Rosemary Munro

Vancomycin Therapy for Methicillin-Resistant Staphylococcus aureus

Ten patients with bacteremia due to methicillin-resistant Staphylococcus aureus were treated with vancomycin. These patients were compared with matched controls, nine bacteremic patients with methicillin-sensitive S. aureus, and one patient with penicillin-sensitive S. aureus. Controls were treated with a penicillin. There were no significant differences in time to defervescence, metastatic infections, relapse, mortality, need for surgical drainage, or duration of therapy. Fifteen of 19 episodes of serious methicillin-resistant S. aureus infection responded to vancomycin. Severe toxic effects included tinnitus, neutropenia, rash, and possible nephrotoxicity. Tolerance (a minimal bactericidal concentration to minimal inhibitory concentration ratio of at least 32), but not a minimal bactericidal concentration of at least 32 mg/L, correlated with therapeutic failure (respectively, p = 0.04 and p = 0.11, Fishers exact test). Bacteremic infections due to methicillin-resistant and methicillin-sensitive S. aureus cause similar morbidity and mortality. Vancomycin is effective but potentially toxic therapy for most serious infections due to methicillin-resistant S. aureus. In-vitro tests may not predict therapeutic efficacy.

Aeromonas septicemia: Relationship of species and clinical features

&NA; Thirteen patients with Aeromonas species septicemia were seen at Westmead Hospital between 1983 and 1987. In 10 patients (77%) septicemia was caused by A. sobria, and in 3 (23%) by A. hydrophila, A. caviae was not isolated. Chronic underlying illness was present in 10 patients (77%), hematological malignancy being the most common (46%). The average age of the patients was 65.8 years. Seven patients (54%) presented with clinical sepsis, diarrhea and abdominal pain. The biliary tract, lung and soft tissue were other primary sites of infection. Nosocomial infection occurred in 5 patients (38%). Cross‐infection was not seen. Contact with fresh water or fish was observed in only 2 patients (15%). The majority of cases occurred in the warmer months of the year. The overall mortality was 46%. All isolates of Aeromonas species were resistant to ampicillin 8 mg/L. Ten isolates were resistant to tobramycin 1 mg/L, and 3 to tobramycin 4 mg/L. In contrast, 3 isolates were resistant to gentamicin 1 mg/L, and none to 4 mg/L. The isolates showed a varied pattern of resistance to other antibiotics tested, but all were susceptible to piperacillin 64 mg/L, imipenem 4 mg/L, ciprofloxacin 1 mg/L, and amikacin 16 mg/L.

Detection and serogroup determination of neisseria meningitidis in CSF by polymerase chain reaction (PCR)

Summary A PCR protocol for the detection and serogroup determination of Neisseria meningitidis in CSF from 85 cases of suspected meningitis was evaluated. Screening assays for both IS 1106 and the ctr A gene were used to detect meningococcal DNA, and a further two assays using the sia D gene were performed to determine the serogroup. PCR results were compared with results of bacteriological culture and discrepant results resolved by analysis of clinical data and further laboratory test results. The resolved sensitivity and specificity of the PCR screening assay were 89 and 100%, and those of bacteriological culture were 37 and 100%, respectively. The sia D B/C PCR assay was able to determine a serogroup in 85% of cases positive by the PCR screening assay compared with 50% of cases where a serogroup was determined by traditional methods. PCR is a useful tool for diagnosis of meningococcal meningitis when Gram stain and culture tests are negative, a situation that may arise when antibiotic treatment has commenced prior to lumbar puncture.

Ultrasound-enhanced latex immunoagglutination test (USELAT) for detection of capsular polysaccharide antigen of Neisseria meningitidis from CSF and plasma

Aim: An ultrasonic instrument, the Immunosonic, was used to evaluate ultrasound‐enhanced latex immunoagglutination testing (USELAT) for detection and serogroup determination of Neisseria meningitidis in clinical specimens. Methods: Eighty‐two CSF and EDTA blood specimens from patients with suspected meningococcal disease (MD) were tested by USELAT. Results were compared with routine laboratory tests for confirmation of MD and discrepant results were resolved by analysis of further laboratory and clinical data. Results: Using the Wellcogen Bacterial Antigen Kit, USELAT was positive in 20 (24%) specimens. The resolved sensitivity of USELAT was 49% compared with 67% for PCR. There were no discrepancies between serogroups indicated by USELAT and serogroups confirmed by PCR or culture grouping. Conclusions: Although USELAT could be performed in laboratories without facilities for PCR testing, a specific ultrasonic instrument is necessary and some experience is required in interpreting results. The lower resolved sensitivity makes USELAT unsuitable as a stand‐alone rapid test, and it added little value to standard laboratory culture with PCR testing.

