Production of BRO beta-lactamases and resistance to complement in European Moraxella catarrhalis isolates

Of the 419 Moraxella catarrhalis isolates collected during the 1997-1999 European SENTRY surveillance study, 385 (92%) were beta-lactamase positive. Twenty-two (5.7%) produced BRO-2 beta-lactamase. Twenty-one new mutations were found in the putative promoter region of the bro genes. Nineteen percent of all isolates tested were complement sensitive. Resistance to beta-lactams is not linked to the phylogenetic lineages associated with susceptibility to complement.     

Contemporary prevalence of BRO beta-lactamases in Moraxella catarrhalis: report from the SENTRY antimicrobial surveillance program (North America, 1997 to 2004)

A total of 7,860 community-acquired Moraxella catarrhalis isolates (SENTRY Antimicrobial Surveillance Program, 1997 to 2004) were tested by broth microdilution methods, and 399 randomly selected strains from North American sites were tested for BRO-1 and BRO-2 by PCR methods. Several antimicrobials remained very active, including amoxicillin-clavulanate (MIC90s, < or =0.25 microg/ml), azithromycin (MIC90s, < or =0.12 microg/ml), ceftriaxone (MIC90s, 0.5 microg/ml), and levofloxacin (MIC90s, < or =0.03 to 0.06 microg/ml). The BRO-2 incidence rates by year were 3 to 4% overall (96 to 97% for BRO-1) and were the highest in Canada (7.9%), with the incidence in the United States being only 2.0%.     

Evaluation of susceptibility patterns and BRO β-lactamase types among clinical isolates of Moraxella catarrhalis

The aims of this study were to detect BRO beta-lactamase types and to evaluate any correlation with the susceptibility patterns of 90 clinical isolates of Moraxella catarrhalis. The overall prevalences of the bro-1 and bro-2 genes were 78% and 12%, respectively. Penicillin G MICs for BRO-1+ isolates were significantly higher than those for BRO-2+ isolates. All the isolates were susceptible to amoxycillin-clavulanate, levofloxacin and cefixime. Resistance to clarithromycin, tetracycline and trimethoprim-sulphamethoxazole was 1.1%, 2.2% and 1.1%, respectively. One-step, length-based PCR was an efficient method to screen for BRO beta-lactamase genes.     

Moraxella catarrhalis: an emerging respiratory pathogen

In the past years Moraxella (Branhamella) catarrhalis has finally gained respect as a pathogen thanks to the many reports of its causal role. The intent of this review is to provide a critical evaluation of the intent of this review is to provide a critical evaluation of the microbiological features (taxonomy, diagnosis, virulence, epidemiology and drug resistance), clinical diseases and therapy of this microorganism     

Disk diffusion versus broth microdilution susceptibility testing of Haemophilus species and Moraxella catarrhalis using seven oral antimicrobial agents: application of updated susceptibility guidelines of the National Committee for Clinical Laboratory Standards.

Susceptibility testing of Haemophilus species and Moraxella catarrhalis is medium and inoculum dependent. Seven oral agents, ampicillin, amoxicillin-clavulanic acid, cefaclor, loracarbef, cefuroxime-axetil, cefixime, and erythromycin, were tested against 400 beta-lactamase-positive and -negative clinically significant respiratory strains of Haemophilus species and 100 strains of M. catarrhalis. Sources of the strains included teaching and regional hospitals and a private laboratory. All strains were tested by broth microdilution and disk diffusion in haemophilus test medium for Haemophilus species and Mueller-Hinton broth and agar for M. catarrhalis. Appropriate National Committee for Clinical Laboratory Standards (NCCLS) standards were followed. For Haemophilus species, by disk diffusion and broth microdilution, respectively, 27 and 27% of strains were resistant to ampicillin, 37 and 5% were resistant to erythromycin, 3 and 0.5% were resistant to cefaclor, 2 and 0.5% were resistant to loracarbef, and 0% were resistant to cefuroxime-axetil, cefixime, and amoxicillin-clavulanic acid. beta-Lactamase-negative ampicillin-resistant strains were not observed. Of M. catarrhalis strains, 56% were resistant to ampicillin by disk diffusion and 95% were resistant by broth microdilution. This species was susceptible to all other agents tested by either method. The disagreements between disk diffusion results and MICs for cefaclor, ampicillin, cefuroxime, and loracarbef that occurred with use of the 1990 NCCLS tables were resolved when the 1992 NCCLS tables were used.     

