Chromogenic Agar Medium Research Articles

Performance of chromID ESBL, a chromogenic medium for detection of Enterobacteriaceae producing extended-spectrum β-lactamases

The chromogenic agar medium chromID ESBL (bioMérieux) was compared with BLSE agar medium (AES) for selective isolation and presumptive identification of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae from clinical samples. A total of 765 samples (468 rectal swabs, 255 urine samples and 42 pulmonary aspirations) obtained from 547 patients was processed. All bacterial strains isolated on either medium were further characterized using biochemical tests, and ESBL producers were confirmed by synergy testing. Genetic characterization of ESBL genes was determined by PCR. A total of 33 ESBL-producing Enterobacteriaceae strains [Escherichia coli (n=16), Klebsiella pneumoniae (n=8), Enterobacter spp. (n=3), Citrobacter spp. (n=5) and Proteus mirabilis (n=1)] was recovered. The sensitivity after 24 h incubation was 88 % for chromID ESBL and 85 % for BLSE agar. At 48 h, the sensitivity of chromID ESBL increased to 94 % and was higher than that obtained with BLSE agar. The positive predictive value at 24 h for chromID ESBL was 38.7 % [95 % confidence interval (95 % CI) 28.3 -50.2 %)], which was significantly higher than that for BLSE agar [15.4 %, 95 % CI 10.1 -21.5 %]. On both media, false-positive results were mostly due to Pseudomonas aeruginosa and to Enterobacteriaceae overproducing chromosomal cephalosporinase (Enterobacter spp.) or a chromosomal penicillinase (Klebsiella oxytoca). This study showed that chromID ESBL, a ready-to-use chromogenic selective medium, is sensitive and specific for rapid, presumptive identification of ESBL-producing Enterobacteriaceae. Its chromogenic properties and its selectivity are particularly useful in specimens containing resident associated flora.

Detection of ESBL bacteria from clinical specimens: evaluation of a new selective medium

Selective screening media for extended-spectrum β-lactamase (ESBL)-producing bacteria are needed to guide antibiotic therapy and institute appropriate infection control measures. This study evaluates a selective cefpodoxime-incorporated chromogenic agar (CCA) medium for the detection of ESBLs from clinical specimens. The medium was formulated specifically for this study. For all culture-positive urine samples and wound swabs from intensive care unit (ICU) patients, CCA was compared with standard laboratory testing procedures and HPA/BSAC guidance on ESBL detection. The CCA medium was also evaluated for ESBL faecal carriage from patients on ICU and the haematology ward. These patients had no prior evidence of colonisation or infection with ESBL-producing bacteria. All ESBL isolates underwent minimum inhibitory concentration (MIC) testing to cefpodoxime. The Miles and Misra method and the ecometric methods were used to quality control the microbiological performance of the CCA medium, which proved satisfactory. A total of 750 specimens were examined (690 urines, 40 faeces, 20 wound swabs). From urine cultures, 92 suspect colonies were followed up. Eighteen were cefpodoxime-resistant on routine disc testing and all were confirmed subsequently as ESBL-positive. Conventional laboratory methods identified only two urinary ESBLs. Wound cultures revealed two suspect colonies, both of which were ESBL-positive and were also detected by routine methods. Faecal samples produced 10 suspect colonies, six of which were ESBL-positive. All ESBLs had cefpodoxime MICs >10 mg /L (75% were >256 mg/L). Thus, primary conventional culture methods cannot be relied upon to detect suspect ESBL-producing bacteria.

A new chromogenic agar medium for detection of potentially virulent Yersinia enterocolitica

