinical strains in the Czech Republic.

Molecular characterization of multidrug-resistant non-typeable Haemophilus influenzae with high-level resistance to cefuroxime, levofloxacin, and trimethoprim-sulfamethoxazole

BACKGROUND

Non-typeable Haemophilus influenzae (NTHi) has become the major cause of invasive H. influenzae diseases in the post-H. influenzae type b vaccine era. The emergence of multidrug-resistant (MDR) NTHi is a growing public health problem. Herein, we investigated the molecular basis of MDR in NTHi. The isolated NTHi were subjected to antimicrobial susceptibility testing for 12 agents. Whole genome and plasmid sequencing were conducted and analyzed to identify significant genetic variations and plasmid-encoded genes conferred antibiotic resistance.

RESULTS

Thirteen (50%) MDR NTHi isolates were obtained; of these, 92.3% were non-susceptible to ampicillin, 30.8% to amoxicillin-clavulanate, 61.5% to cefuroxime, 61.5% to ciprofloxacin/levofloxacin, 92.3% to trimethoprim-sulfamethoxazole, 30.8% to tetracycline, and 7.7% to azithromycin. Eight ampicillin-resistant isolates were β-lactamase positive; of these, 6 carried bla_TEM-1 and 2 carried bla_ROB-1, whereas 4 were β-lactamase negative. Genetic variations in mrdA, mepA, and pbpG were correlated with amoxicillin-clavulanate non-susceptibility, whereas variations in ftsI and lpoA conferred cefuroxime resistance. Five variations in gyrA, 2 in gyrB, 3 in parC, 1 in parE, and 1 in the parC-parE intergenic region were associated with levofloxacin/ciprofloxacin non-susceptibility. Among these genes, 8 variations were linked to high-level levofloxacin resistance. Six variations in folA were associated with trimethoprim-sulfamethoxazole resistance. Plasmid-bearing tet(B) and mef(A) genes were responsible for tetracycline and azithromycin resistance in 4 and 1 MDR isolates, respectively.

CONCLUSIONS

This study clarified the molecular epidemiology of MDR in NTHi. This can benefit the monitoring of drug resistance trends in NTHi and the adequate medical management of patients with NTHi infection.

Antimicrobial Susceptibility Survey of Invasive Haemophilus influenzae in the United States in 2016

Antibiotics are important for the treatment and prevention of invasive Haemophilus influenzae disease. Reduced susceptibility to clinically relevant drugs, except ampicillin, has been uncommon in the United States. Susceptibility of 700 invasive H. influenzae isolates, collected through population-based surveillance during 2016, was assessed for 15 antibiotics using broth microdilution, according to the CLSI guidelines; a subset of 104 isolates were also assessed for rifampin susceptibility using Etest. Genomes were sequenced to identify genes and mutations known to be associated with reduced susceptibility to clinically relevant drugs. A total of 508 (72.6%) had reduced susceptibility to at least one antibiotic and more than half of the isolates exhibited reduced susceptibility to only one (33.6%) or two (21.6%) antibiotic classes. All tested isolates were susceptible to rifampin, a chemoprophylaxis agent, and <1% (n = 3) of isolates had reduced susceptibility to third generation cephalosporins, which are recommended for invasive disease treatment. In contrast, ampicillin resistance was more common (28.1%) and predominantly associated with the detection of a β-lactamase gene; 26.2% of isolates in the collection contained either a TEM-1 or ROB-1 β-lactamase gene, including 88.8% of ampicillin-resistant isolates. β-lactamase negative ampicillin-resistant (BLNAR) isolates were less common and associated with ftsI mutations; resistance to amoxicillin-clavulanate was detected in <2% (n = 13) of isolates. The proportion of reduced susceptibility observed was higher among nontypeable H. influenzae and serotype e than other serotypes. US invasive H. influenzae isolates remain predominantly susceptible to clinically relevant antibiotics except ampicillin, and BLNAR isolates remain uncommon. IMPORTANCE Antibiotics play an important role for the treatment and prevention of invasive Haemophilus influenzae disease. Antimicrobial resistance survey of invasive H. influenzae isolates collected in 2016 showed that the US H. influenzae population remained susceptible to clinically relevant antibiotics, except for ampicillin. Detection of approximately a quarter ampicillin-resistant and β-lactamase containing strains demonstrates that resistance mechanisms can be acquired and sustained within the H. influenzae population, highlighting the continued importance of antimicrobial resistance surveillance for H. influenzae to monitor susceptibility trends and mechanisms of resistance.

Antimicrobial resistance among Haemophilus influenzae isolates responsible for lower respiratory tract infections in Poland, 2005-2019

Haemophilus influenzae is a human-specific pathogen responsible for respiratory tract infections, meningitis, and sepsis. The study aimed to characterize antibiotic resistance in H. influenzae strains isolated from patients with lower respiratory tract infections over 15 years in Poland. The minimum inhibitory concentrations (MICs) of clinically relevant antibiotics were determined by broth microdilution method. Screening for beta-lactam resistance was performed in all isolates following EUCAST recommendation. Finally, relevant changes in penicillin-binding protein 3 (PBP3) were detected by PCR screening. Of the 1481 isolates collected between 2005 and 2019, 12.6%, 0.2%, 17.1%, and 0.2% were resistant to ampicillin, amoxicillin/clavulanate, cefuroxime, and ceftriaxone, respectively. Among them, 74.4% (1102/1481) of isolates were categorized as BLNAS (β-lactamase negative, ampicillin-susceptible), 13.0% (192/1481) as BLNAS with modified PBP3 (mutations in ftsI gene), 2.6% (39/1481) as BLNAR (β-lactamase negative, ampicillin-resistant), and 0.2% had PBP3 modifications typical for high-BLNAR. Production of β-lactamase characterized 9.7% of isolates (8.6% BLPAR-β-lactamase-positive, ampicillin-resistant, and 1.1% BLPACR-β-lactamase-positive, amoxicillin-clavulanate resistant). Three isolates with PBP3 modifications typical for high-BLNAR proved resistant to ceftriaxone (MIC > 0.125 mg/L). Resistance to ciprofloxacin, chloramphenicol, tetracycline, and trimethoprim-sulfamethoxazole was observed in 0.1%, 0.5%, 1.6%, and 24.7% of isolates, respectively. This is the first report of Polish H. influenzae isolates resistant to third-generation cephalosporins. Polish H. influenzae isolates demonstrate similar susceptibility trends as in many other countries. The substantial proportion of β-lactam-resistant isolates and the emergence of those resistant to third-generation cephalosporins are of great concern and should be under surveillance.

