Forward-looking Statement This presentation contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995 regarding, among other things, the potential regulatory path forward for

Corporate Presentation January 8, 2024

Forward-looking Statement This

presentation contains forward-looking statements as defined in the Private Securities Litigation Reform Act of 1995 regarding, among other things, the potential regulatory path forward for tebipenem HBr and the potential approval of tebipenem HBr by

the U.S. Food and Drug Administration (FDA) and the timing thereof; the potential commercialization of tebipenem HBr and its future value, the potential receipt of milestone payments and royalties on future sales of tebipenem HBr under the

GlaxoSmithKline Intellectual Property (No. 3) Limited (GSK) license agreement; the Company's cash runway; the future development and commercialization of SPR206 and SPR720; the potential number of patients who could be treated by tebipenem HBr

and SPR720 and market demand for tebipenem HBr and SPR720 generally; the effectiveness of tebipenem HBr and its potential impact on healthcare resource utilizations; expected broad access across payer channels for tebipenem HBr; the anticipated

shift in treating patients from intravenous to oral administration; the initiation, timing, progress and results of the Company's preclinical studies and clinical trials and its research and development programs, including management's

assessment of such results; the timing of the availability of data from the Company's clinical trials; the timing of the Company's filings with regulatory agencies; product candidate benefits; competitive position; business

strategies; objectives of management; potential growth opportunities; potential market size; reimbursement matters; possible or assumed future results of operations; projected costs and the availability of additional non-dilutive funding from

governmental agencies beyond any initially funded awards. In some cases, forward-looking statements can be identified by terms such as "may," "will," "should," "expect," "plan,"

"aim," "anticipate," "could," "intent," "target," "project," "contemplate," "believe," "estimate," "predict,"

"potential" or "continue" or the negative of these terms or other similar expressions. All statements other than statements of historical facts contained in this presentation are forward-looking statements. The

Company may not actually achieve the plans, intentions or expectations disclosed in these forward-looking statements. Actual results or events could differ materially from the plans, intentions and expectations disclosed in these

forward-looking statements as a result of various factors, including whether the FDA will ultimately approve tebipenem HBr and, if so, the timing of any such approval; whether the FDA will require any additional clinical data or place labeling

restrictions on the use of tebipenem HBr that would add costs for the Company, delay approval and/or reduce the commercial prospects of tebipenem HBr; the Company's need for additional funding; the lengthy, expensive, and uncertain process of

clinical drug development; the Company's reliance on third parties to manufacture, develop, and commercialize its product candidates, if approved; the ability to develop and commercialize the Company's product candidates, if approved;

the potential impact of the COVID-19 pandemic; the Company's ability to retain key personnel; whether results obtained in preclinical studies and clinical trials will be indicative of results obtained in future clinical trials and whether

preliminary data from the Company's clinical trials will be predictive of final results from such trials; the Company's dependence on raising capital and whether the Company's product candidates will advance through the

preclinical development and clinical trial process on a timely basis, or at all, taking into account such factors as the effects of possible regulatory delays, slower than anticipated patient enrollment, manufacturing challenges, clinical trial

design, clinical data requirements and clinical outcomes; whether the results of such clinical trials will warrant submission for approval from the FDA or equivalent foreign regulatory agencies; decisions made by the FDA and

equivalent foreign regulatory agencies with respect to the development and commercialization of the Company's product candidates; the commercial potential of the Company's product candidates; the Company's ability to

obtain adequate third-party reimbursement for its product candidates; whether the Company will satisfy all of the pre-conditions to receipt of the milestone payments under its various license and collaboration agreements; whether BARDA elects to

exercise its second option under the Company's agreement with BARDA; the Company's ability to implement its strategic plans; the Company's ability to obtain, maintain and enforce intellectual property and other proprietary rights

for its product candidates; the risks and uncertainties related to market conditions; whether the Company's cash resources will be sufficient to fund its continuing operations for the periods and/or trials anticipated; and other factors

discussed in the "Risk Factors" section of the Company's periodic reports filed with the U.S. Securities and Exchange Commission (SEC), and risks described in other filings the Company may make with the SEC in the future. The

forward-looking statements included in this presentation represent the Company's views as of the date of this presentation. The Company anticipates that subsequent events and developments will cause its views to change. However, while the

Company may elect to update these forward-looking statements at some point in the future, it specifically disclaims any obligation to do so. These forward-looking statements should not be relied upon as representing the Company's views as of

any date subsequent to the date of this presentation.