Several outbreaks of foodborne yersiniosis have been documented and this disease continues to be source of infections transmitted through foods. The selective agars most commonly used to isolate Yersinia enterocolitica in clinical, food and environmental samples, cefsulodin–irgasan–novobiocin (CIN) and MacConkey (MAC) agars, lack the ability to differentiate potentially virulent Y. enterocolitica from other Yersinia that may be present as well as some other bacterial spp. This study proposes the use of an agar medium, Y. enterocolitica chromogenic medium (YeCM), for isolation of potentially virulent Y. enterocolitica. This agar contains cellobiose as the fermentable sugar, a chromogenic substrate and selective inhibitors for suppression of colony formation by many competing bacteria. All strains of potentially virulent Yersinia of biotypes 1B, and biotypes 2-5 formed convex, red bulls-eye colonies on YeCM that were very similar to those described for CIN agar. However, Y. enterocolitica biotype 1A and other related Yersinia formed colonies that were purple/blue on YeCM while they formed typical red bulls-eye colonies on CIN agar. When a mixture of potentially virulent Y. enterocolitica biotype 1B, Y. enterocolitica biotype 1A and 5 other bacterial species was used to artificially contaminate tofu and then spread-plated on three selective agars, Y. enterocolitica biotype 1B colonies were easily distinguished from other strains on YeCM. However, Y. enterocolitica biotype 1B colonies were indistinguishable from many other colonies on CIN and only distinguishable from those of C. freundii on MAC. When colonies were picked and identified from these agars, typical colonies from YeCM were confirmed only as Y. enterocolitica biotype 1B. Typical colonies on CIN and MAC were found to belong to several competing species and biotypes.

A Prospective Study of the Case-Notes of MRSA-Positive Patients: A Vehicle of MRSA Spread

Methicillin-resistant Staphylococcus aureus (MRSA) has received much publicity and remains a major problem for the health service. The aim of this study was to determine whether case-notes of MRSA-positive patients can act as a vehicle for MRSA transmission. A prospective study was performed of patients with active MRSA infection identified from a microbiology department database. Two swabs were taken from the cover of the case-notes and the page with the most recent entry for identification of MRSA using MRSA ID (Chromogenic agar medium), Pastorex and DNase tests. Positive case-notes were re-swabbed 96 h later. A total of 50 MRSA-positive patients were identified from medical, surgical, high dependency and intensive care wards. Three sets of notes were MRSA positive (3/50; 6%). None of the positive case-notes was positive on re-swabbing at 96 h. Case-notes of MRSA-positive patients can act as carriers of MRSA with the potential to spread MRSA to both healthcare and non-healthcare workers without direct contact with infected patients. We recommend extending the universal precautions to the handling of case-notes belonging to MRSA-infected patients.

A new chromogenic agar medium, chromID VRE, to screen for vancomycin-resistant Enterococcus faecium and Enterococcus faecalis

We compared the performance of a chromogenic agar medium chromID VRE (bioMérieux, Marcy-l'Etoile, France) designed to recover and identify vancomycin-resistant enterococci (VRE) from clinical specimens with bile esculin azide vancomycin (BEAV) agar. For this study, 120 stool specimens were plated on chromID VRE and BEAV and examined after 24 and 48 h. At 24 h, the sensitivity and specificity were as follows: BEAV, 90.2% and 73%, respectively; chromID VRE, 86.3% and 100.0%, respectively. Furthermore, we determined that the sensitivity and specificity of chromID VRE for Enterococcus faecium were 85.4% and 100%, respectively, and for Enterococcus faecalis, 90% and 100%, respectively. We conclude that chromID VRE provides an equivalent sensitivity for the recovery of VRE from stool specimens, with improved specificity, and the added advantage of providing differentiation between vancomycin-resistant E. faecium and E. faecalis.

Evaluation of a Novel Chromogenic Agar Medium for Isolation and Differentiation of Vancomycin-Resistant Enterococcus faecium and Enterococcus faecalis Isolates

The development of reliable and rapid methods for the identification of patients colonized with vancomycin-resistant enterococci (VRE) is central to the containment of this agent within a hospital environment. To this end, we evaluated a prototype chromogenic agar medium (VRE-BMX; bioMérieux, Marcy l'Etoile, France) used to recover VRE from clinical specimens. This medium can also identify isolated colonies as either vancomycin-resistant Enterococcus faecium or Enterococcus faecalis, based on distinct colony colors. We compared the performance of VRE-BMX with bile esculin azide agar supplemented with vancomycin (BEAV). For this study, 147 stool samples were plated on each test medium and examined after 24 and 48 h of incubation. At 24 h, the sensitivity and specificity of each medium were as follows: BEAV, 90.9% and 89.9%, respectively; VRE-BMX, 96.4% and 96.6%, respectively. The positive predictive values (PPV) of VRE-BMX and BEAV at 24 h were 89.8% and 80.7%, respectively. VRE-BMX provided the identification of 10 isolates of vancomycin-resistant E. faecalis and 4 isolates of vancomycin-resistant E. faecium that were not recovered by BEAV. Further, VRE-BMX was capable of identifying patients colonized with both E. faecium and E. faecalis, a feature useful for infection control purposes that is not a function of BEAV. In terms of the recovery of vancomycin-resistant E. faecium and E. faecalis, the sensitivity and PPV were as follows: BEAV, 75.7% and 74.6%, respectively; VRE-BMX, 95.5% and 91.3%, respectively. In this initial evaluation, we found that VRE-BMX provided improved recovery of VRE from stool specimens, with the added advantage of being able to differentiate between vancomycin-resistant E. faecalis and E. faecium. Extending the incubation period beyond 24 h did not significantly improve the recovery of VRE and resulted in decreased specificity.

