- Volume 42, Issue 5, 1995

The effect of azithromycin and erythromycin on growth, cell surface hydrophobicity and the susceptibility to the bactericidal activity of human polymorphonuclear leucocytes (PMNL) was examined in four Streptococcus species. Exposure to either 10 x MIC azithromycin or erythromycin induced a post-antibiotic effect (PAE) of between 2.4 and 4.3 h. Erythromycin caused a longer PAE for S. sanguis than azithromycin under the same conditions. The cell surface charge (hydrophobic or hydrophilic) of the streptococci was altered significantly during PAE; loss of hydrophobicity was induced by both macrolides, and this effect was variable amongst the species. The decrease in hydrophobicity was not related to inhibition of growth. The effect of each drug during PAE on the interaction of opsonised suspensions of the streptococci with human PMNL revealed that erythromycin, and to a lesser extent azithromycin, increased susceptibility to the bactericidal activity of human PMNL; this effect was abolished following PAE. The present study clearly showed that PAE should not only be considered as delayed bacterial growth, but also as modulation of bacterial susceptibility to phagocytosis which may influence the outcome of the host-parasite relationship.

From 1974 to 1994, 504 isolates of Prevotella and Porphyromonas spp. were obtained from 435 (21%) of 2033 specimens from 418 children. They included 160 (32%) Pr. melaninogenica, 105 (21%) Pr. intermedia, 84 (17%) P. asaccharolytica, 58 (12%) Pr. orisbuccae, and 58 (12%) Pr. oralis. Most Prevotella and Porphyromonas spp. were isolated from abscesses (176), pulmonary infections (85), ear infections (82), wound infections (44), peritonitis (38), paronychia (15) and chronic sinusitis (14). Predisposing conditions were noted in 111 (27%) of the cases; these included previous surgery in 41 (10%), foreign body in 36 (9%), neurological deficiencies in 29 (7%), immunodeficiency in 21 (5%), steroid therapy in 12 (4%), diabetes in 8 (2%) and malignancy in 7 (2%). Prevotella and Porphyromonas spp. were the only isolates in 14 (3%) patients, and mixed infection was encountered in 404 (97%). The micro-organisms most commonly isolated with Prevotella and Porphyromonas spp. were anaerobic cocci (393 isolates), Fusobacterium spp. (108), Bacteroides spp. (B. fragilis group) (95), Escherichia coli (56) and other gram-negative anaerobic bacilli (52). Most Bacteroides spp. and E. coli were isolated from intra-abdominal infections and skin and soft tissue infections around the rectal area, whereas most Fusobacterium spp. were isolated from oropharyngeal, pulmonary and head and neck sites. β-Lactamase production was detected in 191 (38%) Prevotella and Porphyromonas isolates from all body sites. All patients antimicrobial therapy, and surgical drainage was performed in 173 (41%) cases. Four patients died from their infection. These data illustrate the spectrum and importance of Prevotella and Porphyromonas spp. in infections in children.

A comparative study of biotyping, antimicrobial susceptibility, whole-cell protein analysis, plasmid analysis, pulsed-field gel electrophoresis of chromosomal DNA and polymerase chain reaction with arbitrary primers of Acinetobacter baumannii isolates from three large hospitals was performed to determine the best markers for epidemiological purposes. Ninety-two isolates were included: 38 belonged to a previously described outbreak and 54 were randomly selected from sporadic cases of infection. Biotyping, whole-cell protein and plasmid analysis were the least discriminatory methods, whereas antimicrobial susceptibility and polymerase chain reaction with arbitrary primers showed moderate discriminatory power. Typing based on pulsed-field gel electrophoresis of chromosomal DNA appeared to be the best discriminatory method (discrimination index of 0.9623). The addition of polymerase chain reaction with arbitrary primers or antimicrobial susceptibility to pulsed-field gel electrophoresis of chromosomal DNA did not further increase the discriminatory power.

Cytokine production was measured in mice during Salmonella typhimurium sepsis and intoxication. In mice given live S. typhimurium (10 cfu/mouse), by intra-peritoneal injection, serum levels of tumour necrosis factor (TNF)-α and interleukin-6 increased steadily from day 1 until day 4. Interferon-γ levels showed a transient peak on day 3. Interleukin-1-α levels were very low. There were high bacterial counts in the livers at day 3 and deaths occurred from day 4 onwards. Intraperitoneal injection of lipopolysaccharide or heat-killed bacteria also induced all of the cytokines, but their time of appearance and levels varied greatly. Cytokine induction by heat-killed bacteria was more marked. Endotoxaemia decreased with time during intoxication and increased during sepsis. Bioactive TNF, as measured by a cytotoxicity assay, was found only in mice given heat-killed bacteria.

Fifty-seven isolates of Candida albicans were obtained from different sites within the oral cavities of 18 dental patients without AIDS or any malignancies. Eleven of the patients had oral candidosis associated with the wearing of dentures. The genotypic relationships of the individual isolates were determined by hybridisation of a C. albicans-specific moderately repetitive sequence, 27A, to EcoRI-digested C. albicans chromosomal DNA. From the DNA profiles, the isolates could be divided into 22 distinct genetic groups. In the majority of patients, a single unique strain of C. albicans appeared to dominate in the oral cavity. Re-infection following antifungal therapy was generally due to the re-emergence of the original infecting strain. The C. albicans strains isolated from dental plates did not form a distinct genetic group. These results suggest that denture stomatitis is due to the outgrowth of commensal strains of C. albicans.

A combined reverse transcription-polymerase chain reaction (RT-PCR) method was employed for the detection of hepatitis C virus (HCV) RNA in serum from patients with chronic active hepatitis, with primers corresponding to the 5′ non-coding region. The diagnosis was based on serological and biochemical methods and on liver biopsy. HCV-RNA was detected in 27 (90%) of 30 sera examined. The nucleotide sequence of PCR-amplified HCV cDNAs (256 bp) was determined from five specimens and heterogeneity varying between 0.58% and 2.89% among the clinical samples and the prototype HCV-1 was found.