Antimicrobial susceptibility of anaerobic bacteria in Belgium as determined by E-test methodology

The objective was to collect recent data on the antibiotic susceptibility of clinically significant anaerobes in Belgium. A total of 333 anaerobic clinical isolates from various body sites were prospectively collected between 2005 and 2007 at two tertiary care hospitals in Belgium. The minimal inhibitory concentrations (MICs) were determined using the E-test method for nine anti-anaerobic antibiotics. Sixty-one percent of the isolates were β-lactamase producers, which explains the poor activity of penicillin. Amoxicillin/clavulanic acid, piperacillin/tazobactam, metronidazole and meropenem were very active against most anaerobes, but around 10% of the Bacteroides fragilis group strains were non-susceptible to the two β-lactam/β-lactamase inhibitors. No resistance was observed to metronidazole, while 3% of the Bacteroides spp. had decreased susceptibility to meropenem (MIC ≥ 4 mg/L). Cefoxitin, clindamycin and moxifloxacin were less active, with 33%, 52% and 57% of the B. fragilis group being non-susceptible respectively. Tigecycline showed consistently good activity against most anaerobes with MIC₅₀ and MIC₉₀ of 0.25 and 2 mg/L. Metronidazole, amoxicillin/clavulanate, piperacillin/tazobactam and meropenem remain good empirical choices when anaerobes are expected in our setting. Because of the occurrence of resistance to most classes of current anti-anaerobic antibiotics, it is recommended that the antimicrobial resistance patterns be monitored regularly in order to guide empirical therapy.     

Antimicrobial resistance,prevalence of resistance genes,and molecular characterization in intestinal Bacteroides fragilis group isolates

Since the level of antimicrobial resistance in Bacteroides fragilis has increased, monitoring the antimicrobial susceptibility could be necessary. The objectives of this study were to (i) investigate the prevalence of species, the occurrence of reduced antimicrobial susceptibility (E‐test method), and antibiotic resistance genes in the B. fragilis group and (ii) evaluate the prevalence of enterotoxigenic B. fragilis and the distribution of bft gene subtypes in hospitalized patients. As many as 475 isolates out of 250 stool samples were detected to be B. fragilis group by using conventional biochemical tests (API‐32A system) and multiplex‐PCR. In addition, 48.2%, 13.9%, 76.6%, and 1.2% of B. fragilis group isolates were resistant (according to EUCAST breakpoint) to piperacillin‐tazobactam, meropenem, clindamycin, and metronidazole, respectively. Six metronidazole‐resistant strains were isolated; B. fragilis (n: 3), B. thetaiotaomicron, B. vulgates, and B. ovatus. The presence of the cfiA, cepA, ermF, and nim genes was observed in 3.8%, 15.9%, 34.1%, and 0.7% of the B. fragilis isolates, respectively. One hundred thirty‐two B. fragilis isolates (27.8%)and 21 B  fragilis isolates (15.9%) turned out to be bft gene positive by multiplex‐PCR; eleven isolates (52.4%) harbored bft‐1, eight isolates (38%) harbored bft‐2 isotypes, and two isolates (9.5%) harbored bft‐3 isotype (16.66%). These bacteria harbor antimicrobial resistance genes that could be transferred to other susceptible intestinal strains. Further investigations on lineage analysis are needed for a better understanding of these bacteria in Iran.     

Development of a EUCAST disk diffusion method for the susceptibility testing of rapidly growing anaerobic bacteria using Fastidious Anaerobe Agar (FAA): a development study using Bacteroides species