Moraxella catarrhalis: from Emerging to Established Pathogen

Moraxella catarrhalis (formerly known as Branhamella catarrhalis) has emerged as a significant bacterial pathogen of humans over the past two decades. During this period, microbiological and molecular diagnostic techniques have been developed and improved for M. catarrhalis, allowing the adequate determination and taxonomic positioning of this pathogen. Over the same period, studies have revealed its involvement in respiratory (e.g., sinusitis, otitis media, bronchitis, and pneumonia) and ocular infections in children and in laryngitis, bronchitis, and pneumonia in adults. The development of (molecular) epidemiological tools has enabled the national and international distribution of M. catarrhalis strains to be established, and has allowed the monitoring of nosocomial infections and the dynamics of carriage. Indeed, such monitoring has revealed an increasing number of B-lactamase-positive M. catarrhalis isolates (now well above 90%), underscoring the pathogenic potential of this organism. Although a number of putative M. catarrhalis virulence factors have been identified and described in detail, their relationship to actual bacterial adhesion, invasion, complement resistance, etc. (and ultimately their role in infection and immunity), has been established in a only few cases. In the past 10 years, various animal models for the study of M. catarrhalis pathogenicity have been described, although not all of these models are equally suitable for the study of human infection. Techniques involving the molecular manipulation of M. catarrhalis genes and antigens are also advancing our knowledge of the host response to and pathogenesis of this bacterial species in humans, as well as providing insights into possible vaccine candidates. This review aims to outline our current knowledge of M. catarrhalis, an organism that has evolved from an emerging to a well-established human pathogen.     

Clinical significance of extended-spectrum beta-lactamases

Extended-spectrum beta-lactamases (ESBLs) have now been described in many hospitals worldwide. While they have been detected in many pathogenic gram-negative bacteria, they are particularly prevalent inKlebsiella isolates. Known risk factors for colonization and/or infection with organisms harboring these enzymes include admission to an intensive care unit, recent surgery, instrumentation, prolonged hospital stay and antibiotic exposure, especially exposure to extended-spectrum beta-lactam agents. In this report three recent epidemics from the USA will be described in which the role of selective antibiotic pressure seems clear. Data from two hospital epidemics, one from New York and another from Stanford, California, will be reviewed briefly. In addition, recent studies describing the spread of extended-spectrum beta-lactamases among nursing home patients in Chicago, Illinois, will be outlined. The limited data available on treatment options for patients infected with ESBL-containing strains will be reviewed, focusing on the activity of piperacillin/tazobactam and imipenem against these otherwise broadly resistant strains. Lastly, attempts to control these organisms, including infection control measures and selective bowel decontamination, will be reviewed.     

Antimicrobial susceptibility of 80 Moraxella catarrhalis strains isolated in the children's hospital of Tunis

Eighty non-repetitive strains of Moraxella catarrhalis, isolated in Tunis Children's Hospital during five years from 1998 to 2002, were tested for their antimicrobial susceptibility, 95% of these strains were isolated from lung samples: 57.5% from trachea products, 35% from sputum and 2.5% from bronchial washings. The majority of strains (72%) were obtained from children under two years old. Antimicrobial susceptibility study showed that 95% of stains were beta-lactamase-producing, therefore they were penicillin G and amoxicillin resistant with high MICs. MIC(90) of penicillin G and amoxicillin of beta-lactamase-producing strains were respectively greater than 32 and 6 mg/l, these MIC decrease with addition of clavulanic acid. In fact, all strains studied were susceptible to the association amoxicillin-clavulanic acid as well as to cefotaxime. Concerning the other antimicrobial groups percentages of resistant strains found were as follows: erythromycin 3.75%, trimethoprim-sulfamethoxazol 12.5% and tetracycline 1.25%. Finally, all strains were susceptible to chloramphenicol, rifampicin and ciprofloxacin.     