Susceptibility of Anaerobic Bacteria to Antimicrobial Agents

&NA; The antimicrobial susceptibility of 1,117 clinical isolates of anaerobic bacteria was determined by the agar dilution technique. Metronidazole was the most active agent; only Propionibacterium acnes and Actinomyces sp. isolates were resistant. Clindamycin and chloramphenical were the next most effective agents. Beta‐lactam antibiotics, with the exception of penicillin, were active against most anaerobes other than the Bacteroides fragilis group. At a breakpoint of 8 mg/l, 25% of Fusobacterium spp. and 30% of the non‐fragilis Bacteroides spp. were resistant to penicillin. The highest resistance to beta‐lactams was seen in the B. fragilis group. Within the indole‐positive members of the group, resistance rates of 71% were seen for cefoxitin, 49% for moxalactam, 79% for cefotaxime, 22% for piperacillin and 89% for penicillin. We conclude that metronidazole has the most predictable in vitro activity against common clinical anaerobic isolates and that resistance to beta‐lactams was frequent and of potential clinical importance as these latter agents are frequently used in the prophylaxis and therapy of mixed anaerobic infections.

Technical note: Use of a selective enrichment broth for isolation of Campylobacter species from human feces

&NA; Isolation of Campylobacter species from 1126 fecal specimens from patients with diarrhea was compared using direct plating and selective enrichment broth. The use of the enrichment broth did not increase the isolation rate, which was 4.2%. While a selective enrichment broth may have advantages where there is delay in transit to the laboratory, or where small numbers of organisms are sought, we do not recommend its use for clinical specimens from patients with diarrhea.

Clostridium beijerinckii endophthalmitis secondary to penetrating ocular injury

Endophthalmitis occurs in five to 10% of injuries involving intraocular foreign bodies. A 52 year old abattoir worker sustained such penetrating ocular trauma and developed fulminant endophthalmitis. Clostridium beijerinckii was isolated from the vitreous humor. Intravitreal vancomycin and amikacin and intravenous penicillin and clindamycin were given. Despite therapeutic vancomycin and amikacin levels in the vitreous, vision was lost and enucleation was ultimately required.

An evaluation of a rapid latex test for the diagnosis of Clostridium difficile-associated diarrhea

&NA; We present here the results of an evaluation of a rapid latex test for detection of CI. stridium difficile‐associated in comparison with our standard cytotoxin assay and culture for C. difficile. Some 515 diarrheal stools were examined. C. difficile was cultured from 70 specimens (13.5%); 53 specimens (10.2%) were positive with the latex test, and 50 (9.6%) by cytotoxin assay. The latex test did not differ significantly from the cytotoxin assay in sensitivity or specificity compared to culture results. There was also no significant difference in the specificity of the latex test compared to cytotoxin assay in patients in whom the diagnosis of C. difficile‐associated diarrhea was negative. Positive and negative predictive values of the latex test for C. difficile‐associated diarrhea were similar to those of cytotoxin assay. The latex test thus appears to be a rapid and practical test for the laboratory diagnosis of C. difficile‐associated diarrhea. To optimize specificity and sensitivity its use should be restricted to patients where the diagnosis is strongly suspected and a rapid answer is required. As it does not distinguish between toxigenic virulent C. difficile strains and non‐toxigenic avirulent strains, it would seem prudent to confirm positive results subsequently by demonstrating in‐vivo or in‐vitro cytotoxin production.

In vitro antibacterial activity of enoxacin (CL-919)

&NA; Antibacterial activity of enoxacin was evaluated against more than 3,700 clinical isolates using the agar‐dilution method and an inoculum of 104‐105 cells per site. For comparison other antibiotics appropriate for each species were also included. For most enterobacteria and for Staphylococcus aureus, Staphylococcus epidermidis and Pseudomonas aeruginosa, the MIC90 of enoxacin was below 2 mg/l. Serratia marcescens was more resistant; the MIC90 being 4 mg/ml. Enoxacin also showed high activity against Campylobacter jejuni and Neisseria gonorrhoeae. Streptococci were comparatively resistant, 32 mg/l to 64 mg/l of the compound being required to inhibit 90% of strains.

The interpretation of microbiology reports by clinicians

Microbiologists know very little about the effectiveness of their reports as a means of communication. We have attempted to investigate this subject by circulating typical reports to the medical staffs of 4 teaching hospitals. The reports were designed to enable us to assess the comprehension of common microbiological terms and to answer certain questions such as the effect of comments and of including antibiotic sensitivities where indications for antibiotic therapy were not definite. Several of the reports were thus prepared in 2 versions, e.g. the presence of a staphylococcus in sputum or a Salmonella in faeces was recorded with or without sensitivities. The need for explanatory comments in many ordinary reports was confirmed. The effect of reporting sensitivities was not clear-cut. In the case of the staphylococcus in sputum this made no difference, whereas significantly more clinicians recommended antibiotic therapy for the Salmonella gastroenteritis when sensitivity results appeared in the report. A number of other findings are discussed.