Rapid 4 to 6 hour detection of extended-spectrum beta-lactamases in a routine laboratory

With the growing frequency of extended-spectrum beta-lactamases (ESBL) among Enterobacteriaceae, treatment of Gram-negative nosocomial infections requires rapid and reliable detection of this enzyme. Quicolor agar (QC agar) (Salubris Inc., Massachusetts, USA) is a novel chromogenic agar medium changing colour within 4 to 6 h due to the metabolic activity of growing bacteria. This study investigated the use of QC agar compared to Mueller Hinton agar (MH) for the detection of ESBL using disk diffusion and E-test. 100 Enterobacteriaceae isolated at Hacettepe University Hospital, of which 50 were predetermined to be ESBL positive and 50 as negative using the CLSI disk diffusion ESBL (phenotypic confirmatory test) criteria. For disk diffusion and E-test, cefotaxime+/-clavulanate (CT/CTL) and ceftazidime+/-clavulanate (TZ/TZL) were used, and for E-test, cefepime+/-clavulanate (PM/PML) was also used. QC agar rapid ESBL results for all strains were in agreement with the standard overnight procedure. All 50 ESBL positives were detected by both methods. For the 50 ESBL negatives, QC agar rapid results from E-test and disk diffusion were in complete accordance with the overnight MH results. Moreover, E-test detected 8 additional ESBL positive strains that disk diffusion missed. For disk diffusion, CT/CTL alone detected all 50 ESBL positives while TZ/TZL alone missed 5 ESBL positives. E-test CT/CTL alone confirmed all 50 ESBL positives and identified 4 additional ESBL-positive strains. When used together, E-test CT/CTL, TZ/TZL and PM/PML identified a total of 58 ESBL positives among the 100 strains tested. QC agar can be used for rapid and reliable ESBL detection within 4 to 6 h, using disk diffusion and E-test ESBL reagents. This rapid method should be further validated using genotype characterized ESBL and other beta-lactamase positive strains.

Evaluation of a New Selective Chromogenic Agar Medium for Detection of Extended-Spectrum β-Lactamase-Producing Enterobacteriaceae

A novel chromogenic agar medium (ESBL-Bx; bioMérieux, Marcy l'Etoile, France) was compared to MacConkey agar supplemented with 2 mg ceftazidime/liter (MCKC) for the selective isolation and presumptive identification of extended-spectrum beta-lactamase (ESBL)-producing Enterobacteriaceae directly from clinical samples. Of a total of 644 clinical specimens (including 551 fecal samples), 496 yielded no growth and 148 yielded growth on one or both media. Overall, 44 ESBL-producing Enterobacteriaceae strains (Escherichia coli [n=17], Enterobacter aerogenes [n=17], Klebsiella spp. [n=5], and Citrobacter freundii [n=5]) were isolated from 37 specimens by a combination of both methods after 18 to 24 h of incubation. The sensitivities were 97.7 and 84.1% for ESBL-Bx and MCKC, respectively, with 43 ESBL-positive strains isolated as colored colonies from 36 specimens on ESBL-Bx versus 37 ESBL-positive organisms isolated from 32 specimens on MCKC. The specificities by specimens were 89 and 91% for ESBL-Bx and MCKC, respectively. On either one of the two media, natural AmpC-hyperproducing Enterobacter spp. (n=25) and Citrobacter spp. (n=14) were the most common false positives as well as non-ESBL-producing Klebsiella oxytoca (n=18) on ESBL-Bx and Morganella morganii (n=10) on MCKC. We conclude that ESBL-Bx is a sensitive and specific medium for the isolation of ESBL-producing Enterobacteriaceae from clinical samples. The main advantages of ESBL-Bx over MCKC reside in its chromogenic character and its sensitivity and selectivity, which enabled the recovery and presumptive identification of most ESBL-producing Enterobacteriaceae within 24 h and reduced by 27% the need for unnecessary identification and confirmation of ESBL testing when disregarding all colorless colonies growing on this medium.