Overcoming the rising incidence and evolving mechanisms of antibiotic resistance by novel drug delivery approaches - An overview

Antimicrobial resistance is a normal evolutionary process for microorganisms. Antibiotics exerted accelerated selective pressure that hasten bacterial resistance through mutation, and acquisition external genes. These genes often carry multiple antibiotic resistant determinants allowing the recipient microbe an instant "super-bug" status. The extent of Antimicrobial Resistance (AMR) has reached a level of global crisis, existing antimicrobials are no long effective in treating infections caused by AMR pathogens. The great majority of clinically available antimicrobial agents are administered through oral and intra-venous routes. Overcoming antibacterial resistance by novel drug delivery approach offered new hopes, particularly in the treatment of AMR pathogens in sites less assessible through systemic circulation such as the lung and skin. In the current review, we will revisit the mechanism and incidence of important AMR pathogens. Finally, we will discuss novel drug delivery approaches including novel local antibiotic delivery systems, hybrid antibiotics, and nanoparticle-based antibiotic delivery systems.

Characterization of Haemophilus influenzae Strains with Non-Enzymatic Resistance to β-Lactam Antibiotics Caused by Mutations in the PBP3 Gene in the Czech Republic in 2010-2018

The surveillance data on antibiotic resistance of Haemophilus influenzae have shown that strains with non-enzymatic resistance to β-lactam antibiotics have been on the rise in the Czech Republic over the last decade. This type of resistance is more difficult to detect than β-lactamase production. Analysis of 228 H. influenzae strains revealed that isolates with non-enzymatic resistance to β-lactams due to mutations in the ftsI gene could be reliably demonstrated by single run testing of susceptibility to amoxicillin/clavulanic acid (sensitivity of detection is 84.6%), cefuroxime (92.6%), ampicillin and penicillin (both 95.7%). Thirty-seven different amino acid substitution combinations were detected in the PBP3 protein at 23 positions (V329I, D350N, S357N, A368T, M377I, S385T, A388V, L389F, P393L, A437S, I449V, G490E, I491V, R501L, A502S, A502T, A502V, V511A, R517H, I519L, N526K, A530S, and T532S). The most common combination (35%) of amino acid substitutions was the combination D350N, M377I, A502V, N526K. Epidemiological typing does not indicate a clonal spread of a particular MLST type. Altogether there has been detected 74 STs. The most prevalent ST 1034 was associated mainly with a combination D350N, M377I, A502V, N526K. Clonal analysis revealed six clonal complexes (CCs) with the founder found, eight CCs without founder and 33 singletons.

Extensively drug-resistant Haemophilus influenzae - emergence, epidemiology, risk factors, and regimen

Background

Concern about Haemophilus influenzae infection has been increasing over recent decades. Given the emergence of H. influenzae with severe drug resistance, we assessed the prevalence of as well as risk factors and potential therapies for extensively drug-resistant (XDR) H. influenzae infection in Taiwan.

Results

In total, 2091 H. influenzae isolates with disk diffusion-based antibiotic susceptibility testing from 2007 to 2018 were enrolled. H. influenzae strains resistant to ampicillin, chloramphenicol, levofloxacin, and trimethoprim-sulfamethoxazole tended to be isolated from patient wards (≧41%), whereas those resistant to amoxicillin-clavulanate, cefotaxime, and cefuroxime were more likely to be isolated from intensive care units (approximately 50%). XDR H. influenzae was first identified in 2007, and its incidence did not significantly change thereafter. Overall prevalence of single, multiple, and extensively drug-resistant H. influenzae over 2007–2018 was 21.5% (n = 450), 26.6% (n = 557), and 2.5% (n = 52), respectively. A stepwise logistic regression analysis revealed that blood culture (odds ratio: 4.069, 95% confidence intervals: 1.339–12.365, P = 0.013) was an independent risk factor for XDR H. influenzae infection. No nosocomial transmission of XDR H. influenzae observed. Antibiotic susceptibility testing results demonstrated that cefotaxime was effective against 78.8% (n = 41) of the XDR strains.

Conclusions

The presence of XDR H. influenzae strains was identified in Taiwan, and cefotaxime was efficacious against most of these strains.

Interplay between β-lactamases and new β-lactamase inhibitors

Resistance to β-lactam antibiotics in Gram-negative bacteria is commonly associated with production of β-lactamases, including extended-spectrum β-lactamases (ESBLs) and carbapenemases belonging to different molecular classes: those with a catalytically active serine and those with at least one active-site Zn²⁺ to facilitate hydrolysis. To counteract the hydrolytic activity of these enzymes, combinations of a β-lactam with a β-lactamase inhibitor (BLI) have been clinically successful. However, some β-lactam-BLI combinations have lost their effectiveness against prevalent Gram-negative pathogens that produce ESBLs, carbapenemases or multiple β-lactamases in the same organism. In this Review, descriptions are provided for medically relevant β-lactamase families and various BLI combinations that have been developed or are under development. Recently approved inhibitor combinations include the inhibitors avibactam and vaborbactam of the diazabicyclooctanone and boronic acid inhibitor classes, respectively, as new scaffolds for future inhibitor design.

Past and Present Perspectives on β-Lactamases

β-Lactamases, the major resistance determinant for β-lactam antibiotics in Gram-negative bacteria, are ancient enzymes whose origins can be traced back millions of years ago. These well-studied enzymes, currently numbering almost 2,800 unique proteins, initially emerged from environmental sources, most likely to protect a producing bacterium from attack by naturally occurring β-lactams. Their ancestors were presumably penicillin-binding proteins that share sequence homology with β-lactamases possessing an active-site serine. Metallo-β-lactamases also exist, with one or two catalytically functional zinc ions. Although penicillinases in Gram-positive bacteria were reported shortly after penicillin was introduced clinically, transmissible β-lactamases that could hydrolyze recently approved cephalosporins, monobactams, and carbapenems later became important in Gram-negative pathogens. Nomenclature is based on one of two major systems. Originally, functional classifications were used, based on substrate and inhibitor profiles. A later scheme classifies β-lactamases according to amino acid sequences, resulting in class A, B, C, and D enzymes. A more recent nomenclature combines the molecular and biochemical classifications into 17 functional groups that describe most β-lactamases. Some of the most problematic enzymes in the clinical community include extended-spectrum β-lactamases (ESBLs) and the serine and metallo-carbapenemases, all of which are at least partially addressed with new β-lactamase inhibitor combinations. New enzyme variants continue to be described, partly because of the ease of obtaining sequence data from whole-genome sequencing studies. Often, these new enzymes are devoid of any phenotypic descriptions, making it more difficult for clinicians and antibiotic researchers to address new challenges that may be posed by unusual β-lactamases.

The return of Pfeiffer's bacillus: Rising incidence of ampicillin resistance in Haemophilus influenzae

Haemophilus influenzae, originally named Pfeiffer's bacillus after its discoverer Richard Pfeiffer in 1892, was a major risk for global health at the beginning of the 20th century, causing childhood pneumonia and invasive disease as well as otitis media and other upper respiratory tract infections. The implementation of the Hib vaccine, targeting the major capsule type of H. influenzae, almost eradicated the disease in countries that adapted the vaccination scheme. However, a rising number of infections are caused by non-typeable H. influenzae (NTHi), which has no capsule and against which the vaccine therefore provides no protection, as well as other serotypes equally not recognised by the vaccine. The first line of treatment is ampicillin, but there is a steady rise in ampicillin resistance. This is both through acquired as well as intrinsic mechanisms, and is cause for serious concern and the need for more surveillance. There are also increasing reports of new modifications of the intrinsic ampicillin-resistance mechanism leading to resistance against cephalosporins and carbapenems, the last line of well-tolerated drugs, and ampicillin-resistant H. influenzae was included in the recently released priority list of antibiotic-resistant bacteria by the WHO. This review provides an overview of ampicillin resistance prevalence and mechanisms in the context of our current knowledge about population dynamics of H. influenzae.

