Antibiogram Typing Research Articles

Recognition of a Nocardia transvalensis complex by resistance to aminoglycosides, including amikacin, and PCR-restriction fragment length polymorphism analysis.

Amikacin resistance, rare among nocardiae, was observed in 58 clinical isolates of nocardiae. All of these isolates hydrolyzed hypoxanthine, and 75 to 100% utilized citrate, D-galactose, and D-trehalose as sole carbon sources. Based on utilization of I-erythritol, D-glucitol, i-myo-inositol, D-mannitol, and ribitol and susceptibility to amoxicillin-clavulanic acid, the 58 isolates were separable into four groups. One group was negative for I-erythritol and ribitol and included all the isolates belonging to Nocardia asteroides complex antibiogram type IV. The remaining three groups were positive for I-erythritol and ribitol and were grouped within Nocardia transvalensis. The group that included the type strain was designated N. transvalensis sensu stricto, and the other two groups were designated new taxons 1 and 2. PCR-restriction fragment length polymorphism (RFLP) analysis of a 439-bp segment of the 65-kDa heat shock protein gene with XhoI and HinfI produced identical patterns for 53 (91%) and 58 (100%) isolates, respectively, and differentiated them from all other Nocardia taxa. NarI- and HaeIII-derived RFLP patterns clearly differentiated each of the four biochemically defined taxa. These four groups were also distinguishable by using the chromogenic substrates in Dade MicroScan test panels. By high-performance liquid chromatography, these isolates exhibited the same unique mycolic acid-ester elution patterns that differed from those of all other clinically significant nocardiae. Gas-liquid chromatographic analysis of fatty acids also produced similar patterns for all isolates that distinguished them from all other Nocardia taxa, but did not differentiate the four taxa within the complex. We propose the designation N. transvalensis complex for these four groups of nocardiae, pending further genetic evaluation.

Differentiation of Staphylococcus xylosus Strains from Italian Sausages by Antibiotyping and Low Frequency Restriction Fragment Analysis of Genomic DNA

The aim of this study was to identify the strengths and weaknesses of two typing methods, antibiogram typing and low-frequency restriction fragment analysis of genomic DNA, for the differentiation of Staphylococcus xylosus strains. Twenty-eight Staphylococcus xylosus strains isolated from Italian fermented sausages (Naples-type salami) and S. xylosus DSM 20266 (Type strain) and DSM 6179 were analysed. Antibiotyping, recorded on the basis of susceptibility testing of 16 antibiotics, allowed 21 antibiogram-types to be distinguished. Pulsed-field gel electrophoresis techniques combined with DNA digestion by infrequently cutting enzymes such as Sma I produced 22 pattern-types among the 30 strains of S. xylosus analysed. The association of antibiotyping and PFGE typing clearly distributed S. xylosus strains into 30 combinations, showing that all the strains can be differentiated. Thus, the combination of these two techniques, in spite of limitations due to instability of a phenotype-based system, actually turned out to be the most reliable methodological approach for differentiating strains of S. xylosus.

Outbreak of septicaemia in neonates caused by Acinetobacter junii investigated by amplified ribosomal DNA restriction analysis (ARDRA) and four typing methods

Septicaemia caused by Acinetobacter occurred in six infants in the neonatal unit. A total of 18 acinetobacters were isolated from blood cultures, cultures of intravascular catheters, and surveillance cultures. Twelve isolates from the six affected infants were identified as Acinetobacter junii by the use of a novel method, amplified ribosomal DNA restriction analysis (ARDRA). Typing of the organisms using the biochemical profiles of the API 20NE system, antibiogram typing, cell envelope protein electrophoresis, and PCR fingerprinting with two primer sets, ERIC1/ERIC2 and ERIC2/ 1026, showed that these 12 isolates were indistinguishable, whereas the remaining six isolates were different. The six infants recovered after therapy with ciprofloxacin alone in five cases and with a combination of ciprofloxacin and gentamicin in one case. This study showed that A. junii is capable of causing a serious, though non-fatal infection in neonates. The combined use of genotypic and phenotypic methods allowed the rapid separation of epidemic from non-epidemic isolates. It is concluded that for a better understanding of the role of the various Acinetobacter genomic species in human pathology, identification of acinetobacters according to the recent taxonomy is imperative.

