Background Data on the prevalence of bacterial and viral co-infections among patients admitted to the ICU for acute respiratory failure related to SARS-CoV-2 pneumonia are lacking. We aimed to assess the rate of bacterial and viral co-infections, as well as to report the most common micro-organisms involved in patients admitted to the ICU for severe SARS-CoV-2 pneumonia. Patients and methods In this monocenter retrospective study, we reviewed all the respiratory microbiological investigations performed within the first 48 h of ICU admission of COVID-19 patients (RT-PCR positive for SARS-CoV-2) admitted for acute respiratory failure. Results From March 13th to April 16th 2020, a total of 92 adult patients (median age: 61 years, 1st–3rd quartiles [55–70]; males: n = 73/92, 79%; baseline SOFA: 4 [3–7] and SAPS II: 31 [21–40]; invasive mechanical ventilation: n = 83/92, 90%; ICU mortality: n = 45/92, 49%) were admitted to our 40-bed ICU for acute respiratory failure due to SARS-CoV-2 pneumonia. Among them, 26 (28%) were considered as co-infected with a pathogenic bacterium at ICU admission with no co-infection related to atypical bacteria or viruses. The distribution of the 32 bacteria isolated from culture and/or respiratory PCRs was as follows: methicillin-sensitive Staphylococcus aureus (n = 10/32, 31%), Haemophilus influenzae (n = 7/32, 22%), Streptococcus pneumoniae (n = 6/32, 19%), Enterobacteriaceae (n = 5/32, 16%), Pseudomonas aeruginosa (n = 2/32, 6%), Moraxella catarrhalis (n = 1/32, 3%) and Acinetobacter baumannii (n = 1/32, 3%). Among the 24 pathogenic bacteria isolated from culture, 2 (8%) and 5 (21%) were resistant to 3rd generation cephalosporin and to amoxicillin–clavulanate combination, respectively. Conclusions We report on a 28% rate of bacterial co-infection at ICU admission of patients with severe SARSCoV-2 pneumonia, mostly related to Staphylococcus aureus, Haemophilus influenzae, Streptococcus pneumoniae and Enterobacteriaceae. In French patients with confirmed severe SARSCoV-2 pneumonia requiring ICU admission, our results encourage the systematic administration of an empiric antibiotic monotherapy with a 3rd generation cephalosporin, with a prompt de-escalation as soon as possible. Further larger studies are needed to assess the real prevalence and the predictors of co-infection together with its prognostic impact on critically ill patients with severe SARS-CoV-2 pneumonia.