β-Lactam resistance among Haemophilus influenzae isolates in Poland

OBJECTIVES

Haemophilus influenzae is a human-specific Gram-negative coccobacillus responsible for a significant number of respiratory tract infections and severe invasive infections such as meningitis and sepsis. The purpose of this study was to characterise the mechanisms of β-lactam resistance among Polish H. influenzae isolates and to evaluate the resistance detection methods applied.

METHODS

This study was conducted on 117 Polish H. influenzae isolates collected in 2012. Minimum inhibitory concentrations were assessed by broth microdilution. All strains were evaluated using the disk diffusion method and the algorithm proposed by the Nordic Committee on Antimicrobial Susceptibility Testing (NordicAST). To detect changes in penicillin-binding protein 3 (PBP3), PCR screening was performed, followed by ftsI gene sequencing.

RESULTS

Neither β-lactamase production nor PBP3 alterations were demonstrated in 76 isolates (65.0%). Susceptibility to ampicillin, amoxicillin, amoxicillin/clavulanic acid, cefuroxime (intravenous) and ceftriaxone was observed in 70.9%, 78.6%, 98.3%, 82.9% and 100% of the isolates, respectively. β-Lactamase production characterised 21 isolates (17.9%). Screening PCR identified 20 isolates (17.1%) with PBP3 alterations, and according to subsequent ftsI sequencing all these strains were finally recognised as gBLNAR (genetically β-lactamase-negative, ampicillin-resistant), among which 65.0% were ampicillin-resistant. According to molecular classification of PBP3 alterations, 95.0% of gBLNAR belonged to group II, representing four subgroups IIa-IId.

CONCLUSIONS

Haemophilus influenzae resistance to antibiotics requires continuous attention, effective detection methods and a rational policy of antibiotic usage. The algorithm proposed by NordicAST can be applied in routine laboratory work, whereas sequencing of the ftsI gene may be useful in molecular epidemiology studies.

Imipenem heteroresistance in nontypeable Haemophilus influenzae is linked to a combination of altered PBP3, slow drug influx and direct efflux regulation

OBJECTIVE

To investigate the potential roles of PBPs, efflux pumps and slow drug influx for imipenem heteroresistance in nontypeable Haemophilus influenzae (NTHi).

METHODS

Fifty-nine NTHi clinical isolates examined in this study were collected at Geneva University Hospitals between 2009 and 2014. Alterations in PBPs were investigated by gene sequencing. To evaluate the affinities of the PBPs to imipenem, steady-state concentration-response experiments were carried out using imipenem in a competition assay with Bocillin-FL. The effect of the carbonyl cyanide m-chlorophenylhydrazone (CCCP) on imipenem susceptibility was assessed using broth dilution and viable cell counting. Using whole-genome sequencing, we explored the potential roles of outer membrane protein P2 (OmpP2), LytM proteins and the dcw gene cluster in imipenem heteroresistance.

RESULTS

All 46 imipenem-heteroresistant isolates (IMI^hR) harboured amino acid substitutions in the ftsI gene, which encodes PBP3, corresponding to 25 different mutation patterns that varied from the ftsI gene mutation patterns found in imipenem-susceptible isolates. Among all PBPs, the highest affinity to imipenem was documented for PBP3 (IC₅₀, 0.004 μg/mL). Different amino acid substitutions and insertions were noted in OmpP2, suggesting a relationship with imipenem heteroresistance. The IMI^hR isolates were affected by CCCP differently and displayed a higher percentage of killing by imipenem in CCCP-treated cells at concentrations ranging between 0.5 and 8 μg/mL.

CONCLUSIONS

The present study provides robust evidence indicating that in combination with the altered PBP3, the slowed drug influx and its enhanced efflux due to the loss of regulation led to the development of imipenem heteroresistance in NTHi.

EUCAST expert rules in antimicrobial susceptibility testing

EUCAST expert rules have been developed to assist clinical microbiologists and describe actions to be taken in response to specific antimicrobial susceptibility test results. They include recommendations on reporting, such as inferring susceptibility to other agents from results with one, suppression of results that may be inappropriate, and editing of results from susceptible to intermediate or resistant or from intermediate to resistant on the basis of an inferred resistance mechanism. They are based on current clinical and/or microbiological evidence. EUCAST expert rules also include intrinsic resistance phenotypes and exceptional resistance phenotypes, which have not yet been reported or are very rare. The applicability of EUCAST expert rules depends on the MIC breakpoints used to define the rules. Setting appropriate clinical breakpoints, based on treating patients and not on the detection of resistance mechanisms, may lead to modification of some expert rules in the future.

Natural evolution of TEM-1 β-lactamase: experimental reconstruction and clinical relevance

TEM-1 β-lactamase is one of the most well-known antibiotic resistance determinants around. It confers resistance to penicillins and early cephalosporins and has shown an astonishing functional plasticity in response to the introduction of novel drugs derived from these antibiotics. Since its discovery in the 1960s, over 170 variants of TEM-1 - with different amino acid sequences and often resistance phenotypes - have been isolated in hospitals and clinics worldwide. Next to this well-documented 'natural' evolution, the in vitro evolution of TEM-1 has been the focus of attention of many experimental studies. In this review, we compare the natural and laboratory evolution of TEM-1 in order to address the question to what extent the evolution of antibiotic resistance can be repeated, and hence might have been predicted, under laboratory conditions. We also use the comparison to gain an insight into the adaptive relevance of hitherto uncharacterized substitutions present in clinical isolates and to predict substitutions not yet observed in nature. Based on new structural insights, we review what is known about substitutions in TEM-1 that contribute to the extension of its resistance phenotype. Finally, we address the clinical relevance of TEM alleles during the past decade, which has been dominated by the emergence of another β-lactamase, CTX-M.