Evaluation of clonal relatedness of extended-spectrum beta-lactamase-producing Proteus mirabilis isolates by quantitative antibiogram and RAPD typing.

OBJECTIVE: To delineate, using two different typing systems, the clonal relatedness of 40 isolates of extended-spectrum beta-lactamase (ESbetaIa)-producing Proteus mirabilis obtained over a period of 7 years in six hospitals in the Paris area and two in Pas-de-Calais. METHODS: Random amplified polymorphic DNA (RAPD) polymerase chain reaction typing was applied by using three random primers on the ESbetaIa-producing P. mirabilis isolates and on isogenic Escherichia coli strains with or without plasmids encoding the representative resistance pattern transferred from P. mirabilis. Quantitative antibiogram typing, which was also applied to the P. mirabilis isolates, was used to define the euclidean distance between these strains. RESULTS: After having demonstrated that P. mirabilis plasmids did not influence chromosomal DNA amplification, we could classify the ESbetaIa-producing P. mirabilis isolates into 12 groups based on RAPD fingerprints. The same isolates were classified into 19 groups by quantitative antibiogram typing. Despite this difference in group numbers, general concordance between the typing systems was observed. This allowed us to show that the greater number of isolates in some hospitals belonged to a single strain and that single isolates obtained in different hospitals generally represented unique strains. CONCLUSIONS: A small number of ESbetaIa-producing P. mirabilis strains was isolated during 7 years in the eight medical centers studied, and the number of different strains identified suggested that inter-hospital transfer had not occurred.

Multiresistant Staphylococcus epidermidis in a neonatal care unit

OBJECTIVE: To study the presence and diversity of types of Staphylococcus epidermidis in the neonatal intensive care unit of a university hospital. METHODS: During a period of 6 weeks, samples were taken from nose, external auditory canal, axilla, groin and umbilicus from consecutively admitted patients. Patients were sampled two times a week for up to 2 weeks. Isolates of S. epidermidis were characterized by antibiogram, plasmid pattern and biotype. RESULTS: Fifteen patients were included. Each patient was sampled in one to four successive surveys, depending on the admission period. A total of 128 isolates of S. epidermidis were obtained and allocated to seven antibiogram types, 36 plasmid types and 14 biotypes. One plasmid type found in 58 isolates (six patients) corresponded with one multiresistant antibiogram type. The number of isolates with these characteristics increased per neonate from the first survey to the fourth. Nineteen isolates from four patients were allocated to a second plasmid type and were of a common antibiogram type. The remaining 34 plasmid types were sporadic. No clear correspondence of biotypes with antibiogram or plasmid types was found. CONCLUSIONS: The present study revealed the increase in colonization of a multiresistant type of S. epidermidis in the compromised patients during admission to the ward. Further studies have to assess whether this type remains persistent in the ward.

Typing ofSalmonella entericaserovar Saintpaul: An outbreak investigation

During the summer of 1993 an outbreak of human salmonellosis caused by Salmonella serovar Saintpaul occurred in Denmark. A total of 35 isolates originating from pigs, turkeys and imported foodstuffs, and 10 human isolates were compared following their characterization by agglutination of the 0:5 factor, antibiogram typing, plasmid profiling, ribotyping and pulsed field gel electrophoresis, in order to identify the most probable source of infection. After typing, the source of the investigated outbreak remains obscure because so far no isolates with traits of the outbreak strain have been recovered from production animals. Presence of the 0:5 factor and absence of plasmids in human and porcine isolates pointed to pork as the source of infection, whereas human isolates and all Danish isolates from turkeys had the same ribotype, indicating that turkey was the infection source. A possible explanation for the failure to find isolates with traits of the outbreak strain could be the presence of a third, but so far unidentified, source. The present investigation illustrates the necessity of using more than one epidemiological typing method for outbreak investigation. This is especially important when the organism involved is relatively uncommon and little is known about its diversity and distribution.