Moraxella catarrhalis bacterium without endotoxin, a potential vaccine candidate

Lipooligosaccharide (LOS) is a major surface component of Moraxella catarrhalis and a possible virulence factor in the pathogenesis of human infections caused by this organism. The presence of LOS on the bacterium is an obstacle to the development of vaccines derived from whole cells or outer membrane components of the bacterium. An lpxA gene encoding UDP-N-acetylglucosamine acyltransferase responsible for the first step of lipid A biosynthesis was identified by the construction and characterization of an isogenic M. catarrhalis lpxA mutant in strain O35E. The resulting mutant was viable despite the complete loss of LOS. The mutant strain showed significantly decreased toxicity by the Limulus amebocyte lysate assay, reduced resistance to normal human serum, reduced adherence to human epithelial cells, and enhanced clearance in lungs and nasopharynx in a mouse aerosol challenge model. Importantly, the mutant elicited high levels of antibodies with bactericidal activity and provided protection against a challenge with the wild-type strain. These data suggest that the null LOS mutant is attenuated and may be a potential vaccine candidate against M. catarrhalis.     

A multicenter study of the antimicrobial susceptibility of Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis isolated from patients with community-acquired lower respiratory tract infections in 1999 in Portugal

A nationwide multicenter study (including 25 laboratories) of the antimicrobial susceptibility of bacterial pathogens commonly associated with community-acquired lower respiratory tract infections (LRTI), with testing undertaken in a central laboratory, was conducted in Portugal in 1999. Antimicrobial resistance in Haemophilus influenzae has not increased in the last decade. Of the 498 isolates tested, 12.4% produced beta-lactamase and >95% were susceptible to all antimicrobials except ampicillin. In contrast, there was a rapid increase of resistance in Streptococcus pneumoniae. Of the 312 isolates tested, 24.7% exhibited decreased susceptibility to penicillin (13.5% showed low-level and 11.2% high-level resistance), 13.8% were resistant to erythromycin, clarithromycin and azithromycin, and 13.6% to cefuroxime and to tetracycline. Of the 38 Moraxella catarrhalis tested, 81.6% produced beta-lactamase. Resistance to penicillin, cefuroxime, erythromycin, clarithromycin, and azithromycin in S. pneumoniae and beta-lactamase production in H. influenzae were significantly higher in pediatric patients than in adults. Overall, amoxycillin/clavulanate was the most active antimicrobial agent in vitro against H. influenzae, S. pneumoniae, and M. catarrhalis isolated from patients with community-acquired LRTI in Portugal.     

Comparison of in vitro activities of tigecycline with other antimicrobial agents against Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis in Taiwan

We compared the in vitro activities of tigecycline to those of other agents against 300 nonduplicate isolates of Streptococcus pneumoniae (194 isolates), Haemophilus influenzae (60 isolates), and Moraxella catarrhalis (46 isolates) recovered from patients treated in three major hospitals in Taiwan from August through December, 2003. All of these isolates were inhibited at 0.5 mg/L of tigecycline. For S. pneumoniae isolates, 72% were not susceptible to penicillin (69% intermediate and 3% resistant) and 96% were not susceptible to azithromycin. Among the 178 isolates resistant to azithromycin, 53 isolates (30%) had the M phenotype and 70% had the cMLSB phenotype. The rate of nonsusceptibility to ertapenem, telithromycin, moxifloxacin, and quinupristindalfopristin in S. pneumoniae was 3%, 2%, 1%, and 57%, respectively. For H. influenzae, 36 (60%) were not susceptible to ampicillin, among which 31 possessed beta-lactamase. A high rate (8.3%) of H. influenzae isolates with beta-lactamase-negative and ampicillin-resistant phenotype was found. All H. influenzae isolates were susceptible to azithromycin, but 40% of them were not susceptible to clarithromycin. Ninety-eight percent (44 isolates) of M. catarrhalis possessed beta-lactamase. All three fluoroquinolones tested were highly active (MIC90 < or =0.12 mg/L) against H. influenzae and M. catarrhalis.     

The rise and spread of a new pathogen: seroresistant Moraxella catarrhalis

The nosocomial human pathogen Moraxella catarrhalis is one the most important agents of human respiratory tract infections. This species is composed of two distinct lineages, one of only moderate virulence, the so-called serosensitive subpopulation, and a second, the seroresistant one, which is enriched among strains that harbor two major virulence traits: complement resistance and adherence to epithelial cells. Using a suite of population genetics tools, we show that the seroresistant lineage is also characterized by higher homologous recombination and mutation rates at housekeeping genes relative to its less pathogenic counterpart. Thus, sex and virulence have evolved in tandem in M. catarrhalis. Moreover, phylogenetic and Bayesian analyses that take into account recombination between the two clades show that the ancestral group was avirulent, is possibly 70 million years old, and must have infected mammals prior to the evolution of humans, which occurred later. The younger seroresistant isolates went through an important population expansion some 5 million years ago, coincident with the hominid expansion. This rise and spread was possibly coupled with a host shift and the acquisition of virulence genes.     