Mutant ftsI genes in the emergence of penicillin-binding protein-mediated beta-lactam resistance in Haemophilus influenzae in Norway

The most important mechanism for beta-lactam resistance in beta-lactamase-negative ampicillin-resistant (BLNAR) isolates of Haemophilus influenzae is the alteration of penicillin-binding protein 3 (PBP3) as a result of ftsI gene mutations. The present study aimed to map PBP3 alterations and to determine the correlation to beta-lactam resistance in respiratory tract isolates of H. influenzae in Norway, as well as assess the contribution of clonal spread to the emergence of PBP3-mediated resistance. Twenty-three beta-lactamase negative respiratory tract isolates with resistance to penicillins and 23 susceptible control isolates were examined by determination of beta-lactam MICs, ftsI sequencing and molecular typing by pulsed-field gel electrophoresis (PFGE). Ampicillin MIC ranges in the resistant group and the control group were 1-2 mg/L and 0.125-0.5 mg/L, respectively. All isolates in the resistant group had the PBP3 substitution Asn526-->Lys and were thus categorized as group II low-BLNAR. No control isolate met the genetic BLNAR (gBLNAR) criteria. The PBP3 substitution patterns corresponded well to those observed in previous European studies. Eighty-three percent (19/23) of the resistant isolates belonged to two clones, demonstrating the capability of low-BLNAR strains of clonal dissemination. Combined analysis of ftsI DNA sequences and PFGE patterns revealed distinctly different ftsI alleles in genetically indistinguishable isolates and identical copies of the same ftsI allele in unrelated isolates. A possible explanation of this observation is the recombinational exchange of ftsI alleles. This phenomenon, as well as the possibility of endemic European gBLNAR strains, should be further investigated.

Antimicrobial resistance in Haemophilus influenzae

Haemophilus influenzae is a major community-acquired pathogen causing significant morbidity and mortality worldwide. Meningitis and bacteremia due to type b strains occur in areas where the protein-conjugated type b vaccine is not in use, whereas nontypeable strains are major causes of otitis media, sinusitis, acute exacerbations of chronic bronchitis, and pneumonia. Antibiotic resistance in this organism is more diverse and widespread than is commonly appreciated. Intrinsic efflux resistance mechanisms limit the activity of the macrolides, azalides, and ketolides. beta-Lactamase production is highly prevalent worldwide and is associated with resistance to ampicillin and amoxicillin. Strains with alterations in penicillin binding proteins, particularly PBP3 (beta-lactamase negative ampicillin resistant and beta-lactamase positive amoxicillin-clavulanate resistant), are increasing in prevalence, particularly in Japan, with increasing resistance to ampicillin, amoxicillin, amoxicillin-clavulanate, and many cephalosporins, limiting the efficacy of expanded-spectrum cephalosporins against meningitis and of many oral cephalosporins against other diseases. Most strains remain susceptible to the carbapenems, which are not affected by penicillin binding protein changes, and the quinolones. The activity of many oral agents is limited by pharmacokinetics achieved with administration by this route, and the susceptibility of isolates based on pharmacokinetic and pharmacodynamic parameters is reviewed.

Optimizing the management of community-acquired respiratory tract infections in the age of antimicrobial resistance

Community-acquired respiratory tract infections (CARTIs) are the most common reason for prescribing antibiotics in the primary care setting. However, over the last decade, the management of CARTIs has become increasingly complicated by the steady increase in prevalence of drug-resistant pathogens responsible for these infections. As a result, significant attention has been directed at understanding the mechanisms of pathogen acquisition of resistance, drivers of resistance and methods for preventing the development of resistance. Data from recent surveillance studies suggest a slowing or decline in resistance rates to agents, such as beta-lactams, macrolides, tetracyclines and folic acid metabolism inhibitors. However, resistance to one antimicrobial family--the fluoroquinolones--while still low, appears to be on the increase. This is of significant concern given the rapid increase in resistance noted with older antibiotics in recent history. While the clinical implications of antibacterial resistance are poorly understood, the overall rates of antimicrobial resistance, as reported in recent surveillance studies, do not correspond to current rates of failure in patients with CARTIs. This disconnection between laboratory-determined resistance and clinical outcome has been termed the in vitro-in vivo paradox and several explanations have been offered to explain this phenomenon. Solving the problem of antimicrobial resistance will be multifactorial. Important factors in this effort include the education of healthcare providers, patients and the general healthcare community regarding the hazards of inappropriate antibiotic use, prevention of infections through vaccination, development of accurate, inexpensive and timely point-of-care diagnostic tests to aid in patient assessment, institution of objective treatment guidelines and use of more potent agents, especially those with a focused spectrum of activity, earlier in the treatment of CARTIs as opposed to reserving them as second-line treatment options. Ultimately, the single-most important factor will be the judicious use of antibiotics, as fewer antibiotic prescriptions lead to fewer antimicrobial-resistant bacteria.

Antimicrobial drug use and resistance among respiratory pathogens in the community

There is substantial evidence that the overuse of antibiotics is a major cause for the emergence of resistance in respiratory pathogens in the community. However, it is also recognized that the mechanisms of resistance, the cost of resistance to the fitness of the organism, and the ability of the resistant strain to disseminate are all important contributors to this problem. Therefore, when developing strategies to control and/or prevent the emergence of resistance, health care professionals must take each of these factors into consideration. As we enter a new era in the use of fluoroquinolones for the treatment of respiratory tract infections, we have an opportunity to apply such lessons learned in the past to minimize or prevent the development of resistance to this class of antimicrobial drugs in the future.

Resistance patterns of lower respiratory tract pathogens in Europe

Resistance to antimicrobial drugs in the major respiratory tract pathogens is known to vary profoundly depending on geographic location. In Europe high rates (>44%) of penicillin-resistance in pneumococci have been recorded in France and Spain, while countries like The Netherlands, the Czech Republic, Austria and Italy are only marginally affected. Similarly, the incidence of macrolide resistance differs widely among European nations with figures ranging from 45.9% (France) to 1.5% (The Netherlands). Significant percentages (>20%) of co-trimoxazole and doxycycline resistance have been found in France, Spain, Italy, Hungary, Poland and Belgium. The prevailing mechanism of resistance in Haemophilus influenzae is represented by beta-lactamase synthesis for which considerable variations (from 0 to 38.5%) have been evidenced. Ampicillin resistant beta-lactamase negative H. influenzae are very uncommon. Over 90% of Moraxella catarrhalis isolates are beta-lactamase producers without big differences among European countries.

Resistance patterns of Haemophilus influenzae

Haemophilus influenzae is an important respiratory tract pathogen, and the prevalence of strains resistant to the antibiotics used to treat it has increased since the 1970s. Data on H. influenzae have been gathered in the Alexander Project, an ongoing, international surveillance study. They reveal that beta-lactamase production is the primary mechanism for H. influenzae resistance and that the resistance has a wide geographical variation, reaching critical levels in some countries. Unlike many techniques used in the past, Alexander Project methods provide accurate, reproducible susceptibility data, allowing the comparison of resistance prevalence over time and between areas. Traditional antimicrobial breakpoints are being superseded by more accurate and clinically relevant methods of predicting drug efficacy, such as time above the MIC, AUC:MIC ratios and pharmacodynamic breakpoints. Continued surveillance for resistance and susceptibility testing of H. influenzae is vital to maximize the benefits of antimicrobial therapy and to contain the spread of infection.

