Biomedical subjects
Publications and source records attributed to I J Mitchelmore.
A case of brain abscess involving Haemophilus paraphrophilus and Actinomyces odontolyticus is presented. This combination of organisms has not previously been described. All brain abscess specimens should routinely be processed rapidly and cultured for a prolonged period to ensure recovery of fastidious organisms which may have implications for antibiotic therapy.
Samples of pus aspirated from 53 peritonsillar abscesses were examined in detail for aerobic and anaerobic bacteria, and the microbiological results correlated with clinical data in 44 cases. In 45 samples (85%) cultures were positive: 7 yielded organisms consistent with an aerobic infection, mainly Lancefield group A beta-haemolytic streptococci (5/7), and 38 yielded organisms consistent with an anaerobic infection. The anaerobic infections were usually mixed, but in two cases Fusobacterium necrophorum was isolated in pure culture. Peptostreptococcus micros and Streptococcus milleri were the predominant isolates in this group. Direct Gram stain smear and gas-liquid chromatography were useful indicators of the type of infection present. Samples from ten patients (18.9%) grew one or more beta-lactamase-producing isolates. Of the 25 patients prescribed antibiotics by their general practitioners prior to admission, 18 received one or more beta-lactam antibiotics. Most cases of peritonsillar abscess were due to mixed anaerobic infections, Lancefield group A beta-haemolytic streptococci playing a central role in only a minority of cases. In light of these findings and the possibility of infection with beta-lactamase-producing isolates, it is suggested that the first-line antibiotic therapy in this group of patients should include a chemotherapeutic agent directed against anaerobic bacteria.
The bacterial flora of the tonsil surface and core was compared in patients suffering from recurrent tonsillitis. Surface swabs and tonsil core tissues were received as paired samples from 50 patients admitted for elective tonsillectomy. Analysis of paired samples from individual patients revealed differences in the bacterial flora of the tonsil core and the tonsil surface. Of 366 aerobic isolates, 30% grew from the surface alone, 26% from the core only and 44% from both sites. Of 290 anaerobic isolates, 35% grew from the surface alone, 33% from the core only and 31% from both sites. The total number of isolates from surface and core samples was similar (average 9.2 and 8.8, respectively). The range of species isolated was also similar for both surface and core samples, as was the proportion of organisms producing beta-lactamase from each site (10.7% and 9.5%, respectively). Eighty-two percent of patients carried beta-lactamase-producing organisms on either the tonsil surface or in the core tissue. A surface swab does not reliably reflect the types of organisms present in the tonsil core in individual patients. Anaerobes are a major component of tonsil surface and core bacterial flora in patients with recurrent tonsillitis. The high carriage rate of beta-lactamase-producing organisms in the tonsils should be considered when selecting antimicrobial therapy for persistent or recurrent tonsillitis.
The clinical importance of the gram-positive anaerobic cocci (GPAC) isolated in 1987 at St Bartholomew's Hospital, London, is assessed. Of about 800 anaerobic isolates, 209 (27%) were GPAC, of which 67 (32%) were from abscesses and 22 (11%) were in pure growth. Four species comprised 77% of the 168 isolates available for study: Peptostreptococcus magnus (55 isolates, 33%), P. micros (23, 14%), P. asaccharolyticus (24, 14%) P. asaccharolyticus (24, 14%) and P. anaerobius (27, 16%). Different species were associated with different sites, from P. magnus (usually skin-associated sites; normally cultured with aerobes, infrequently with other anaerobes), P. asaccharolyticus (distributed widely) and P. anaerobius (usually genitourinary and gastrointestinal; always below the diaphragm) to P. micros (always deep sites with other anaerobes). P. magnus was isolated from 15 abscesses and was obtained in pure culture from 11 specimens, six of them abscesses developing from infected sebaceous cysts. P. micros was usually isolated from soft tissue abscesses, never from the skin, and with a characteristic mixed flora consisting of "Streptococcus milleri" and anaerobic gram-negative rods. P. heliotrinreducens was a rare isolate from similar specimens. P. asaccharolyticus was cultured from a wide variety of sites, typically mixed with both aerobes and anaerobes, and frequently from abscesses. Most isolates of P. anaerobius came from gastrointestinal or female genitourinary specimens, never from above the diaphragm and rarely from the skin; cultures were usually heavily mixed. Isolates of P. vaginalis and the "bGAL" group made up 11% of str ains and were usally cultured from superficial sites, P. vaginalis often from post-operative wound infections with Staphylococcus aureus.(ABSTRACT TRUNCATED AT 250 WORDS)
