Antimicrobial susceptibility and β-lactamase characterization ofBranhamella catarrhalisisolates from 1983/1984 and 1988

[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.

Genetic trends in a population evolving antibiotic resistance

The evolution of antibiotic resistance provides a well-documented, rapid, and recent example of a selection driven process that has occurred in many bacterial species. An exhaustive collection of Moraxella catarrhalis that spans a transition to chromosomally encoded penicillin resistance was used to analyze genetic changes accompanying the transition. The population was characterized by high haplotypic diversity with 148 distinct haplotypes among 372 isolates tested at three genomic regions. The power of a temporally stratified sample from a single population was highlighted by the finding of high genetic diversity throughout the transition to resistance, population numbers that remained high over time, and no evidence of departures from neutrality in the allele frequency spectra throughout the transition. The direct temporal analysis documented the persistence, antibiotic status, and haplotypic identity of strains undergoing apparent clonal expansions. Several haplotypes that were beta-lactamase nonproducers in early samples converted to producers in later years. Maintenance of genetic diversity and haplotype conversions from sensitive to resistant supported the hypothesis that penicillin resistance determinants spread to a diverse array of strains via horizontal exchange. Genetic differentiation between sample years, estimated by F(ST), was increasing at a rate that could cause complete haplotype turnover in less than 150 years. Widespread linkage disequilibrium among sites within one locus (copB) suggested recent mutation followed by clonal expansion. Nonrandom associations between haplotypes and resistance phenotypes provided further evidence of clonal expansion for some haplotypes. Nevertheless, the population structure was far from clonal as evidenced by a relatively low frequency of disequilibria both within sites at a second locus (M46) as well as between loci. The haplotype-antibiotic resistance association that was accompanied by gradual haplotype turnover is consistent with a hypothesis of genetic drift at marker loci with directional selection at the resistance locus.

Molecular characterization of the beta-lactamases from clinical isolates of Moraxella (Branhamella) catarrhalis obtained from 24 U.S. medical centers during 1994-1995 and 1997-1998

The beta-lactamases from 403 Moraxella (Branhamella) catarrhalis clinical isolates obtained during 1994-1995 and 1997-1998 U.S. multicenter surveillance studies were characterized by isoelectric focusing. The overall prevalences of the BRO-1 and BRO-2 enzymes among beta-lactamase-positive isolates were estimated to be 97.5 and 2.5%, respectively. The minimum inhibitory concentrations (MICs) of ampicillin for all BRO-2-producing isolates were </=1 microg/ml; however, numerous beta-lactamase-positive isolates for which the ampicillin MICs were </=1 microg/ml produced the BRO-1 enzyme (88. 1%).

Long-term trends in susceptibility of Moraxella catarrhalis: a population analysis

A retrospective, population analysis of antimicrobial susceptibility patterns was performed on Moraxella catarrhalis isolates recovered from a single medical centre to detect temporal trends and infer potential mechanisms of reduced susceptibility. The duration of this study, June 1984 to July 1994, encompassed the period during which the frequency of beta-lactamase production expanded from 30 to 96% in the population. MICs of penicillin G, cefamandole, ceftriaxone, amoxycillin/clavulanate, imipenem, clarithromycin, tetracycline, ciprofloxacin and trimethoprim/sulphamethoxazole for a representative sample of 375 isolates were determined. Analyses were conducted to test for variation in susceptibility among isolates, correlations of susceptibility levels among different antimicrobial agents, and temporal patterns in susceptibility. All antimicrobials except clarithromycin displayed significant differences among isolates within years, and mean MICs of all antimicrobial agents except tetracycline and clarithromycin varied significantly between years. Temporal trends to a reduction in susceptibility were detected to four of five beta-lactam antimicrobials (all except cefamandole). Significant correlations in MICs were uncovered among all pairs of four beta-lactam antimicrobials in both producers and non-producers of beta-lactamase. In contrast, cefamandole MICs were correlated only with ceftriaxone and penicillin, and these were limited to beta-lactam producing isolates; cefamandole and amoxycillin/clavulanate showed a correlation limited to non-producing isolates. For some antimicrobials, trends toward decreasing susceptibility may have been caused by an increased proportion of beta-lactamase producing isolates in the population, but the observation of significant decreases in susceptibility limited to beta-lactamase-producing isolates suggests that the underlying factors were different forms of beta-lactamase, beta-lactamase-dependent modifiers and/or additional factors.

Moraxella catarrhalis: clinical significance, antimicrobial susceptibility and BRO beta-lactamases

Moraxella catarrhalis is an important pathogen of humans. It is a common cause of respiratory infections, particularly otitis media in children and lower respiratory tract infections in the elderly. Colonisation of the upper respiratory tract appears to be associated with infection in many cases, although this association is not well understood. Nosocomial transmission is being increasingly documented and the emergence of this organism as a cause of bacteremia is of concern. The widespread production of a beta-lactamase enzyme renders Moraxella catarrhalis resistant to the penicillins. Cephalosporins and beta-lactamase inhibitor combinations are effective for treatment of beta-lactamase producers, and the organism remains nearly universally susceptible to the macrolides, fluoroquinolones, tetracyclines and the combination of trimethoprim and sulfamethoxazole. Two major beta-lactamase forms, BRO-1 and BRO-2, have been described on the basis of their isoelectric focusing patterns. The BRO-1 enzyme is found in the majority of beta-lactamase-producing isolates and confers a higher level of resistance to strains than BRO-2. The BRO enzymes are membrane associated and their production appears to be mediated by chromosomal determinants which are transmissible by an unknown mechanism. The origin of these novel proteins is unknown.