Diversified clinical-stage portfolio

Developing Therapies for Rare and Multi-drug Resistant Infectious Diseases SPR720, positioned for near-term inflection Partnership milestones, cash and cash equivalents, expected to provide runway into late 2025 NTM-PD: non-tuberculous mycobacterial

pulmonary disease; QIDP: qualified infectious disease product 1. Winthrop KL, et al. Ann Am Thorac Soc 2020; 17:178-85. Late-stage development pipeline Focused on oral, small molecule drugs Indications with high unmet need in addressable

patient populations Orphan drug and/or QIDP designations Strong global intellectual property Potential novel, oral, first-line treatment for non-tuberculous mycobacterial pulmonary disease (NTM-PD) Rare disease with ~245,000 diagnosed patients

in developed markets1 No approved first-line therapies Proof-of-concept top-line data anticipated in 2H 2024 Supported by World Class Partnerships

Maturing Pipeline with Differentiated

Clinical Assets Wholly Owned Asset Indication Preclinical Phase 1 Phase 2 Phase 3 Partnered Assets SPR720 Tebipenem HBr SPR206 Anticipated Milestone NTM-PD Top-line Data (2H 2024) Complete Enrollment (2H 2025) Initiate Phase 21 Non-dilutive Funding

Alliances: Worldwide Rights (ex. Asia) Spero Retains Rights in United States cUTI HABP/VABP China Europe cUTI: complicated urinary tract infection; HABP: hospital-acquired bacterial pneumonia; NTM-PD: non-tuberculous mycobacterial pulmonary disease;

VABP: ventilator-associated bacterial pneumonia 1. Contingent on IND clearance and non-dilutive funding availability

Progressive Lung Damage NTM:

non-tuberculous mycobacteria; NTM-PD: NTM pulmonary disease; Kim RD, et al. Am J Respir Crit Care Med 2008; 178:1066-74. 1. All cause mortality Patients Need an Effective Oral Therapy Early in Their Disease Journey NTM-PD: Chronic Debilitating

Disease with 5-year Mortality Rate of 35%1 NTM Species Patient Characteristics Sign/Symptom Frequency (%) M. avium complex (80-85%) Fatigue 83 M. abscessus Cough 78 M. xenopi Sputum (phlegm) 67 M. fortuitum Short of breath 65 M.

kansasii Night sweats 54 M. malmoense Fever 44 M. simiae Hemoptysis 29 Weight loss 3.7 5.2 kg Structural lung disease Exposure to NTM bacteria (e.g. water, soil) Immuno- compromised

NTM-PD Patient Journey To Diagnosis

Leads to Sub-optimal Treatment Choices Guidance-based 1L SOC aims to reduce microbial burden measured by SCC Environmental exposure to MAC Pre-existing risk factors lead to MAC colonization in pulmonary tissue Clinical manifestations emerge and

worsen over time Diagnosis primarily by pulmonologists (mostly at specialized treatment centers) Non-cavitary form (~80%) Cavitary form (~20%) Azythromycin + Ethambutol + Rifampin Azythromycin + Ethambutol + Rifampin +/- IV Amikacin Sputum culture

conversion occurs in up to 67% of patients receiving a susceptibility-based treatment Even when culture conversion is achieved, recurrence occurs in up to 50% of patients Lack of Effective Outcomes Safety/Intolerability Azithromycin: QT

prolongation, GI intolerability (nausea, vomiting, bloating, abdominal pain), increasing resistance Ethambutol: Optic neuritis, hepatoxicity, peripheral neuropathy Rifampin: Hepatotoxicity, GI intolerability, immunologic reactions, drug-drug

interactions No approved first-line treatment for NTM-PD patients Unmet Medical Need: Better Tolerability and Effectiveness, Fewer Drug-Drug Interactions, Shorter Therapy Duration 1L: first line; GI: gastrointestinal; MAC: Mycobacterium avium

complex; NTM-PD: nontuberculous mycobacterial pulmonary disease; SCC: sputum culture conversion (to negative); SOC: standard of care; The voice of the Patient, Non-Tuberculous Mycobacterial (NTM) Lung Infection Public Meeting: October 15,

2015; Report Date: April 2016. Hamed KA and Tillotson G. Expert Rev Respir Med 2023;17:973-88.