ObjectivesAntimicrobial resistance among anaerobic bacteria is increasing, leading to a growing demand for inexpensive and reliable susceptibility testing methods. The aim of this study was to determine the suitability of Fastidious Anaerobe Agar (FAA) as a medium for disk diffusion for rapidly growing anaerobic bacteria.MethodsReproducibility of zone diameters and quality of growth were tested using six quality control (QC) strains. We compared four anaerobic incubation systems, two incubation temperatures (35°C and 37°C), and FAA from four manufacturers. The effect of incubation for 16–20 hours instead of 24 hours was tested on ten randomly selected isolates of the Bacteroides fragilis group. The final method was tested on 170 clinical B. fragilis-group isolates and compared to agar dilution MICs.ResultsAfter 24 hours' incubation, all QC strains demonstrated confluent growth. The different anaerobic incubation systems were equal regarding quality of growth and zone diameters. Incubation at 35°C resulted in slightly larger zones (1–2 mm) than at 37°C. Except for Acumedia FAA, the different manufacturers showed good agreement in zone diameters. All B. fragilis-group isolates displayed confluent growth after 16–20 hours. Metronidazole inhibition zones correlated well with the reference MICs. There was an area of poorer separation for meropenem and piperacillin–tazobactam between 19-27 and 14-23 mm respectively. Prolonged incubation (40–44 h) of clindamycin resulted in better separation and the area of overlap was reduced from 13 to 8 mm compared with 16–20 hours' incubation.ConclusionFAA is a suitable medium for disk diffusion of these rapidly growing anaerobic bacteria.     

Activité du doripénème sur les bactéries anaérobies strictes

Aims of the study

This study examines the activity of doripenem, a new carbapenem compound compared with amoxicillin-clavulanic acid, piperacillin + tazobactam, imipenem, clindamycin and metronidazole against 316 anaerobes.

Methods

Inoculum preparation and agar dilution method were performed according to the CLSI method for anaerobes (M11A7).

Results

At a concentration of 4 μg/ml doripenem and imipenem (IMP) inhibited 122 (96 %) and 126 (99 %) strains of the Bacteroides fragilis group, respectively. In contrast, doripenem appeared more potent than IMP against Gram-positive anaerobes inhibiting at the same concentration of 4 μg/ml 145/145 strains (100 %) versus 115/145 for IMP (79.3 %). Against 316 anaerobic strains, the carbapenem doripenem had an MIC₅₀ of 0.25 μg/ml and an MIC₉₀ of 2 μg/ml. Results were similar to those for imipenem (MIC₅₀ of 0.125 μg/ml and MIC₉₀ of 4 μg/ml). If we consider the resistant breakpoints of the two carbapenems as defined by EUCAST, the resistance rate for doripenem (MIC > 4 μg/ml) 1.6 % is similar to that of imipenem (MIC > 8 μg/ml) 1.3 %.

Conclusion

Thus independently of the PK/PD parameters the two carbapenems demonstrated very close activity; doripenem was more potent on Gram-positive anaerobes and slightly less potent against Gram-negative anaerobes mainly the B. fragilis group. Further clinical studies are needed to assess its usefulness in patients.     

Clinical significance of anaerobic bacteremias in a general hospital

Summary A prospective study was designed to investigate anaerobic bacteremias and evaluate their incidence and significance in a general hospital. One or more blood cultures positive for anaerobic microorganisms were analyzed from each of a total of 61 patients hospitalized between January 1988 and April 1992, in accordance with an established protocol. The clinical repercussions of bacteremia were also analyzed. Two percent of blood cultures were positive for anaerobes, with an incidence of 0.6 cases per 1000 hosphitalized patients. The most frequently isolated anaerobes were Bacteroides fragilis and Clostridium perfringens. Intraabdominal disease was the route of entry in 50% of the patients. A death rate of 37.3 % was mostly attributed to B. fragilis. Hospitalization in the surgical department, nosocomial acquisition, previous surgery, critical initial clinical status and the presence of complications were significantly associated with increased death rates. No significant differences were found in the clinical course between patients whose antibiotic treatment was judged adequate and those for whom it was considered inadequate. The frequency and incidence of anaerobic bacteremia was low in our hospital. The well-known clinical and epidemiological characteristics of these infections facilitates their prompt diagnosis and empirical treatment with antibiotics of proven effectiveness against anaerobes.     