Trends in antimicrobial susceptibility of bacterial pathogens of the respiratory tract

Rates of antimicrobial resistance have been increasing in bacteria responsible for community-acquired lower respiratory tract infections in the United States. Nearly 100% of clinical isolates of Moraxella catarrhalis now produce beta-lactamase, an enzyme that renders this pathogen resistant to such agents as penicillin, ampicillin, and amoxicillin. However, this organism remains nearly uniformly susceptible to alternative oral antimicrobials, such as cephalosporins, macrolides, tetracyclines, beta-lactamase inhibitor combinations, and the combination of trimethoprim/sulfamethoxazole. The susceptibility of M. catarrhalis to these agents is not expected to change markedly in the next few years. A linear increase in the prevalence of beta-lactamase-mediated ampicillin resistance has been evident among isolates of nontypeable Haemophilus influenzae during the past decade in the United States. By the year 2000, 45-50% of isolates are likely to produce beta-lactamase. Although the susceptibility of this organism to alternative oral antimicrobials varies, rates of resistance to cefuroxime axetil, cefpodoxime, cefixime, azithromycin, and perhaps clarithromycin remain < 1%. The rate of penicillin resistance among isolates of Streptococcus pneumoniae, which has increased steadily in recent years, currently stands at approximately 25% in the United States and will likely reach 40-50% during the next 5-10 years. Because of cross-resistance, in general all beta-lactam antimicrobials have reduced activity against penicillin-resistant strains of S. pneumoniae. A 1994-1995 survey found that 3.4% of S. pneumoniae isolates were highly resistant to cefotaxime, and 4-8% were resistant to chloramphenicol, tetracycline, and the macrolides. Resistance to these antimicrobials has usually followed the emergence of penicillin resistance in other countries. Therefore, S. pneumoniae resistance to these drugs is expected to increase markedly during the next few years in the United States.

Antibiotic susceptibility of upper respiratory tract pathogens in Sweden: a seven year follow-up study including loracarbef. Swedish Respiratory Tract Study Group

The antibiotic susceptibility of Haemophilus influenzae, Moraxella catarrhalis, Streptococcus pyogenes and Streptococcus pneumoniae was investigated in five different geographical areas of Sweden in 1990 and compared with results from similar investigations performed in 1983 and 1986. Tests on 100 isolates per species and laboratory were performed by the disk diffusion method, and 10% of the strains plus all resistant ones were sent to the central laboratory for determination of MICs of ampicillin, phenoxymethylpenicillin, cefaclor, loracarbef, erythromycin, tetracycline and trimethoprim/sulfamethoxazole. Beta-lactamase production was found in 7% of H. influenzae and 71% of M. catarrhalis, and reduced susceptibility to penicillin in 3% of S. pneumoniae. Low frequencies (1-3%) of tetracycline resistance were found in H. influenzae and in the 2 streptococcal species, in which also less than 1% of the strains were resistant to erythromycin. Resistance to trimethoprim/sulfamethoxazole occurred in 7% (range 3-14%) of H. influenzae and in 3% of S. pneumoniae. Cefaclor was active against all streptococci except against S. pneumoniae with reduced susceptibility to penicillin. It was active against beta-lactamase negative strains of M. catarrhalis but had, according to the SIR-system, intermediate activity against H. influenzae. Loracarbef was twice as active as cefaclor against H. influenzae but equally active against the 3 other species tested.

Antibiotic resistance in Haemophilus influenzae: mechanisms, clinical importance and consequences for therapy

Invasive and non-invasive infections caused by Haemophilus influenzae are frequently diagnosed in children below the age of 5 years. The treatment of choice for these infections was ampicillin. However, since the early 1970s the increasing prevalence of resistance to ampicillin and other antibiotics has necessitated major changes in antibiotic therapy. This article summarizes some of the important clinical features of diseases caused by H. influenzae. The epidemiology, the problems with in vitro susceptibility testing and the mechanisms of resistance to major antibiotics are reviewed. The consequences of antibiotic resistance for the treatment of diseases caused by H. influenzae are discussed.

Parasite diversity and the evolution of diploidy, multicellularity and anisogamy

It may be reasonably assumed that a diversity of parasite genotypes in any one cell or organism is more harmful than a population of uniform genotypes. If this is accepted the following consequences follow: (i) Parasite mixing, due to cytoplasm mixing, at the time of zygote formation is a new and additional cost of sex. The rapid divisions typical of zygotic cleavage may be viewed as an adaptation to minimize the degree of mixing of parasites in each daughter cell. The faster the divisions the less chance parasite populations have to grow and mix. Mitosis is the fastest form of cell division. Prolongation of the diploid phase follows as a consequence of mitosis in a diploid zygote. This view is unusual in that it demands no advantage per se to the possession of two chromosome sets. (ii) The cells of the blastula formed from rapid zygotic divisions are different as regards their symbiotic inclusions. If the right to gametogenesis is restricted, then every replicator symbiont and nuclear genome alike and hence every cell of the developing embryo, will have an incentive to compete. Selection between the clonal blastula cells would result in the cells of low parasite diversity forming the gametes. Thus, germ line restriction is in the interests of the nuclear genome. Controlling the right to gametogenesis is only possible if the blastula remains intact. Hence, multicellularity might have evolved so as to enable the limitation of the right to gametogenesis and hence reduce the parasite diversity of gametes. Inter-cell competition during embryogenesis is central to Buss's seminal notion of the evolution of developmental complexity within the metazoa. The above theory provides the missing motive force behind such competition. (iii) For a given zygote size, the fittest zygotes are those produced by the gametes most disparate in size because these have a lower diversity of parasites. This may be the advantage of anisogamy. The novelty of this new view of anisogamy is that it puts a premium on sperm being very small, in order to exclude parasites from sperm cytoplasm. The hypothesis is briefly tested by examining if there are alternative means of parasite limitation in organisms with large gametes.

Antibiotic susceptibilities and drug resistance in Moraxella (Branhamella) catarrhalis

PURPOSE

To summarize current knowledge of drug susceptibility and mechanisms of drug resistance in Moraxella (Branhamella) catarrhalis.

MATERIALS AND METHODS

The current medical literature was reviewed, with careful attention to recent studies of the BRO beta-lactamases.

RESULTS

Although intrinsically resistant to a small group of drugs that included vancomycin and trimethoprim, acquired drug resistance in Branhamella catarrhalis was unknown in the early years of antimicrobial therapy. During 1976 to 1977, however, two previously unrecognized beta-lactamases appeared in this species almost simultaneously around the world. At the same time these enzymes, now known as BRO-1 and BRO-2, also appeared in two closely related commensal species of Moraxella. Within four years the BRO enzymes were found in up to 75 percent of B. catarrhalis in the United States where they provide low-level resistance to penicillin and ampicillin but not to most cephalosporins. The BRO genes appear to be chromosomal but are readily transferred by conjugation within the Moraxella genus. Resistance to aminoglycosides and trimethoprim-sulfamethoxazole has been reported from Spain, and resistance to both erythromycin and tetracycline has recently been described among United States isolates of B. catarrhalis.

CONCLUSION

Despite this drug resistance, numerous oral and parenteral agents are available and appear useful for treatment of clinical disease, including amoxicillin/clavulanic acid, erythromycin, the tetracyclines, ciprofloxacin, and trimethoprim/sulfamethoxazole. Recent changes in drug resistance in this species suggest that continued monitoring of drug resistance in B. catarrhalis is needed.