Staphylococcal and other Bacterial Species Associated with Intramammary Infections in Danish Dairy Herds

Four thousand six hundred forty-five quarter milk samples from 1179 cows from 20 commercial dairy herds were examined in order to determine the prevalence of bacterial species. A total of 859 isolates from 839 (18.1%) culture positive samples could be assigned to 34 different species and subspecies. Diagnostics of staphylococcal species was based on conventional procedures able to differentiate between all 36 species and subspecies presently acknowledged. Staphylococcus aureus was found in 10.2% of the samples and was the most common species isolated. Streptococcus dysgalactiae (1.6%) and Streptococcus uberis (1.4%) were the second and third most common species isolated. Seventeen different coagulase negative staphylococcal species (CNS) were found in 4.1% of the samples. The most frequently isolated CNS were S. epidermidis (1.3%), S. chromogenes (1.0%) and S. simulans (0.7%). Isolates of S. aureus were phage typed, and isolates of S. epidermidis were investigated by phage typing, antibiogram typing, and biotyping. A total of 378 (79.9%) isolates of S. aureus could be typed by phages, assigning them to 18 different phage types. However, 6 phage types accounted for 92.1% of the typable isolates. One to 2 phage types predominated within each herd. Eleven (18%) isolates of S. epidermidis could be typed by phages, assigning the isolates to 3 different types. Biotyping of S. epidermidis produced a total of 8 different types, the most common accounting for 29.5% of the isolates. A total of 6 different antibiogram types were observed among all isolates of S. epidermidis. Resistance towards penicillin (36.1%), tetracycline (9.8%) and streptomycin (9.8%), were recorded in the isolates of S. epidermidis. However, 35 (57.4%) of the isolates were susceptible to all 12 antibiotics tested.

Familial carriage of methicillin-resistant Staphylococcus aureus and subsequent infection in a premature neonate.

During routine surveillance of patients in a Neonatal Intensive Care Unit (NICU), an alert infection-control practitioner confirmed the relationship of the index patient (sibling 3) who had a methicillin-resistant Staphylococcus aureus (MRSA) infection to an infant sibling (sibling 2) who had been admitted to the hospital 7 months previously with an MRSA infection. Cultures of nasal specimens obtained from the index patient's parents and two other siblings also yielded MRSA for two of the family members, the mother and sibling 1. The strains were typed by antibiogram, plasmid analysis, and genomic DNA typing. The isolates from sibling 1, sibling 2, the mother, and one isolate from sibling 3 were found to be identical by all techniques. The other isolates from sibling 3 shared the same genomic type but had no detectable plasmids. These findings suggest that transmission of this strain occurred at least three times within this family and that at least one family member was colonized with the same strain for 7 months or more. Recognition that family members may serve as reservoirs for nosocomial infections with MRSA raises important issues for infection control.

Evaluation of phenotypic and genotypic methods for epidemiological typing of Staphylococcus aureus isolates from bovine mastitis in Denmark

The value of five different typing methods (antibiogram typing, biotyping, phage typing, plasmid profiling and restriction fragment length polymorphism of the gene encoding 16S and 23S ribosomal RNA (ribotyping)), in discriminating 105 Staphylococcus aureus strains from bovine milk samples obtained from 105 different Danish dairy herds was investigated. A total of 85 strains (81%) proved susceptible to all of the 11 antibiotics tested, and the remaining 20 strains could be divided into 5 different antibiogram patterns. The predominant resistance pattern, penicillin resistance, was observed in 15 (75%) of the 20 antibiotic resistant strains. Biotyping assigned the strains to 14 different types, with the most common type accounting for 25.7% of the strains. Ninety eight (93.3%) strains could be typed by phages, assigning them to 19 different phage types. The predominant phage type accounted for 31.5% of the strains. Eight different plasmid profiles was observed among 24 (23%) strains harbouring plasmids. Ribotyping yielded 30 different types, with the most common accounting for 29.5% of the strains. The single most discriminatory typing method was ribotyping (0.863) followed by biotyping (0.842) and phage typing (0.795). Plasmid profiling (0.395) and antibiogram typing (0.327) had low discriminatory indices. Correspondence among ribotypes and the presence or absence of plasmids were observed, as was some degree of correspondence between ribotype, phage type and biotype. In general the correspondence between phage type and ribotype were stronger than between biotype and ribotype and between biotype and phage type. All combinations of two or more methods led to an improved index of discrimination compared to the individual methods indicating, that some subdivision of types had taken place. The combination of phage, bio- or ribotyping or all three methods in combination are considered to be an efficient combination of typing methods epidemiological investigation of S. aureus mastitis.