Trends in the susceptibility of commonly encountered clinically significant anaerobes and susceptibilities of blood isolates of anaerobes to 16 antimicrobial agents,including fidaxomicin and rifaximin, 2008–2012, northern Taiwan

We investigated the antimicrobial resistance trends and profiles of clinical anaerobic isolates in northern Taiwan. Trends in the susceptibility of five commonly encountered clinical anaerobic isolates to seven agents from 2008 to 2012 were measured using the Cochran–Armitage trend test. The minimum inhibitory concentrations (MICs) of 16 antimicrobial agents, including fidaxomicin and rifaximin, against anaerobic blood isolates from two medical centers were determined using the agar dilution method. During the study period, susceptibility data on 11,105 isolates were evaluated. Metronidazole and chloramphenicol retained excellent activities. Around 20–30 % of isolates of Bacteroides and Prevotella species were resistant to ampicillin–sulbactam, cefmetazole, flomoxef, and clindamycin. Of the 507 tested blood isolates, the rates of resistance to commonly used agents were much higher, namely, 16.2 % for amoxicillin–clavulanate, 15.6 % for ampicillin–sulbactam, 24.7 % for cefmetazole, and 36.1 % for clindamycin. Notably, 13.5 % of B. fragilis isolates were resistant to ertapenem. Also, 15.2 % of B. uniformis, 17.2 % of other Bacteroides species, 14.3 % of Prevotella species, and 14 % of Clostridium other than C. perfringens isolates were resistant to moxifloxacin. Cefoperazone–sulbactam was active against most isolates, except for Clostridium species other than perfringens (resistance rate, 18.6 %). Fidaxomicin exerted poor activities against most anaerobes tested (MIC₉₀ of >128 μg/ml for B. fragilis and all isolates), except for C. perfringens (MIC₉₀ of 0.03 μg/ml) and Peptostreptococcus micros (MIC₉₀ of 2 μg/ml). However, rifaximin showed a wide range of susceptibilities against the tested anaerobes (MIC₉₀ of 0.5 μg/ml for B. fragilis). The emergence of resistance to ertapenem and moxifloxacin among bacteremic anaerobes highlights the need for continuous monitoring.     

Bacteroides fragilis RecA protein overexpression causes resistance to metronidazole

Bacteroides fragilis is a human gut commensal and an opportunistic pathogen causing anaerobic abscesses and bacteraemias which are treated with metronidazole (Mtz), a DNA damaging agent. This study examined the role of the DNA repair protein, RecA, in maintaining endogenous DNA stability and its contribution to resistance to Mtz and other DNA damaging agents. RT-PCR of B. fragilis genomic DNA showed that the recA gene was co-transcribed as an operon together with two upstream genes, putatively involved in repairing oxygen damage. A B. fragilis recA mutant was generated using targeted gene inactivation. Fluorescence microscopy using DAPI staining revealed increased numbers of mutant cells with reduced intact double-stranded DNA. Alkaline gel electrophoresis of the recA mutant DNA showed increased amounts of strand breaks under normal growth conditions, and the recA mutant also showed less spontaneous mutagenesis relative to the wild type strain. The recA mutant was sensitive to Mtz, ultraviolet light and hydrogen peroxide. A B. fragilis strain overexpressing the RecA protein exhibited increased resistance to Mtz compared to the wild type. This is the first study to show that overexpression of a DNA repair protein in B. fragilis increases Mtz resistance. This represents a novel drug resistance mechanism in this bacterium.     

Metronidazole-sensitive organisms in children with severe acute malnutrition: an evaluation of the indication for empiric metronidazole treatment

ObjectivesChildren with severe acute malnutrition (SAM) are treated with empiric amoxicillin or penicillin and gentamicin because of the high risk of severe infections. Experts have suggested, based on available evidence, adding metronidazole to cover anaerobic bacteraemia and diarrhoea caused by Giardia duodenalis or Clostridium difficile. The objective of this study was to assess the importance of these infections in children with SAM.MethodsChildren from 6 months to 15 years with SAM were enrolled and followed clinically. Aerobic and, when patient weight permitted, anaerobic blood cultures were done using Bactec® system, and isolates identified with matrix-assisted laser desorption ionization–time of flight mass spectrometry. Stool samples were tested for C. difficile, G. duodenalis and Entamoeba histolytica by PCR.ResultsA total of 334 children were enrolled and 174 out of 331 (53%) for which data on this was available had diarrhoea. Of 273 patients tested by blood culture, 11 had bacteraemia (4.0%, 95% CI 2.3–7.1%) but none with strict anaerobic bacteria (0/153, 95% CI 0–2.4%). There was no difference in the prevalence of C. difficile between children with (5/128, 4%) and without (7/87, 8%) diarrhoea (OR 0.47, 95% CI 0.14–1.53), and no difference in the prevalence of Giardia between these groups (78/138, 60% vs. 46/87, 53%; OR 1.34, 95% CI 0.77–2.32). Children with C. difficile had higher mortality than those without this infection (3/11, 27%, vs. 7/186, 4%; OR 43, 95% CI 3.9–483).ConclusionOur results do not provide support for empiric metronidazole to cover for anaerobic bacteraemia. Trials evaluating the effect of empiric treatment and its effect on G. duodenalis and C. difficile are warranted.     