Antibiotic Susceptibilities Among Recent Clinical Isolates of Haemophilus influenzae and Moraxella catarrhalis from Fifteen Countries

 Between July 1998 and July 1999, 3,060 Haemophilus influenzae and 1,486 Moraxella catarrhalis strains were isolated in 31 centers in 15 countries in order to determine their antimicrobial susceptibilities and the presence of β-lactamase production in Haemophilus influenzae. Overall 17.1% of the Haemophilus influenzae isolates were β-lactamase positive, while more than 95% were susceptible to amoxicillin/clavulanate, cefaclor, loracarbef, cefuroxime, azithromycin and ciprofloxacin. Eleven (0.3%) isolates were β-lactamase positive and ampicillin resistant and 7 (0.2%) isolates were ciprofloxacin resistant. The minimum inhibitory concentrations for 90% of the isolates tested were lowest for ciprofloxacin (0.03) and highest for cefprozil (8) against Moraxella catarrhalis.     

Vaccine development for non-typeable Haemophilus influenzae and Moraxella catarrhalis: progress and challenges

An urgent need exists for vaccines to prevent infections caused by nontypeable Haemophilus influenzae and Moraxella catarrhalis. These bacteria cause otitis media in children, a clinical problem associated with enormous morbidity and cost. H. influenzae and M. catarrhalis also cause lower respiratory tract infections in adults with chronic lung disease. Infections in this clinical setting are associated with disability and death. Recent progress in identifying potential vaccine antigens in both bacteria raises great promise in developing effective vaccines. This paper reviews the key issues in vaccine development for H. influenzae and M. catarrhalis, including areas where progress has been stalled, and proposes areas that deserve investigation in the next 5 years.     

Cloning and Expression of the Moraxella catarrhalis Lactoferrin Receptor Genes

The lactoferrin receptor genes from two strains of Moraxella catarrhalis have been cloned and sequenced. The lfr genes are arranged as lbpB followed by lbpA, a gene arrangement found in lactoferrin and transferrin receptor operons from several bacterial species. In addition, a third open reading frame, orf3, is located one nucleotide downstream of lbpA. The deduced lactoferrin binding protein A (LbpA) sequences from the two strains were found to be 99% identical, the LbpB sequences were 92% identical, and the ORF3 proteins were 98% identical. The lbpB gene was PCR amplified and sequenced from a third strain of M. catarrhalis, and the encoded protein was found to be 77% identical and 84% similar to the other LbpB proteins. Recombinant LbpA and LbpB proteins were expressed from Escherichia coli, and antisera raised to the purified proteins were used to assess antigenic conservation in a panel of M. catarrhalis strains. The recombinant proteins were tested for the ability to bind human lactoferrin following gel electrophoresis and electroblotting, and rLbpB, but not rLbpA, was found to bind lactoferrin. Bactericidal antibody activity was measured, and while the anti-rLbpA antiserum was not bactericidal, the anti-rLbpB antisera were found to be weakly bactericidal. Thus, LbpB may have potential as a vaccine candidate.     

Clinical relevance of antimicrobial susceptibility testing

In recent years, significant resistance to antimicrobial agents has been encountered among certain anaerobic bacteria. Susceptibility patterns vary from region to region, but even within a given region susceptibility is not always predictable. Initially, therapy of mixed anaerobic infections must be empirical, based on the nature of the infection, the usual flora of such infections, anticipated modification of this flora by pathophysiologic processes or prior antimicrobial therapy, and evaluation of Gram stains from appropriate specimens. If the infection does not respond well or the patient requires long-term therapy, antimicrobial susceptibility testing may be indicated in order to provide optimum therapy. Susceptibility testing is also indicated for determination of the usual patterns in a particular hospital, for monitoring geographical patterns, and to determine the activity of new antimicrobial agents.