Pillows, an unexpected source of Acinetobacter

From 1989 until 1992 an increase in the number of isolations of Acinetobacter was observed in a community hospital in The Netherlands. The organisms were spread throughout the hospital and a common source was suspected. Feather pillows were found to harbour high numbers of acinetobacters. Replacement with synthetic pillows and correction of the laundry procedure resulted in a significant reduction of Acinetobacter isolations. A number of isolates from patients and from pillows were indistinguishable using biotyping, antibiogram typing and cell envelope protein typing. By the use of DNA-DNA hybridization most isolates were identified to A. baumannii and the unnamed closely related genomic species 13. A number of isolates, mostly from pillows, were identified as A. radioresistens. The outcome of cultivation, intervention and typing suggests that the feather pillows played an important role in the outbreak.

Quantitative antibiogram typing using inhibition zone diameters compared with ribotyping for epidemiological typing of methicillin-resistant Staphylococcus aureus

Antibiogram typing of methicillin-resistant Staphylococcus aureus with selected antibiotics was evaluated as a primary epidemiological typing tool and compared with ribotyping. Antibiograms were derived with the Kirby-Bauer disk diffusion method by using erythromycin, clindamycin, cotrimoxazole, gentamicin, and ciprofloxacin. For typing, antibiogram data were analyzed by similarity analysis of disk zone diameters (quantitative antibiogram typing). One hundred seventy-two isolates were typed. Reproducibility reached 98% for the quantitative antibiogram and 100% for ribotyping. With three selected restriction enzymes (EcoRV, HindIII, and KpnI), 40 epidemiologically unrelated isolates could be classified into 21 ribotypes, whereas quantitative antibiogram typing classified these isolates into 19 groups. To evaluate the discriminatory power of the methods, we calculated an index of discrimination from data obtained with these 40 isolates. This index takes into consideration both the number of types defined by the typing method and their relative frequencies. With both ribotyping and quantitative antibiogram typing, high discrimination indices (0.972 and 0.954, respectively) were obtained. When epidemiological links between patients (ward, period of hospitalization, and contacts between staff and patients) were compared with the results of ribotyping or the quantitative antibiogram typing method, it appeared that both methods were able to discriminate epidemiological clusters, with only a few discrepancies. In conclusion, quantitative antibiogram typing, although not necessarily based on genomic markers, is a simple method which enables a reliable workup of methicillin-resistant S. aureus epidemic when sophisticated molecular typing methods are not available.

Long-term Efficacy of Intranasal Mupirocin Ointment

We investigated the long-term effect of a single 5-day application of intranasal mupirocin calcium ointment on Staphylococcus aureus nasal and hand colonization. The subjects were 68 healthy volunteers who were health care workers with stable S aureus nasal carriage and who had participated in a randomized, double-blind placebo-controlled clinical trial of intranasal mupirocin ointment. A 1-year prospective cohort study of S aureus nasal carriers after treatment with active drug or placebo was performed. Cultures were obtained from all subjects 6 and 12 months after therapy. All subjects returned for the 6-month visit; 63 (93%) were examined at 1 year. The major outcome measure was the relative proportion of any S aureus cultured at either site at 6 and 12 months. The S aureus isolates were typed by restriction endonuclease analysis of plasmid DNA and by antibiotic susceptibility tests; the similarity of nasal and hand isolate "fingerprints" was compared. At 6 months, nasal carriage was 48% in the treatment group vs 72% in controls (relative risk, 0.68; 95% confidence interval, 0.45 to 1.02; P = .054); at 1 year, nasal carriage was 53% vs 76%, respectively (relative risk, 0.70; 95% confidence interval, 0.48 to 1.02; P = .056). Hand carriage at 6 months was significantly reduced among mupirocin recipients relative to controls (15% and 48%; P = .04, adjusted for the baseline rate of hand carriage). Thirty-six percent of treated subjects were recolonized in the nares with a new strain at 1 year, whereas 34% had reisolation of the original strain after initially negative posttherapy cultures. During the year of follow-up, hand carriage was observed at least once in two thirds of the subjects. Nearly all of the hand isolates (87%) exactly matched the subjects' coincident nasal plasmid fingerprint and antibiogram type. A single brief treatment course of intranasal mupirocin was effective in reducing nasal S aureus carriage for up to 1 year. When S aureus was recovered after nasal decolonization, the new isolate was as likely to represent colonization with a new strain as reisolation of the original strain. Staphylococcus aureus hand carriage was significantly decreased 6 months after therapy, further implicating the nares as the primary reservoir site for hand carriage.

