Emerging and unusual microorganisms in nosocomial infections

Although Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Pseudomonas aeruginosa represent more than half of the microorganisms responsible for nosocomial infections, especially post-operative (National Prevalence Survey 2022), others, encountered more rarely, require a rigorous interpretation of the microbiological results because of their presence in the commensal state, particularly on the skin, which raises the question of possible contamination: Cutibacterium acnes, a small anaerobic Gram-positive bacilli with cultures requires prolonged culture incubation ; it is found in 3 to 12% of osteoarticular infections, especially with foreign equipment to which he can adhere. The diagnosis is sometimes obvious (fistula, biological inflammatory syndrome) but it is rather an atypical and chronic picture with normal or subnormal laboratory examinations (ESR, CRP). Bacteriology then documents the infection through deep and numerous samples. Coagulase-negative staphylococci, especially S. epidermidis, S. haemolyticus and S. caprae, are also responsible for nosocomial infections, favoured by the presence of foreign materials: intravascular catheters, cardiac pacing boxes, CSF bypass valves, osteoarticular prostheses. Their frequency appears to be underestimated, due to the failure of conventional microbiological techniques, advantageously complemented by molecular biology. Although the case law is limited, several judgments of the TAs or CAAs have concluded, after expert reports, that postoperative infections caused by these bacteria are nosocomial.