Clinical and microbiological features of bacteraemia with Gram-positive anaerobic cocci: a population-based retrospective study

ObjectivesGram-positive, anaerobic cocci (GPAC) can cause infections in humans. Only a few cases of bacteraemia with GPAC have been reported. We describe the clinical and microbiological characteristics of GPAC bacteraemia.MethodsA retrospective population-based study of GPAC bacteraemia 2012–2016 in southern Sweden was performed. GPAC were identified using matrix-associated laser desorption ionization time-of-flight mass spectrometry or 16S rRNA gene sequencing. Etests were used to determine antibiotic susceptibilities. Data on patient and infection characteristics, treatment, and outcome were collected from the medical records.ResultsA total of 226 episodes of GPAC bacteraemia in adults were studied; this corresponds to an annual incidence of 3.4 cases per 100,000 persons per year. The bacteria identified were Anaerococcus spp. (n = 43), Atopobium spp. (n = 7), Blautia spp. (n = 1), Finegoldia spp. (n = 15), Parvimonas spp. (n = 100), Peptoniphilus spp. (n = 52), Peptostreptococcus spp. (n = 2), and Ruminococcus spp. (n = 9) of which 200 isolates were identified to the species level. Resistance to imipenem and piperacillin was not identified, whereas resistance among the 229 isolates to penicillin was detected in four, to metronidazole in six, and clindamycin in 16 isolates. The median age of patients was 73 years (55–83, IQR), 57% were male and comorbidities were common. Fifty-one per cent of infections were polymicrobial. In 60% of cases a focus of infection was identified. Forty per cent of patients had either organ dysfunction or shock. The 30-day mortality was 11%, and nosocomial infections were over-represented among the deceased.ConclusionsGPAC bacteraemia is much more common than previously reported. GPAC-bacteraemia is a condition with significant mortality mainly affecting elderly persons with comorbidities.     

Funktionen der körpereigenen Abwehr gegen Anaerobier bei Gesunden und Patienten mit chronisch-septischer Granulomatose

Summary Different strains ofBacteroides fragilis exhibit great differences in sensitivity towards serum from healthy volunteers. In the presence of 10% autologous serum, neutrophilic granulocytes and monocytes (macrophages) caused significant killing ofB. fragilis. The measured phagocytic and killing activity of the cells is comparable to their activity against aerobic bacteria (S. aureus). In four patients with chronic granulomatous disease of childhood, phagocytosis was normal but killing ofB. fragilis andS. aureus in granulocytes or monocytes (macrophages) was appreciably lowered. This malfunction of the cells was accompanied by a disturbance in oxidative metabolism and inadequate iodination after phagocytosis ofB. fragilis. The results suggest that granulocytes and monocytes play an important role in host defense against endogenous infections with anaerobes.