In vitro activity of new antibiotics against Haemophilus influenzae

The activity of sulbactam/ampicillin, aztreonam, cefetamet, cefixime, ciprofloxacin, enoxacin, fleroxacin and ofloxacin was determined against 160 Haemophilus influenzae strains using a standardized microdilution method. The strains were categorized into four groups according to beta-lactamase production and their resistance to ampicillin, chloramphenicol, erythromycin, tetracycline and cotrimoxazole. All isolates tested, regardless of their beta-lactamase production or resistance to the above mentioned drugs, were susceptible to the nine antibiotics. The most active antimicrobial agents were aztreonam, cefixime, and the two quinolone derivatives ciprofloxacin and ofloxacin.

Mechanisms of beta-lactam resistance in Haemophilus influenzae

Haemophilus influenzae has become increasingly resistant to beta-lactam antibiotics. Three major mechanisms, both enzymatic and non-enzymatic, are involved. Enzymatic resistance is mainly due to production of a TEM-1 plasmid-mediated beta-lactamase, and in some cases to a new enzyme ROB-1. Of the non-enzymatic mechanisms, decreased permeability due to alteration of outer membrane proteins seems to be rare in comparison to decreased affinity of penicillin-binding proteins for beta-lactam antibiotics. Enzymatic resistance is present in about 10-20% of clinical isolates, while non-enzymatic resistance is present only in 2-4%.

Haemophilus influenzae: antibiotic susceptibility

Ampicillin resistance was first reported among clinical isolates of Haemophilus influenzae in 1972. Reports of chloramphenicol resistance followed shortly thereafter. The principal mechanism of resistance to these two antibiotics is enzymatic. Although other mechanisms have been described, they are found in comparatively few strains. The genetic information for the inactivating enzymes is plasmid mediated and therefore readily transmissible to susceptible strains. Consequently, effective therapy for invasive disease caused by this pathogen has been seriously compromised. As antibiotic susceptibility became less predictable, in vitro testing became increasingly important. Unfortunately, the standardization of methods for laboratory testing has been slow and complicated by the fastidious nature of the organisms. This review traces the development of antibiotic resistance in H. influenzae, discusses the mechanisms which appear to be important in mediating resistance, explores newer antimicrobial agents which might be useful in the treatment of infection, and analyzes the various approaches to in vitro testing.

Distribution and resistance patterns of Haemophilus influenzae: a European cooperative study

The first European survey of the prevalence of antibiotic resistance in Haemophilus influenzae was conducted between February and October 1986. Eighty laboratories in nine countries participated (Austria, Belgium, France, FRG, The Netherlands, Spain, Sweden, Switzerland and the UK). A total of 1,961 clinical isolates was examined for type b encapsulation, beta-lactamase production and susceptibility to ampicillin, chloramphenicol, cefaclor, erythromycin and tetracycline, using a unique microdilution method. The proportion of isolates resistant to these antibiotics varied considerably between individual countries. The highest prevalence of ampicillin resistance was found in Spain (30.6%), and the lowest in the FRG (1.6%), with a mean value of 10% for all countries. Chloramphenicol resistance was highest in Spain (24.9%) and Belgium (10.9%) and lowest in The Netherlands (0.6%) and Austria (0.5%), with a mean value of 4.7%. Resistance to erythromycin ranged from 27% of the isolates in The Netherlands to 1.1% in Austria. For tetracycline, values ranged from 1.5% in the UK to 17.8% in Belgium and 25.4% in Spain. The lowest mean prevalence of resistance was observed for cefaclor (breakpoint 8 mg/l): 5% or less in all countries. These inter-country differences could only partially be explained by variations in the proportion of type b strains, the source of the isolates and the mode of collection.

Influence of growth medium and supplement on growth of Haemophilus influenzae and on antibacterial activity of several antibiotics

In the present study, five non-beta-lactamase- and five beta-lactamase-producing strains of Haemophilus influenzae were used to determine whether three different growth media, Mueller-Hinton broth and agar, brain heart infusion broth and agar, and tryptic soy broth and agar, and their added supplements (0.2% hemin-0.1% IsoVitaleX, 1% hemin-1% IsoVitaleX, 2% sheep blood, 10% Fildes enrichment, 5% Fildes enrichment, 1% supplement B, 5% horse erythrocytes, and 2% hemoglobin-1% IsoVitaleX) would influence the growth rate of this microorganism and the antibacterial activity of eight antibiotics, including ampicillin, tetracycline, chloramphenicol, gentamicin, cefamandole, erythromycin, trimethoprim-sulfamethoxazole (TMP-SMX), and cefoperazone. The growth curve studies were carried out with an initial inoculum of 10(4) bacteria per ml, and MICs were determined with an inoculum of 5 X 10(5) microorganisms. Mueller-Hinton broth, brain heart infusion broth, and tryptic soy broth enriched with 5% Fildes resulted in a maximal growth of more than 10(8) CFU/ml at 24 h. When 10% Fildes or 2% sheep blood was added as enrichment to Mueller-Hinton broth, a considerable reduction in the growth rate of H. influenzae strains resulted (P less than 0.01). Significant variations in MICs (P less than 0.01) were observed with chloramphenicol, TMP-SMX, erythromycin, and cefoperazone when brain heart infusion agar, Mueller-Hinton agar, or tryptic soy agar was used. Chloramphenicol, gentamicin, erythromycin, and TMP-SMX were all affected by the different enrichments added to Mueller-Hinton agar. MICs were in general higher with 5% Fildes enrichment and lower with 1% supplement B. Cefoperazone was the only drug which exhibited a lower MIC in 5% Fildes enrichment for ampicillin-resistant H. influenzae strains.

An animal source for the ROB-1 beta-lactamase of Haemophilus influenzae type b

The most common cause of ampicillin resistance in Haemophilus influenzae type b is production of TEM-1 beta-lactamase; however, a novel enzyme with a similar substrate profile but a quite different isoelectric point has also been described. This beta-lactamase, designated ROB-1, has not been found previously in any other organism. In a survey of 46 ampicillin-resistant H. influenzae type b isolates, we found a second human isolate that produces ROB-1 and discovered that ampicillin-resistant isolates of the porcine pathogen Haemophilus pleuropneumoniae also produced ROB-1. In both Haemophilus species ROB-1 production was determined by plasmids that had considerable DNA sequence homology. However, the ROB-1 and TEM-1 beta-lactamase genes were not related. Our findings suggest that this form of ampicillin resistance has an animal reservoir and that conditions fostering its prevalence in animal strains may play a role in the spread of resistance to human pathogens.