A collection of 256 clinical strains and 40 reference strains of gram-positive anaerobic cocci (GPAC) was studied, to characterise the recognised species more fully and to define groups of strains which might correspond to previously undescribed species. The methods used were: gas-liquid chromatography (GLC) for the detection of volatile fatty acids (VFAs); determination of the pre-formed enzyme profile with a commercially available kit, ATB 32A; microscopic appearance; colonial morphology; and antibiotic sensitivity tests. Strains were placed in one of five VFA groups according to their GLC profile; 96% of strains were further assigned to 12 groups by their enzyme profile. There was less than 99% agreement between the two methods. Of 111 clinical strains in the VFA-negative group, 110 gave one of three distinct enzyme profiles corresponding to Peptostreptococcus magnus, P. micros and P. heliotrinreducens. The assignment of strains to groups based on their microscopic appearance and colonial morphology agreed well with groupings according to enzyme profile. Identification of butyrate-producing GPAC was unsatisfactory because it relied heavily on the enzyme profile; testing for indole production was of limited discriminative value. Most strains of P. asaccharolyticus and P. indolicus were very similar in enzyme profile, microscopic appearance and colonial morphology, but a sub-group of P. asaccharolyticus could be distinguished. A further indole-positive group corresponding to Hare group III was also noted. Strains of P. prevotii and P. tetradius were very similar, but easily distinguished from other butyrate-producing GPAC. However, 45% of the butyrate-producing cocci could not be assigned to recognised species; most of these were assigned to one of two new groups, the ADH group and the bGAL group, by their enzyme profile, microscopic appearance and smell. Four strains that produced a terminal VFA peak of isovaleric acid formed a new group designated 'ivoricus'. Reliable features for the identification of P. anaerobius were GLC (all GPAC that produced isocaproic acid were identified as P. anaerobius), enzyme profile and sensitivity to SPS. Two clinical strains that produced caproci acid were identified as Hare group VIII; they were distinguished from Peptococcus niger by their enzyme profile and colonial morphology. A phenotypic classification based on GLC and enzyme profile is presented, with a method for the identification of most strains of GPAC within 48 h of primary isolation.
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Two systems for detecting pre-formed enzymes, RapID ANA and a prototype system from API, were compared in a blind study for their ability to identify 69 gram-positive anaerobic cocci isolated from clinical specimens. Both systems were able to identify Peptostreptococcus anaerobius, Ps. asaccharolyticus and Ps. micros accurately without the need for further tests. The prototype API system identified all isolates of Ps. magnus correctly, but the RapId ANA system misidentified several isolates as Ps. micros. Numerous different enzyme patterns were found with the indole-negative, butyrate-producing cocci (Ps. prevotii and Ps. tetradius), suggesting that this group of organisms may be heterogeneous. We conclude that kits for detecting preformed enzymes are of considerable potential for the identification of gram-positive anaerobic cocci in clinical laboratories.
The preformed (constitutive) enzyme profiles of 30 type strains and reference strains of gram-positive anaerobic cocci were determined with two commercial systems, RapID ANA and a prototype system from API. Both systems identified Peptostreptococcus anaerobius, Ps. asaccharolyticus, Ps. indolicus, Ps. magnus and Ps. micros accurately, except for one strain of Ps. magnus misidentified as Ps. micros by the RapID ANA system. The indole-negative, butyrate-producing cocci (classified at present as Ps. prevotii and Ps. tetradius) produced several different, unique patterns with the prototype API system, but the results with RapID ANA were often misleading. Eight strains of Hare group cocci produced previously described profiles. Four strains of streptococci produced profiles easily distinguished from those of the gram-positive anaerobic cocci. We conclude that most gram-positive anaerobic cocci can be identified rapidly and reliably to the species level by their preformed enzyme profiles, providing that their underlying classification is sound. Problems were encountered with the butyrate-producing cocci, which appear to be a more heterogeneous group of organisms than is currently acknowledged; further taxonomic studies on these organisms are required.