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Abkürzungen NBT Nitroblautetrazolium - B. fragilis Bacteroides fragilis Herrn Prof. Dr. A.K. Kleinschmidt zum 70. Geburtstag gewidmet     

Agreement of Direct Antifungal Susceptibility Testing from Positive Blood Culture Bottles with the Conventional Method for Candida Species

Early availability of antifungal susceptibilities can ensure timely institution of targeted therapy in candidemia, which can improve patient outcomes. This study prospectively determines the agreement between the results of direct testing of antifungal susceptibilities from blood culture bottles by disk diffusion and Etest and the results of standardized susceptibility testing methods; direct testing would allow susceptibility results to be available 1 to 2 days earlier. A total of 104 blood cultures with different Candida species (28% C. albicans, 27% C. parapsilosis, 26% C. tropicalis, etc.) were evaluated between January 2012 and May 2013 for agreement of fluconazole, voriconazole, and amphotericin B susceptibility results by disk diffusion. Agreement in MICs obtained by Etest was determined for fluconazole (21 isolates), voriconazole (28 isolates), amphotericin (29 isolates), and caspofungin (29 isolates). The kappa scores for categorical agreement were highest for fluconazole by disk diffusion (0.902, standard error [SE] = 0.076) and Etest (1.00, SE = 0.218) and for amphotericin B by disk diffusion (1.00, SE = 0.098). The Pearson correlation (r) of zone diameters was strongest for fluconazole (0.69) and amphotericin (0.70) and moderate for voriconazole (0.60), and the Pearson correlation of MICs was strongest for fluconazole (0.94) and caspofungin (0.88). However, the moderate correlation of amphotericin MICs with zone diameters (−0.42) precludes the use of amphotericin B disk diffusion for susceptibility testing. There were no very major errors; however, there were 1 (1%) major and 5 (4.8%) minor errors with disk diffusion and 4 (13.3%) minor errors with Etest. Thus, antifungal disk diffusion directly from blood culture bottles is a rapid and easy method for fluconazole and voriconazole susceptibility testing for timely tailoring of candidemia therapy.     

Frequency and associated factors for carbapenem-non-susceptible Bacteroides fragilis group bacteria colonization in hospitalized patients: Case control study in a university hospital in Turkey

PurpuseThe carbapenem-resistant Bacteroides fragilis group (CR-BFG) bacteria have been reported in several countries recently with increasing global attention. The high incidence of CR-BFG isolated from our hospitalized patients has become an important problem. Therefore, we aimed to determine the frequency and associated factors for intestinal colonization by carbapenem-non-susceptible BFG (CNS-BFG) among adult patients hospitalized at intensive care units, neurosurgery and internal medicine wards in our hospital.MethodsRectal swabs (n = 1200), collected from 766 patients between February 2014 and March 2015, were inoculated onto kanamycin-vancomycin-leaked blood agar containing 0.125 mg/L meropenem. The isolates were identified by MALDI-TOF MS. Susceptibility testing was performed by agar dilution method. The carbapenemase gene (cfiA) was detected by PCR. Logistic regression analysis was used to evaluate the associated factors for intestinal colonization by CNS-BFG.ResultsA total 180 non-duplicate BFG isolates were obtained from 164 patients.Ten different species, including Parabacteroides distasonis (n = 46, 25.6%), and Bacteroides fragilis (n = 30; 16.6%), were identified. Twenty-five percent of the isolates were non-susceptible to meropenem (MIC >2 mg/L). The highest prevalence of meropenem resistant strains (MIC >8 mg/L) was detected among B. fragilis (n = 12), followed by Parabacteroides spp. (n = 4). All but one B. fragilis strains were cfiA gene positive. Hospital admission, increasing Charlson score, use of antibiotics; including carbapenems in past three months, colonization with other accompanying carbapenem-resistant Gram negative bacteria (Enterobacteriaceae, Acinetobacter baumannii and Pseudomonas aeruginosa), and having undergone surgical operations were significantly associated with RCS- BFG colonization.ConclusionsThe high carriage rate of CNS-BFG in hospitalized patients may lead to worse clinical outcomes, such as serious infections and mortality, and deserves attention.     