Strong NTM-PD Patient Community Voices

Unmet Therapeutic Need 97% 84% 72% 53% 42% NTM: non-tuberculous mycobacteria; NTM-PD: NTM pulmonary disease; 1. Flume PA, et al. Chest 2021; 159:537-43. N=465 US patients with NTM-PD1 If your treatment could change one thing about your NTM lung

infection, what would that be? "Less Coughing, less shortness of breath, less fatigue" "I am most concerned with TOTAL lung health getting this infection under control means I am less likely to have exacerbations that in

turn require additional antibiotics in the future" "Get rid of the bleeding, get rid of the mucous, get rid of the NTM"

SPR720 For Treatment-na ve and

Treatment-experienced Non-refractory Patients Diagnosed patient opportunity estimated to be ~245,000 across US, Europe*, and Japan1 Increasing prevalence estimated at 6 10% annually in the US2 Europe: ~15,000 Japan: ~135,000 US: ~95,000 SPR720

Aims to be the Principal Foundation to a First-line SOC Combination Drug Regimen for NTM-PD *Europe refers to Germany, United Kingdom, Italy, Netherlands and France. NTM-PD: non-tuberculous mycobacterial pulmonary disease; SOC: standard of care. 1.

Winthrop KL, et al. Ann Am Thorac Soc 2020; 17:178-85 2. Hamed KA and Tillotson G. Expert Rev Respir Med 2023;17:973-88.

SPR720 Well-positioned for Unmet

Patient Needs in First-line Setting M.: Mycobacterium; MAC: M. avium complex; NTM: non-tuberculous mycobacteria; SOC: standard of care; QIDP: qualified infectious disease product; 1. Brown-Elliott BA, et al. Antimicrob Agents Chemother. 2018

62:e01503-18. 2. Aragaw WW, et al. Microbiol Spectr 2022;10:e0132121. Improve first-line SOC regimen Potency against multiple NTM pathogens, including MAC and M. abscessus1 Novel mechanism of action with no evidence of cross resistance against

marketed antibiotics1 and low propensity for selection of resistance2 Data to-date support potential for efficacy, macrophage penetration, and safety/tolerability May be administered with or without food Composition of matter patent through

2032 Granted Orphan Drug Designation and QIDP designations

SPR720 is an Aminobenzimidazole, a

Novel Pharmacophore Oral, small molecule Gyrase B inhibitor Novel mechanism of action not exploited by current antibiotics No cross resistance to current SOC agents Low propensity for selection of resistance Penetrates lung macrophages

Differentiated advantages in vitro & in vivo Activity includes MAC and MAB isolates resistant to SOC agents, including macrolide-resistant MAC Evidence of activity as stand-alone agent and in combination with SOC agents Phosphate ester

prodrug Active moiety Oral absorption

Novel Mechanism of Action Not

Exploited by Existing Antibiotics SPR719, active moiety of SPR720 pro-drug, inhibits ATPase activity of bacterial DNA gyrase B DNA gyrase B is distinct from gyrase A, the target of fluoroquinolones Blocks introduction of negative supercoils in DNA

and traps chromosome in a positively charged state that impacts cell physiology and division Inhibits bacterial DNA synthesis resulting in death of bacterial cell 2 ATP GyrB inhibitors ATPase TOPRIM fluoroquinolones GyrB GyrA ATPase: F0F1-ATP

Synthase; TOPRIM: Topoisomerase-primase domain; Winthrop KL, et al. Expert Rev Anti Infect Ther 2023; 21:1177-87.

In vitro Data Demonstrate Potent

Activity Against Range of NTM Species NTM Species N SPR719 MIC90 (mg/L) Amikacin MIC90 (mg/L) M. avium complex 41 2 32 M. abscessus subsp. abscessus 30 4 16 M. abscessus subsp. massiliense 10 2 16 M. chelonae 10 4 32 M. fortuitum group 10 1 1

M. immunogenum 10 8 16 M. simiae 10 2 16 MIC90: minimum inhibitory concentration at which 90% of isolates were inhibited; NTM: non-tuberculous mycobacteria; SPR719 is the active moiety of the prodrug SPR720 and is used for in vitro testing.

Brown-Elliott BA, et al. Antimicrob Agents Chemother 2018; 62:e01503-18.SPR720, Investigator Brochure Edition 5; 07Apr2022.

In Vivo Data Demonstrate Increased

Potency When Combined with SOC Untreated SPR720 as monotherapy and in combination with SOC agents SPR720 monotherapy activity Dose-response Improved efficacy of current SOC combination regimen BID: twice daily; CFU: colony forming units; CLR:

clarithromycin; EMB: ethambutol; SOC: standard of care; QD: once daily Verma D, et al. Open Forum Infect Dis 2020; 7(Suppl 1):S809.