Evaluation of a new chromogenic agar medium for isolation and identification of Group B streptococci

To evaluate a new chromogenic agar as a screening medium for the isolation of Group B streptococci from high vaginal swabs from pregnant women. The medium was evaluated with 195 high vaginal swabs referred for antenatal screening and compared with blood agar and Granada medium. The new chromogenic medium showed 100% sensitivity for the detection of Group B streptococci, and also showed a positive predictive value of 100%. Granada medium also showed excellent sensitivity and specificity and both media were superior to blood agar. The new chromogenic medium showed excellent performance for the detection of Group B streptococci from clinical samples. This is the first chromogenic medium described for the detection of Group B streptococci. The medium offers an effective and convenient alternative to conventional media, currently used in clinical laboratories.

Evaluation of S. aureus ID, a Chromogenic Agar Medium for the Detection of Staphylococcus aureus

Screening for staphylococci among various patient populations has become important for appropriate therapeutic management and for control of nosocomial infections. The purpose of this study is to evaluate the in vitro sensitivity and specificity of a chromogenic agar medium, S. aureus ID (bioMérieux, France), for the identification of Staphylococcus aureus. A well-defined collection of S. aureus and coagulase-negative staphylococci (CNS) was used. The methicillin-resistant S. aureus (MRSA) isolates were collected in The Netherlands and all had a unique typing pattern. The methicillin-susceptible S. aureus (MSSA) and CNS were isolated from cultures of blood. The isolates were inoculated on Columbia agar plates with 5% sheep blood and incubated for 24 h at 35 degrees C. From the resulting cultures, a suspension of 0.5 McFarland was made and subsequently 10 mul was streaked on a S. aureus ID plate using a sterile loop. The results were read after 24 h and 48 h of incubation at 35 degrees C. Growth of colonies showing green coloration was considered to be positive (indicating S. aureus). A total of 519 S. aureus strains were tested (249 MSSA, 270 MRSA). The sensitivity to detect S. aureus was 96.5% (501/519) after 24 h and 97.5% (506/519) after 48 h. A total of 478 CNS were tested. The specificity was 98.5% (471/478) after 24 h and 98.3% (470/478) after 48 h. The differences between 24 h and 48 h incubation were not statistically significant. S. aureus ID is highly sensitive and specific to differentiate between S. aureus and CNS in vitro. Since the performance does not significantly differ between 24 h or 48 h of incubation, samples need only 1 day of incubation before optimal results can be obtained.

Evaluation of Two Chromogenic Agar Media for Recovery and Identification of Staphylococcus aureus Small-Colony Variants

To identify the most rapid and reliable technique for recovery and identification of Staphylococcus aureus small-colony variants (SCVs), the colonial appearance of 106 isolates representing SCVs and the normal phenotype were evaluated on two newly described chromogenic agar media. Although almost all of the SCVs grew on the chromogenic agar media, they did not exhibit a change of color. In comparison with conventional media, S. aureus ID agar (SAID; bioMerieux, La Balme Les Grottes, France) showed the most reliable results, with 49 of 53 SCVs tested growing either as an SCV colony or with a normal phenotype after only 24 h of incubation. Growth of SCVs was often not detected before 72 h of incubation on some of the media tested. In conclusion, the most accurate and rapid method to detect both the species S. aureus and the SCV phenotype is to inoculate specimens onto both Columbia blood agar and SAID.

魚介類からの<I>Vibrio vulnificus</I>の定量検出方法の検討

To quantify the number of Vibrio vulnificus in shellfish, we compared the most probable number (MPN) combined with a culture (MPN-culture) or polymerase-chain reaction (PCR) assay (MPN-PCR) to a quantitative PCR assay. Enrichment in alkaline peptone water by MPN was conducted at 25 and 35 degrees C. Enrichment at 35 degrees C was superior or similar to enrichment at 25 degrees C in over 65% of samples by MPNculture and in more than 75% of samples by MPN-PCR assay. V. vulnificus was more easily isolated on chromogenic agar medium during culture, MPN-PCR assay was superior or similar to MPNculture in over 90% of samples by enrichment at 25 degrees C and to over 88% of samples by enrichment at 35 degrees C. The number of V. vulnificus by quantitative PCR assay was similar to that of MPN-PCR assay in 6 of 8 samples but not from MPNculture. V. vulnificus contamination was frequently detected in samples from Kyushu Island.