Typing by serovar, antibiogram, plasmid content, riboprobing, and isoenzyme typing to determine whether Neisseria gonorrhoeae isolates requiring proline, citrulline, and uracil for growth are clonal

Neisseria gonorrhoeae isolates requiring proline, citrulline, and uracil for growth (PCU-) have homogeneous phenotypes; most are plasmid-free, belong to few serovars, and are significantly associated with intermediate levels of susceptibility to penicillin, tetracycline, erythromycin, and cefoxitin. Because of their lack of variation by these criteria, molecular typing methods, ribotyping (restriction fragment length polymorphism [RFLP] of rRNA genes), and multilocus enzyme electrophoresis were explored as tools for further distinguishing PCU- isolates. By ribotyping, selected PCU- isolates could be separated into four groups on the basis of the hybridization patterns (RFLPs) of SmaI- and AvaII-digested DNA with probes containing rRNA sequences. Most of the isolates (18 of 23 isolates) belonged to a single RFLP (group I). One isolate each was in groups II and IV, and three isolates were in group III. All isolates except one, isolate NS791, had similar multilocus enzyme electrophoresis patterns. Strain NS791 was unusual in that it contained a variant cryptic plasmid with an insert in the 0.46-kb MspI-HinfI fragment of the 4.2-kb plasmid, it was the only isolate belonging to RFLP group IV, and it differed in its multilocus enzyme electrophoresis pattern, having different mobilities for glyceraldehyde phosphate dehydrogenase, phosphoglucose isomerase, 6-phosphogluconate dehydrogenase, and glutamate dehydrogenase. Serovars of PCU- isolates appeared to be more indicative of strain divergence than RFLP or isoenzyme typing. Multilocus enzyme electrophoresis indicated that PCU- isolates are clonal.

Hospital infection with Acinetobacter spp.: an increasing problem

During the last few years, among nosocomial pathogens, Acinetobacter spp. have given rise to an increasing number of nosocomial infections. Acinetobacter strains are widely distributed in nature; in hospitals, the human skin is the likely source for most outbreaks of hospital infections. The organism has been frequently found in the inanimate environment, especially in moist situations and it has been isolated from various types of opportunistic infections (septicaemia, endocarditis, meningitis, pneumonia, skin and wound sepsis and urinary tract infection). For epidemiological studies, various typing methods such as biotyping, bacteriocin typing and serology have been developed. More recently electrophoretic patterns of cell-envelope proteins and plasmid analysis have proved useful in differentiating outbreak strains. Antibiogram typing may be useful but the antibiotic resistance of Acinetobacter spp. has changed rapidly within the last few years and thus antibiotyping must be complemented by other typing systems. New methods such as electrophoretic analysis of isoenzymes, definition of plasmidotype profiles or restriction endonuclease digestion of chromosomal DNA are under investigation.

Outbreaks of infection with methicillin-resistantStaphylococcus aureuson neonatal and burns units of a new hospital

Multiple introductions of methicillin-resistant Staphylococcus aureus (MRSA) strains occurred to a new hospital in Hong Kong. Two years of clinical microbiological surveillance of the resulting outbreaks was combined with laboratory investigation by phage and antibiogram typing, and plasmid profiling. The outbreaks on the special care baby (SCBU) and burns (BU) units were studied in detail, and colonization of staff and contamination of the environment were investigated. MRSA were spread by the hands of staff on the SCBU, where long-term colonization of dermatitis was important, but were probably transmitted on the BU by a combination of the airborne, transient hand-borne and environmental routes. Simple control measures to restrict hand-borne spread on the SCBU were highly effective, but control was not successful on the BU.

Drug-resistant coagulase-negative skin staphylococci: Evaluation of four marker systems and epidemiology in an orthopaedic ward

Drug-resistant coagulase-negative staphylococci (DRCNS) in orthopaedic patients and ward staff were studied. A significant increase in the DRCNS carriage rate was observed among the 16 patients studied after 14 days of hospitalization with levels approaching that of the staff. Patients receiving dicloxacillin prophylaxis (n = 9) were more likely to be colonized with methicillin-resistant CNS, while patients receiving no antibiotics (n = 7) became to a larger extent colonized with multiple DRCNS. The combined data from species determination, biochemical, plasmid, and antibiogram typing revealed a considerable diversity among DRCNS; 64 types were distinguished among 112 DRCNS isolates selected for study after exclusion of apparently duplicate isolates. Plasmid plus antibiogram typing yielded almost as many types (61); whereas species determination plus antibiogram distinguished only 33 types. Although a novel computerized 96-reaction biotyping method alone enabled differentiation of 17 biotypes, most DRCNS isolates belonged to one of three major biotypes limiting the usefulness of this method. Ten of the 64 (16%) DRCNS types identified comprised 50 of the 112 (45%) isolates. These were isolated from staff and from patients on day 14, suggesting a nosocomial origin.