Phase 1 SAD/MAD: Dose Response

Observed With No Evidence Of Food Effect Mean plasma concentration-time curves following single ascending dosing (SAD) of SPR720 MAD: multiple ascending dose; SAD: single ascending dose Talley AK, et al. Antimicrob Agents Chemother 2021;

Phase 1 SAD/MAD: Favorable

Safety/Tolerability Profile 500 mg and 1000 mg doses evaluated over 7- and 14-days Dose-dependent increase in plasma exposure No SAEs reported; mild GI symptoms at 1500 mg doses One discontinuation at 1500 mg dose: Grade 2 pancreatic enzyme

elevation that was asymptomatic, monitorable and reversible Phase 1 Results Show SPR720 was Well-tolerated with Exposures above Predicted Therapeutic Levels GI: gastrointestinal; MAD: multiple ascending dose; SAD: single ascending dose; SAE: serious

adverse event Talley AK, et al. Antimicrob Agents Chemother 2021; 65:e0120821.

Phase 2a Designed to Achieve

Proof-of-Concept Study SPR720-202 (NCT05496374): Phase 2a study in NTM-PD N SPR719 MIC50 A Study to Evaluate the Efficacy, Safety, Tolerability, and Pharmacokinetics of SPR720, as Compared With Placebo for the Treatment of Participants With

Mycobacterium avium Complex (MAC) Pulmonary Disease 30 2 Treatment Population Five Treatment Arms Endpoints Treatment-na ve/experienced (non-refractory) patients with NTM due to M. avium complex Approximately 35 patients 56 Days of

Dosing Placebo, n=9 SPR720 (500 mg), n=9 SPR720 (1000 mg), n=9 SPR720 (1000 mg), n=4 SPR720 (500 mg BID), n=4 Primary Endpoint: 1. Microbiological response

Secondary Endpoints: 1. Safety & tolerability 2. How patients feel & function 3.

Plasma PK 27 patients randomized 1:1:1 (blinded) Intense PK substudy (open label) BID: twice daily; MAC: Mycobacterium avium complex; NTM-PD: non-tuberculous mycobacterial pulmonary disease; PK: pharmacokinetics

Comprehensive Data Set Anticipated

in 2H 2024 We anticipate a robust dataset to inform the registrational path for SPR720 as first-line therapy for NTM-PD Microbiological response to demonstrate anti-NTM activity in patients Patient-reported outcomes to inform primary endpoint in

later trials PK in patients Intrapulmonary PK from bronchoalveolar lavage (BAL) study, in healthy volunteers Determine PK of co-administered SPR720, azithromycin and ethambutol in healthy volunteers

Confirm safety/tolerability profile evidenced in prior studies BAL: bronchoalveolar lavage; NTM-PD: non-tuberculous mycobacterial pulmonary disease; PK: pharmacokinetics

SPR720 Well Positioned to Become

the Foundation of First-line NTM-PD Therapy Key Attribute* SPR720 SPRO Epatraborole ANTX Arikayce INSM MNKD101 MNKD Novel MOA X X MAC MIC90 2 mg/L X1 X2 Low Propensity for Resistance X3 ?

Macrolide-Resistant MAC Activity ? Oral Administration X X No Food Effect N/A N/A MOA: mechanism of action; MAC: Mycobacterium avium complex; MIC: minimum inhibitory concentration;

MIC90: MIC at which 90% of isolates were inhibited; NA: not applicable. 1.White TK et al. Open Forum Infect Dis. 2023;10(Suppl 2):ofad500.1758. 2.Brown-Elliott BA, et al. Antimicrob Agents Chemother. 2018 Oct 24;62:e01503-18. 3. O'Dwyer K. et al.

Antimicrob Agents Chemother. 2015 Jan;59:289-98. * The above table describes features of different first-line, pre-commercial, NTM-PD therapies and is based on publicly available data. It does not represent the results of head-to-head comparison

Large Market Opportunity for cUTI

Patients to Be Treated at Home Targeted patients often cycle through multiple therapies 7.9 M UTI Patients in the US 2.7 M Market 780 K IV Carbapenem Piperacillin/tazobactam 1.9 M 2nd line Oral (Resistant/ Failed) Lack of effective oral treatment