Diagnostic

• Diagnostic methods for enterobacteria include microscopy, culture on various media, biochemical identification, antigen analysis (for Shigella, Salmonella and EPEC), and indirect methods such as the Widal reaction in typhoid fever and antibodies against yersinia.
• Gram stain is used to differentiate G- rods like enterobacteria from other bacteria.
• Endo agar is used to identify enterobacteria, Vibrionaceae, and G- non-fermenters.
• Hajna medium remains red and does not change color, allowing non-fermenters to be differentiated by not fermenting glucose.
• Oxidase is positive in Vibrionaceae, unlike enterobacteria.
• Catalase is positive in enterobacteria.
• Enterobacteria are Oxidase- and glucose fermenters.
• Vibrionaceae are Oxidase+ glucose fermenters.
• G- non-fermenters may be Oxidase positive or negative, and never ferment glucose.
• Enterococci are sometimes coccobacilli.
• Endo agar is used to orientate Obligatory pathogens and Opportune pathogens inside enterobacteria.
• Lactose differentiation is done on Endo agar, with obligatory having pale colonies (L -) on the same medium and opportune having dark red surroundings (L +).
• XLD agar is used to identify Salmonella, with pale colonies with a black center (the center is like a yolk in a fried egg), and other bacteria do not grow at all or grow in colonies of different morphology.
• MAL agar gives results similar to those on XLD agar (slightly different colors of some colonies etc.).
• CIN is used to identify Yersinia, with dark pink colonies.
• Hajna medium is used for biochemical identification.
• MIU test is a biochemical test.
• Švejcar plate is a biochemical test.
• In ENTERO test 16 the first reaction is an ONPG.
• In antigen analysis the intestinal pathogens are isolated E. coli in case of suspicion for EPEC or STEC, but usually not the other groups of E. coli, determing the serovar.
• In antigen analysis if a Salmonella Enteritidis is found, it should be positive for agglutination both for body and flagellar antigens.
• Each Salmonella has its specific antigenic structure.
• Tests of ATB susceptibility are not performed for stool strains, but are performed in UTI origin strains, therefore some antibiotics are anti-UTI like nitrofurantoin.
• Obligatory pathogens such as Salmonella, Shigella, and Yersinia are tested to make the diagnosis surer and for epidemiological reasons.
• Carbapenemase detection involves carbapenemases which confer the largest antibiotic-resistance spectrum, and can hydrolyze not only carbapenems but also broad-spectrum penicillins, oxymino-cephalosporins, and cephamycins.
• E. coli agglutination for EPEC involves detecting any of 12 main serovars belonging to EPEC.
• ESBL and ampC β-lactamases are detected by verifying the presence of two types of beta-lactamases at the same time, and differences between the antibiotic discs are typical for either ESBL-type β-lactamase or constitutive-type ampC beta-lactamase.
• Salmonella agglutination involves the detection of two types of antigens: body (O) antigens and flagellar (H) antigens.
• ENTERO test 16 or 24 is a biochemical test, with the first reaction being the ONPG test (a test tube with reagent strip, like in VPT test in StaphyTest and StreptoTest).
• Antigen analysis is usually done using slide agglutination.
• To diagnose from unknown to enterobacteria we use Gram stain, Endo medium, Hajna medium, oxidase + and catalase -.
• In antigen analysis of obligatory strains (salmonella, shigella, yersinia) we use it for confirmation through agglutination.
• In ATB susceptibilty ESBL producers, the effect of ceftazidime and aztreonam is weak, but is enhanced by clavulanate (a β- lactamase inhibitor). We use: ceftazidime (CAZ), aztreonam (ATM) co-amoxicillin (amoxicillin with clavulanate) (AMC)
• Treatment for enterobacteria are: Ampicillin, Cephalothin, Tetracycline, Cefuroxime, Ciprofloxacin.