Aerobic and Anaerobic Microbiology of Surgical-Site Infection Following Spinal Fusion

The aerobic and anaerobic microbiology of surgical-site infections (SSI) following spinal fusion was retrospectively studied. This was done by reviewing the clinical and microbiological records at the Naval Hospital in Bethesda, Md., from 1980 to 1992. Aspirates of pus from 25 infection sites showed bacterial growth. Aerobic bacteria only were recovered from 9 (36%) specimens, anaerobic bacteria only were recovered from 4 (16%), and mixed aerobic and anaerobic bacteria were recovered from 12 (48%). Sixty isolates were recovered: 38 aerobes (1.5 isolates per specimen) and 22 anaerobes (0.9 isolate per specimen). The predominant aerobes were Escherichia coli (n = 8) and Proteus sp. (n = 7). The predominant anaerobes were Bacteroides fragilis group (n = 9) and Peptostreptococcus sp. (n = 6) isolates. An increase in recovery of E. coli and B. fragilis was noted in patients with bowel or bladder incontinence. This study highlights the polymicrobial nature of SSI and the importance of anaerobic bacteria in SSI following spinal fusion.     

Diagnostic performance of blood culture bottles for vitreous culture compared to conventional microbiological cultures in patients with suspected endophthalmitis

The purpose of this investigation was to evaluate the performance of blood culture bottles in comparison to conventional microbiological culture techniques in detecting causative microorganisms of endophthalmitis and to determine their anti-infective susceptibility profiles. All consecutive cases with clinically suspected endophthalmitis in a university-based ophthalmology department between January 2009 and December 2016 were analysed in this retrospective comparative case series. Samples from 247 patients with suspected endophthalmitis underwent microbiological diagnostic work-up. All three culture methods were performed from 140 vitreous specimens. Vitreous fluid specimens were inoculated in blood culture bottles, aerobic and anaerobic broth solutions, and on solid media. Anti-infective susceptibility profiles were evaluated by semi-automated methods and/or gradient diffusion methods. Microorganisms were grown in 82 of 140 specimens for which all methods were performed (59%). Microorganisms were more frequently grown from blood culture bottles (55%) compared to broth solution (45%, p?=?0.007) and solid media (33%, p?<?0.0001). Considerable differences in the performance among culture media were detected for fungal pathogens. All grown fungi were detected by blood culture bottles (11 of 11, 100%). Broth solution recovered 64% and solid media 46% of grown fungi. No Gram-positive bacterium was resistant to vancomycin and all Gram-negative pathogens except for one isolate were susceptible to third-generation cephalosporins. In suspected endophthalmitis patients, blood culture bottles have a higher overall pathogen detection rate from vitreous fluid compared to conventional microbiological media, especially for fungi. The initial intravitreal antibiotic therapy with vancomycin plus third-generation cephalosporins appears to be an appropriate treatment approach for bacterial endophthalmitis.     

Tightly controlled response to oxidative stress; an important factor in the tolerance of Bacteroides fragilis

The exposure of Bacteroides fragilis to highly oxygenated tissues induces an oxidative stress due to a shift from the reduced condition of the gastrointestinal tract to an aerobic environment of host tissues. The potent and effective responses to reactive oxygen species (ROS) make the B. fragilis tolerant to atmospheric oxygen for several days. The response to oxidative stress in B. fragilis is a complicated event that is induced and regulated by different agents. In this review, we will focus on the B. fragilis response to oxidative stress and present an overview of the regulators of responses to oxidative stress in this bacterium.     

Detection of bacterial and yeast species with the Bactec 9120 automated system with routine use of aerobic, anaerobic, and fungal media

During the period 2006 and 2007, all blood cultures required by four units at high infective risk and most of those required by other units of the University Hospital of Palermo, Palermo, Italy were performed using a Bactec 9120 automated blood culture system with a complete set of Plus Aerobic/F, Plus Anaerobic/F, and Mycosis IC/F bottles. The aim of the study was to enable the authors to gain firsthand experience of the culture potentialities of the three different media, to obtain information regarding the overall and specific recovery of bacteria and yeasts from blood cultures in the hospital, and to reach a decision as to whether and when to utilize anaerobic and fungal bottles. Although very few bloodstream infections (1.8%) were associated with obligate anaerobes, the traditional routine use of anaerobic bottles was confirmed because of their usefulness, not only in the detection of anaerobes, but also in that of gram-positive cocci and fermentative gram-negative bacilli. In this study, Mycosis IC/F bottles detected 77.4% of all the yeast isolates, 87.0% of yeasts belonging to the species Candida albicans, and 45.7% of nonfermentative gram-negative bacilli resistant to chloramphenicol and tobramycin. In order to improve the diagnosis of fungemia in high-risk patients, the additional routine use of fungal bottles was suggested when, as occurred in the intensive-care unit and in the hematology unit of the University Hospital of Palermo, high percentages of bloodstream infections are associated with yeasts, and/or antibiotic-resistant bacteria and/or multiple bacterial isolates capable of inhibiting yeast growth in aerobic bottles.     