Tolerance of Haemophilus influenzae to beta-lactam antibiotics

Two hundred clinical isolates of Haemophilus influenzae were tested for tolerance (MBC/MIC greater than or equal to 32) to ampicillin and cefotaxime by broth dilution tests. Of 200 strains, 9 were tolerant to ampicillin, and 10 were tolerant to cefotaxime. Tolerant organisms were identified in both systemic and nonsystemic infections and among different biotypes and serotypes of H. influenzae. These tolerant isolates were compared with nontolerant isolates by broth dilution and killing curves with log-phase and stationary-phase inocula. Both tolerant and nontolerant bacteria in log phase were killed more rapidly by antibiotics than bacteria in stationary-phase growth. When tested against 11 different beta-lactams, several patterns of tolerance were observed. Six of the ten strains were tolerant to aztreonam, four were tolerant to cefuroxime, three were tolerant to cefamandole, and two were tolerant to cefoxitin. Strain H130 was tolerant to all beta-lactam antibiotics studied. None of the 10 tolerant H. influenzae isolates were tolerant to chloramphenicol, rifampin, tobramycin, ciprofloxacin, enoxacin, and trimethoprim-sulfamethoxazole. Although the clinical significance of tolerance is not determined, this study suggests that the bactericidal activity (MBC) of beta-lactam antibiotics against H. influenzae should be determined in cases of severe infections in which clinical response is slow or unsatisfactory.

Genetic and biochemical properties of AER-1, a novel carbenicillin-hydrolyzing beta-lactamase from Aeromonas hydrophila

A novel carbenicillin-hydrolyzing beta-lactamase has been discovered in a blood isolate of Aeromonas hydrophila. The enzyme resembles plasmid-determined carbenicillinases in substrate profile but differs in isoelectric point (pI 5.9) and molecular weight (22,000) and has been termed AER-1. No evidence for a plasmid location could be obtained in A. hydrophila, but the AER-1 gene and resistance to chloramphenicol, streptomycin, and sulfonamide could be transferred by mobilization with IncP plasmids to Escherichia coli, where the gene cluster inserted at a unique chromosomal site. The linked resistances are similar to those found on multiresistance beta-lactamase transposons, but since insertion of the A. hydrophila gene cluster was site specific and recA+ dependent, the cluster is not a functional transposon.

Recognition and clinical significance of mechanisms of bacterial resistance to beta-lactams

Resistance to beta-lactams may be difficult to recognize. This is due to the difficulty in detecting these resistances, when the routine tests performed in diagnostic laboratories are interpreted in the usual manner. Since failure to recognize this type of resistance may have serious consequences for the patient, it is essential that it be detected when present. For the detection of methicillin resistance of Staphylococcus aureus a standardized method using either a medium containing 5% NaCl or a low incubation temperature is advocated. Methicillin resistance of S. epidermidis can only be recognized reliably by means of a quantitative test and incubation for 42-48 h. Resistance of Haemophilus influenzae to ampicillin may be intrinsic or it may be caused by a TEM beta-lactamase; a beta-lactamase test should be used to detect the latter type of resistance. Inducible cephalosporinase may be responsible for the rapid development of resistance of some bacterial species to cefamandole, even during therapy. If a stable beta-lactamase production is attained by mutation, resistance to other beta-lactams will usually be present as well. Routine induction tests should be performed for all isolates of species of Enterobacter, Serratia, Citrobacter and Proteus, indole-positive. The same type of 'hidden' resistance may be present in Pseudomonas aeruginosa, with regard to cefotaxime and other third-generation cephalosporins. Beta-lactamase-positive Neisseria gonorrhoeae can easily be recognized by a beta-lactamase test. In addition, the results of diffusion tests allow one to distinguish between beta-lactamase-positive and beta-lactamase-negative strains. Recognition of those strains of N. gonorrhoeae having a decreased susceptibility to penicillin is only possible when well-standardized quantitative tests are used.

Mechanism of resistance of an ampicillin-resistant, beta-lactamase-negative clinical isolate of Haemophilus influenzae type b to beta-lactam antibiotics

The mechanism of non-beta-lactamase-mediated beta-lactam resistance in a clinical isolate of Haemophilus influenzae type b was studied. This clinical isolate showed up to a 32-fold increase in MICs of a wide variety of beta-lactams, including moxalactam and cefotaxime, although no beta-lactamase activity was detected, even after attempted induction. Transformation of broad-spectrum beta-lactam resistance into ampicillin-susceptible H. influenzae RDnov was accomplished. Examination of the outer membrane protein profile of the resistant parent by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of Triton X-100-extracted membranes revealed an unusual major outer membrane protein band at a molecular weight of 45,000. This outer membrane protein profile did not transform with beta-lactam resistance. Permeability differences were noted between the resistant strain and the nonisogenic susceptible strain of H. influenzae, although these penetration differences were not transformed. Comparison of the penicillin-binding protein profile of a resistant transformant with that of a susceptible parent with both whole-membrane preparations and whole-cell labeling, revealed a major reduction in binding affinity to penicillin-binding proteins 3a and 3b (molecular weights, 68,000 and 65,000, respectively). Thus, alteration in penicillin-binding proteins 3a and 3b correlated with the beta-lactam resistance.

Antimicrobial susceptibility of 103 strains of Haemophilus ducreyi isolated in Johannesburg

Of 103 strains of Haemophilus ducreyi isolated in Johannesburg, 96 produced beta-lactamase and were resistant to penicillin and ampicillin. Most strains showed resistance to tetracycline, sulfisoxazole, and sulfamethoxazole. All isolates were susceptible to rifampin, erythromycin, and cefoxitin, moderately susceptible to trimethoprim-sulfamethoxazole (1:19) and minocycline, and somewhat less susceptible to doxycycline.

Spread of a "Pseudomonas-specific" beta-lactamase to plasmids of enterobacteria

Eleven isolates including Escherichia coli, Salmonella enteritidis, and Shigella sonnei, obtained in Brazil, Hong Kong, Indonesia, Thailand, and the United States, were found to produce beta-lactamase of the PSE-1 type, which was previously considered to be Pseudomonas specific. The enterobacterial strains produced a beta-lactamase with the same isoelectric point, immunological reactions, and substrate profile as those of the prototype PSE-1 enzyme determined by Pseudomonas plasmid RPL11. The producer strains were resistant to multiple antibiotics, and all contained plasmids, ranging in size from 37 x 10(6) to 130 x 10(6), that belonged to at last six incompatibility groups. Plasmids of IncH2 and IncFIme were shown to contain 8 x 10(6)-molecular-weight transposons Tn1401 and Tn1402 that encoded PSE-1 beta-lactamase production, resistance to streptomycin and spectinomycin via AAD(3"), and resistance to sulfonamide. PSE-1 beta-lactamase was not Pseudomonas specific and appeared to have spread among plasmids found in enterobacteria by transposition.

Ampicillin treatment failure of apparently beta-lactamase-negative Haemophilus influenzae type b meningitis due to novel beta-lactamase

Documented ampicillin treatment failures of systemic Haemophilus influenzae type b infections have been associated with synthesis of a TEM-1 beta-lactamase. A patient with H. influenzae type b meningitis in whom ampicillin treatment failed is described; the isolate was beta-lactamase-negative according to the cell suspension chromogenic cephalosporin assay. The false-negative result occurred in a strain which elaborated a novel, plasmid-mediated beta-lactamase with characteristics which distinguish it from TEM-1 beta-lactamase. Clinically important ampicillin resistance in H. influenzae type b occurs by mechanisms other than by synthesis of TEM-1 beta-lactamase. Diagnostic microbiology laboratories should perform antibiotic susceptibility tests in addition to tests for beta-lactamase production.