The beta-lactamases of Moraxella (Branhamella) catarrhalis isolated from Danish children

Two distinct beta-lactamases have been isolated from Moraxella catarrhalis: the stronger acting BRO-1 enzyme and the weaker acting BRO-2. Several reports have noted an effect of penicillin and ampicillin on infections caused by M. catarrhalis in spite of the presence of beta-lactamase production. The purpose of this work was to charaterize the beta-lactamases of M. catarrhalis isolated from Danish children regarding type and susceptibility, and to relate these findings to the eradication of beta-lactamases-producing strains by use of antibiotic treatment with penicillin or ampicillin. MICs for penicillin V, ampicillin, cefuroxime and amoxicillin/clavulanic acid (2:1) were determined in 70 strains of M. catarrhalis: 46 strains from children with lower respiratory tract infection (LRTI) and 24 strains from respiratory healthy children, beta-lactamase production was found in 59 strains. The BRO-1 enzyme was identified by isoelectric focusing in 55 strains (93.2%) and BRO-2 in 3 strains (5.1%); in 1 strain no isoelectric bands were produced. All strains were susceptible to cefuroxime and amoxicillin/clavulanic acid, and non-beta-lactamase-producing strains were susceptible to penicillin and ampicillin. For the beta-lactamase-producing strains, MIC50 of penicillin was 8.0 micrograms/ml, while MIC50 of ampicillin was 1.0 microgram/ml and MIC90 of ampicillin was 2.0 micrograms/ml. M. catarrhalis was more often eradicated from the children who received antibiotic treatment with penicillin or ampicillin than from those who did not receive any treatment, indicating an in vivo effect of penicillin and ampicillin in spite of the beta-lactamase production.

Branhamella catarrhalis in children and adults. A study of prevalence, time of colonisation, and association with upper and lower respiratory tract infections

The colonisation rate of Branhamella catarrhalis in patients from 0 to 45 years of age was examined. Of 561 women admitted to hospital in labour, 6 (1%) carried B. catarrhalis in their throats but none carried the organism in their vaginas. None of 534 newborn babies became colonised at birth or during their 5 days' stay in hospital. Neither were 102 neonates < 1 month of age in hospital colonised. The maximum colonisation rate during childhood was observed in children 1-48 months of age with 143 of 266 (54%) children colonised. Among children 4-15 years of age, four of 57 (7%) children with healthy respiratory tracts were colonised. Significantly more children with upper or lower respiratory tract infections (RTI) were colonised (68%) than were children without such infections (36%), (P < 0.001). After recovery from RTI, the isolation rate in the RTI group fell to that of the non-RTI group. A seasonal variation in prevalence was not observed. Of all the strains of B. catarrhalis isolated, 84% produced beta-lactamase.

Screening method for beta-lactamase substrate profiles

A disc diffusion method, based on the idea of Klundert, for screening of substrate profiles of beta-lactamases was developed in order to perform epidemiological studies. The method was tested against 30 different reference beta-lactamases and 59 clinical isolates known to produce TEM-1, SHV-1 and BRO-1. The reproducibility and discriminating power of the disc diffusion method made it possible to differentiate between eight types of substrate profiles for the 30 reference beta-lactamases and to differentiate between TEM-1, SHV-1 and BRO-1 from clinical isolates. In combination with analytical isoelectric focusing the disc diffusion method gives a reliable identification of beta-lactamases.

Current trends in bacterial respiratory pathogens

The relationship of virulence and antimicrobial susceptibility with morbidity due to bacterial respiratory pathogens is complex and evolving. Ultimately, decreasing the incidence of pneumonia due to bacterial pathogens will be dependent on successful preparation and distribution of effective vaccines. Until effective vaccines are widely available, control of a majority of respiratory infections will depend on promotion of rational therapeutic strategies. Though limited to a few specific serotypes and strains, changes in virulence of bacterial respiratory pathogens have been noted. Co-infections due to multiple respiratory pathogens may increase morbidity; however, the epidemiology of co-infections is not clear. Relationships between respiratory viruses and bacteria may exist that increase virulence of both agents, but information regarding these relationships awaits further investigation. Resistance of respiratory pathogens to the more commonly used antimicrobials, such as penicillin, erythromycin, chloramphenicol, and cotrimoxazole, is being documented globally with increasing frequency. The evolution of antimicrobic resistance, especially among strains of Streptococcus pneumoniae, the most common and deadly agent of lower respiratory tract infections, provides impetus to develop and promote effective pneumococcal vaccines and to search for new and effective antimicrobials.

Beta-lactamase production in Branhamella catarrhalis isolated from lower respiratory tract secretions in Danish children: an increasing problem

Findings in specimens from the lower respiratory tract of children were reviewed retrospectively in order to assess the rate of Branhamella catarrhalis and beta-lactamase production. B. catarrhalis was isolated in 139 of 756 samples (18.4%) in 1986 and 211 of 723 samples (29.2%) in 1989. Beta-lactamase production was found in 55.6% of B. catarrhalis strains in 1986 and 80.1% in 1989 (p less than 0.001). Prevalence of beta-lactamase in B. catarrhalis has now reached the same level in Europe as in the USA.