Rectal colonization and frequency of enterococcal cross-transmission among prolonged-stay patients in two Swedish intensive care units

The aims of this study were to gain insight into the dynamics of the rectal flora during prolonged ICU stay, with a particular focus on colonization and cross-transmission with resistant pathogens, and to evaluate methods for the rapid isolation of relevant bacteria from rectal swabs. Patients admitted to a general intensive care unit (GICU) or a cardiothoracic ICU (TICU) at the University Hospital of Linköping, Sweden, between 1 November 2001 and January 2002 with a length of stay > 5 d were included (n = 20). Chromogenic UTI agar medium was used for discrimination of different species, and appropriate antibiotics were added to detect resistance. Direct plating was compared to enrichment broth for a subset of specimens. The study showed an early alteration in rectal flora, with a dramatic decrease in Gram-negative rods in favour of Gram-positive bacteria. An ampicillin- and high-level gentamicin resistant clone of Enterococcus faecium was found in 6 of 10 patients in the GICU and 2 of 11 patients in the TICU. Enrichment broth did not enhance the detection of Gram-negative bacteria compared to direct plating on Chromogenic UTI medium, but enrichment broths were needed for optimal detection of resistant Gram-positive bacteria.

Prevalence of pandemic thermostable direct hemolysin-producing Vibrio parahaemolyticus O3:K6 in seafood and the coastal environment in Japan.

Although thermostable direct hemolysin (TDH)-producing Vibrio parahaemolyticus has caused many infections in Asian countries, the United States, and other countries, it has been difficult to detect the same pathogen in seafoods and other environmental samples. In this study, we detected and enumerated tdh gene-positive V. parahaemolyticus in Japanese seafoods with a tdh-specific PCR method, a chromogenic agar medium, and a most-probable-number method. The tdh gene was detected in 33 of 329 seafood samples (10.0%). The number of tdh-positive V. parahaemolyticus ranged from <3 to 93/10 g. The incidence of tdh-positive V. parahaemolyticus tended to be high in samples contaminated with relatively high levels of total V. parahaemolyticus. TDH-producing strains of V. parahaemolyticus were isolated from 11 of 33 tdh-positive samples (short-necked clam, hen clam, and rock oyster). TDH-producing strains of V. parahaemolyticus were also isolated from the sediments of rivers near the coast in Japan. Representative strains of the seafood and sediment isolates were examined for the O:K serovar and by the PCR method specific to the pandemic clone and arbitrarily primed PCR and pulsed-field gel electrophoresis techniques. The results indicated that most O3:K6 tdh-positive strains belonged to the pandemic O3:K6 clone and suggested that serovariation took place in the Japanese environment.

Evaluation of a chromogenic agar medium for isolation of Escherichia coli O26

CT-O26 medium, a chromogenic agar medium which has been recently developed for selective isolation of Escherichia coli O26, was evaluated isolating E. coli O26 from 25 g of food samples artificially contaminated with ca. 2 colony forming units of the organism. After food samples were cultured in modified E. coli broth with novobiocin at 42 °C for 18 h, the culture was streakily plated onto CT-O26 medium and rhamnose MacConkey agar medium with cefixime and tellurite (CT-RMAC) which has been reported as an effective medium for isolation of E. coli O26. CT-O26 medium was more effective than CT-RMAC for isolating E. coli O26 from ground beef, liver and alfalfa sprouts samples. E. coli O26 was isolated from all ground beef and liver samples in combination with plating onto O26 medium and immunomagnetic separation (IMS) method.

