[Moraxella catarrhalis: virulence and resistance mechanisms]

Pneumonia caused by Moraxella catarrhalis in haematopoietic stem cell transplant patients. Report of two cases and review of the literature

Moraxella catarrhalis is a gram negative diplococcus that causes a variety of upper and lower respiratory tract infections. Patients with malignant, hematological disorders treated with intensive cytotoxic chemotherapy, and recipients of various forms of haematopoietic stem cell transplant receiving immunosuppressive agents are at high risk of developing severe infections and septic complications. Early detection of the organism and prompt treatment with appropriate antibiotics provide both resolution of the infection and prevention of further consequences. Two patients with haematopoietic stem cell transplant who developed pneumonia caused by M. catarrhalis at King Faisal Specialist Hospital and Research Centre in Riyadh are reported and the literature is reviewed. To our knowledge, these are the first case reports of M. catarrhalis pneumonia in haematopoietic stem cell transplant patients.

Endotoxin activity of Moraxella osloensis against the grey garden slug, Deroceras reticulatum

Moraxella osloensis is a gram-negative bacterium associated with Phasmarhabditis hermaphrodita, a slug-parasitic nematode that has prospects for biological control of mollusk pests, especially the grey garden slug, Deroceras reticulatum. This bacterium-feeding nematode acts as a vector that transports M. osloensis into the shell cavity of the slug, and the bacterium is the killing agent in the nematode-bacterium complex. We discovered that M. osloensis produces an endotoxin(s), which is tolerant to heat and protease treatments and kills the slug after injection into the shell cavity. Washed or broken cells treated with penicillin and streptomycin from 3-day M. osloensis cultures were more pathogenic than similar cells from 2-day M. osloensis cultures. However, heat and protease treatments and 2 days of storage at 22 degrees C increased the endotoxin activity of the young broken cells but not the endotoxin activity of the young washed cells treated with the antibiotics. This suggests that there may be a proteinaceous substance(s) that is structurally associated with the endotoxin(s) and masks its toxicity in the young bacterial cells. Moreover, 2 days of storage of the young washed bacterial cells at 22 degrees C enhanced their endotoxin activity if they were not treated with the antibiotics. Furthermore, purified lipopolysaccharide (LPS) from the 3-day M. osloensis cultures was toxic to slugs, with an estimated 50% lethal dose of 48 microg per slug, thus demonstrating that the LPS of M. osloensis is an endotoxin that is active against D. reticulatum. This appears to be the first report of a biological toxin that is active against mollusks.

Pathogenicity of Moraxella osloensis, a bacterium associated with the nematode Phasmarhabditis hermaphrodita, to the slug Deroceras reticulatum

Moraxella osloensis, a gram-negative bacterium, is associated with Phasmarhabditis hermaphrodita, a nematode parasite of slugs. This bacterium-feeding nematode has potential for the biological control of slugs, especially the grey garden slug, Deroceras reticulatum. Infective juveniles of P. hermaphrodita invade the shell cavity of the slug, develop into self-fertilizing hermaphrodites, and produce progeny, resulting in host death. However, the role of the associated bacterium in the pathogenicity of the nematode to the slug is unknown. We discovered that M. osloensis alone is pathogenic to D. reticulatum after injection into the shell cavity or hemocoel of the slug. The bacteria from 60-h cultures were more pathogenic than the bacteria from 40-h cultures, as indicated by the higher and more rapid mortality of the slugs injected with the former. Coinjection of penicillin and streptomycin with the 60-h bacterial culture reduced its pathogenicity to the slug. Further work suggested that the reduction and loss of pathogenicity of the aged infective juveniles of P. hermaphrodita to D. reticulatum result from the loss of M. osloensis from the aged nematodes. Also, axenic J1/J2 nematodes were nonpathogenic after injection into the shell cavity. Therefore, we conclude that the bacterium is the sole killing agent of D. reticulatum in the nematode-bacterium complex and that P. hermaphrodita acts only as a vector to transport the bacterium into the shell cavity of the slug. The identification of the toxic metabolites produced by M. osloensis is being pursued.

[Antibiotic sensitivity of important pathogens of bacterial respiratory tract infections in Northeast Germany]

BACKGROUND

There is still a lack of comprehensive study results about resistance of bacterial respiratory pathogens from the east of the Federal Republic of Germany.

METHODS

In Greifswald we isolated in 1995 and 1996 320 strains of typical pathogens and tested their susceptibility to 14 antibiotics, using the microbouillon dilution method.

RESULTS

Pneumococci and beta-haemolytic streptococci were completely susceptible to penicillin and all other beta-lactam-antibiotics, clindamycin and vancomycin. 4.8% of pneumococci and 10.0% of Streptococcus pyogenes isolates were resistant to erythromycin. This should lead to a more differentiated use of macrolides as concerns these pathogens, especially as penicillin still has high efficacy in these cases. Pneumococci had resistance rates of 4.8%, 9.5% and 6.7% to cotrimoxazole, tetracycline and ofloxacin, respectively. No strain of Haemophilus influenzae produced a beta-lactamase, 2.6% of strains were relatively resistant to ampicillin, even in combination with sulbactam. Cefaclor, erythromycin and tetracycline had restricted efficacy of 16.7%, 14.1% and 53.8%, respectively. Cefuroxime, cefixime, cefepime, imipenem and ofloxacin all had complete efficacy. 77.8% of Moraxella catarrhalis isolates were beta-lactamase positive. Strains were susceptible to erythromycin, ofloxacin and all tested beta-lactam-antibiotics except ampicillin and cefaclor. There was a relative resistance to clindamycin and tetracyclin of 22.2% and 2.2%, respectively.

DISCUSSION

We present our results in national and international comparison, describe tendencies of resistance, give reasons for the low incidence of penicillin resistance in pneumococci in Germany and draw conclusions for empirical chemotherapy.