Microbial pathogens from goat mastitis and phage-typing of Staphylococcus aureus Isolates

Examination of milk from goats yielded 41 strains from 40 clinically affected halves; 15 were Staphylococcus aureus, 6 Staph. epidermis, 1 Streptococcus agalactiae, 2 Strept. dysgalactiae, 5 Strept. uberis, 2 Coryne-bacterium pyogenes, 3 Escherichia coli, 3 Pasteurella spp. and 4 Mycoplasma spp. One half had dual infection of Staph. aureus and Strept. dysgalacitiae. Twenty two of the 297 milk samples from apparently normal halves also harboured pathogens comprising of 9 Staph. aureus, 1 Strept. agalactiae, 2 E. coli, 2 Pasteurella spp., 2 Candida albicans and 6 Mycoplasma spp. Most of the bacterial isolates were sensitive to many broad spectrum antibiotics. Twenty of the 24 Staph. aureus isolates were phase typable by a set of 23 human Staphylococcal International Phages suggesting the utility of these phages for the typing of goat strains. The isolates were grouped into 15 phage-types, many of which have been reported from human infections in Iraq. This indicates the possibility of association of human strains of Staph. aureus in caprine mastitis. No definite correlation could be noted between antibiogram and phage types of Staph. aureus strains.

Transmission of group B streptococci. Traced by use of multiple epidemiologic markers.

During a three-week period, septicemia caused by group B Streptococcus, serotype III, developed in four infants born at a community hospital. The first infant had early-onset disease; late-onset disease that appeared, from epidemiologic data, to be nosocomial developed in the other three infants. Bacteriophage typing and antimicrobial susceptibility testing confirmed the relatedness of the isolates. A prospective study designed to differentiate between vertical and nosocomial transmission of group B Streptococcus showed that of 82 infants, 21 (26%) were culture-positive during their hospitalization, and nine of these infants (43%) had been culture-negative at birth. Although serotype III strains were recovered from four of nine infants with apparently nosocomial acquisition, none of the isolates displayed an antibiogram or bacteriophage type similar to that of the isolates involved in the recent cluster. Bacteriophage typing and antimicrobial susceptibility testing in addition to the use of serotyping may be helpful in epidemiologic studies of group B Streptococcus.

Serratia species isolated from patients in a general hospital

A survey carried out between 1 May 1979 and 30 April 1980 yielded 119 isolates of Serratia spp. from 58 patients. Ninty-one per cent of the patients were compromised, 86 per cent had undergone recent surgery and 79 per cent had received antimicrobial therapy within 14 days prior to serratia isolation. The principal sources of the isolates were the intensive care and peripheral vascular units. The combined use of antibiogram, serological and phage typing revealed both epidemiological episodes and sporadic isolation of these organisms suggesting that the population of Serratia spp. in this hospital is heterogeneous. Fifty-seven per cent of the isolates were resistant to carbenicillin and 30 per cent resistant to gentamicin. Gentamicin resistance was exclusively plasmid-mediated whereas resistance to carbenicillin was equally divided between plasmid-mediated and chromosomal mechanisms.

Discrimination of urinary strains of Escherichia coli by five typing methods.

A series of 156 cultures of Escherichia coli isolated from sequential urines from 20 patients with urinary-tract infection was examined by biotyping, resistotyping, haemagglutinin typing, O serotyping and antibiogram typing. From 10 of the patients, we repeatedly isolated cultures of a single strain; from each of the other 10 patients, different strains were discriminated. All cultures were typable by biotyping and resistotyping, and those techniques should prove practicable for laboratories not able to perform complete serological analysis. Only a minority (43.6%) of the cultures was typed with a limited range of 24 commercial O sera. Maximum discrimination of strains was achieved by the combined use of several of these techniques.