Development of chromogenic agar medium for isolation of enterohaemorrhagic Escherichia coli O26

Agar media for isolation of enterohaemorrhagic Escherichia coli (EHEC) have been developed primarily for E. coli O157, because this bacterium has most frequently caused EHEC infection. However, there have been few studies for isolation of other serotypes of EHEC, and media appropriate for isolation of such organisms, especially from food samples, are not yet available. Among such serotypes, E. coli O26 has often been isolated from clinical specimens from patients and animals, but not from food samples in outbreaks, because of lack of an appropriate method for isolation. In this study, we tried to develop a new chromogenic agar medium for selective isolation of E. coli O26 using the characteristics of E. coli O26. Fifteen strains of E. coli O26, 11 strains of E. coli O157 and 36 strains of other sero-types E. coli were tested for fermentation of rhamnose, cellobiose, dulcitol, salicin, raffinose, sorbitol, sucrose, lactose, mannitol, arabinose, maltose, xylose and glucose. Rhamnose was fermented by all E. coli strains except for E. coli O26. The other substrates were not effective for differentiating E. coli O26 from the other strains of E. coli. Thus the medium containing rhamnose and 5-bromo-4-chloro-3-indolyl-beta-D-galactopyranoside, which is a substrate of beta-galactosidase specific to coliforms, produced a color of E. coli O26 colonies different from colors of the other bacteria. Furthermore, cefixime and sodium tellulite were added to the composition of the medium for gaining higher selectivity.

Application of a chromogenic medium and the PCR method for the rapid confirmation of L. monocytogenes in foodstuffs

Detection of Listeria monocytogenes in foodstuffs by conventional cultivation methods carried out according to EN ISO guidelines is rather time-consuming. Therefore, two alternative methods were applied for rapid confirmation of L. monocytogenes in foodstuffs. Inoculum from liquid selective broth was plated on PALCAM and OXFORD agar and on chromogenic agar medium RAPID L. mono. Suspect colonies from PALCAM were confirmed according to EN ISO standards and by the multiplex PCR method. In total, 990 samples of foodstuffs were investigated and 63 strains of L. monocytogenes were isolated. The chromogenic medium RAPID L. mono provided results comparable to PCR, it is easier to handle and provides considerable financial savings.

ABC Medium, a New Chromogenic Agar for Selective Isolation of Salmonella spp

We describe a new chromogenic agar medium, ABC medium (alphabeta-chromogenic medium), which includes two substrates, 3, 4-cyclohexenoesculetin-beta-D-galactoside and 5-bromo-4-chloro-3-indolyl-alpha-D-galactopyranoside, to facilitate the selective isolation of Salmonella spp. This medium exploits the fact that Salmonella spp. may be distinguished from other members of the family Enterobacteriaceae by the presence of alpha-galactosidase activity in the absence of beta-galactosidase activity. A total of 1, 022 strains of Salmonella spp. and 300 other gram-negative strains were inoculated onto this medium. Of these, 1,019 (99.7%) strains of Salmonella spp. produced a characteristic green colony, whereas only 1 strain (0.33%) of non-Salmonella produced a green colony. A total of 283 stool samples were cultured onto desoxycholate citrate (DC) agar and ABC medium by direct inoculation and after selective enrichment in selenite broth. Overall, the sensitivity and specificity were superior for ABC medium (100 and 90.5%, respectively) than for DC agar (88 and 26.9%, respectively). We conclude that ABC medium offers a high degree of specificity for the detection of Salmonella spp. in stool samples.

Evaluation of a new chromogenic agar medium for the identification of urinary tract pathogens

This study evaluated the performance of CPS ID2 (bioMérieux) compared to that of conventionally used selective agar for the identification of bacteria responsible for urinary tract infections. This medium detects bacterial enzymes using chromogenic substrates. Two hundred and nineteen samples of urine were tested in order to evaluate new CPS ID2 in comparison to blood agar and MacConkey agar. According to our results, the CPS ID2 agar is an easy, rapid and sensitive method for the screening of colonies suspected of being Escherichia coli, reducing the number of biochemical tests needed. Also, enterococci and Proteae can be easily detected. Other micro-organisms require further identification. The greatest value of this medium is the accurate identification of polymicrobial cultures.

Evaluation of two new chromogenic media for detection ofSalmonella in stools

A clinical collaborative study was conducted to compare two new chromogenic agar media, Rambach agar and the Salmonella Detection and Identification Medium (SMID) (bioMérieux, France), with two conventional media, Salmonella-Shigella agar and Hektoen agar. Thirty-nine Salmonella strains involving 14 serotypes were isolated from 1,454 stool specimens. After enrichment in a selective broth, 100% sensitivity was obtained with each medium. The SMID and Rambach agars are considerably more specific than the conventional media. Although SMID agar detects all Salmonella serotypes, it is not as specific as Rambach agar, which requires a complementary test (C8 esterase test) to detect all serotypes.