Dissemination of resistance plasmids among gentamicin-resistant enterobacteria from hospital patients

Out of 184 patients who were infected or colonised with gentamicin-resistant enterobacteria, 17 (9%) harboured more than one strain. Single antibiotic-resistance plasmids were common to more than one of the different organisms isolated from nine patients, strongly suggestive of in-vivo conjugation. An "epidemic" plasmid with a molecular weight of approximately 110 megadaltons was found in 11 distinct strains isolated from four patients. Seven of the organisms harbouring this plasmid were Klebsiella aerogenes. Spread of multiple-resistance plasmids among endemic gentamicin-resistant enterobacteria is not uncommon, and these organisms provide a reservoir of plasmids that may ultimately spread to more pathogenic genera.

Inconsistency of synergy between the beta-lactamase inhibitor CP-45,899 and beta-lactam antibiotics against multiply drug-resistant Enterobacteriaceae and pseudomonas species

Synergy between CP-45,899 and ampicillin or newer beta-lactam antibiotics against multiply drug-resistant Enterobacteriaceae and Pseudomonas species was inconsistent. In contrast, synergy between CP-45,899 and ampicillin against beta-lactamase-producing strains of Haemophilus influenzae type b and Bacteroides fragilis was consistent and marked.

Isolation and partial characterization of outer and inner membranes from encapsulated Haemophilus influenzae type b

A method has been developed to separate the cell envelope of encapsulated (type b) Haemophilus influenzae into its outer and inner membrane components with procedures that avoided two problems encountered in fractionation of this envelope: (i) the tendency of the outer and inner membranes to hybridize and (ii) the tendency of the apparently fragile inner membrane to fragment into difficulty sedimentable units. Log phage cells, whose lipids were radioactively labeled, were lysed by passage through a French press. The lysate was applied to a discontinuous sucrose gradient, and envelope-rich material was collected by centrifugation onto a cushion of dense sucrose under carefully controlled conditions. This material was then further fractionated by isopycnic centrifugation in a sucrose gradient to yield four membrane fractions which were partially characterized. On the basis of their radioactivity, buoyant density, ultrastructure, polypeptide composition, and content of phospholipid, protein, lipopolysaccharide, and succinic dehydrogenase, these fractions were identified as follows: fraction 1, outer membrane vesicles with very little inner membrane contamination (less than 4%); fraction 2, outer membrane vesicles containing entrapped inner membrane; fraction 3, a protein-rich fraction of inner membrane; fraction 4, a protein-poor fraction of inner membrane. Fractions 3 and 4 contained about 25% outer membrane contamination.

Outer membrane protein composition in disease isolates of Haemophilus influenzae: pathogenic and epidemiological implications

The outer membrane protein composition of 50 disease isolates of Haemophilus influenzae has been determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. All strains, including 28 strains of serotype b, one strain each of serotypes a, c, d, e, and f, and 17 untypable strains, had an outer membrane protein composition typical of gram-negative bacteria, i.e., these membranes contained two to three dozen proteins with four to six proteins accounting for most of their protein content. Variation in the mobility of these major outer membrane proteins from strain to strain was common but not universal; the observed patterns provided useful data and new insight into the epidemiology of type b disease. The basic findings can be summarized as follows: (i) All 50 strains possessed three proteins (one minor and two major) each having identical mobilities. The other proteins, both major and minor, varied in mobility. (ii) All type b strains possessed a fourth (major) protein of identical mobility. (iii) The 28 type b strains, on the basis of the mobility of the six major outer membrane proteins, could be divided into eight subtypes. Of all the other strains examined, both typable and untypable, only the serotype a strain belonged to one of these subtypes. (iv) The untypable strains showed considerable variation in the mobilities of their major outer membrane proteins. Of these 17 strains, 13 had an additional major outer membrane protein not present in encapsulated strains. (v) The outer membrane protein composition of a single strain remained unchanged after many passages on solid media, but varied with the growth phase. (vi) The outer membrane protein composition of isolates obtained from nine patients during an epidemic of type b meningitis varied, indicating that a single strain was not responsible for the epidemic. At least five different strains were responsible for these nine cases. (vii) Identical outer membrane protein compositions were observed in the following: in a type b strain and a mutant of this strain deficient in capsule production, indicating that the level of capsule synthesis is not obviously related to outer membrane protein composition; in type b strains isolated from different anatomic sites of patients acutely ill with meningitis, indicating that the strain associated with bacteremia is the same as that isolated from the cerebrospinal fluid; in type b strains isolated from siblings who contracted meningitis at about the same time, indicating infection with the same strain; and in type b strains isolated from the initial and repeat infection of a single patient, suggesting that reinfection was due to the same strain.

Biotypes of capsulated and non-capsulated Haemophilus influenzae. Correlation between biotypes and beta-lactamase production

396 Haemophilus influenzae strains were biotyped according to Kilian. 393 of the strains were assigned to biotypes I to V, while 3 strains remained unclassified. Eighty-nine per cent of the capsulated strains produced both urease and ornithine decarboxylase, biotypes I or IV, while 95 per cent of the non-capsulated strains produced only one of the enzymes, biotypes II, III, or V. Of consecutive strains from the upper respiratory tract, the incidence of beta-lactamase-positive strains was higher among capsulated than among non-capsulated strains (p less than 0.025). None of 133 non-capsulated beta-lactamase-positive strains produced both urease and ornithine decarboxylase, in contrast to 15 out of 147 non-capsulated beta-lactamase-negative strains (p less than 0.001). The type e strains were all of biotype IV and 3 of 7 consecutive strains were beta-lactamase-positive.

In vitro antimicrobial activity of cefoperazone, cefotaxime, moxalactam (LY127935), azlocillin, mezlocillin, and other beta-lactam antibiotics against Neisseria gonorrhoeae and Haemophilus influenzae, including beta-lactamase-producing strains

Minimum inhibitory concentrations and agar disk diffusion tests were determined on clinical isolates of beta-lactamase-positive and beta-lactamase-negative Neisseria gonorrhoeae and Haemophilus influenzae with the newer beta-lactam antibiotics, cefoperazone, cefotaxime, moxalactam (LY127935), azlocillin, mezlocillin, and piperacillin, and with seven older beta-lactam antibiotics. All the drugs were active against beta-lactamase-negative strains of N. gonorrhoeae and H. influenzae. The drug most active against beta-lactamase-positive N. gonorrhoeae was cefotaxime, followed closely by cefoperazone, moxalactam, piperacillin, and mezlocillin. The drugs most active against beta-lactamase-positive strains of H. influenzae were cefotaxime, moxalactam, cefoperazone, and cefamandole.