DNA-based methods employing amplification primers or probes for detecting, identifying, and quantifying in a test sample DNA from (i) any bacterium, (ii) the species Streptococcus agalactiae, Staphylococcus saprophyticus, Enterococcus faecium, Neisseria meningitidis, Listeria monocytogenes and Candida albicans, and (iii) any species of the genera Streptococcus, Staphylococcus, Enterococcus, Neisseria and Candida are disclosed. DNA-based methods employing amplification primers or probes for detecting, identifying, and quantifying in a test sample antibiotic resistance genes selected from the group consisting of blatem, blarob, blashv, blaoxa, blaZ, aadB, aacC1, aacC2, aacC3, aacA4, aac6′-IIa, ermA, ermB, ermC, mecA, vanA, vanB, vanC, satA, aac(6′)-aph(2″), aad(6), vat, vga, msrA, sul and int are also disclosed. The above microbial species, genera and resistance genes are all clinically relevant and commonly encountered in a variety of clinical specimens. These DNA-based assays are rapid, accurate and can be used in clinical microbiology laboratories for routine diagnosis. These novel diagnostic tools should be useful to improve the speed and accuracy of diagnosis of microbial infections, thereby allowing more effective treatments. Diagnostic kits for (i) the universal detection and quantification of bacteria, and / or (ii) the detection, identification and quantification of the above-mentioned bacterial and fungal species and / or genera, and / or (iii) the detection, identification and quantification of the above-mentioned antibiotic resistance genes are also claimed.