Performance of VITEK-2 Compact and overnight MicroScan panels for direct identification and susceptibility testing of Gram-negative bacilli from positive FAN BacT/ALERT blood culture bottles

We describe the reliability of the VITEK-2 Compact and overnight MicroScan panels for direct identification and susceptibility testing from the BacT/ALERT blood culture system when using FAN (FA and FN) bottles. A simple procedure, in two centrifugation steps, was designed to remove the charcoal particles present in FA and FN bottles. A total of 113 positive blood cultures showing Gram-negative rods were investigated. Enterobacteriaceae were isolated in 104 cases, and Pseudomonas aeruginosa in nine. The MicroScan system correctly identified 106 (93.8%) of the 113 isolates. The seven identification errors included P. aeruginosa (three), Enterobacter cloacae (one), Escherichia coli (one), Klebsiella oxytoca (one), and Klebsiella pneumoniae (one). The VITEK-2 system correctly identified 109 (96.5%) of the 113 samples obtained directly from the blood culture bottles. The four unidentified isolates were Enterobacter cloacae (two), Escherichia coli (one), and P. aeruginosa (one). MicroScan yielded 4/779 (0.5%) very major errors and 28/2825 (0.9%) minor errors. VITEK-2 yielded 2/550 (0.36%) very major errors, 1/1718 (0.05%) major error, and 32/2373 (1.3%) minor errors. Both systems provided excellent identification (correlation of >90%) and susceptibility (correlation of >98%) results. The average times required to obtain identification and susceptibility results using the direct test applied to the VITEK-2 Compact system were 4.57 ± 1.37 h and 6.52 ± 1.64 h, respectively. The VITEK-2 compact system provided results on the same day that the blood culture was found to be positive.     

Diagnosis of anaerobic infection by gas chromatographic estimation of volatile fatty acids

Nine hundred and eighty-one fluid specimens were analysed by culture and by gas chromatography. The presence of obligate anaerobes was best predicted if one or more of the volatile acids isobutyric, butyric, isovaleric, valeric, isocaproic or caproic acid were detected in the specimen. Propionic acid was not a good indicator of the presence of obligate anaerobes. The agreement between gas chromatography and culture for obligate anaerobes in the main study (841 specimens, 232 culture positive) was: co-positivity 82%; co-negativity 92%. Falsely negative specimens contained anaerobes which had probably not produced sufficient of their characteristic volatile fatty acids to be detected. When it was the sole infecting anaerobe,Bacteroides fragilis seemed especially likely to be missed by gas chromatography. Forty-five of the 51 falsely positive specimens probably represented failure to culture anaerobes rather than spurious volatile fatty acid detection.     

Resistance Trends in Antimicrobial Susceptibility of Anaerobic Bacteria, Part I

Despite the suggestions of both the Clinical and Laboratory Standards Institute (CLSI) and the American Society for Microbiology (ASM) Manual of Clinical Microbiology that hospitals should test individual patient isolates to assist in their care, periodically establish patterns of resistance for certain anaerobes, and include these data in the hospital antibiogram, anaerobic susceptibility studies are performed in only a minority of clinical laboratories and their patterns of susceptibility are obtainable mostly from published surveys conducted by a small number of research centers scattered worldwide. The Bacteroides fragilis group species, the most frequently studied anaerobes, have been reported to vary in their frequencies of resistance to all antimicrobial agents worldwide. Limited data exist about the resistance patterns of other genera and species. Part I of this two-part article reviews the methods used for anaerobic susceptibility testing and the correlation of in vitro susceptibility test results with clinical data and antimicrobial resistance that has been reported for gram-negative and gram-positive anaerobes. Part II of this article will review mechanisms of resistance among anaerobes to commonly used antimicrobial agents.